Karen Beer, PA-C, MSPAS, RD, LD, CDE

The surfaces of the human body exposed to the environment are colonized by microbes—the majority of which reside in the intestinal tract. Collectively, the microbial cells that live in and on us (bacteria, eukaryotes, viruses, fungi, and archaea) make up our microbiota, and their genetic material constitutes our microbiome. There are at least 100 times more genes in the human microbiome than in the human genome.^1,2

With the help of recent technologic advances in genetic sequencing, we’re beginning to understand more about this vast biological habitat. We know that the microbiota plays a role in vitamin production, energy harvest and storage, and fermentation and absorption of undigested carbohydrates. It also has bidirectional influence on the central nervous system and neuropsychologic health and is involved in the maturation and development of the immune system.

A healthy biome is characterized by bacterial diversity and richness. Gut microbiota is mostly comprised of Firmicutes (64%), Bacteroidetes (23%), Proteobacteria (8%), and Actinobacteria (3%).² The distribution of these bacteria is largely determined by diet; individuals who follow a diet high in animal fat have a Bacteroides-dominant pattern, whereas those who follow a carbohydrate-rich diet tend toward a Prevotella-dominant pattern.^1-3

Lack of bacterial diversity and overgrowth of pathobacteria results in dysbiosis, an imbalance in the gut’s microbial composition. Alterations in the proportions of bacteria are thought to result in metabolic disease. As such, dysbiosis is correlated with obesity and diabetes, as well as other diseases (eg, inflammatory bowel disease, multiple sclerosis, Crohn disease, and rheumatoid arthritis).^1-3 At this time, however, it is unclear whether these bacterial imbalances cause or result from disease.

ROLE IN TYPE 2 DIABETES

The microbiome of patients with type 2 diabetes (T2DM) is characterized by reduced levels of Firmicutes and Clostridia and an increased ratio of Bacteroidetes:Firmicutes (this ratio correlates with plasma glucose concentration).^4,5 Interestingly, although T2DM and obesity are closely related, available data indicate that gut microbiome changes are not always identical between these two patient populations. In some studies, the microbiome of obese individuals involves a decreased Bacteroidetes:Firmicutes ratio, in contrast to the increase seen with T2DM—which raises the question of whether the same or different factors cause these two entities.^1,5-7

Patients with T2DM also have decreased amounts of butyrate-producing bacteria in their microbiomes. Butyrate, acetate, and propionate are short-chain fatty acids (­SCFAs) fermented in the large intestine by bacteria from dietary fiber. These SCFAs play an important role in energy metabolism and are critical for modulating immune responses and tumorigenesis in the gut. Butyrate, in particular, provides energy for colonic epithelial cells. By feeding colonic cells, butyrate helps to maintain intestinal integrity and prevent translocation—a process that moves gram-negative intestinal bacteria across the lumen of the gut, causing endotoxemia. Endotoxemia triggers a low-grade inflammatory response, and low-grade inflammation is thought to underlie T2DM.^2,5,6

Therapeutic interventions—such as dietary modifications, prebiotics, probiotics, antibiotics, metformin, fecal transplantation, and bariatric surgery—can effectively alter the composition of gut bacteria. It has been proposed that these interventions could be harnessed to prevent and treat T2DM in the future.² So, what might these interventions have (or not have) to offer?

ANTIBIOTICS

Antibiotics are useful for eradicating pathogenic bacteria, but they can also destroy beneficial intestinal commensals in the process. Therefore, concern about the widespread use of antibiotics in humans and livestock has increased. Subtherapeutic use of antibiotics, which has been common in farm animals throughout the past 50 years to increase growth and food production, has been shown to affect metabolic pathways—particularly with respect to SCFAs—in mouse studies.⁶

Recent data on humans have linked antibiotic treatment in early infancy to long-term effects on microbial diversity and childhood overweight. Similarly, long-term use of IV vancomycin in adults has been linked to an increased obesity risk. But it’s not just long-term exposure that poses a threat; even short courses of oral antibiotics can have profound and irreversible ­effects on intestinal microbial diversity and composition. For example, short-term use of oral vancomycin was found to impair peripheral insulin sensitivity in males with metabolic syndrome associated with ­altered gut microbiota, while amoxicillin did not.⁶

PREBIOTICS AND PROBIOTICS

Prebiotics are indigestible carbohydrates that improve host health by stimulating the growth and activity of colonic bacteria. Most prebiotics are oligosaccharides, which can travel through the upper GI system undigested. When they reach the colon, they are fermented to produce SCFAs that stimulate the growth of microbes that reside there. Prebiotics come from a wide variety of food sources, including asparagus, barley, garlic, onions, and wheat bran.^2,3 Pickled and fermented foods (eg, kimchi, sauerkraut, yogurt, miso) are good sources of both prebiotics and probiotics.²

Bifidobacteria and lactobacilli are the most commonly used strains in foods and supplements containing probiotics. These live microorganisms bring about specific changes in the composition and activity of gut microbiota: they secrete antimicrobial substances, compete with pathogenic bacteria, strengthen the intestinal barrier, and modulate the immune system.^2,3,6 Research on human and animal models suggests that administering probiotics may help manage diabetes.²

DIETARY MODULATION

Dietary changes have been shown to modify the bacterial metabolic activity of the human gut. In one study, obese adults with T2DM were placed on either a fat- or carbohydrate-restricted diet, and it was found that their levels of Bacteroidetes increased and Firmicutes decreased.⁷

In another study, patients with T2DM adhered to one of two calorie-controlled diets: a high-fiber macrobiotic diet or a Mediterranean-style (control) diet. The macrobiotic diet was high in complex carbohydrates, legumes, fermented products, sea salt, and green tea and was free of animal protein, fat, and added sugar. Both diets were effective at improving dysbiosis—ecosystem diversity increased, and health-promoting SCFA producers were replenished. However, the macrobiotic diet was more effective than the control diet at reducing fasting and postprandial glucose, A1C, serum cholesterol, insulin resistance, BMI, and waist and hip circumferences; and only the macrobiotic diet counteracted the inflammation-producing bacterial groups.⁸

METFORMIN

Metformin has therapeutic effects on microbial composition and SCFA synthesis. In a microbiome comparison study, patients with T2DM treated with metformin had more butyrate-producing bacteria than their untreated counterparts. The trend toward increased Lactobacillus seen in the context of T2DM was reduced or reversed by metformin treatment. Researchers were able to tell which patients were (and were not) treated based on their gut microbiome taxonomic signature.⁹

