Aging is a process that alters our physiology in ways such as decreasing the secretion of anabolic hormones, e.g., growth hormone and insulin-like growth factor (IGF-1) . Also, aging changes body composition, including a progressive increase in body fat, especially visceral adipocytes, which is linked to increased plasma concentrations of insulin and leptin and increased insulin resistance . Furthermore, as we age, we see a decrease in muscle mass (sarcopenia), strength and functional capacity with an increased risk of obesity and type 2 diabetes .
Previous research has shown a decrease in muscle protein synthesis after consumption of a normal protein meal in elderly populations . A higher dose (2.8 g) of leucine compared to a smaller dose (1.7 g) was effective in stimulating protein synthesis is elderly people whereas both these doses stimulated protein synthesis in younger people. Very few studies investigated the effect of long-term supplementation with leucine on body composition.
Recent research tested the hypothesis that leucine supplementation during most of the adult life of rats might alter body composition by decreasing body fat and attenuating the loss of lean mass, in addition to promoting metabolic risk indicators of acquired chronic diseases . Elderly rats (6 months old) were divided into two groups, one group received 4% leucine for 40 weeks, and the other group received a control diet for 40 weeks. This time period represented much of their adult lives. The investigators evaluated bod weight, food intake, chemical carcass composition, indicators of acquired chronic diseases, and indicators of protein nutritional status.
The following are the key findings of this research:
Supplementation with leucine attenuated weight gain, body fat accumulation, and hyperleptinemia associated with aging. Long-term supplementation with leucine significantly attenuated fat gain as shown by the mass of visceral fat depots and the percentage of total body fat. Leptin concentration is an indicator of the amount of body fat . The serum leptin concentration was significantly higher in control animals compared with the adult group.
Lipid and glycemic profiles were not affected by leucine supplementation. Supplementation with leucine did not prevent loss of body protein and muscle protein during aging.
Results from this study confirm previous findings showing that leucine supplementation promotes a decrease in body fat . Leucine supplementation did not affect the metabolic indicators of acquired chronic diseases (i.e. total cholesterol, triacylglycerol, glycemia). In addition, long-term supplementation with leucine was ineffective in attenuating the negative effects of aging on indicators of protein nutritional status such as muscle RNA, protein concentration, total body protein, and lean mass.
It’s important to keep in mind that there was no exercise stimulus in this research. There may be an additive effect of enhancing leucine concentration in the diet coupled with resistance exercise on the same age group as used in this study. Also, the effects of leucine combined with resistance exercise may be different in this age group on protein mass. Nevertheless, it is clear that leucine promotes fat loss as aging occurs.
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