Low Carbohydrate Diets and Energy Expenditure

I have written several posts regarding the effects of carbohydrate, particularly high carbohydrate diets, with respect to increased risks for obesity, type 2 diabetes, and cardiovascular disease. The evidence of the link between carbohydrate consumption and disease risk has led to the formulation of a model referred to as the carbohydrate-insulin model of obesity. This model addresses the observations of an increased ratio of insulin to glucagon concentrations after consumption of a meal with a high glycemic load. This change in hormone levels results in a shift of metabolism away from oxidation of fuels, such as fats, to one of storage of fats in adipose tissue. This change in metabolism is believed to be the trigger for increased appetite and consequent food cravings, which in turn predisposes an individual to weight gain.

ARE THERE BENEFITS TO LOW CARBOHYDRATE HIGH FAT (LCHF) DIETS?

A recent study utilized a long-term randomized trial to address the benefits of a low carbohydrate diet on energy consumption while on a weight loss maintenance diet:

Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial

The study was carried out over a period of three years and involved a protocol has been a randomized controlled trial with run-in and test phases. During the protocol participants were instructed to minimize or eliminate refined grains and added sugars and maximize intake of vegetables and other minimally processed foods.

The run-in refers to where participants in the study had restricted energy intake so as to promote weight loss. The run-in phase occurred over a 9-10 week period. Participants were randomly assigned, after reaching the targeted weight loss, to diets that were either high, moderate, or low carbohydrate. These test diets were continued for a period of 20 weeks. During this 20 week period there were adjustments to participants total energy intake to maintain their weight loss to within 2 kg (4.4 pounds) of the level achieved before randomization.

The study participants were adults aged 18 to 65 years with a BMI [weight (kg)/height (m²)] of 25 or higher (a BMI ≥ 30 is considered obese) and body weight less than 160 kg (353 pounds). Participants were screened for participation before pre-weight loss assessments.

During the run-in phase of the study, the macronutrient composition of the run-in diet was 45% of total energy from carbohydrate, 30% from fat, and 25% from protein. Individual energy needs were determined based upon resting requirements with the methods used outlined in this and prior publications on the Framingham long-term study. Energy intake was restricted to 60% of estimated needs. After the run-in phase, energy intake was adjusted to stabilize body weight of each participant.

During the test phase, high, moderate, and low carbohydrate diets varied in carbohydrate (60%, 40%, and 20% of total energy, respectively) and fat (20%, 40%, and 60%, respectively), with protein fixed at 20%. Protein intake was fixed in view of its higher thermic effect to provide a more specific test of the carbohydrate-insulin model. The relative amounts of added sugar (15% of total carbohydrate), saturated fat (35% of total fat), and sodium (3000 mg/2000 kcal) were held constant across diets.

Results from this 20 week trial found that total energy expenditure was significantly greater in participants that were assigned to the low carbohydrate diet when compared to participants on the high carbohydrate diet of similar protein content. Regardless of the specific mechanisms involved, this study showed that dietary quality can affect energy expenditure independently of body weight. This result holds promise as means to treating obesity. It is important to understand that other potentially contributory components of energy expenditure include the thermic effect of food, total activity of brown adipose tissue, an individuals autonomic tone, nutrient cycling, and an individuals level of fidgeting and related non-exercise activity induced thermogenesis.

One of the many stomach derived hormones is ghrelin, a hormone that induces a sensation of hunger, was found to be produced at a lower level in participants assigned to the low carbohydrate diet. In addition to inducing a sensation of hunger, ghrelin lowers energy expenditure and promotes fat deposition.

TAKE HOME: This study, one part of many associated with the long-term Framingham study, clearly shows that a low glycemic load, high fat diet can be adopted to facilitate weight loss maintenance beyond the conventional focus on restricting energy intake and encouraging physical activity. Paying attention to ones diet composition may reduce the level and intensity of physical activity required to lose weight and keep it off.