FECAL MICROBIOTA TRANSPLANT

Fecal microbiota transplant, also known as stool transplant or bacteriotherapy, is the process of transferring fecal bacteria from a healthy individual into a recipient. It is used in the treatment of recurrent Clostridium difficile colitis to replenish beneficial bacteria in the digestive tract following use of wide-spectrum antibiotics. In a double-blind randomized controlled trial, insulin-resistant men received either autologous (reinfusion of one’s collected feces) or allogenic (feces from a lean donor) infusions. Allogenic transplantation resulted in significantly increased intestinal microbial diversity and increased levels of butyrate-producing species, accompanied by significantly improved peripheral muscle sensitivity to insulin.^1,6

BARIATRIC SURGERY

Bariatric surgery, specifically Roux-en-Y gastric bypass (RYGBP), is a powerful tool used to treat obesity. In six patients (five of whom had diabetes) treated with RYGBP, dramatic changes to the gut microbiota were seen at three months following surgery. BMI was reduced by 15% to 32%, C-reactive protein decreased in five of six patients, and T2DM was alleviated in all. Postoperatively, there was a striking shift towards higher amounts of Proteobacteria and lower relative amounts of Firmicutes and Bacteroides in the gut phyla. Postoperative increases in certain bacteria were more profound than the amount in lean controls, suggesting these changes are related to alterations in the gut, not lower body weight.^4,6

CONCLUSION

We are just beginning to understand the microbiome and its relationship to health and disease. For patients with T2DM, a variety of interventions may be used to return the gut microbiota to health. Dietary interventions, prebiotics and probiotics, fecal microbial transplant, and bariatric surgery can influence gut microbial composition, with the goal of preventing and/or treating disease. In the future, gut microbial signatures may serve as early diagnostic markers.

The surfaces of the human body exposed to the environment are colonized by microbes—the majority of which reside in the intestinal tract. Collectively, the microbial cells that live in and on us (bacteria, eukaryotes, viruses, fungi, and archaea) make up our microbiota, and their genetic material constitutes our microbiome. There are at least 100 times more genes in the human microbiome than in the human genome.^1,2

With the help of recent technologic advances in genetic sequencing, we’re beginning to understand more about this vast biological habitat. We know that the microbiota plays a role in vitamin production, energy harvest and storage, and fermentation and absorption of undigested carbohydrates. It also has bidirectional influence on the central nervous system and neuropsychologic health and is involved in the maturation and development of the immune system.

A healthy biome is characterized by bacterial diversity and richness. Gut microbiota is mostly comprised of Firmicutes (64%), Bacteroidetes (23%), Proteobacteria (8%), and Actinobacteria (3%).² The distribution of these bacteria is largely determined by diet; individuals who follow a diet high in animal fat have a Bacteroides-dominant pattern, whereas those who follow a carbohydrate-rich diet tend toward a Prevotella-dominant pattern.^1-3

Lack of bacterial diversity and overgrowth of pathobacteria results in dysbiosis, an imbalance in the gut’s microbial composition. Alterations in the proportions of bacteria are thought to result in metabolic disease. As such, dysbiosis is correlated with obesity and diabetes, as well as other diseases (eg, inflammatory bowel disease, multiple sclerosis, Crohn disease, and rheumatoid arthritis).^1-3 At this time, however, it is unclear whether these bacterial imbalances cause or result from disease.

ROLE IN TYPE 2 DIABETES

The microbiome of patients with type 2 diabetes (T2DM) is characterized by reduced levels of Firmicutes and Clostridia and an increased ratio of Bacteroidetes:Firmicutes (this ratio correlates with plasma glucose concentration).^4,5 Interestingly, although T2DM and obesity are closely related, available data indicate that gut microbiome changes are not always identical between these two patient populations. In some studies, the microbiome of obese individuals involves a decreased Bacteroidetes:Firmicutes ratio, in contrast to the increase seen with T2DM—which raises the question of whether the same or different factors cause these two entities.^1,5-7

Patients with T2DM also have decreased amounts of butyrate-producing bacteria in their microbiomes. Butyrate, acetate, and propionate are short-chain fatty acids (­SCFAs) fermented in the large intestine by bacteria from dietary fiber. These SCFAs play an important role in energy metabolism and are critical for modulating immune responses and tumorigenesis in the gut. Butyrate, in particular, provides energy for colonic epithelial cells. By feeding colonic cells, butyrate helps to maintain intestinal integrity and prevent translocation—a process that moves gram-negative intestinal bacteria across the lumen of the gut, causing endotoxemia. Endotoxemia triggers a low-grade inflammatory response, and low-grade inflammation is thought to underlie T2DM.^2,5,6

Therapeutic interventions—such as dietary modifications, prebiotics, probiotics, antibiotics, metformin, fecal transplantation, and bariatric surgery—can effectively alter the composition of gut bacteria. It has been proposed that these interventions could be harnessed to prevent and treat T2DM in the future.² So, what might these interventions have (or not have) to offer?

ANTIBIOTICS

Antibiotics are useful for eradicating pathogenic bacteria, but they can also destroy beneficial intestinal commensals in the process. Therefore, concern about the widespread use of antibiotics in humans and livestock has increased. Subtherapeutic use of antibiotics, which has been common in farm animals throughout the past 50 years to increase growth and food production, has been shown to affect metabolic pathways—particularly with respect to SCFAs—in mouse studies.⁶

Recent data on humans have linked antibiotic treatment in early infancy to long-term effects on microbial diversity and childhood overweight. Similarly, long-term use of IV vancomycin in adults has been linked to an increased obesity risk. But it’s not just long-term exposure that poses a threat; even short courses of oral antibiotics can have profound and irreversible ­effects on intestinal microbial diversity and composition. For example, short-term use of oral vancomycin was found to impair peripheral insulin sensitivity in males with metabolic syndrome associated with ­altered gut microbiota, while amoxicillin did not.⁶

PREBIOTICS AND PROBIOTICS

Prebiotics are indigestible carbohydrates that improve host health by stimulating the growth and activity of colonic bacteria. Most prebiotics are oligosaccharides, which can travel through the upper GI system undigested. When they reach the colon, they are fermented to produce SCFAs that stimulate the growth of microbes that reside there. Prebiotics come from a wide variety of food sources, including asparagus, barley, garlic, onions, and wheat bran.^2,3 Pickled and fermented foods (eg, kimchi, sauerkraut, yogurt, miso) are good sources of both prebiotics and probiotics.²

