Weight loss leads to a marked decrease in nonresting energy expenditure in ambulatory human subjects

Do adaptive changes in metabolic rate favor weight regain in weight-reduced individuals? An examination of the set-point theory

BACKGROUND

Obese persons generally regain lost weight, suggesting that adaptive metabolic changes favor return to a preset weight.

OBJECTIVE

Our objective was to determine whether adaptive changes in resting metabolic rate (RMR) and thyroid hormones occur in weight-reduced persons, predisposing them to long-term weight gain.

DESIGN

Twenty-four overweight, postmenopausal women were studied at a clinical research center in four 10-d study phases: the overweight state (phase 1, energy balance; phase 2, 3350 kJ/d) and after reduction to a normal-weight state (phase 3, 3350 kJ/d; phase 4, energy balance). Weight-reduced women were matched with 24 never-overweight control subjects. After each study phase, assessments included RMR (by indirect calorimetry), body composition (by hydrostatic weighing), serum triiodothyronine (T(3)), and reverse T(3) (rT(3)). Body weight was measured 4 y later, without intervention.

RESULTS

Body composition-adjusted RMR and T(3):rT(3) fell during acute (phase 2) and chronic (phase 3) energy restriction (P: < 0.01), but returned to baseline in the normal-weight, energy-balanced state (phase 4; mean weight loss: 12.9 +/- 2.0 kg). RMR among weight-reduced women (4771 +/- 414 kJ/d) was not significantly different from that in control subjects (4955 +/- 414 kJ/d; P: = 0.14), and lower RMR did not predict greater 4-y weight regain (r = 0.27, NS).

CONCLUSIONS

Energy restriction produces a transient hypothyroid-hypometabolic state that normalizes on return to energy-balanced conditions. Failure to establish energy balance after weight loss gives the misleading impression that weight-reduced persons are energy conservative and predisposed to weight regain. Our findings do not provide evidence in support of adaptive metabolic changes as an explanation for the tendency of weight-reduced persons to regain weight.

Overnutrition and undernutrition as modifiers of metabolic processes in disease states

Both overnutrition and undernutrition affect energy metabolism, with overnutrition raising energy expenditure and undernutrition lowering it. Fever is a powerful stimulator of thermogenesis. In diseases such as cancer, AIDS, diabetes mellitus, and rheumatoid arthritis, whether energy expenditure is increased or decreased often depends on how advanced the disorder is. Early on, when the greater protein turnover characteristic of these conditions is paramount, energy expenditure is increased. In addition, in diseases such as cancer, AIDS, and rheumatoid arthritis in which cytokines are released, the cytokines' thermogenic effect initially increases the metabolic rate. However, as the disease becomes more advanced and leads to cachexia, energy expenditure drops below normal. Acute conditions such as burns and trauma significantly raise energy expenditure, primarily by increasing sympathetic response and the release of catecholamines, which are powerful stimulators of energy expenditure.

Energy, substrate and protein metabolism in morbid obesity before, during and after massive weight loss

OBJECTIVE

To investigate the effect of surgically induced weight loss on energy, substrate and protein metabolism of morbidly obese patients.

DESIGN

A prospective, clinical intervention study of morbidly obese patients before and after surgical treatment.

SUBJECTS

Eight morbidly obese patients (BMI 47.88+/-7.03).

METHODS

Total energy expenditure (TEE; doubly labeled water method), sleeping metabolic rate (SMR; respiration chamber), body composition (deuterium oxide component of doubly labeled water), substrate metabolism (48 h dietary records, 48 h urine collection and gaseous exchange in the respiration chamber) and whole body protein turnover (primed-continuous infusion of L-[1-13C]-leucine) were measured before, 3 and 12 months after vertical banded gastroplasty (VBG).

RESULTS

The TEE decreased as a result of a decreased SMR (64%) and non-SMR (36%; P=0.001). SMR as a function of fat-free mass (FFM) decreased after weight loss (P<0.05). The physical activity index (PAI), defined as TEE/SMR, was low and was not influenced by weight loss. Protein and carbohydrate oxidation decreased significantly after VBG (P<0.05), although 3 months after VBG protein oxidation did not decrease enough to prevent loss of FFM. The energy used for protein turnover was approximately 24% of SMR and did not change after weight loss.

