Energy metabolism of overweight women before, during and after weight reduction, assessed by indirect calorimetry

Abstract

Previous studies had suggested that periods of low energy intake evoke compensatory adaptations in energy metabolism, which retard weight loss, and promote weight regain when energy intake returns to normal. The aim of this thesis was to investigate whether a slimming (low-energy) diet based on alternating energy intake could counteract this decrease in energy requirement. The persistance of the reduction of energy metabolism was studied 1 month and approximately 1 year after weight reduction.The effects of three slimming diets were compared pairwise in three separate studies. To this end, a cross-over design was used (fig. 2). Two alternating diets (diet AB/100: one day solely bread, water. coffee and tea, the other day providing 100 % (normal diet) the daily energy need and diet A50/100: one day providing 50 % of the daily energy need, the other day 100 %) and one continuous diet (C50: providing 50 % of daily energy need every day) were prescribed or supplied. Ten women participated in each study. First each subject lived on a weight-maintenance diet (S100) for 8 days, then two periods of low energy intake, of 4 weeks each, followed immediately afterwards. Energy balances were determined during the final 8 days of each diet period. The 24 hour energy expenditure was measured in a respiration chamber for 2 or 3 successive days. The activity pattern in the respiration chamber was standardized. Dopplermeters and actometers were used to record physical activity.Follow-up measurements of energy balance were made on ten subjects 1 month after slimming and on eight subjects energy balance was determined approximately 1 year after slimming. Weight-maintenance diets, adjusted for weight loss, were supplied during the follow-up measurement periods.Over the first 4 weeks of slimming body weights decreased by averages of 5.8 kg (C50), 4.5 kg (AB/100) and 3.9 kg (A50/100). The average weight losses over 8 weeks were 6.9 to 9.0 kg. After 8 weeks at a low energy intake 24 hour energy expenditure had declined by 12 - 15 %. This decline was partly (50 %) accounted for by the reductions in body weight and partly (30 %) by reduced dietary induced thermogenesis. The remaining part (20 %) of the decline was probably due to the reduced cost and amount of physical activity which was indicated by Dopplermeter counts and actometer counts.Sleeping energy expenditure also decreased during slimming by 6 - 13 %, but this was no more than could be expected from weight loss.Weight reduction by alternating (low with normal) low energy intakes resulted in a reduction of energy expenditure which, when weight loss and energy intake were taken into account, was similar to the reduction by continuous low energy intake, thus alternating low energy intake did not prevent energy expenditure rates from declining.Subjects participating in the follow-up studies maintained their reduced body weights successfully. Their 24 hour energy expenditure rates in the follow-up studies were still below the rates measured before slimming. When body weight and energy intake were taken into account, both the 24 hour energy expenditure values and the sleeping energy expenditure values were the same before slimming, and 1 month or 1 year after slimming.The changes of energy metabolism were determined by alterations in body weight and energy intake and probably in physical activity as well. It remains to be investigated whether other adaptive mechanisms are evoked when energy intake is restricted more severely or for longer periods.</TT