Bifidobacteria and lactobacilli are the most commonly used strains in foods and supplements containing probiotics. These live microorganisms bring about specific changes in the composition and activity of gut microbiota: they secrete antimicrobial substances, compete with pathogenic bacteria, strengthen the intestinal barrier, and modulate the immune system.^2,3,6 Research on human and animal models suggests that administering probiotics may help manage diabetes.²

DIETARY MODULATION

Dietary changes have been shown to modify the bacterial metabolic activity of the human gut. In one study, obese adults with T2DM were placed on either a fat- or carbohydrate-restricted diet, and it was found that their levels of Bacteroidetes increased and Firmicutes decreased.⁷

In another study, patients with T2DM adhered to one of two calorie-controlled diets: a high-fiber macrobiotic diet or a Mediterranean-style (control) diet. The macrobiotic diet was high in complex carbohydrates, legumes, fermented products, sea salt, and green tea and was free of animal protein, fat, and added sugar. Both diets were effective at improving dysbiosis—ecosystem diversity increased, and health-promoting SCFA producers were replenished. However, the macrobiotic diet was more effective than the control diet at reducing fasting and postprandial glucose, A1C, serum cholesterol, insulin resistance, BMI, and waist and hip circumferences; and only the macrobiotic diet counteracted the inflammation-producing bacterial groups.⁸

METFORMIN

Metformin has therapeutic effects on microbial composition and SCFA synthesis. In a microbiome comparison study, patients with T2DM treated with metformin had more butyrate-producing bacteria than their untreated counterparts. The trend toward increased Lactobacillus seen in the context of T2DM was reduced or reversed by metformin treatment. Researchers were able to tell which patients were (and were not) treated based on their gut microbiome taxonomic signature.⁹

FECAL MICROBIOTA TRANSPLANT

Fecal microbiota transplant, also known as stool transplant or bacteriotherapy, is the process of transferring fecal bacteria from a healthy individual into a recipient. It is used in the treatment of recurrent Clostridium difficile colitis to replenish beneficial bacteria in the digestive tract following use of wide-spectrum antibiotics. In a double-blind randomized controlled trial, insulin-resistant men received either autologous (reinfusion of one’s collected feces) or allogenic (feces from a lean donor) infusions. Allogenic transplantation resulted in significantly increased intestinal microbial diversity and increased levels of butyrate-producing species, accompanied by significantly improved peripheral muscle sensitivity to insulin.^1,6

BARIATRIC SURGERY

Bariatric surgery, specifically Roux-en-Y gastric bypass (RYGBP), is a powerful tool used to treat obesity. In six patients (five of whom had diabetes) treated with RYGBP, dramatic changes to the gut microbiota were seen at three months following surgery. BMI was reduced by 15% to 32%, C-reactive protein decreased in five of six patients, and T2DM was alleviated in all. Postoperatively, there was a striking shift towards higher amounts of Proteobacteria and lower relative amounts of Firmicutes and Bacteroides in the gut phyla. Postoperative increases in certain bacteria were more profound than the amount in lean controls, suggesting these changes are related to alterations in the gut, not lower body weight.^4,6

CONCLUSION

We are just beginning to understand the microbiome and its relationship to health and disease. For patients with T2DM, a variety of interventions may be used to return the gut microbiota to health. Dietary interventions, prebiotics and probiotics, fecal microbial transplant, and bariatric surgery can influence gut microbial composition, with the goal of preventing and/or treating disease. In the future, gut microbial signatures may serve as early diagnostic markers.

The surfaces of the human body exposed to the environment are colonized by microbes—the majority of which reside in the intestinal tract. Collectively, the microbial cells that live in and on us (bacteria, eukaryotes, viruses, fungi, and archaea) make up our microbiota, and their genetic material constitutes our microbiome. There are at least 100 times more genes in the human microbiome than in the human genome.^1,2

With the help of recent technologic advances in genetic sequencing, we’re beginning to understand more about this vast biological habitat. We know that the microbiota plays a role in vitamin production, energy harvest and storage, and fermentation and absorption of undigested carbohydrates. It also has bidirectional influence on the central nervous system and neuropsychologic health and is involved in the maturation and development of the immune system.

A healthy biome is characterized by bacterial diversity and richness. Gut microbiota is mostly comprised of Firmicutes (64%), Bacteroidetes (23%), Proteobacteria (8%), and Actinobacteria (3%).² The distribution of these bacteria is largely determined by diet; individuals who follow a diet high in animal fat have a Bacteroides-dominant pattern, whereas those who follow a carbohydrate-rich diet tend toward a Prevotella-dominant pattern.^1-3

Lack of bacterial diversity and overgrowth of pathobacteria results in dysbiosis, an imbalance in the gut’s microbial composition. Alterations in the proportions of bacteria are thought to result in metabolic disease. As such, dysbiosis is correlated with obesity and diabetes, as well as other diseases (eg, inflammatory bowel disease, multiple sclerosis, Crohn disease, and rheumatoid arthritis).^1-3 At this time, however, it is unclear whether these bacterial imbalances cause or result from disease.

ROLE IN TYPE 2 DIABETES

The microbiome of patients with type 2 diabetes (T2DM) is characterized by reduced levels of Firmicutes and Clostridia and an increased ratio of Bacteroidetes:Firmicutes (this ratio correlates with plasma glucose concentration).^4,5 Interestingly, although T2DM and obesity are closely related, available data indicate that gut microbiome changes are not always identical between these two patient populations. In some studies, the microbiome of obese individuals involves a decreased Bacteroidetes:Firmicutes ratio, in contrast to the increase seen with T2DM—which raises the question of whether the same or different factors cause these two entities.^1,5-7

Patients with T2DM also have decreased amounts of butyrate-producing bacteria in their microbiomes. Butyrate, acetate, and propionate are short-chain fatty acids (­SCFAs) fermented in the large intestine by bacteria from dietary fiber. These SCFAs play an important role in energy metabolism and are critical for modulating immune responses and tumorigenesis in the gut. Butyrate, in particular, provides energy for colonic epithelial cells. By feeding colonic cells, butyrate helps to maintain intestinal integrity and prevent translocation—a process that moves gram-negative intestinal bacteria across the lumen of the gut, causing endotoxemia. Endotoxemia triggers a low-grade inflammatory response, and low-grade inflammation is thought to underlie T2DM.^2,5,6

Therapeutic interventions—such as dietary modifications, prebiotics, probiotics, antibiotics, metformin, fecal transplantation, and bariatric surgery—can effectively alter the composition of gut bacteria. It has been proposed that these interventions could be harnessed to prevent and treat T2DM in the future.² So, what might these interventions have (or not have) to offer?

