Energy Expenditure during Weight-Loss Maintenance

According to data from the National Health and Nutrition Examination Survey from 1999 to 2006, only 1 out of 6 overweight and obese American adults reported maintaining weight loss of at least 10% for 1 year. Long-term success rates may be even lower in dietary weight loss trials due to the elimination of reporting bias.

Behavior contributes to the inability of most people to maintain clinically significant weight loss; the motivation to adhere to strict dietary regimens diminishes over time. Another contributing factor may be that weight loss elicits biologic adaptations such as a decline in energy expenditure (adaptive thermogenesis) and an increase in hunger. The adaptations work to promote weight gain.

Because metabolic pathways vary in energetic efficiency, dietary composition could affect energy expenditure directly by virtue of macronutrient differences or indirectly through hormonal responses to diets that regulate metabolic pathways. It is thought that diets designed to attenuate the increase in blood glucose levels after eating and low-carbohydrate diets may confer a metabolic advantage.

Researchers recently conducted a controlled feeding study to determine the effects of 3 weight-loss maintenance diets on energy expenditure, hormones, and components of the metabolic syndrome. They reported the results in the Journal of the American Medical Association [2012;307(24):2627-2634].

The primary outcome measure of the 3-way crossover study was resting energy expenditure (REE). Secondary outcomes were total energy expenditure (TEE), hormone levels, and metabolic syndrome components.

The intervention was designed to test diets that (1) would encompass a range of macronutrient composition and glycemic control, (2) have been commonly recommended for the treatment of obesity, and (3) be physiologically sustainable for long periods of time. After achieving 10% to 15% weight loss while consuming a run-in diet, participants consumed an isocaloric low-fat diet (60% of energy from carbohydrates, 20% from fat, 20% from protein; high glycemic load), a low-glycemic index diet (40% from carbohydrates, 40% from fat, and 20% from protein; moderate glycemic load), and a very low-carbohydrate diet (10% from carbohydrates, 60% from fat, and 30% from protein; low glycemic load) in random order, each for 4 weeks.

The cohort included 32 participants (17 men and 15 women); 11 of the original cohort did not complete the intervention. Mean age of the 21 completers was 30.3 years, mean height was  174.3 cm, mean weight was 105.0 kg, and mean body mass index was 34.4 kg/m². During the run-in phase, completers lost a mean of 14.3 kg (13.6% of baseline body weight).

Compared with the pre-weight-loss baseline, the decrease in REE was greatest with the low-fat diet (mean -205 kcal/d), followed by the low-glycemic index diet (-166 kcal/d) and the very low-carbohydrate diet (-138 kcal/d); overall P=.03; P for trend by glycemic load=.009. The pattern in TEE was similar: mean, -423 kcal/d for the low-fat diet; -297 kcal/d for the low-glycemic diet, and -97 kcal/d for the very low-carbohydrate diet (overall P=.03; P for trend by glycemic load <.001).

There was also a variation in hormone levels and metabolic syndrome components during weight maintenance by diet. Serum leptin was highest with the low-fat diet, followed by the low-glycemic index diet and then the very low-carbohydrate diet (14.9 ng/mL, 12.7 ng/mL, and
11.2 ng/mL, respectively; overall P<.001). Cortisol excretion measured with a 24-hour urine collection and serum thyroid-stimulating hormone also differed in a linear fashion by glycemic load. Compared with the other 2 diets, serum triiodothyronine was lower with the very low-carbohydrate diet.

Regarding components of the metabolic syndrome, indexes of peripheral and hepatic insulin sensitivity were lowest with the low-fat diet. However, no consistent favorable pattern appeared with any of the diets.

In conclusion, the researchers stated, “Among overweight and obese young adults compared with pre-weight-loss energy expenditure, isocaloric feeding following 10% to 15% weight loss resulted in decreases in REE and TEE that were greatest with the low-fat diet, intermediate with the low-glycemic index diet, and least with the very low-carbohydrate diet.”