Nicolas D. Knuth

Metabolic Slowing with Massive Weight Loss despite Preservation of Fat-Free Mass

CONTEXT An important goal during weight loss is to maximize fat loss while preserving metabolically active fat-free mass (FFM). Massive weight loss typically results in substantial loss of FFM potentially slowing metabolic rate. OBJECTIVE Our objective was to determine whether a weight loss program consisting of diet restriction and vigorous exercise helped to preserve FFM and maintain resting metabolic rate (RMR). PARTICIPANTS AND INTERVENTION We measured body composition by dual-energy x-ray absorptiometry, RMR by indirect calorimetry, and total energy expenditure by doubly labeled water at baseline (n = 16), wk 6 (n = 11), and wk 30 (n = 16). RESULTS At baseline, participants were severely obese (× ± SD; body mass index 49.4 ± 9.4 kg/m(2)) with 49 ± 5% body fat. At wk 30, more than one third of initial body weight was lost (-38 ± 9%) and consisted of 17 ± 8% from FFM and 83 ± 8% from fat. RMR declined out of proportion to the decrease in body mass, demonstrating a substantial metabolic adaptation (-244 ± 231 and -504 ± 171 kcal/d at wk 6 and 30, respectively, P < 0.01). Energy expenditure attributed to physical activity increased by 10.2 ± 5.1 kcal/kg.d at wk 6 and 6.0 ± 4.1 kcal/kg.d at wk 30 (P < 0.001 vs. zero). CONCLUSIONS Despite relative preservation of FFM, exercise did not prevent dramatic slowing of resting metabolism out of proportion to weight loss. This metabolic adaptation may persist during weight maintenance and predispose to weight regain unless high levels of physical activity or caloric restriction are maintained.

Calorie for Calorie, Dietary Fat Restriction Results in More Body Fat Loss than Carbohydrate Restriction in People with Obesity

Dietary carbohydrate restriction has been purported to cause endocrine adaptations that promote body fat loss more than dietary fat restriction. We selectively restricted dietary carbohydrate versus fat for 6 days following a 5-day baseline diet in 19 adults with obesity confined to a metabolic ward where they exercised daily. Subjects received both isocaloric diets in random order during each of two inpatient stays. Body fat loss was calculated as the difference between daily fat intake and net fat oxidation measured while residing in a metabolic chamber. Whereas carbohydrate restriction led to sustained increases in fat oxidation and loss of 53 ± 6 g/day of body fat, fat oxidation was unchanged by fat restriction, leading to 89 ± 6 g/day of fat loss, and was significantly greater than carbohydrate restriction (p = 0.002). Mathematical model simulations agreed with these data, but predicted that the body acts to minimize body fat differences with prolonged isocaloric diets varying in carbohydrate and fat.

Metabolic adaptation following massive weight loss is related to the degree of energy imbalance and changes in circulating leptin

To measure changes in resting metabolic rate (RMR) and body composition in obese subjects following massive weight loss achieved via bariatric surgery or calorie restriction plus vigorous exercise.

IDEAL aging is associated with lower resting metabolic rate: the Baltimore Longitudinal Study of Aging.

To assess the associations among age, health status, and resting metabolic rate (RMR) in a large population of older adults.

Of Greek Heroes, Wiggling Worms, Mighty Mice, and Old Body Builders

HERACLES (Hercules according to the Romans) was probably the earliest and greatest body builder of all times and, without doubt, the greatest hero of Greek mythology. His conception, the result of a brief affair between the supreme deity Zeus and a mortal woman, made Zeuss wife Hera furious. She surreptitiously inserted two deadly snakes into Heracles crib. According to legend, that evening, a nurse found the delighted baby giggling and joyfully playing with a strangled serpent in each hand. Are stronger people already stronger at birth, as the Heracles legend seems to suggest? Is the destiny of our muscles already encoded in our genes (1)? Perhaps more importantly, what is the role of genetics as opposed to behavioral and environmental factors in the maintenance of muscle mass and strength with aging?

Increased Physical Activity Associated with Less Weight Regain Six Years After “The Biggest Loser” Competition

The aim of this study was to explore how physical activity (PA) and energy intake (EI) changes were related to weight loss and regain following “The Biggest Loser” competition.