CONCLUSIONS

Compensatory processes that oppose weight loss of morbidly obese patients exist, as demonstrated by the disproportional reduction of SMR, and a low PAI. Protein turnover is not a major contributor to the disproportional reduction of SMR.

Energy expenditure and free-living physical activity in black and white women: comparison before and after weight loss

BACKGROUND

The prevalence of obesity is higher in black than in white women. Differences in energy economy and physical activity may contribute to this difference.

OBJECTIVE

The objective of this study was to compare free-living energy expenditure and physical activity in black and white women before and after weight loss.

DESIGN

Participants were 18 white and 14 black women with body mass indexes (in kg/m(2)) between 27 and 30. Diet, without exercise, was used to achieve a weight loss of >/=10 kg and a body mass index <25. After 4 wk of energy balance in overweight and normal-weight states, body composition was assessed by using a 4-compartment model, sleeping and resting energy expenditures were assessed by using a chamber calorimeter, physiologic stress of exercise and exercise economy were measured by using standardized exercise tasks, and daily energy expenditure was assessed by using doubly labeled water.

RESULTS

Weight loss averaged 12.8 kg. Sleeping and resting energy expenditures decreased in proportion to changes in body composition. Weight reduction significantly improved physiologic capacity for exercise in both groups of women, making it easier for them to be physically active. Black women had lower body composition-adjusted energy requirements than did white women-both before and after weight loss-during sleep (9% lower, 519 kJ/d; P < 0.001), at rest (14% lower, 879 kJ/d; P < 0.001), during exercise (6% lower; P < 0. 05), and as a daily total (9% lower, 862 kJ/d; P < 0.06). By contrast, free-living physical activity was similar between the groups.

CONCLUSIONS

Weight-reduced women had metabolic rates appropriate for their body sizes. Black women had lower resting and nonresting energy requirements in both overweight and normal-weight states than did white women and did not compensate with greater physical activity, potentially predisposing them to greater weight regain.

Predictors of weight gain: the biological-behavioural debate

The rapidly increasing prevalence of obesity, in spite of an unchanged gene pool, makes it interesting to search for biological factors which increase the susceptibility at the individual level as well as searching for the responsible environmental factors. Among the identified metabolic factors is a low resting metabolic rate for given body size and composition, a high respiratory quotient (RQ) indicating a low fat oxidation and a low spontaneous physical activity, all factors which are regarded as being under substantial genetic influence. Among the environmental factors, it is low levels of physical activity, increasing inactivity and a high fat diet that are probably the most important ones. In this review we have focused on controversies in this area. Understanding the interaction between the constitutional biological factors and the environmentally determined lifestyle factors it is important to produce better options for both the prevention and treatment of obesity.

Effects of hypocaloric dietary treatment enriched in oleic acid on LDL and HDL subclass distribution in mildly obese women

OBJECTIVE

To study the effects of a carbohydrate-enriched (HiCarbo) or olive-oil-enriched (HiMUFA) hypocaloric diet on plasma lipoprotein levels and physical properties.

DESIGN

A six-month follow-up dietary intervention study with a HiCarbo diet providing 60% of total calories as complex carbohydrates, 15% as proteins and 25% as fats [10% saturated (SFA); 7% monounsaturated (MUFA); 8% polyunsaturated fatty acids (PUFA)]; or a HiMUFA diet with 40% complex carbohydrates, 15% proteins and 45% fats (10% SFA; 27% MUFA; 8% PUFA).

SUBJECTS

Twenty consecutive, mildly obese, normolipidemic premenopausal women (11 on HiCarbo and nine on HiMUFA diets) and 14 age- and sex-matched, lean controls.

MEASUREMENTS

Body mass index (BMI), waist/hip ratio, plasma lipoproteins, apolipoprotein (apo) AI and B, LDL and HDL density distribution, and phospholipid fatty acid composition at baseline, and after 3 and 6 months on dietary treatment.

