By Shelby Stoner, PHASE IV Exercise Physiologist
Previous articles in the Hormone Series:
Leptin, the satiety hormone, is a hormone that is released from adipose tissue, more commonly known as fat. Leptin does not affect food intake like its counterpart ghrelin (the hunger hormone), instead it alters food intake and controls energy expenditure over the long term. It does so by inhibiting hunger so the body does not trigger hunger responses when it does not need energy. Leptin has more of a profound effect when we lose weight and levels of the hormone fall. In some cases, this stimulates an increase in appetite and food intake, which is why it can be so difficult to lose those few extra pounds!
Since leptin is produced by fat cells, it makes sense that our body composition has a direct effect on how much leptin is released. The more fat an individual has, the more leptin they will have circulating in their blood and vice versa. However, those that are obese have unusually high levels of leptin. This is because in most obese individuals, the brain does not respond to leptin which causes an increase in food intake despite excess fat stores, a concept known as “leptin resistance.” A similar process occurs in those with type 2 diabetes with insulin resistance, causing the unusually high levels of circulating insulin. Unfortunately, the cause of leptin resistance is still unclear. Considering that obesity is a primary health concern and that many people who lose weight regain part if not all of that weight and that leptin is involved in regulating eating behavior, understanding the impact of exercise on leptin concentrations and the regulation of leptin release and/or synthesis is an important public health concern.
The effect of exercise on leptin concentrations is currently controversial. Several studies have reported that exercise may result in circulating leptin reductions depending on the duration and caloric expenditure while others have reported no significant changes in leptin concentrations. Weltman et al. (2000) found that 30 min of exercise at various intensities and caloric expenditures in healthy young men did not cause modifications in leptins levels during and post exercise. In this study, the intensity and short duration of exercise did not appear to be sufficient enough to affect the leptin concentration in these young subjects. Another study by Bouassida et al. (2004) demonstrated that 45 seconds of supra-maximal exercise at 120% of peak aerobic power was not associated with a reduction of leptin levels in 5 males and 12 females who were physically active. However, it was noted that other hormones such as cortisol, which can affect leptin concentrations, increased in the subjects in response to exercise as expected. In general, the studies suggest that short-term exercise (<60 minutes) and exercise that generated energy expenditures less than 800 kcals do not affect leptin concentrations.
However, other studies examining the effects of exercise on leptin concentrations have shown that exercise of longer durations and greater energy expenditures may actually reduce leptin concentrations post-exercise. Essig et al. (2000) reported lower leptin concentrations in trained males after exercise tests expending 800 and 1500 kcals respectively. These authors concluded that the decrease in leptin concentrations was preceded by a decrease in insulin concentrations 24-48 hours during recovery. Leptin responses after much longer durations of exercise have also been reported, including Leal-Cerro et al. (1998) which controlled the variations of the circadian rhythm of leptin after a marathon and found significant reductions in the participants’ leptin concentrations. These authors associated the leptin decrease with the large energy expenditure generated by the marathon. All in all, the decrease in leptin concentrations post-exercise are largely attributed to long-term exercise (>60 min) and exercises that generated a sufficient energy imbalance (>800 kcal).
As a general consensus from looking at the effects of physical activity on varying hormones, exercise and training can reduce fat mass, which plays a significant role in hormonal concentrations, including insulin, cortisol, growth hormone, and other metabolites such as free fatty acids and lactic acid. Overall, the variance in literature regarding the specific effects of exercise on leptin concentrations is related to many factors such as the intensity and duration of exercise, the nutritional status of the subject, and the caloric imbalance imposed by the exercise.
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