ANTIBIOTICS

Antibiotics are useful for eradicating pathogenic bacteria, but they can also destroy beneficial intestinal commensals in the process. Therefore, concern about the widespread use of antibiotics in humans and livestock has increased. Subtherapeutic use of antibiotics, which has been common in farm animals throughout the past 50 years to increase growth and food production, has been shown to affect metabolic pathways—particularly with respect to SCFAs—in mouse studies.⁶

Recent data on humans have linked antibiotic treatment in early infancy to long-term effects on microbial diversity and childhood overweight. Similarly, long-term use of IV vancomycin in adults has been linked to an increased obesity risk. But it’s not just long-term exposure that poses a threat; even short courses of oral antibiotics can have profound and irreversible ­effects on intestinal microbial diversity and composition. For example, short-term use of oral vancomycin was found to impair peripheral insulin sensitivity in males with metabolic syndrome associated with ­altered gut microbiota, while amoxicillin did not.⁶

PREBIOTICS AND PROBIOTICS

Prebiotics are indigestible carbohydrates that improve host health by stimulating the growth and activity of colonic bacteria. Most prebiotics are oligosaccharides, which can travel through the upper GI system undigested. When they reach the colon, they are fermented to produce SCFAs that stimulate the growth of microbes that reside there. Prebiotics come from a wide variety of food sources, including asparagus, barley, garlic, onions, and wheat bran.^2,3 Pickled and fermented foods (eg, kimchi, sauerkraut, yogurt, miso) are good sources of both prebiotics and probiotics.²

Bifidobacteria and lactobacilli are the most commonly used strains in foods and supplements containing probiotics. These live microorganisms bring about specific changes in the composition and activity of gut microbiota: they secrete antimicrobial substances, compete with pathogenic bacteria, strengthen the intestinal barrier, and modulate the immune system.^2,3,6 Research on human and animal models suggests that administering probiotics may help manage diabetes.²

DIETARY MODULATION

Dietary changes have been shown to modify the bacterial metabolic activity of the human gut. In one study, obese adults with T2DM were placed on either a fat- or carbohydrate-restricted diet, and it was found that their levels of Bacteroidetes increased and Firmicutes decreased.⁷

In another study, patients with T2DM adhered to one of two calorie-controlled diets: a high-fiber macrobiotic diet or a Mediterranean-style (control) diet. The macrobiotic diet was high in complex carbohydrates, legumes, fermented products, sea salt, and green tea and was free of animal protein, fat, and added sugar. Both diets were effective at improving dysbiosis—ecosystem diversity increased, and health-promoting SCFA producers were replenished. However, the macrobiotic diet was more effective than the control diet at reducing fasting and postprandial glucose, A1C, serum cholesterol, insulin resistance, BMI, and waist and hip circumferences; and only the macrobiotic diet counteracted the inflammation-producing bacterial groups.⁸

METFORMIN

Metformin has therapeutic effects on microbial composition and SCFA synthesis. In a microbiome comparison study, patients with T2DM treated with metformin had more butyrate-producing bacteria than their untreated counterparts. The trend toward increased Lactobacillus seen in the context of T2DM was reduced or reversed by metformin treatment. Researchers were able to tell which patients were (and were not) treated based on their gut microbiome taxonomic signature.⁹

FECAL MICROBIOTA TRANSPLANT

Fecal microbiota transplant, also known as stool transplant or bacteriotherapy, is the process of transferring fecal bacteria from a healthy individual into a recipient. It is used in the treatment of recurrent Clostridium difficile colitis to replenish beneficial bacteria in the digestive tract following use of wide-spectrum antibiotics. In a double-blind randomized controlled trial, insulin-resistant men received either autologous (reinfusion of one’s collected feces) or allogenic (feces from a lean donor) infusions. Allogenic transplantation resulted in significantly increased intestinal microbial diversity and increased levels of butyrate-producing species, accompanied by significantly improved peripheral muscle sensitivity to insulin.^1,6

BARIATRIC SURGERY

Bariatric surgery, specifically Roux-en-Y gastric bypass (RYGBP), is a powerful tool used to treat obesity. In six patients (five of whom had diabetes) treated with RYGBP, dramatic changes to the gut microbiota were seen at three months following surgery. BMI was reduced by 15% to 32%, C-reactive protein decreased in five of six patients, and T2DM was alleviated in all. Postoperatively, there was a striking shift towards higher amounts of Proteobacteria and lower relative amounts of Firmicutes and Bacteroides in the gut phyla. Postoperative increases in certain bacteria were more profound than the amount in lean controls, suggesting these changes are related to alterations in the gut, not lower body weight.^4,6

CONCLUSION

We are just beginning to understand the microbiome and its relationship to health and disease. For patients with T2DM, a variety of interventions may be used to return the gut microbiota to health. Dietary interventions, prebiotics and probiotics, fecal microbial transplant, and bariatric surgery can influence gut microbial composition, with the goal of preventing and/or treating disease. In the future, gut microbial signatures may serve as early diagnostic markers.

Prescribed diets can be trying for both patients and providers; patients often struggle to adhere to them, and providers must determine which plan is suitable for which patient. The optimal diet for patients with diabetes—and whether it is sustainable—remains controversial.

A plant-based diet high in polyunsaturated and monounsaturated fats, with limited saturated fat and avoidance of trans-fatty acids, is supported by the American Association of Clinical Endocrinologists. Caloric restriction is recommended when weight loss is appropriate.¹ The American Diabetes Association (ADA) recommends a Mediterranean-style diet rich in monounsaturated fats with carbohydrates from whole grains, vegetables, fruits, legumes, and dairy products, and an emphasis on foods higher in fiber and lower in glycemic load.²

Additionally, the ADA, the American Association of Diabetes Educators, and the Academy of Nutrition and Dietetics advise that all individuals with diabetes receive individualized Medical Nutrition Therapy (MNT), preferably with a registered dietitian nutritionist (RDN) knowledgeable and skilled in providing diabetes-specific nutrition education. MNT delivered by an RDN has been shown to reduce A1C levels by up to 2% in people with type 2 diabetes (T2DM).³

This flexibility in recommendations creates uncertainty about the correct dietary choice. Several diet plans are endorsed for the management of diabetes, including Mediterranean, low carbohydrate, Paleolithic, vegan, high fiber, and glycemic index (GI). Which should your patients adhere to? Several randomized controlled trials (RCTs), meta-analyses, and literature reviews have examined and compared the benefits of these eating habits for management of diabetes.

