The American Diabetes Association (ADA) recommends weight loss for the prevention and control of type 2 diabetes (T2DM). Though the ADA does not recommend one diet over another, it specifically mentions that the Mediterranean and low-fat or low-carbohydrate diets may play roles in weight loss for individuals with prediabetes or with T2DM.1
Studies have suggested, however, that the nutrient composition of certain diets may help in glycemic control, above and beyond weight loss itself. Many authorities, including the ADA, American Heart Association, Canadian Diabetes Association, and the European Association for the Study of Diabetes (EASD), recommend that carbohydrates should constitute 50-60% of total daily energy intake, and total fat should be ≤30% of daily intake.2 Beyond that, which diets might be best for the prevention and control of T2DM?
Perhaps the most extensively researched diet, evidence for the benefits of the Mediterranean diet date back to the 1960s, when Ancel Keys realized that people who lived near the Mediterranean had lower rates of chronic disease and longer life expectancies than those in other areas of the world. In both 2010 and 2013, UNESCO listed the Mediterranean diet as an Intangible Cultural Heritage of Humanity.
Research points to a role for the Mediterranean diet in controlling chronic inflammation implicated in conditions like the metabolic syndrome, diabetes, obesity, and cardiovascular disease (CVD).
A recent systematic review3 looking at 24 studies published through May 2014, found “good evidence” that following the Mediterranean diet has “favorable” effects on glycemic control and risk for CVD. Another recent review that included 8 meta-analyses and 5 RCTs published through January 2015, found that following the Mediterranean diet could increase the probability of remission from metabolic syndrome by 49% over 2-5 years, and decrease the risk of developing diabetes by 19-23%, compared to other diets.4
Results from the PREDEMID trial in Spain, one of the largest RCTs looking at the role of the Mediterranean diet in cardiometabolic disease, found a 52% reduction over 4 years in the incidence of diabetes among 418 participants who followed the Mediterranean diet, compared to those on a low-fat diet.5 Ten year results among over 3000 participants in the ATTICA cohort trial in Greece found that moderate adherence to the Mediterranean diet decreased diabetes risk by 49%, and high adherence decreased diabetes risk by 62%, compared to low adherence.6
All this points to the Mediterranean diet as a major player in diabetes prevention. The emphasis seems to be holistic, highlighting the combined effect of dietary components.
Low Carbohydrate Diets
Low carbohydrate diets usually restrict carbs to 20-60 grams/day. Many variations exist, such as the low carbohydrate, high-protein Atkins diet and the low carbohydrate Zone diet.
Studies have suggested that following a low carbohydrate diet may improve diabetes control, as well as lead to weight loss and improved lipids. 8 Some authors caution, however, that these benefits may apply only in the short-term, and that long-term adherence to low carbohydrate diets may pose certain risks.8 Such risks include vitamin deficiencies, reduced fiber intake, and renal dysfunction (for patients on high protein diets). Diets high in protein from animal sources may also increase the risk of total mortality.9
Not all carbs are the same, with some studies suggesting that lower glycemic diets may help in diabetes prevention.10 A recent randomized trial,11 though, found that five weeks of following a low-carb, low-glycemic index diet did not improve insulin sensitivity, lipid levels, or systolic blood pressure, compared to a high-carb, high glycemic index diet. The trial included 163 overweight individuals with prehypertension but without diabetes. Low-carb, low-glycemic index diets as well as high-carb high-glycemic index diets were based on a healthy DASH-style diet, suggesting that an overall healthy diet may be more beneficial than the independent contribution of low glycemic index foods.11
As one of the “newest” players on the scene, the Paleo diet includes foods thought to have existed before the invention of agriculture. The diet includes “wild” plant foods and meats, fish, roots, eggs, and nuts, and excludes grains, legumes, dairy, salt, refined sugar, and processed oils. It is high in fiber, antioxidants, and poly- and mono-unsaturated fats, but lacks calcium, which may require supplementation.12
Small studies have started trickling in, suggesting that the Paleo diet may help prevent obesity and the metabolic syndrome. In a randomized crossover study, researchers randomized 13 patients with T2DM on oral antihyperglycemics to the paleo diet vs. a diabetes diet. They found that the Paleo diet significantly lowered HbA1c, triglycerides, diastolic blood pressure, and BMI, compared to the diabetes diet.13
Another study compared the Paleo diet to the Mediterranean diet in 29 patients with ischemic heart disease and glucose intolerance or T2DM. Over twelve weeks, the study found that the Paleo diet significantly improved glucose tolerance, but the Mediterranean diet did not.14
A third study randomized 24 patients to the Paleo diet or an ADA recommended diet for three weeks. While metabolic measures improved in both groups, the Paleo group experienced more improvements in HbA1c and insulin sensitivity.15
Which Diet Works Best?