RESULTS

Body weight progressively decreased during the first 3 months and then it stabilized during the following 3 months (-11% vs. baseline in both groups; P < 0.01). LDL-Cholesterol decreased significantly in both groups. HDL-Cholesterol increased significantly in the HiMUFA group, whereas a decreased level was observed in the HiCarbo group. At baseline the obese women had higher very low density lipoprotein (VLDL) and dense LDL-Cholesterol, and lower HDL2 cholesterol levels than the controls; these abnormalities persisted in the HiCarbo diet, whilst a significant decrease in the dense LDL associated with an increase in the HDL2 cholesterol was seen in the HiMUFA diet. HDL3 was not affected by either diet. The LDL/HDL-Cholesterol ratio was not affected by the HiCarbo diet, whilst it was significantly reduced after 6 months of HiMUFA diet as compared with baseline. Apo AI increased in the HiMUFA group, and decreased in the HiCarbo group.

CONCLUSIONS

Both diets were effective in decreasing body weight. At steady weight conditions, only the HiMUFA diet improved LDL and HDL subclass distribution abnormalities present in mildly obese normolipidemic women.

Resting energy expenditure in reduced-obese subjects in the National Weight Control Registry

BACKGROUND

Weight loss in obese subjects is associated with a reduction in resting metabolic rate (RMR). Whether the reduction can be explained solely by a reduction in lean body mass remains controversial.

OBJECTIVE

Our objective was to determine whether the reduction in RMR after weight loss was proportional to the decrease in lean mass alone or was greater than could be explained by body composition.

DESIGN

We measured the RMR, fasting respiratory quotient (RQ), and body composition in 40 reduced-obese subjects [ie, 7 men and 33 women who had lost > or = 13.6 kg (30 lb) and maintained the loss for > or = 1 y] enrolled in the National Weight Control Registry and 46 weight-matched control subjects (9 men, 37 women).

RESULTS

A stepwise multiple regression found lean mass, fat mass, age, and sex to be the best predictors of RMR in both groups. After adjusting RMR for these variables, we found no significant difference in RMR (5926 +/- 106 and 6015 +/- 104 kJ/d) between the 2 groups (P = 0.35). When we adjusted fasting RQ for percentage body fat and age, the reduced-obese group had a slightly higher (0.807 +/- 0.006) RQ than the control group (0.791 +/- 0.005, P = 0.05). This may have been due to the consumption of a diet lower in fat or to a reduced capacity for fat oxidation in the reduced-obese group.

CONCLUSION

These results show that in at least some reduced-obese individuals there does not seem to be a permanent obligatory reduction in RMR beyond the expected reduction for a reduced lean mass.

Regulation of body weight in humans

The mechanisms involved in body weight regulation in humans include genetic, physiological, and behavioral factors. Stability of body weight and body composition requires that energy intake matches energy expenditure and that nutrient balance is achieved. Human obesity is usually associated with high rates of energy expenditure. In adult individuals, protein and carbohydrate stores vary relatively little, whereas adipose tissue mass may change markedly. A feedback regulatory loop with three distinct steps has been recently identified in rodents: 1) a sensor that monitors the size of adipose tissue mass is represented by the amount of leptin synthesized by adipose cells (a protein encoded by the ob gene) which determines the plasma leptin levels; 2) hypothalamic centers, with specific leptin receptors, which receive and integrate the intensity of the signal; and 3) effector systems that influence the two determinants of energy balance, i.e., energy intake and energy expenditure. With the exception of a few very rare cases, the majority of obese human subjects have high plasma leptin levels that are related to the size of their adipose tissue mass. However, the expected regulatory responses (reduction in food intake and increase in energy expenditure) are not observed in obese individuals. Thus obese humans are resistant to the effect of endogenous leptin, despite unaltered hypothalamic leptin receptors. Whether defects in the leptin signaling cascade play a role in the development of human obesity is a field of great actual interest that needs further research. Present evidences suggest that genetic and environmental factors influence eating behavior of people prone to obesity and that diets that are high in fat or energy dense undermine body weight regulation by promoting an overconsumption of energy relative to need.

