The Role of Leptin in Weight Control
In 1994, scientists discovered that fat tissue in mice and rats produces the protein leptin. New research shows the possible correlation between leptin levels and obesity in humans.
What is Leptin?
Leptin is a protein manufactured by our body’s fat cells. It appears that the level of leptin circulating in our bloodstream is directly proportional to the total amount of body fat, or adipose tissue, we possess. Women, who have a higher percentage of body fat than men, have higher leptin concentrations. Leptin acts in the hypothalamus, a part of our brain that is responsible for coordinating many body functions, including appetite and satiety. Leptin may suppress appetite, resulting in decreased food intake and weight loss.
Role of the Hypothalamus in Weight Control
Researchers know that the hypothalamus plays a significant role in appetite and energy expenditure. A variety of signals control the amount we eat: sensory signals such as smell and taste, physical signals such as a feeling of fullness, and chemical signals from the gastrointestinal system to the brain. Leptin enters the metabolic pathway in which hormones travel through the bloodstream to the brain, delivering messages about food intake and energy expenditure.
Leptin and Weight Loss
Researchers have noted that diets, especially very low calorie diets, cause a rapid and marked decrease in leptin levels circulating in the bloodstream. This lack of leptin is responsible for the increase in appetite often found when people drastically reduce calorie intake.
Leptin & Weight Loss Study
A recent study in The New England Journal of Medicine reports that daily injections of leptin over one year led to decreased appetite and weight loss. The researchers studied a 9-year old girl with a genetic mutation that prevented her body from producing leptin. Before the study began, she weighed 208 pounds, of which 123 pounds were body fat. Conventional methods had failed to produce any weight loss.
After one year of leptin injections, the girl lost 36 pounds, primarily in body fat.
Obesity Clinics Test Leptin Injections
A randomized, controlled trial performed in six different obesity clinics looked at the effects of leptin on 73 obese men and women. Researchers reported in The Journal of the American Medical Association that daily injections of leptin led to a mean weight loss of 15 pounds in a 24-week treatment period.
More than 95 percent of the lost weight was from body fat.
There was considerable variation in the amount of weight that individual subjects lost during the treatment. Subjects who took the highest daily doses of leptin also lost the most weight.
It is important to note that during this study, the research subjects also followed a weight reduction diet; however, those subjects in the placebo group who did not receive leptin only lost an average of 3.75 pounds in 24 weeks. The researchers believe that the effect of the diet was minimal since subjects who took leptin lost almost five times as much weight.
Leptin – the Latest Weight Loss Miracle?
Possibly. Because leptin is a protein, it must be injected into the body and cannot be taken orally as a pill or capsule.
Some people appear to have a decreased sensitivity to leptin, and do not lose weight when treated with leptin injections.
In addition, the amount of leptin produced in the body varies significantly from one person to the other, even when amount of body fat is similar.
Individual differences in leptin production or resistance may be at least part of the reason why some people have a more difficult time losing weight and maintaining that weight loss.
There currently are only a few descriptions of leptin gene mutation in humans, so leptin therapy is not a panacea for weight control for the majority of overweight people.
Leptin-Weight Loss Mechanism Still Unclear
The exact mechanism of leptin’s action on energy and appetite regulation has yet to be determined. Although the latest results are promising, more studies are needed before researchers completely understand leptin’s role in weight loss for the general population.
Source: Lynn Grieger, RD, CD, CDE
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