Refeeding after fasting in rats: effects of duration of starvation and refeeding on food efficiency in diet-induced obesity

Article Abstract:

People who have been severely obese are generally not able to maintain a stable weight after having lost weight. Studies indicate that the weight loss and subsequent regain are related to the size and number of fat cells. Research with rats has found that normal animals that have been starved regain weight without increasing food intake by increasing the efficiency of food use, while obese rats which have been starved do not have improved efficiency during refeeding. The mechanisms which regulate fat tissue metabolism are still unclear, despite such studies. The effects of 4, 8, 15, or 25 days of starvation and of varied refeeding periods on fat cell size and number, body protein composition, and liver stores of glycogen (stored glucose) in rats were studied. The results suggest that in rats, overfeeding during obesity development causes thermogenesis (heat production), which wastes some of the extra ingested calories; this is the state of low food efficiency. When starvation follows obesity, the thermogenesis persists, and the combination of thermogenesis and energy intake reduction results in effective weight loss. However, thermogenesis declines during starvation when fat tissues start to empty; food efficiency then increases, and is maintained until fat cells are refilled. The study found a close correlation between degree of fat cell filling and food efficiency, which may suggest a possible signal system. However, whether the signal is one of the known functions of the sympathetic nervous system (a part of the autonomic or involuntary nervous system that makes adrenalin), or whether there are as yet undetermined signals emanating from fat tissues is unclear. These findings, if applicable to humans, suggest that below a certain levels of fat cell filling, food efficiency increases, with weight gains likely. Further work is needed to elucidate the regulation of fat cells in humans. (Consumer Summary produced by Reliance Medical Information, Inc.)

Health aspects, Body weight, Adipose tissues, Adipose tissue, Fat cells, Adipocytes

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Resting metabolic rate in weight-cycling collegiate wrestlers compared with physically active, noncycling control subjects

Article Abstract:

To improve the treatment of obesity, some researchers are focusing on understanding the effect of dieting on the resting metabolic rate (RMR), the rate at which calories are burned for basic physiological processes while at rest. One theory of why dieters tend to regain the weight they have lost is that restricting caloric intake slows metabolism, so that less energy is needed in the future. However, it is not clear if dieting reduces the RMR over the long term. Wrestlers are a group of athletes who typically go on sudden diets to reach a certain weight limit for competition; after the match or the season they often regain this weight. To determine whether this weight-cycling lowers the RMR, 12 college wrestlers who had competed (with weight-cycling) for at least three seasons were compared with 13 nonwrestlers (controls). All the subjects were men, aged about 19 to 20 years. The controls were of similar weight and body composition to the wrestlers, but had maintained a stable weight. The RMR was measured before, during, and after the wrestling season, and it was found that at baseline (before the season) the wrestlers actually had a significantly higher RMR than the controls. During the wrestling season, after the wrestlers had lost weight, their RMR was not significantly different from that of the controls. After the season, the findings were the same as at baseline, with the RMR of wrestlers higher than that of controls. It was concluded that the repeated cycles of dieting and weight regain did not cause a long-term reduction in the RMR of these wrestlers. (Consumer Summary produced by Reliance Medical Information, Inc.)

Training, Food and nutrition, Wrestlers

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Adaptive changes in energy expenditure during refeeding following low-calorie intake: evidence for a specific metabolic component favoring fat storage

Article Abstract:

Experts agree that when the caloric intake of either humans or animals is restricted to below the individual's energy requirement, the amount of energy expended, or burned, drops. This phenomenon has important applications, both in the treatment of obesity and the management of undernutrition in economically deprived societies. What is not clear is how and why the energy expenditure drops when food intake is limited. The explanation may simply be that when the amount of calories consumed is inadequate, the mass of metabolically active tissues (such as muscle) decreases; since these tissues use calories at a rapid rate, less energy is expended. An additional effect of calorie restriction may be that food is converted to useful energy more efficiently; this process would involve a slowed metabolic rate. A study was conducted to investigate the latter effect of dieting, known as the metabolic component. Rats were fed only 50 percent of their caloric needs for either 10 or 30 days; they were then fed a normal diet (''refeeding'') for 25 days. Compared with untreated control rats, the food-restricted rats (both 10-day and 30-day groups) had a net 15 percent reduced energy expenditure during refeeding; this was attributed to a slowed metabolic rate. The energy saved by reducing caloric expenditure was deposited as fat, and may represent a means for storing energy in preparation for repeated food shortages. This adaptive mechanism may be responsible for the tendency of obese persons to easily regain weight lost while dieting. (Consumer Summary produced by Reliance Medical Information, Inc.)

Starvation

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