Childhood obesity

Approximately 10% of children are obese. Twin and adoption studies demonstrate a large genetic component to obesity, especially in adults. However, the increasing prevalence of obesity over the last 20 years can only be explained by environmental factors. In most obese individuals, no measurable differences in metabolism can be detected. Few children engage in regular physical activity. Obese children and adults uniformly underreport the amount of food they eat. Obesity is particularly related to increased consumption of high-fat foods. BMI is a quick and easy way to screen for childhood obesity. Treating childhood obesity relies on positive family support and lifestyle changes involving the whole family. Food preferences are influenced early by parental eating habits, and when developed in childhood, they tend to remain fairly constant into adulthood. Children learn to be active or inactive from their parents. In addition, physical activity (or more commonly, physical inactivity) habits that are established in childhood tend to persist into adulthood. Weight loss is usually followed by changes in appetite and metabolism, predisposing individuals to regain their weight. However, when the right family dynamics exist--a motivated child with supportive parents--long-term success is possible.

Circadian temperature and cortisol rhythms during a constant routine are phase-delayed in hypersomnic winter depression

Circadian temperature, cortisol, and thyroid-stimulating hormone (TSH) rhythms during a constant routine were assessed in 6 female controls and 6 female patients with hypersomnic winter depression (seasonal affective disorder, SAD) before and after morning bright light treatment. After sleep was standardized for 6 days, the subjects were sleep-deprived and at bed rest for 27 hours while rectal temperature, cortisol, and TSH levels were assessed. The minimum of the fitted rectal temperature rhythm was phase-delayed in the SAD group compared to the controls 5:42 AM vs. 3:16 AM (p < .005); with bright light treatment, the minimum advanced from 5:42 AM to 3:36 AM (p = .06). The minimum of the cortisol rhythm was phase-delayed in the SAD group compared to the control group, 12:11 AM vs. 10:03 PM (P < .05); with bright light treatment, the minimum advanced from 12:11 AM to 10:38 PM (P = .06) [corrected]. The acrophase of the TSH rhythm was not significantly phase-delayed in SAD subjects compared to control, though the trend appeared to be toward a phase-delay (p = .07). After bright light therapy, the TSH acrophase was not significantly different in the SAD subjects; the trend was a phase-advance (p = .09). Overall, the data suggest that circadian rhythms are phase-delayed relative to sleep in SAD patients and that morning bright light phase-advances those rhythms.

Regulation of body adiposity and the problem of obesity

The hypothesis that body adiposity is homeostatically regulated is the focus of an intensive research effort, and support for this concept is rapidly growing. While generating optimism about the future of obesity treatment, these advances also bear on our current approach to the obese patient. The observation that body adiposity appears to be subject to regulation in obese as well as lean individuals suggests that common forms of obesity may result from a primary disorder of the weight-regulatory system. As a result, voluntary efforts to lower body adiposity activate compensatory responses that limit weight loss and facilitate weight regain. The use of weight-reduction strategies based on caloric restriction, therefore, effectively pits the will of the obese individual against his or her own intrinsic weight-regulatory system. Until more effective approaches to weight reduction are available, we suggest that clinical intervention should focus on patient education and strategies to limit weight gain or modestly lower weight. Since the combination of a low-fat diet with an exercise program appears to reduce the level at which body weight is regulated without active caloric restriction, this approach may be appropriate for many obese individuals.

Obesity genes and the regulation of body fat content

Physiological investigation has demonstrated that the central nervous system monitors body composition and adjusts energy intake and expenditure to stabilize total adipose tissue mass. Genetic variations in the signalling molecules involved in this regulatory system account for the heritable component of body fat content. The application of molecular techniques to rodent models of Mendelian obesity has resulted in the characterization of five loci at which mutations produce an abnormal accumulation of body fat. The genes at these loci include agouti, which encodes a molecule that antagonizes the binding of alpha melanocyte-stimulating hormone to its receptor; fat, which encodes carboxypeptidase E; tubby, which encodes a putative phosphodiesterase; obese, which encodes a circulating satiety protein; and diabetes, which encodes the receptor for the obese gene product. A more detailed understanding of the functional interrelationships of these genes should lead to important new insights into the causes and potential therapies for human obesity.