MEDITERRANEAN

The Mediterranean diet incorporates plant foods such as greens, tomatoes, onions, garlic, herbs, whole grains, legumes, nuts, and olive oil as the primary source of fat. A crossover trial of adults with T2DM demonstrated a statistically significant A1C reduction (from 7.1% to 6.8%) after 12 weeks on the Mediterranean diet.⁴

In a systematic review of 20 RCTs, Ajala et al analyzed data for nearly 3,500 patients with T2DM who adhered to either a low-carbohydrate, vegetarian, vegan, low-GI, high-fiber, Mediterranean, or high-protein diet for at least six months. The researchers found that Mediterranean, low-carbohydrate, low-GI, and high-protein diets all led to A1C reductions—but the largest reduction was observed with patients on the Mediterranean diet. Low-carbohydrate and Mediterranean diets resulted in the most weight loss.⁵

LOW-CARBOHYDRATE

Low-carbohydrate diets have decreased in popularity due to concerns about their effects on renal function, possible lack of nutrients, and speculation that their macronutrient composition may have effects on weight beyond those explained by caloric deficit. A meta-analysis of 13 studies of adults with T2DM following a low-carbohydrate diet (≤ 45% of calories from carbohydrates) demonstrated beneficial effects on fasting glucose, A1C, and triglyceride levels. Nine of the studies evaluated glycemic control and found A1C reduction with lower carbohydrate diets; the greatest reductions in A1C and triglycerides were correlated with the lowest carbohydrate intakes. No significant effects were seen for total, HDL, or LDL cholesterol.⁶

In the literature review by Ajala et al, low-carbohydrate, low-GI, and Mediterranean diets all improved lipid profiles. HDL cholesterol increased the most with a low-carbohydrate diet.⁵

A two-week study of 10 adults with T2DM found that just one week on a low-carbohydrate diet decreased the average 24-h plasma glucose from 135 mg/dL to 113 mg/dL. Over the two-week study period, triglycerides decreased by 35%, cholesterol by 10%, and A1C by 0.5%. Patients were allowed to consume as much protein and fat as desired. Food sources included beef and ground turkey patties, chicken breasts, turkey, ham, steamed vegetables, butter, diet gelatin, and a limited amount of cheese. Mean calorie intake decreased from 3,111 to 2,164 calories/d. Carbohydrate intake decreased from 300 to 20 g/d. Weight loss was entirely explained by the mean energy deficit.⁶ Patients experienced no difference in hunger, satisfaction, or energy level with a low-carb diet compared to their usual diet.⁷

A literature review of six studies examined the effects of low-carb diets (between 20-95 g/d) on body weight and A1C in patients with T2DM. Three of the studies restricted carbohydrate intake to less than 50 g/d. All reported reductions in body weight and A1C. In two studies, the majority of the weight loss was explained by a decrease in body fat, not loss of water weight. No deleterious effects on cardiovascular disease risk, renal function, or nutritional intake were seen. The researchers concluded that low-carb diets are safe and effective over the short term for people with T2DM.⁸

PALEOLITHIC

The Paleolithic diet (also referred to as the caveman diet, Stone Age diet, and hunter-gatherer diet) involves eating foods believed to have been available to humans before agriculture—this period began about 2.5 million years ago and ended about 100,000 years ago. Food sources include wild animal meat (lean meat and fish) and uncultivated plant foods (vegetables, fruits, roots, eggs, and nuts). It excludes grains, legumes, dairy products, salt, refined sugar, and processed oils.

In a randomized crossover study of 13 participants with T2DM, the Paleolithic diet improved glucose control and several cardiovascular disease markers, compared to a standard diabetes diet. The Paleolithic diet resulted in significantly lower A1C, triglycerides, diastolic blood pressure, body weight, BMI, and waist circumference, as well as increased HDL. Despite receiving no instruction to restrict calories, patients on the Paleolithic diet consumed fewer calories and carbohydrates, and more protein and fat, than those on the standard diabetes diet. The caloric deficit accounted almost exactly for the observed difference in weight loss between the two groups.⁹

GLYCEMIC INDEX

The GI measures the blood glucose level increase in the two hours after eating a particular food, with 100 representing the effect of glucose consumption. Low-GI food sources include beans, peas, lentils, pasta, pumpernickel bread, bulgur, parboiled rice, barley, and oats, while high-GI foods include potatoes, wheat flour, white bread, most breakfast cereals, and rice.

A meta-analysis compared the effects of high- and low-GI diets on glycemic control in 356 patients with diabetes. Ten of 14 studies documented improvements in A1C and postprandial plasma glucose with lower GI diets. Low-GI diets reduced A1C by 0.43% after an average duration of 10 weeks. The average GI was 83 for high-GI diets and 65 for low-GI diets. The researchers concluded that selecting low-GI foods has a small but clinically relevant effect on medium-term glycemic control, similar to that offered by medications that target postprandial blood glucose excursions.¹⁰

Low-GI diets resulted in lower A1C and higher HDL but no significant change in weight, according to Ajala et al.⁵

HIGH-FIBER

A survey of 15 studies examined the relationship between fiber intake and glycemic control. Interventions ranged from an additional 4 to 40 g of fiber per day, with a mean increase of 18.3 g/d. Additional fiber lowered A1C by 0.26% in 3 to 12 weeks, compared to placebo. The overall mean fasting blood glucose reduction was 15.32 mg/dL. No study lasted more than 12 weeks, but it is inferred that a longer study could result in a greater A1C reduction. Current dietary guidelines for patients with diabetes exceed the amount of fiber included in most of these studies.¹¹

VEGAN

Ajala et al observed that patients on a vegan diet had lower total cholesterol, LDL, and A1C levels, compared to those on a low-fat diet. At 18 months, the vegetarian diet demonstrated improvement in glucose control and lipids, but not weight loss.⁵

In one RCT, a low-fat vegan diet was shown to improve glycemic control and lipid levels more than a conventional diabetes diet did. A1C decreased by 1.23% over 22 weeks, compared to 0.38% in the conventional diet group. Body weight decreased by 6.5 kg and LDL cholesterol decreased by 21.2% with the vegan diet, compared with a weight loss of 3.1 kg and a 10.7% LDL reduction in the conventional diet group.¹²

Patients on the vegan diet derived energy primarily from carbohydrates (75%), protein (15%), and fat (10%) by eating fruits, vegetables, grains, and legumes. Portion size and caloric and carbohydrate intake were not restricted. The conventional diet involved a caloric intake mainly from a combination of carbohydrates and monounsaturated fats (60% to 70%), protein (15% to 20%), and saturated fat (< 7%). The diet was individualized based on caloric needs and participants’ lipid levels. All participants were given calorie intake deficits of 500 to 1000 kcal/d.¹³ Participants rated both diets as satisfactory, with no significant differences between groups. The researchers concluded that a low-fat vegan diet has acceptability similar to that of a more conventional diabetes diet.¹²

CONCLUSION

Diabetes management strategies may incorporate a variety of dietary plans. While study populations are small and study durations relatively short, the aforementioned diets show improvement in biochemical markers such as fasting glucose, A1C, and lipid levels. The Mediterranean diet is believed to be sustainable over the long term, given the duration of time that people in the region have survived on it. Low-carbohydrate diets, including the Atkins and Paleolithic diets, are very effective at lowering A1C and triglycerides. Vegetarian/vegan diets may be more acceptable to patients than previously thought.

