Long-term effects of dieting on resting metabolic rate in obese outpatients

Article Abstract:

It has long been believed by some that dieting adversely affects the metabolic rate of the dieter and exacerbates the long-term effort at weight control; others report no such effect. The resting metabolic rate (RMR) is known to decline rapidly in response to calorie restriction, but after dieting a chronic effect on the RMR is considered to be related to changes in a person's fat-free mass. This study measured the RMR of 18 obese women participating in two different weight loss regimens. Half of the women consumed 1,200 kcal per day for 48 weeks (BDD, balanced-deficit diet), and the other half consumed a very-low-calorie-diet (VLCD), consisting of a liquid formula (OPTIFAST 70), for 16 weeks. The formula provided 420 kcal per day, and was gradually supplemented with food so that the calorie intake was 1,200 kcals per day from week 24 to week 48. During the eighth week all of the women began exercising, which consisted mostly of walking for 10 to 20 minutes two to five times per week and working up to 20 to 40 minute periods three to five times per week. The RMR was measured eight times during the study period. The patients on the VLCD lost approximately twice as much weight as the BDD group during all phases of the first 25 weeks. At week 17 the VLCD patients had a mean weight loss of approximately 50 lbs (about 70 percent fat) compared to approximately 24 lbs (about 90 percent fat) for the BDD group. By week 48 the VLCD group had lost an average of about 47.5 lbs (75 percent fat) while the BDD group had lost about 40 lbs (90 percent fat). The RMR fell almost 20 percent in the VLCD patients during the first month, and continued to fall over the next three months reaching a low at week 17; during this period the BDD group's RMR fell an average of approximately 13 percent. The RMR increased dramatically when the VLCD patients started to eat again, and eventually matched that of the BDD group. The RMRs among both groups were significantly lower after the weight loss, but this was in relation to the new fat-free mass level and did not signify a suppression. Fall in RMR does not seem to be prevented by exercise during caloric restriction, but exercise during dieting may be associated with favorable long-term changes in RMR. This study concludes that dieting with moderate exercise can lead to a normal long-term reduction in RMR that is associated with a lowered body weight, not with an abnormal depression of the metabolic rate. (Consumer Summary produced by Reliance Medical Information, Inc.)

Health aspects, Metabolism

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Long-term evaluation of cardiac function in obese patients treated with a very-low-calorie diet: a controlled clinical study of patients without underlying cardiac disease

Article Abstract:

Very-low-calorie diets (VLCDs) are used for treating obese people who were unable to lose weight while following a less extreme diet restriction. VLCDs are low in fat and high in protein, providing 45 to 100 grams protein per day in 400 to 800 calories. The average weekly weight loss on this type of diet ranges from three to four and a half pounds. Some of the early VLCDs, available in 1976 and 1977, were associated with fatal heart disorders because of protein, vitamin, and mineral deficiencies, and prolonged periods of dieting. The VLCDs that are available today are high in protein, vitamins and minerals, and studies have indicated that these diets do not cause heart problems. However, these studies were limited to a period of seven weeks or less, and VLCDs are usually followed for 12 to 16 weeks. Therefore, in the current study, the effect of a VLCD on the heart was determined over a 16-week period in 12 obese women, with no history of heart disease, who followed a 420 calorie/day liquid diet for 16 weeks and then were switched to a 1,200 calorie/day balanced diet for the remainder of the study period (until 45 weeks). A different group of eight obese women followed a 1,200 calorie/day balanced diet, and six others did not follow any form of diet. Electrocardiograms were performed prior to the beginning of the study and again at weeks 3, 9, 13, 17, 19 and 45, in order to detect changes in the electrical activity of the heart. The average weight loss during the 16-week VLCD was 47 pounds. During the same period, those following the balanced diet lost an average of 23 pounds and those who were not dieting gained an average of 6 pounds. There were no symptoms or abnormalities in heart function during the study period. It is concluded that VLCDs, when used for up to 16 weeks under appropriate medical supervision, provide a safe and effective means for weight loss in obese patients who do not have a prior history of heart disease. (Consumer Summary produced by Reliance Medical Information, Inc.)

Heart, Diet therapy

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Controlled trial of the metabolic effects of a very-low-calorie diet: short- and long-term effects

Article Abstract:

A very-low-calorie diet (VLCD) is a weight reduction diet that supplies 300 to 600 calories per day; it is considered an extreme form of dieting because such a small proportion of the individual's energy needs are met. Following a VLCD may lower the resting energy expenditure (REE, calories used while resting) by as much as 20 percent. This is the body's natural adaptation to semi-starvation; it attempts to conserve energy by reducing the metabolic rate. To a dieter, reduction of REE is undesirable. REE falls quickly on a VLCD diet, but is thought to rise again when food intake increases; research has not shown how much it increases during re-alimentation (refeeding). In a group of 16 obese dieters, REE, weight and body composition were measured over 24 weeks. For the first four weeks, all subjects followed a 1,000 to 1,200 calorie balanced-deficit diet (BDD). Then nine subjects continued the BDD and the other seven followed a VLCD for eight weeks. During this time, the REE of subjects on the VLCD was reduced by 17 percent, but the REE of subjects on the BDD was essentially unchanged. For the next 12 weeks the VLCD subjects gradually increased their food intake to reach 1,000 to 1,200 calories per day, the same as the BDD group. By the end of the study, the REE levels of the two groups were not significantly different at 11 percent below baseline in the VLCD group and two percent below baseline in the BDD group. In the VLCD group, REE had partially returned to baseline from a low of 17 percent below baseline. Weight loss was 12.1 percent of body weight for VLCD subjects and 10.6 percent for BDD subjects. This included some loss of fat-free mass, approximately four percent, in both groups. In conclusion, the less extreme BDD appears to offer an advantage over the VLCD because it causes a smaller reduction in REE. (Consumer Summary produced by Reliance Medical Information, Inc.)

Care and treatment, Energy metabolism

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