A meta-analysis of the effects of exercise and/or dietary restriction on resting metabolic rate

A meta-analysis was used to examine the independent and interactive effects of dietary restriction, endurance exercise training and gender on resting metabolic rate (RMR). Sixty different group means (covering approximately 650 subjects) were identified from the scientific literature and subjected to meta-analysis techniques. Collectively (i.e., all groups combined), body weight loss was greater (P < 0.05) for men (approximately 18 kg) than for women (approximately 12 kg). There were no statistically significant exercise training or gender effects on RMR during weight loss. Collectively (i.e., all groups combined), dietary restriction resulted in a -0.59 kJ.min-1 (approximately -12%) decrease in RMR (P < 0.05). When normalized to body weight, RMR was reduced by less than 2% (P < 0.05). These data suggest that exercise training does not differentially affect RMR during diet-induced weight loss. In addition, decreases in resting metabolism appear to be proportional to the loss of the metabolically active tissue.

Influence of altered body weight on energy expenditure

Long-term metabolic studies indicate that over-feeding underfeeding to gain and lose body weight produce consistent increases and decreases in energy expenditure. These changes occur in both lean and obese subjects and cause deviations from the normal relationship between energy expenditure and metabolic body size. The low energy expenditure/metabolic body size in the reduced obese may contribute to the difficulty in maintaining the reduced body weight.

The role of energy expenditure in energy regulation: findings from a decade of research

The role of energy expenditure in energy regulation remains a subject of continuing controversy. New data have emerged from studies conducted over the last decade demonstrating that energy expenditure is a critical factor contributing to successful energy regulation in normal individuals, as well as to the disregulation of energy balance that characterizes obesity. Reduced energy expenditure appears to facilitate weight gain in individuals susceptible to obesity and also appears to reduce the extent of body energy loss during undereating in both lean and obese individuals. The magnitude of the reduction in energy expenditure during, and perhaps after, weight loss is greater than expected on the basis of the reduction in body weight and appears to occur in response to undefined underlying determinants of energy regulation. In addition, exercise intervention studies and cross-sectional investigations of the relationship between energy expenditure for physical activity and body composition demonstrate an apparent equilibration between physical activity and body fat content. This equilibration is suggestive of a direct influence of physical activity on the underlying metabolic determinants of energy balance.

Changes in energy expenditure resulting from altered body weight

BACKGROUND

No current treatment for obesity reliably sustains weight loss, perhaps because compensatory metabolic processes resist the maintenance of the altered body weight. We examined the effects of experimental perturbations of body weight on energy expenditure to determine whether they lead to metabolic changes and whether obese subjects and those who have never been obese respond similarly.

METHODS

We repeatedly measured 24-hour total energy expenditure, resting and nonresting energy expenditure, and the thermic effect of feeding in 18 obese subjects and 23 subjects who had never been obese. The subjects were studied at their usual body weight and after losing 10 to 20 percent of their body weight by underfeeding or gaining 10 percent by overfeeding.

RESULTS

Maintenance of a body weight at a level 10 percent or more below the initial weight was associated with a mean (+/- SD) reduction in total energy expenditure of 6 +/- 3 kcal per kilogram of fat-free mass per day in the subjects who had never been obese (P < 0.001) and 8 +/- 5 kcal per kilogram per day in the obese subjects (P < 0.001). Resting energy expenditure and nonresting energy expenditure each decreased 3 to 4 kcal per kilogram of fat-free mass per day in both groups of subjects. Maintenance of body weight at a level 10 percent above the usual weight was associated with an increase in total energy expenditure of 9 +/- 7 kcal per kilogram of fat-free mass per day in the subjects who had never been obese (P < 0.001) and 8 +/- 4 kcal per kilogram per day in the obese subjects (P < 0.001). The thermic effect of feeding and nonresting energy expenditure increased by approximately 1 to 2 and 8 to 9 kcal per kilogram of fat-free mass per day, respectively, after weight gain. These changes in energy expenditure were not related to the degree of adiposity or the sex of the subjects.

CONCLUSIONS

Maintenance of a reduced or elevated body weight is associated with compensatory changes in energy expenditure, which oppose the maintenance of a body weight that is different from the usual weight. These compensatory changes may account for the poor long-term efficacy of treatments for obesity.