The long-term impact of any eating pattern will likely relate to adherence; adherence is more likely when patients find a diet to be acceptable, palatable, and easy to prepare. Diet selection should incorporate patient preferences and lifestyle choices, and when possible, should involve an RDN with expertise in diabetes.

Prescribed diets can be trying for both patients and providers; patients often struggle to adhere to them, and providers must determine which plan is suitable for which patient. The optimal diet for patients with diabetes—and whether it is sustainable—remains controversial.

A plant-based diet high in polyunsaturated and monounsaturated fats, with limited saturated fat and avoidance of trans-fatty acids, is supported by the American Association of Clinical Endocrinologists. Caloric restriction is recommended when weight loss is appropriate.¹ The American Diabetes Association (ADA) recommends a Mediterranean-style diet rich in monounsaturated fats with carbohydrates from whole grains, vegetables, fruits, legumes, and dairy products, and an emphasis on foods higher in fiber and lower in glycemic load.²

Additionally, the ADA, the American Association of Diabetes Educators, and the Academy of Nutrition and Dietetics advise that all individuals with diabetes receive individualized Medical Nutrition Therapy (MNT), preferably with a registered dietitian nutritionist (RDN) knowledgeable and skilled in providing diabetes-specific nutrition education. MNT delivered by an RDN has been shown to reduce A1C levels by up to 2% in people with type 2 diabetes (T2DM).³

This flexibility in recommendations creates uncertainty about the correct dietary choice. Several diet plans are endorsed for the management of diabetes, including Mediterranean, low carbohydrate, Paleolithic, vegan, high fiber, and glycemic index (GI). Which should your patients adhere to? Several randomized controlled trials (RCTs), meta-analyses, and literature reviews have examined and compared the benefits of these eating habits for management of diabetes.

MEDITERRANEAN

The Mediterranean diet incorporates plant foods such as greens, tomatoes, onions, garlic, herbs, whole grains, legumes, nuts, and olive oil as the primary source of fat. A crossover trial of adults with T2DM demonstrated a statistically significant A1C reduction (from 7.1% to 6.8%) after 12 weeks on the Mediterranean diet.⁴

In a systematic review of 20 RCTs, Ajala et al analyzed data for nearly 3,500 patients with T2DM who adhered to either a low-carbohydrate, vegetarian, vegan, low-GI, high-fiber, Mediterranean, or high-protein diet for at least six months. The researchers found that Mediterranean, low-carbohydrate, low-GI, and high-protein diets all led to A1C reductions—but the largest reduction was observed with patients on the Mediterranean diet. Low-carbohydrate and Mediterranean diets resulted in the most weight loss.⁵

LOW-CARBOHYDRATE

Low-carbohydrate diets have decreased in popularity due to concerns about their effects on renal function, possible lack of nutrients, and speculation that their macronutrient composition may have effects on weight beyond those explained by caloric deficit. A meta-analysis of 13 studies of adults with T2DM following a low-carbohydrate diet (≤ 45% of calories from carbohydrates) demonstrated beneficial effects on fasting glucose, A1C, and triglyceride levels. Nine of the studies evaluated glycemic control and found A1C reduction with lower carbohydrate diets; the greatest reductions in A1C and triglycerides were correlated with the lowest carbohydrate intakes. No significant effects were seen for total, HDL, or LDL cholesterol.⁶

In the literature review by Ajala et al, low-carbohydrate, low-GI, and Mediterranean diets all improved lipid profiles. HDL cholesterol increased the most with a low-carbohydrate diet.⁵

A two-week study of 10 adults with T2DM found that just one week on a low-carbohydrate diet decreased the average 24-h plasma glucose from 135 mg/dL to 113 mg/dL. Over the two-week study period, triglycerides decreased by 35%, cholesterol by 10%, and A1C by 0.5%. Patients were allowed to consume as much protein and fat as desired. Food sources included beef and ground turkey patties, chicken breasts, turkey, ham, steamed vegetables, butter, diet gelatin, and a limited amount of cheese. Mean calorie intake decreased from 3,111 to 2,164 calories/d. Carbohydrate intake decreased from 300 to 20 g/d. Weight loss was entirely explained by the mean energy deficit.⁶ Patients experienced no difference in hunger, satisfaction, or energy level with a low-carb diet compared to their usual diet.⁷

A literature review of six studies examined the effects of low-carb diets (between 20-95 g/d) on body weight and A1C in patients with T2DM. Three of the studies restricted carbohydrate intake to less than 50 g/d. All reported reductions in body weight and A1C. In two studies, the majority of the weight loss was explained by a decrease in body fat, not loss of water weight. No deleterious effects on cardiovascular disease risk, renal function, or nutritional intake were seen. The researchers concluded that low-carb diets are safe and effective over the short term for people with T2DM.⁸

PALEOLITHIC

The Paleolithic diet (also referred to as the caveman diet, Stone Age diet, and hunter-gatherer diet) involves eating foods believed to have been available to humans before agriculture—this period began about 2.5 million years ago and ended about 100,000 years ago. Food sources include wild animal meat (lean meat and fish) and uncultivated plant foods (vegetables, fruits, roots, eggs, and nuts). It excludes grains, legumes, dairy products, salt, refined sugar, and processed oils.

