Health Effects of Low-Carbohydrate Diets: Where Should New Research Go? There has been considerable debate about the metabolic effects of restricting carbohydrate intake in weight and diabetes management. However, the American Diabetes Association has noted that weight and metabolic improvements can be achieved with low carbohydrate, low fat (implicitly higher carbohydrate), or a Mediterranean style diet (usually an intermediate level of carbohydrate). Our paper addresses variability in the definition for low or restricted carbohydrate, the effects of carbohydrate restriction on diabetes-related health outcomes, strategies for restricting carbohydrate intake, and potential genetic variability in response to dietary carbohydrate restriction. Issues for wellness support supplement future research are also addressed. There has been considerable debate about the effects of restricting carbohydrate intake in weight and diabetes management.1-4 Carbohydrate intake is the primary determinant of post-prandial glycemia. Monitoring carbohydrate intake is used to determine insulin dosage. Weight loss and metabolic improvement have been achieved with widely varying levels of carbohydrate intake. Our paper will address variability in the definition for low or restricted carbohydrate diets, the effects of carbohydrate restriction on diabetes metrics, strategies for restricting carbohydrate intake, and genetic predictors of response to dietary carbohydrate.
The lack of a consistent definition for “low carbohydrate diets” complicates efforts to compare studies throughout the literature.9 While very low-carbohydrate diets are often defined by the absolute amount of carbohydrate intake, usually less than 70 grams per day, other levels of dietary carbohydrate are usually defined based on the proportion of energy intake as illustrated in Table 1. As the energy level of the diet decreases, the proportion of energy from carbohydrate increases. For example, a diet containing 200 grams of carbohydrate might be classified as moderately low for a 2,000 calorie intake, moderate-carbohydrate at 1,500 calories and high-carbohydrate at 1,200 calories. A recent systemic review of macronutrients in diabetes management noted that the terms “conventional” or “traditional” carbohydrate diet were often used to describe the comparison diet for evaluation of lower carbohydrate diets.5 The review found that the terms “diabetic” or “ADA” were frequently used as well. In general, the comparison diets contained 55-65% of energy from carbohydrate.
In contrast to most low carbohydrate diets, which focus on number of grams of carbohydrate or the percent of energy from carbohydrate,9 Paleolithic nutrition is based on the principles of evolutionary biology with a focus on the low carbohydrate options available to the hunter-gatherers.13-17 This dietary approach, which is often referred to as the Paleo diet, targets restriction of grains, dairy products, and all refined food items. Carbohydrate sources that are encouraged include fruits, vegetables, and nuts. The total carbohydrate is approximately 35-40% of energy intake although no specific amount is considered to be the goal. What are the diabetes-related health effects of low-carbohydrate diets? The metrics for evaluating the effectiveness of low-carbohydrate diets in the management of diabetes include weight, glycemia, cardiovascular risk indices, and other health indicators. In our 2009 review of low-carbohydrate diets in this journal, we noted that low-carbohydrate diets may achieve better early weight loss than comparison diets higher in carbohydrate, but weight loss was comparable for studies that were one year or longer.18 Systematic reviews by the ADA 5 and by Castaneda-Gonzalez et al,19 which examined clinical trials of low carbohydrate diets in diabetes management, reported no consistent differences in weight loss among the diets being compared.
9 studies),3,20-27 which evaluated the effects of low carbohydrate diets in diabetes management, only three trials were of 12 month duration or longer.24,26,27 None of these longer term trials reported a significant difference in weight loss in the comparison between low-carbohydrate diet and other dietary strategies. Our previous review of low-carbohydrate diets18 in diabetes management reported that weight loss appeared to be better when the analysis was restricted to completers. Without the weight results of study dropouts, which may be close to half of those who were randomized, the findings would be biased18 In a recent preference trial, Hussian et al.28 found a significantly greater 24-week weight loss among participants with diabetes who opted for a low-carbohydrate ketogenic diet than those who opted for a low caloric diet without carbohydrate restriction (12 kg vs 7 kg loss).28 However, the participants with diabetes who opted for the low-carbohydrate ketogenic diet were more obese (40.0 vs.
Individuals with diabetes who self-select to follow low-carbohydrate diet may achieve a substantial weight loss, but longer-term studies suggest that recommending low-carbohydrate diets to all overweight individuals with diabetes does not yield any greater weight loss benefit than other dietary strategies. A 2012 ADA review5 examined research studies that addressed the effects of lowering total carbohydrate intake on glycemic control in patients with diabetes. 4 studies).34-37 In general, the lower carbohydrate treatment condition resulted in lower A1c levels and wellness support supplement (my response) lower doses of anti-diabetic medications than the higher carbohydrate comparison diet.5 However, the role of weight loss complicated interpretation of these findings, which was noted to be a confounder by the ADA review group.5 Meta-analyses by Kodama et al. 38 and by Kirk et al.,9 which compared low-carbohydrate diets with higher carbohydrate conventional carbohydrate diets, reported similar conclusions. The effects of carbohydrate restriction on improving glycemic control largely disappeared when the trial was one year or MedicGLP.com longer in duration when results were reported on the basis of intention-to-treat.18,24 However, the Esposito et al.