Metabolic predictors of obesity. Contribution of resting energy expenditure, thermic effect of food, and fuel utilization to four-year weight gain of post-obese and never-obese women

This prospective study was designed to identify abnormalities of energy expenditure and fuel utilization which distinguish post-obese women from never-obese controls. 24 moderately obese, postmenopausal, nondiabetic women with a familial predisposition to obesity underwent assessments of body composition, fasting and postprandial energy expenditure, and fuel utilization in the obese state and after weight loss (mean 12.9 kg) to a post-obese, normal-weight state. The post-obese women were compared with 24 never-obese women of comparable age and body composition. Four years later, without intervention, body weight was reassessed in both groups. Results indicated that all parameters measured in the post-obese women were similar to the never-obese controls: mean resting energy expenditure, thermic effect of food, and fasting and postprandial substrate oxidation and insulin-glucose patterns. Four years later, post-obese women regained a mean of 10.9 kg while control subjects remained lean (mean gain 1.7 kg) (P < 0.001 between groups). Neither energy expenditure nor fuel oxidation correlated with 4-yr weight changes, whereas self-reported physical inactivity was associated with greater weight regain. The data suggest that weight gain in obesity-prone women may be due to maladaptive responses to the environment, such as physical inactivity or excess energy intake, rather than to reduced energy requirements.

The role of exercise in weight loss

Aerobic exercise has traditionally been viewed as a critical component of most weight-reduction programs. The resulting weight loss from the exercise alone, however, is often disappointing. Researchers too frequently fail to take into account the normal energy expenditure associated with living; the degree of obesity; the intensity and duration of the exercise itself; the activity during the recovery period; food intake before and after the exercise; and the age, gender, and training status of the individuals. Nor do they consider variations in baseline resting metabolic rates. In this article, the authors explore the effect of the intensity of aerobic exercise on weight loss, emphasizing the inability of many obese individuals to maintain an intensity level sufficient to produce significant weight loss. Aerobic exercise should be emphasized for its health benefits rather than as a short-term method of enhancing weight loss.

Animal models of obesity--theories of aetiology

The multiplicity of proposed mechanisms for obesity is confusing and many questions remain to be answered. A review of all the proposed mechanisms for obesity suggests that they can be placed in two groups (Table 3). The first centres on the role of the hypothalamus in the regulation of body weight. With further knowledge it may be possible to find unifying mechanisms originating in the brain for the set-point theory, the autonomic nervous system imbalance hypothesis, the thermogenesis, hyperphagia and the hyperinsulinaemia hypotheses and the gestational undernutrition hypothesis. This group of mechanisms suggests that obesity is due to altered function of central regulatory mechanisms and that the various related hypotheses are merely looking at different aspects of the same problem. The second centres on abnormalities intrinsic to the adipocyte and could link the fat cell and perinatal overnutrition theories. This group of theories suggests that an abnormality at the fat cell level, either genetic or acquired, can result in the excessive accumulation of fat. The two groups are not contradictory. The ability to develop obesity as a result of a fat cell abnormality does not negate the existence of regulatory central mechanisms since there is a finite capacity for these mechanisms to operate.

Total and resting energy expenditure in obese women reduced to ideal body weight

Obesity could be due to excess energy intake or decreased energy expenditure (EE). To evaluate this, we studied 18 obese females (148 +/- 8% of ideal body weight [IBW], mean +/- SD) before and after achieving and stabilizing at IBW for at least 2 mo and a control group of 14 never obese females (< 110% of IBW or < 30% fat). In the obese, reduced obese, and never obese groups, the percent of body fat was 41 +/- 4%, 27 +/- 4%, and 25 +/- 3%; total energy expenditure (TEE) was 2704 +/- 449, 2473 +/- 495, and 2259 +/- 192 kcal/24 h; while resting metabolic rate was 1496 +/- 169, 1317 +/- 159, and 1341 +/- 103 kcal/24 h, respectively. 15 obese subjects who withdrew from the study had a mean initial body composition and EE similar to the subjects who were successful in achieving IBW. In 10 subjects followed for at least one year after stabilizing at IBW there was no significant relationship between the deviation from predicted TEE at IBW and weight regain. These studies indicate that, in a genetically heterogeneous female population, neither the propensity to become obese nor to maintain the obese state are due to an inherent metabolic abnormality characterized by a low EE.

