In addition to important lifestyle factors including weight loss and physical activity, progress is being made to understand how food choices help manage risk factors for type-2 diabetes (T2D).
The current state of the evidence supporting how nutrients and foods contribute to T2D risk was recently reviewed in a paper published in the Journal of Nutrition by Maki and Phillips, who stated:
“diets rich in refined dietary carbohydrate [particularly those with a high glycemic index] may elevate T2D risk; however, the appropriate combination of macronutrients to optimize metabolic health has not been fully described.” (Maki, 2014)
If dietary refined carbohydrate is to be reduced, what macronutrient(s) should be increased to maintain energy needs and optimize metabolic health? The available evidence appears to support that cereal fibers (Liu, 2002; Weickert, 2011), lean protein sources (Gadgil, 2013; Weickert, 2011), and vegetable oils (Alhazmi, 2012) are potentially suitable replacements for sugars and starches.
With regard to disease risk, it is important to consider the type and source of dietary fiber. Vegetable and fruit fiber intakes have not been associated with lower risk for T2D; whereas higher intake of fibers from cereal products has been associated with lower risk in a dose-dependent manner (Liu, 2002; Schulze, 2007).
The beneficial effects observed with a moderate increase in dietary protein may be partially a result of increased satiety and thermogenesis (both of which may aid in weight loss), and appear to vary with metabolic state and intake level. Maki and Phillips note:
“partial substitution of protein for refined carbohydrate may have beneficial effects on serum lipid profile without adversely affecting insulin sensitivity, but a high protein intake (>30% of energy) may have an adverse impact on insulin sensitivity.”
Further, a study conducted by Weickert and colleagues (Weickert, 2011) in overweight adults with metabolic syndrome showed that:
“[At] moderate protein and cereal fiber intake (20-25% of energy and 35 g/d, respectively), insulin sensitivity after 6 week of intervention was improved to a degree similar to that observed during the high-cereal-fiber condition…” (Maki, 2014)
Mediterranean diet patterns are characteristically high in unsaturated oleic acid. The PREDIMED trial utilized a Mediterranean diet pattern supplemented with either extra-virgin olive oil (1 L/week) or nuts (30 g/day) (Salas-Salvado, 2011). Both of the modified Mediterranean diets cut 4-year T2D risk in half when compared to the control condition that simply counseled subjects to adhere to a low-fat diet.
Other dietary exposures and specific foods (e.g., polyphenols, dairy, coffee, and berries) that may impact blood glucose, insulin sensitivity, and inflammation are being actively explored for a potential contribution to T2D risk.
The overall state of the current evidence, as summarized by Maki and Phillips, is as follows:
“a dietary pattern that contains a relatively low amount of refined-carbohydrate/high-glycemic index foods and that emphasizes foods containing low-glycemic index carbohydrates, cereal fibers, slowly digested starches, lean sources of proteins, and vegetable fats is likely to be associated with an improved T2D risk factor profile.”
Alhazmi, A, E Stojanovski, M McEvoy, and ML Garg. “Macronutrient intakes and development of type 2 diabetes: a systematic review and meta-analysis of cohort studies.” J Am Coll Nutr 2012;31:243-58.
Gadgil, MD, LJ Appel, E Yeung, CA Anderson, FM Sacks, ER Miller III. “The effects of carbohydrate, unsaturated fat, and protein intake on measures of insulin sensitivity: results from the OmniHeart trial.” Diabetes Care 2013;36:1132-7.
Liu, S. “Intake of refined carbohydrates and whole grain foods in relation to risk of type 2 diabetes mellitus and coronary heart disease.” J Am Coll Nutr 2002;21:298-306.
Maki, KC and AK Phillips. “Dietary substitutions for refined carbohydrate that show promise for reducing risk of Type 2 Diabetes in men and women.” J Nutr 2015;145(1)159S-163S.
Salas-Salvado, J, M Bullo, N Babio, MA Martinez-Gonzalez, N Ibarrola-Jurado, J Basora, R Estruch, MI Covas, D Corella, F Aros, et al. “Reduction in the incidence of type 2 diabetes with the Mediterranean diet: results of the PREDIMED-Reus nutrition intervention randomized trial.” Diabetes Care2011;34:14-9.
Schulze, MB, M Schulz, C Heidemann, A Schienkiewitz, K Hoffmann, H Boeing. “Fiber and magnesium intake and incidence of type 2 diabetes: a prospective study and meta-analysis.” Arch Intern Med2007;167:956-65.
Weickert, MO, M Roden, F Isken, D Hoffmann, P Nowotny, M Osterhoff, M Blaut, C Alpert, O Gogebakan, C Bumke-Vogt, et al. “Effects of supplemented isoenergetic diets differing in cereal fiber and protein content on insulin sensitivity in overweight humans.” Am J Clin Nutr 2011;94:459-71.
Kevin C. Maki, Ph.D. is the Founder and Chief Science Officer for the Midwest Center for Metabolic and Cardiovascular Research (MC-MCR) in Chicago, Illinois. He specializes in the design and conduct of clinical studies in human nutrition, metabolism and chronic disease risk factor management. Dr. Maki also holds an Adjunct Faculty position in Biostatistics and Applied Epidemiology at DePaul University. He is a certified Clinical Lipid Specialist and a Fellow of the National Lipid Association, The Obesity Society and the American College of Nutrition, as well as a member of the Board of Governors of the Accreditation Council for Clinical Lipidology.
Views expressed by the author may not be those of the Egg Nutrition Center.
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