A recent review2 covered 20 RCTs that measured adherence for six months or more, and compared low-carbohydrate, vegetarian, vegan, low-glycemic index, high fiber, Mediterranean, and high-protein diets, vs. lowfat, high-glycemic index, ADA, EASD and low-protein diets. It found:
• Low carbohydrate, low-glycemic index, Mediterranean and high protein diets all improved glycemic control (HbA1c reductions of -0.12% (p=0.04), -0.14% (p=0.008), -0.47% (p<0.00001, and -0.28% (p<0.00001).
• The Mediterranean diet had the largest effect on HbA1c, similar to that seen with medication.
• Low-carb and Mediterranean diets led the largest weight loss (-0.69 kg (p=0.21) and -1.84 kg (p<0.0001), respectively).
• Low carb diets provided better weight loss, glycemic control, and lipid profiles than low-fat diets.
“Dietary behaviors and choices are often personal, and it is usually more realistic for a dietary modification to be individualized rather than to use a one-size-fits-all approach for each person,” the authors concluded, “The diets reviewed in this study show that there may be a range of beneficial dietary options for people with T2DM.”
Take Home Points
• Research suggests that the Mediterranean diet may be a major player in diabetes prevention and control.
• Low carbohydrate diets may play a role in weight loss, but could pose certain risks, especially if high in protein.
• Low glycemic index diets may play a role in diabetes prevention and control, but research is conflicting.
• Preliminary research suggests that the Paleo diet may play a role in diabetes prevention.
• Patients may benefit from choosing from a range of diets and an individualized approach.
1. American Diabetes Association. Standards of Medical Care in Diabetes - 2013. 2013;36(1):s1-e4.
2. Ajala O, et al. Systematic review and meta-analysis of different dietary approaches to the management of type 2 diabetes. Am J Clin Nutr. 2013 Mar;97(3):505-516.
3. Sleiman D, et al. Effect of Mediterranean diet in diabetes control and cardiovascular risk modification: a systematic review. Front Public Health. 2015 Apr 28;3:69.
4. Esposito K, et al. A journey into a Mediterranean diet and type 2 diabetes: a systematic review with meta-analyses. BMJ Open. 2015 Aug 10;5(8):e008222.
5. Salas-Salvadó J, et al. Reduction in the incidence of type 2 diabetes with the Mediterranean diet: results of the PREDIMED-Reus nutrition intervention randomized trial. Diabetes Care. 2011 Jan;34(1):14-19.
6. Koloverou E, et al. Adherence to Mediterranean diet and 10-year incidence (2002-2012) of diabetes: correlations with inflammatory and oxidative stress biomarkers in the ATTICA cohort study. Diabetes Metab Res Rev. 2015 Jun 24. [Epub ahead of print]
7. Thomas DE, Elliott EJ. The use of low-glycaemic index diets in diabetes control. Br J Nutr. 2010 Sep;104(6):797-802.
8. Czyżewska-Majchrzak Ł, et al. The use of low-carbohydrate diet in type 2 diabetes - benefits and risks. Ann Agric Environ Med. 2014;21(2):320-326.
9. Trichopoulou A, et al. Low-carbohydrate-high-protein diet and long-term survival in a general population cohort. Eur J Clin Nutr. 2007 May;61(5):575-581.
10. Dong JY, et al. Dietary glycaemic index and glycaemic load in relation to the risk of type 2 diabetes: a meta-analysis of prospective cohort studies. Br J Nutr. 2011 Dec;106(11):1649-1654.
11. Sacks FM, et al. Effects of high vs low glycemic index of dietary carbohydrate on cardiovascular disease risk factors and insulin sensitivity: the OmniCarb randomized clinical trial. JAMA. 2014 Dec 17;312(23):2531-2541.
12. Klonoff DC. The beneficial effects of a Paleolithic diet on type 2 diabetes and other risk factors for cardiovascular disease. J Diabetes Sci Technol. 2009 Nov 1;3(6):1229-1232.
13. Jönsson T, et al. Beneficial effects of a Paleolithic diet on cardiovascular risk factors in type 2 diabetes: a randomized cross-over pilot study. Cardiovasc Diabetol. 2009 Jul 16;8:35.
14. Lindeberg S, et al. A Palaeolithic diet improves glucose tolerance more than a Mediterranean-like diet in individuals with ischaemic heart disease. Diabetologia. 2007 Sep;50(9):1795-807.
15. Masharani U, et al. Metabolic and physiologic effects from consuming a hunter-gatherer (Paleolithic)-type diet in type 2 diabetes. Eur J Clin Nutr. 2015 Aug;69(8):944-948.