In a randomized crossover study of 13 participants with T2DM, the Paleolithic diet improved glucose control and several cardiovascular disease markers, compared to a standard diabetes diet. The Paleolithic diet resulted in significantly lower A1C, triglycerides, diastolic blood pressure, body weight, BMI, and waist circumference, as well as increased HDL. Despite receiving no instruction to restrict calories, patients on the Paleolithic diet consumed fewer calories and carbohydrates, and more protein and fat, than those on the standard diabetes diet. The caloric deficit accounted almost exactly for the observed difference in weight loss between the two groups.⁹

GLYCEMIC INDEX

The GI measures the blood glucose level increase in the two hours after eating a particular food, with 100 representing the effect of glucose consumption. Low-GI food sources include beans, peas, lentils, pasta, pumpernickel bread, bulgur, parboiled rice, barley, and oats, while high-GI foods include potatoes, wheat flour, white bread, most breakfast cereals, and rice.

A meta-analysis compared the effects of high- and low-GI diets on glycemic control in 356 patients with diabetes. Ten of 14 studies documented improvements in A1C and postprandial plasma glucose with lower GI diets. Low-GI diets reduced A1C by 0.43% after an average duration of 10 weeks. The average GI was 83 for high-GI diets and 65 for low-GI diets. The researchers concluded that selecting low-GI foods has a small but clinically relevant effect on medium-term glycemic control, similar to that offered by medications that target postprandial blood glucose excursions.¹⁰

Low-GI diets resulted in lower A1C and higher HDL but no significant change in weight, according to Ajala et al.⁵

HIGH-FIBER

A survey of 15 studies examined the relationship between fiber intake and glycemic control. Interventions ranged from an additional 4 to 40 g of fiber per day, with a mean increase of 18.3 g/d. Additional fiber lowered A1C by 0.26% in 3 to 12 weeks, compared to placebo. The overall mean fasting blood glucose reduction was 15.32 mg/dL. No study lasted more than 12 weeks, but it is inferred that a longer study could result in a greater A1C reduction. Current dietary guidelines for patients with diabetes exceed the amount of fiber included in most of these studies.¹¹

VEGAN

Ajala et al observed that patients on a vegan diet had lower total cholesterol, LDL, and A1C levels, compared to those on a low-fat diet. At 18 months, the vegetarian diet demonstrated improvement in glucose control and lipids, but not weight loss.⁵

In one RCT, a low-fat vegan diet was shown to improve glycemic control and lipid levels more than a conventional diabetes diet did. A1C decreased by 1.23% over 22 weeks, compared to 0.38% in the conventional diet group. Body weight decreased by 6.5 kg and LDL cholesterol decreased by 21.2% with the vegan diet, compared with a weight loss of 3.1 kg and a 10.7% LDL reduction in the conventional diet group.¹²

Patients on the vegan diet derived energy primarily from carbohydrates (75%), protein (15%), and fat (10%) by eating fruits, vegetables, grains, and legumes. Portion size and caloric and carbohydrate intake were not restricted. The conventional diet involved a caloric intake mainly from a combination of carbohydrates and monounsaturated fats (60% to 70%), protein (15% to 20%), and saturated fat (< 7%). The diet was individualized based on caloric needs and participants’ lipid levels. All participants were given calorie intake deficits of 500 to 1000 kcal/d.¹³ Participants rated both diets as satisfactory, with no significant differences between groups. The researchers concluded that a low-fat vegan diet has acceptability similar to that of a more conventional diabetes diet.¹²

CONCLUSION

Diabetes management strategies may incorporate a variety of dietary plans. While study populations are small and study durations relatively short, the aforementioned diets show improvement in biochemical markers such as fasting glucose, A1C, and lipid levels. The Mediterranean diet is believed to be sustainable over the long term, given the duration of time that people in the region have survived on it. Low-carbohydrate diets, including the Atkins and Paleolithic diets, are very effective at lowering A1C and triglycerides. Vegetarian/vegan diets may be more acceptable to patients than previously thought.

The long-term impact of any eating pattern will likely relate to adherence; adherence is more likely when patients find a diet to be acceptable, palatable, and easy to prepare. Diet selection should incorporate patient preferences and lifestyle choices, and when possible, should involve an RDN with expertise in diabetes.

Prescribed diets can be trying for both patients and providers; patients often struggle to adhere to them, and providers must determine which plan is suitable for which patient. The optimal diet for patients with diabetes—and whether it is sustainable—remains controversial.

A plant-based diet high in polyunsaturated and monounsaturated fats, with limited saturated fat and avoidance of trans-fatty acids, is supported by the American Association of Clinical Endocrinologists. Caloric restriction is recommended when weight loss is appropriate.¹ The American Diabetes Association (ADA) recommends a Mediterranean-style diet rich in monounsaturated fats with carbohydrates from whole grains, vegetables, fruits, legumes, and dairy products, and an emphasis on foods higher in fiber and lower in glycemic load.²

Additionally, the ADA, the American Association of Diabetes Educators, and the Academy of Nutrition and Dietetics advise that all individuals with diabetes receive individualized Medical Nutrition Therapy (MNT), preferably with a registered dietitian nutritionist (RDN) knowledgeable and skilled in providing diabetes-specific nutrition education. MNT delivered by an RDN has been shown to reduce A1C levels by up to 2% in people with type 2 diabetes (T2DM).³

This flexibility in recommendations creates uncertainty about the correct dietary choice. Several diet plans are endorsed for the management of diabetes, including Mediterranean, low carbohydrate, Paleolithic, vegan, high fiber, and glycemic index (GI). Which should your patients adhere to? Several randomized controlled trials (RCTs), meta-analyses, and literature reviews have examined and compared the benefits of these eating habits for management of diabetes.

MEDITERRANEAN

The Mediterranean diet incorporates plant foods such as greens, tomatoes, onions, garlic, herbs, whole grains, legumes, nuts, and olive oil as the primary source of fat. A crossover trial of adults with T2DM demonstrated a statistically significant A1C reduction (from 7.1% to 6.8%) after 12 weeks on the Mediterranean diet.⁴

In a systematic review of 20 RCTs, Ajala et al analyzed data for nearly 3,500 patients with T2DM who adhered to either a low-carbohydrate, vegetarian, vegan, low-GI, high-fiber, Mediterranean, or high-protein diet for at least six months. The researchers found that Mediterranean, low-carbohydrate, low-GI, and high-protein diets all led to A1C reductions—but the largest reduction was observed with patients on the Mediterranean diet. Low-carbohydrate and Mediterranean diets resulted in the most weight loss.⁵

