Changes in body composition and fat distribution in response to weight loss and weight regain

This thesis describes the effects of weight loss and subsequent weight regain on body composition, fat distribution and resting energy expenditure in moderately obese men and moderately obese premenopausal women. Participants were subjected to a controlled 4.2 MJ/day energy deficit diet for 13 weeks, and re-examined more than one year after weight loss intervention. Five techniques to assess the changes in body composition after weight loss (on average 12.2 ± 3.7 kg (mean ± SD)) were compared. The results from densitometry (hydrostatic weighing) and the deuterium oxide dilution technique were similar, whereas, bioelectrical impedance and two anthropometric methods (skinfold thicknesses and body mass index) showed larger reductions in fat-free mass (FFM) than estimated by densitometry and the dilution technique. These findings were similar in both sexes. Magnetic resonance imaging (MRI) was used to assess the reductions after weight loss in the visceral and subcutaneous abdominal fat depots and the subcutaneous fat depot at trochanter level. The proportional reduction of fat was largest in the visceral depot (men 40%, women 33%) and less fat was lost subcutaneously, especially at trochanter level (men 29%, women 26%). The reductions in visceral fat as measured by MRI were compared with changes in anthropometric measurements. The change in waist-to-hip ratio (WHR) was not related to the change in visceral fat, and the change in sagittal-to-transverse abdominal diameter ratio was only moderately associated with visceral fat loss in both sexes. During the follow-up of 67 weeks after weight loss, 80% of the weight lost was regained on average. In men but not in women, the reduction in resting metabolic rate (RMR) after weight loss was larger than expected from the losses of FFM and fat mass. The RMR returned to baseline level in both sexes after weight regain. The reduction in RMR was not related to later weight regain. Percentage body fat and amount of visceral fat also nearly returned to the level similar to that before weight loss.It is concluded that bioelectrical impedance and anthropometric measurements are not as good as densitometry or the deuterium-oxide dilution method for the evaluation of changes in body composition. Only approximate estimates of visceral fat can be achieved by anthropometry. As a consequence, the assessment of changes in visceral fat by anthropometry is limited. Finally, one weight cycle as observed in this study does not lead to a permanently reduced RMR, nor to a greater body fatness nor to an increase in visceral fat compared with initial levels.