Metabolic efficiency and energy expenditure during short-term overfeeding
Introduction
An energy intake that exceeds energy expenditure for longer periods will lead to weight gain. However, when healthy adults are overfed, most persons gain less weight than expected from the excess energy intake and show a wide inter-individual range in weight gain on the same overfeeding regime [1], [2], [3], [4], [5], [6]. One possible explanation is that some persons can increase their energy expenditure when overeating to resist weight gain. Whether there are adaptive physiological changes in energy expenditure is studied intensively. While some investigators found evidence for adaptive thermogenesis [7] others did not [1], [8], [9] but accuracy and sophistication of methods used to measure energy expenditure and physical activity could be improved. Three overfeeding studies, approximately comparable in amount and duration of overfeeding, measured free-living energy expenditure with doubly labeled water but reached different conclusions. Levine et al. [5] found that individual changes in non-exercise activity thermogenesis (NEAT), defined as the thermogenesis associated with fidgeting, maintenance of posture and other activities of daily life, could explain differences in fat gain in subjects overfed with 4.2 MJ/day for 56 days. Diaz et al. [3] found no evidence for any adaptive energy-dissipating mechanism when overfeeding subjects with 50% more energy than baseline requirements (mean 6.2 MJ/day) for 42 days. Also, Roberts et al. [4] did not find a significant increase in energy expenditure in young and older men overfed with 4.2 MJ/day for 21 days.
Diet composition is known to influence energy expenditure, as different substrates will increase dietary induced thermogenesis (DIT) to various degrees. DIT is greater on a high protein and carbohydrate diet than on a fat diet [10]. In several studies the metabolic response to overfeeding diets of different composition (low-protein, high-carbohydrate, high-fat) has been investigated [6], [7], [11], [12]. These experiments show considerable inter-individual differences in energy cost of weight gain within and between experiments. Stock [13] and Dulloo and Jacquet [14] showed that differences were most noticeable when diets were unbalanced with respect to protein and therefore suggested that overfeeding low-protein diets could serve as a tool to exaggerate individual differences in energetic efficiency by maximizing DIT. We overfed 14 healthy females with a low-protein diet to investigate whether efficiency of weight gain is related to adaptive differences in BMR and physical activity.
Section snippets
Subjects
Fourteen healthy female subjects, aged 19–36 years, participated in the study. Characteristics of the subjects are shown in Table 1. Before participating in the study subjects were medically screened by a detailed health questionnaire. Subjects had had a stable body weight (body weight changes ≤ 2 kg) for at least a year at the start of the study. Three were light smokers, they maintained their habitual smoking pattern during the study. All subjects received verbal and written information and
Dietary intake
Table 2 summarizes the changes in energy balance parameters induced by overfeeding. Self-selected baseline diets provided mean percentages energy of 14 ± 2% from protein, 30 ± 3% from fat and 57 ± 4% from carbohydrates. The macronutrient composition of the overfeeding diets was as intended: 7% of energy from protein, 40% from fat and 53% from carbohydrates, which was low in protein on a relative basis (%) and on an absolute basis (61 ± 6.1 g/day). The mean energy intake during baseline was 9.2 ± 1.2
Discussion
The relevance of adaptive changes in thermogenesis in the etiology of obesity is controversial as such changes are believed to be no more than a few percent [23], [24]. With prolonged overfeeding changes in energy expenditure are of the order of 5–15%, which depends on the type and amount of overfeeding (DIT) [25], [26]. The unexplained large inter-individual variation in efficiency of weight gain with overfeeding [1], [2], [3], [4], [5], [6] shows that the matter of adaptive thermogenesis is
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