LOW-CARBOHYDRATE

Low-carbohydrate diets have decreased in popularity due to concerns about their effects on renal function, possible lack of nutrients, and speculation that their macronutrient composition may have effects on weight beyond those explained by caloric deficit. A meta-analysis of 13 studies of adults with T2DM following a low-carbohydrate diet (≤ 45% of calories from carbohydrates) demonstrated beneficial effects on fasting glucose, A1C, and triglyceride levels. Nine of the studies evaluated glycemic control and found A1C reduction with lower carbohydrate diets; the greatest reductions in A1C and triglycerides were correlated with the lowest carbohydrate intakes. No significant effects were seen for total, HDL, or LDL cholesterol.⁶

In the literature review by Ajala et al, low-carbohydrate, low-GI, and Mediterranean diets all improved lipid profiles. HDL cholesterol increased the most with a low-carbohydrate diet.⁵

A two-week study of 10 adults with T2DM found that just one week on a low-carbohydrate diet decreased the average 24-h plasma glucose from 135 mg/dL to 113 mg/dL. Over the two-week study period, triglycerides decreased by 35%, cholesterol by 10%, and A1C by 0.5%. Patients were allowed to consume as much protein and fat as desired. Food sources included beef and ground turkey patties, chicken breasts, turkey, ham, steamed vegetables, butter, diet gelatin, and a limited amount of cheese. Mean calorie intake decreased from 3,111 to 2,164 calories/d. Carbohydrate intake decreased from 300 to 20 g/d. Weight loss was entirely explained by the mean energy deficit.⁶ Patients experienced no difference in hunger, satisfaction, or energy level with a low-carb diet compared to their usual diet.⁷

A literature review of six studies examined the effects of low-carb diets (between 20-95 g/d) on body weight and A1C in patients with T2DM. Three of the studies restricted carbohydrate intake to less than 50 g/d. All reported reductions in body weight and A1C. In two studies, the majority of the weight loss was explained by a decrease in body fat, not loss of water weight. No deleterious effects on cardiovascular disease risk, renal function, or nutritional intake were seen. The researchers concluded that low-carb diets are safe and effective over the short term for people with T2DM.⁸

PALEOLITHIC

The Paleolithic diet (also referred to as the caveman diet, Stone Age diet, and hunter-gatherer diet) involves eating foods believed to have been available to humans before agriculture—this period began about 2.5 million years ago and ended about 100,000 years ago. Food sources include wild animal meat (lean meat and fish) and uncultivated plant foods (vegetables, fruits, roots, eggs, and nuts). It excludes grains, legumes, dairy products, salt, refined sugar, and processed oils.

In a randomized crossover study of 13 participants with T2DM, the Paleolithic diet improved glucose control and several cardiovascular disease markers, compared to a standard diabetes diet. The Paleolithic diet resulted in significantly lower A1C, triglycerides, diastolic blood pressure, body weight, BMI, and waist circumference, as well as increased HDL. Despite receiving no instruction to restrict calories, patients on the Paleolithic diet consumed fewer calories and carbohydrates, and more protein and fat, than those on the standard diabetes diet. The caloric deficit accounted almost exactly for the observed difference in weight loss between the two groups.⁹

GLYCEMIC INDEX

The GI measures the blood glucose level increase in the two hours after eating a particular food, with 100 representing the effect of glucose consumption. Low-GI food sources include beans, peas, lentils, pasta, pumpernickel bread, bulgur, parboiled rice, barley, and oats, while high-GI foods include potatoes, wheat flour, white bread, most breakfast cereals, and rice.

A meta-analysis compared the effects of high- and low-GI diets on glycemic control in 356 patients with diabetes. Ten of 14 studies documented improvements in A1C and postprandial plasma glucose with lower GI diets. Low-GI diets reduced A1C by 0.43% after an average duration of 10 weeks. The average GI was 83 for high-GI diets and 65 for low-GI diets. The researchers concluded that selecting low-GI foods has a small but clinically relevant effect on medium-term glycemic control, similar to that offered by medications that target postprandial blood glucose excursions.¹⁰

Low-GI diets resulted in lower A1C and higher HDL but no significant change in weight, according to Ajala et al.⁵

HIGH-FIBER

A survey of 15 studies examined the relationship between fiber intake and glycemic control. Interventions ranged from an additional 4 to 40 g of fiber per day, with a mean increase of 18.3 g/d. Additional fiber lowered A1C by 0.26% in 3 to 12 weeks, compared to placebo. The overall mean fasting blood glucose reduction was 15.32 mg/dL. No study lasted more than 12 weeks, but it is inferred that a longer study could result in a greater A1C reduction. Current dietary guidelines for patients with diabetes exceed the amount of fiber included in most of these studies.¹¹

VEGAN

Ajala et al observed that patients on a vegan diet had lower total cholesterol, LDL, and A1C levels, compared to those on a low-fat diet. At 18 months, the vegetarian diet demonstrated improvement in glucose control and lipids, but not weight loss.⁵

In one RCT, a low-fat vegan diet was shown to improve glycemic control and lipid levels more than a conventional diabetes diet did. A1C decreased by 1.23% over 22 weeks, compared to 0.38% in the conventional diet group. Body weight decreased by 6.5 kg and LDL cholesterol decreased by 21.2% with the vegan diet, compared with a weight loss of 3.1 kg and a 10.7% LDL reduction in the conventional diet group.¹²

Patients on the vegan diet derived energy primarily from carbohydrates (75%), protein (15%), and fat (10%) by eating fruits, vegetables, grains, and legumes. Portion size and caloric and carbohydrate intake were not restricted. The conventional diet involved a caloric intake mainly from a combination of carbohydrates and monounsaturated fats (60% to 70%), protein (15% to 20%), and saturated fat (< 7%). The diet was individualized based on caloric needs and participants’ lipid levels. All participants were given calorie intake deficits of 500 to 1000 kcal/d.¹³ Participants rated both diets as satisfactory, with no significant differences between groups. The researchers concluded that a low-fat vegan diet has acceptability similar to that of a more conventional diabetes diet.¹²

CONCLUSION

Diabetes management strategies may incorporate a variety of dietary plans. While study populations are small and study durations relatively short, the aforementioned diets show improvement in biochemical markers such as fasting glucose, A1C, and lipid levels. The Mediterranean diet is believed to be sustainable over the long term, given the duration of time that people in the region have survived on it. Low-carbohydrate diets, including the Atkins and Paleolithic diets, are very effective at lowering A1C and triglycerides. Vegetarian/vegan diets may be more acceptable to patients than previously thought.

The long-term impact of any eating pattern will likely relate to adherence; adherence is more likely when patients find a diet to be acceptable, palatable, and easy to prepare. Diet selection should incorporate patient preferences and lifestyle choices, and when possible, should involve an RDN with expertise in diabetes.