Low Carbohydrate Dietary Approaches for People With Type 2 Diabetes—A Narrative Review

Although carbohydrate restriction is not a new approach for the management of Type 2 diabetes, interest in its safety and efficacy has increased significantly in recent years. The purpose of the current narrative review is to summarise the key relevant research and practical considerations in this area, as well as to explore some of the common concerns expressed in relation to the use of such approaches. There is a strong physiological rationale supporting the role of carbohydrate restriction for the management of Type 2 diabetes, and available evidence suggests that low carbohydrate dietary approaches (LCDs) are as effective as, or superior to, other dietary approaches for its management. Importantly, LCDs appear to be more effective than other dietary approaches for facilitating a reduction in the requirement for certain medications, which leads to their effects on other health markers being underestimated. LCDs have also been demonstrated to be an effective method for achieving remission of Type 2 diabetes for some people. The available evidence does not support concerns that LCDs increase the risk of cardiovascular disease, that such approaches increase the risk of nutrient deficiencies, or that they are more difficult to adhere to than other dietary approaches. A growing number of organisations support the use of LCDs as a suitable choice for individuals with Type 2 diabetes.

A Randomised Crossover Trial: Exploring the Dose-Response effect Of Carbohydrate restriction on glycaemia in people with type 2 diabetes (D-ROC2)

The role of carbohydrate restriction in the management of glycemia in type 2 diabetes (T2D) has been a subject of immense debate and controversy partly due to low-carbohydrate trials being confounded by multiple factors including degree of calorie restriction, dietary protein content, and by no clear definition of a low-carbohydrate diet. The current study sought to provide insight into the relationship between carbohydrate restriction and glycemia by testing the effect of varying doses of carbohydrate on continuous glucose concentrations within a range of intakes defined as low-carbohydrate while controlling for confounding factors. This was a randomised crossover trial in participants with T2D testing 5 different 6-day eucaloric, isocaloric dietary treatments with varying carbohydrate contents (10%, 15%, 20%, 25%, and 30% kcal). Diets were kept isocaloric by exchanging %kcal from carbohydrate with predominantly unsaturated fat, keeping protein constant at 15% kcal. Daily self-weighing was employed to ensure participants maintained their weight throughout each treatment arm. Between dietary treatments, participants underwent a washout period of at least 7 days and were advised to maintain their habitual diet. Glycemic control was assessed using a continuous glucose monitoring device that was placed while the participant was on their normal diet, and was worn for the 6 days of each treatment. 12 participants completed the study. There were no differences in 24-hour and postprandial sensor glucose concentrations between the 30%kcal and 10%kcal doses (7.4 +/- 1.1mmol/L vs 7.6 +/- 1.4mmol/L (P=0.28) and 8.0 +/- 1.4mmol/L vs 8.3 +/- 1.3mmol/L (P=0.28) respectively). In our exploratory analyses we did not find any dose-response relationship between carbohydrate intake and glyaemia. A small amount of weight loss occurred in each treatment arm (range: 0.4 to 1.1kg over the 6 days) but adjusting for these differences did not influence the primary or secondary outcomes. Modest changes in dietary carbohydrate content in the absence of weight loss while keeping dietary protein intake constant do not appear to influence glucose concentrations in people with T2D.

Carbohydrate Restriction with or without Exercise Training Improves Blood Pressure and Insulin Sensitivity in Overweight Women

Objective: The purpose of this study was to evaluate the effects of a 4-week low-carbohydrate diet (LC) with or without exercise training on cardiometabolic health-related profiles in overweight/obese women. Methods: Fifty overweight/obese Chinese women (age: 22.2 ± 3.3 years, body mass index (BMI): 25.1 ± 3.1 kg·m−2) were randomized to either a LC control group (LC-CON, n = 16), a LC and high-intensity interval training group (LC-HIIT, n = 17), or a LC and moderate-intensity continuous training group (LC-MICT, n = 17). All groups consumed LC for 4 weeks, while the LC-HIIT and LC-MICT groups followed an additional five sessions of HIIT (10 × 6 s cycling sprints and 9 s rest intervals, 2.5 min in total) or MICT (cycling continuously at 50–60% of peak oxygen uptake (VO2peak) for 30 min) weekly. Blood pressure, fasting glucose, insulin sensitivity, and several metabolic or appetite regulating hormones were measured before and after intervention. Results: Significant reductions in body weight (− ~2.5 kg, p < 0.001, η2 = 0.772) and BMI (− ~1 unit, p < 0.001, η2 = 0.782) were found in all groups. Systolic blood pressure was reduced by 5–6 mmHg (p < 0.001, η2 = 0.370); fasting insulin, leptin, and ghrelin levels were also significantly decreased (p < 0.05), while insulin sensitivity was improved. However, there were no significant changes in fasting glucose, glucagon, and gastric inhibitory peptide levels. Furthermore, no group differences were found among the three groups, suggesting that extra training (i.e., LC-HIIT and LC-MICT) failed to trigger additional effects on these cardiometabolic profiles. Conclusions: The short-term carbohydrate restriction diet caused significant weight loss and improved blood pressure and insulin sensitivity in the overweight/obese women, although the combination with exercise training had no additional benefits on the examined cardiometabolic profiles. Moreover, the long-term safety and effectiveness of LC needs further study.

Glycolytically impaired glial cells fuel neural metabolism via β-oxidation

Neuronal function is highly energy demanding and thus requires efficient and constant metabolite delivery. Like their mammalian counterparts Drosophila glia are highly glycolytic and provide lactate to fuel neuronal metabolism. However, flies are able to survive for several weeks in the absence of glial glycolysis1. Here, we study how glial cells maintain sufficient nutrient supply to neurons under conditions of carbohydrate restriction. We show that glycolytically impaired glia switch to fatty acid breakdown via β-oxidation and provide ketone bodies as an alternate neuronal fuel. Moreover, flies also rely on glial β-oxidation under starvation conditions with glial loss of β-oxidation increasing susceptibility to starvation. Further, we show that glial cells act as a metabolic sensor in the brain and can induce mobilization of peripheral energy stores to ensure brain metabolic homeostasis. In summary, our study gives pioneering evidence on the importance of glial β-oxidation and ketogenesis for brain function, and survival, under adverse conditions, like malnutrition. The glial capacity to utilize lipids as an energy source seems to be conserved from flies to humans.