Low-carb, low-fat diet gurus face off. Interview by Joan Stephenson

Nutritional modulation of insulin resistance

Insulin resistance has been proposed as the strongest single predictor for the development of Type 2 Diabetes (T2DM). Chronic oversupply of energy from food, together with inadequate physical activity, have been recognized as the most relevant factors leading to overweight, abdominal adiposity, insulin resistance, and finally T2DM. Conversely, energy reduced diets almost invariably to facilitate weight loss and reduce abdominal fat mass and insulin resistance. However, sustained weight loss is generally difficult to achieve, and distinct metabolic characteristics in patients with T2DM further compromise success. Therefore, investigating the effects of modulating the macronutrient composition of isoenergetic diets is an interesting concept that may lead to additional important insights. Metabolic effects of various different dietary concepts and strategies have been claimed, but results from randomized controlled studies and particularly from longer-term-controlled interventions in humans are often lacking. However, some of these concepts are supported by recent research, at least in animal models and short-term studies in humans. This paper provides an update of the current literature regarding the role of nutrition in the modulation of insulin resistance, which includes the discussion of weight-loss-independent metabolic effects of commonly used dietary concepts.

Maintenance on a ketogenic diet: voluntary exercise, adiposity and neuroendocrine effects

Introduction

Adherence to low-carbohydrate, ketogenic diets has been associated with greater weight loss in the short-term than low-fat, calorie-restricted diets. However, consumption of ketogenic diets may result in decreased voluntary exercise and thus render long-term weight loss and maintenance of weight loss difficult.

Methods

Rats were maintained on either a non-ketogenic chow (CH) diet or a low-carbohydrate, ketogenic diet (KD) for 6 weeks. Half of each dietary group was sedentary, while the other half was given access to a running wheel. Running wheel activity (total distance and meters/minute), plasma leptin and insulin, adiposity, and hypothalamic mRNA for neuropeptide Y (NPY) and proopiomelanocortin (POMC) were measured to assess activity-related effects in animals maintained on KD.

Results

With access to a running wheel, rats on KD engaged in similar levels of voluntary activity as CH rats and both dietary groups decreased caloric intake. Caloric intake increased over time such that it was significantly greater than sedentary controls after one month of access to the wheels, however body weight remained decreased. Sedentary rats maintained on KD had increased adiposity and plasma leptin levels and decreased hypothalamic POMC mRNA, as compared to sedentary CH rats. KD rats with access to a running wheel had similar levels of adiposity and plasma leptin levels as CH rats with access to running wheels, but significantly increased POMC mRNA in the arcuate.

Conclusion

We demonstrate that maintenance on KD does not inhibit voluntary activity in a running wheel. Furthermore, prevention of KD-related increased adiposity and plasma leptin, as measured in sedentary KD rats, significantly increases levels of the anorexigenic neuropeptide POMC mRNA.

The contribution of changes in diet, exercise, and stress management to changes in coronary risk in women and men in the Multisite Cardiac Lifestyle Intervention Program

BACKGROUND

The relative contribution of health behaviors to coronary risk factors in multicomponent secondary coronary heart disease (CHD) prevention programs is largely unknown.

PURPOSE

Our purpose is to evaluate the additive and interactive effects of 3-month changes in health behaviors (dietary fat intake, exercise, and stress management) on 3-month changes in coronary risk and psychosocial factors among 869 nonsmoking CHD patients (34% female) enrolled in the health insurance-based Multisite Cardiac Lifestyle Intervention Program.

METHODS

Analyses of variance for repeated measures were used to analyze health behaviors, coronary risk factors, and psychosocial factors at baseline and 3 months. Multiple regression analyses evaluated changes in dietary fat intake and hours per week of exercise and stress management as predictors of changes in coronary risk and psychosocial factors.

RESULTS

Significant overall improvement in coronary risk was observed. Reductions in dietary fat intake predicted reductions in weight, total cholesterol, low-density lipoprotein cholesterol, and interacted with increased exercise to predict reductions in perceived stress. Increases in exercise predicted improvements in total cholesterol and exercise capacity (for women). Increased stress management was related to reductions in weight, total cholesterol/high-density lipoprotein cholesterol (for men), triglycerides, hemoglobin A1c (in patients with diabetes), and hostility.

CONCLUSIONS

Improvements in dietary fat intake, exercise, and stress management were individually, additively and interactively related to coronary risk and psychosocial factors, suggesting that multicomponent programs focusing on diet, exercise, and stress management may benefit patients with CHD.

Obesity and Nutrition in Women Throughout Adulthood

Nutritional challenges are particularly relevant to women. Almost 62% of women are overweight; of these women, 33% are obese. The incidence of obesity is even greater in non-Hispanic Black and Mexican American women. Women who are overweight or obese experience a greater number of adverse health outcomes, including an increased incidence of cardiovascular disease and breast and colon cancer. Dietary patterns influence health outcomes, with a heart-healthy pattern having the most positive health outcomes. Health care providers should encourage women to consume a diet high in fruits and vegetables and low in total and saturated fats.