Dim light melatonin onset and circadian temperature during a constant routine in hypersomnic winter depression

The onset of melatonin secretion under dim light conditions (DLMO) and the circadian temperature rhythm during a constant routine were assessed in 6 female controls and 6 female patients with winter depression (seasonal affective disorder, SAD) before and after bright light treatment. After sleep was standardized for 6 days, the subjects were sleep-deprived and at bedrest for 27 h while core temperature and evening melatonin levels were determined. The DLMO of the SAD patients was phase-delayed compared with controls (2310 vs 2138); with bright light treatment, the DLMO advanced (2310 to 2135). The minimum of the fitted rectal temperature rhythm was phase-delayed in the SAD group compared with the controls (0542 vs 0316); with bright light treatment, the minimum advanced (0542 vs 0336).

Body composition and sleeping metabolic rate in response to a 5-month endurance-training programme in adults

This study examined the effect of exercise training on body composition and sleeping metabolic rate (SMR) in 15 men and 13 women who participated in a 20-week training programme aimed at running a half marathon. Body mass (BM) was measured after waking up, fasted and with an empty bladder. Body composition was assessed using densitometry. The SMR was measured from 0300-0600 hours during an overnight sleep in a respiration chamber. Assessment of SMR was at least 36 h after the last period of exercise training. After 20 weeks of endurance training no change in BM was observed. However, body composition changed significantly. On average men lost 2.4 kg body fat (P less than 0.01) and gained 1.7 kg fat free mass (FFM) (P less than 0.01). In women fat loss averaged 0.9 kg after 20 weeks (P less than 0.01), while FFM increased by 1.0 kg (P less than 0.05). Loss of fat mass was significantly larger in males (P less than 0.05). No changes in SMR were found, either in absolute terms, or when normalised for BM or FFM. Therefore, we have concluded that exercise training has no chronic, long-term effect on SMR. A possible explanation for this outcome in view of the different findings in similar studies is discussed.

The effect of a 5-month endurance-training programme on physical activity: evidence for a sex-difference in the metabolic response to exercise

The effect of a 5-month endurance training programme on physical activity and average daily metabolic rate (ADMR) was studied. Subjects were 16 males and 16 females preparing for a half marathon. Total physical activity, measured using an accelerometer, had increased by 62% and 63% after 20 weeks in males and females, respectively. Physical activity during the non-exercise part of the day did not change although in males it tended to increase (15%, NS). The ADMR had increased significantly in males after 8 and 20 weeks (+2.3 and +3.3 MJ.day-1, respectively, P less than 0.05) and exceeded the net energy expenditure for endurance-training three to four times. In females no significant increase in ADMR was found (+1.5 and +1.3 MJ.day-1, after 8 and 20 weeks, respectively). In females the change in ADMR could be largely attributed to the net cost of running itself and a small increase (10%) in resting metabolic rate during the time of day they were awake. In males a discrepancy was observed between the increase of ADMR and the expenditure due to exercise and non-exercise activities. We suggest exercise stimulates habitual physical activity and diet-induced thermogenesis in males but not in females.

Treatment of obesity

Decreases in resting metabolic rate and thermic effect of exercise during and after caloric restriction contribute to a reduced rate of weight reduction and subsequent difficulty in weight maintenance. Increasing exercise increases the thermic effect of exercise and prevents a decrease in resting metabolic rate, thereby, improving the rate of weight loss. A combined program of caloric restriction, exercise, and behavior therapy (including relapse prevention training and social support systems) is the most successful approach to long term weight reduction efforts. Pharmacologic treatment is currently limited, but there are three areas of development: agents which reduce energy intake, inhibitors of lipid synthesis, and thermogenesis enhancers. Evidence for improving efficiency of weight loss prevention and prevention of weight regain during repeated cycles of dieting (yo-yo phenomenon) exists in rat studies but not in a preliminary human investigation.