Leptin and Appetite: Feeling Full or Fleeced?
Up until a few years ago, scientists believed that fat tissue (also called adipose tissue) was a metabolically inactive organ that just padded your organs, insulated your body, and when accumulated in excess, expanded your waist-line. In 1994, researchers at Rockefeller University identified leptin as the hormone actually produced by fat tissue that signified satiety–or the feeling of fullness–in a group of obese mice they were studying.
Since then, the idea of leptin as a weight-loss “miracle” has been touted by supplement makers and everyone else with an interest in the lucrative weight-loss industry. While plenty of scholarly papers and animal studies regularly analyze the role of leptin, as a consumer, exactly how effective is leptin or leptin-containing products for weight-management? And how can you really promote appetite control for weight-loss?
Leptin’s Broken Promises
Essentially, leptin tells your fat stores that you have enough fat stored up in your body. When adequate fat mass exists, your fat cells secrete leptin. Theoretically, your accumulation of additional fat will stop with the introduction of leptin into the bloodstream. Nutrition researchers, and later the dietary supplement industry, used this relationship to surmise that if you can figure out how to increase leptin production, you can halt fat storage and promote weight loss in someone who would otherwise continue to get fatter.
While genetically mutant obese mice that had no leptin production lost weight when injected with leptin, the same has not held true when applied to human subjects. Contrary to public opinion, scientific literature has never demonstrated that ingested or injected leptin has induced weight loss in otherwise healthy overweight humans. Because the mechanism by which leptin works is not entirely understood and because there are basically no humans who entirely lack leptin production, the reason why overweight humans who were given leptin but did not lose weight is also somewhat of a mystery.
Losing Weight the Approved-Drug Way
To date, there are no FDA-approved weight-loss drugs that utilize leptin as the weight-loss-inducing ingredient. At any given moment there is probably a slew of drug companies researching the potential for leptin in a weight-loss drug, but it is not currently a viable option for American consumers.
Supplement manufacturers are still on the leptin bandwagon, however, and you can find hordes of weight-loss dietary supplements claiming to have leptin as an active ingredient. Because the dietary supplement industry is highly unregulated, consumers should take caution and know that the likelihood of leptin causing weight loss is the only slim thing about these claims.
The two drugs that are approved for long-term weight-loss and maintenance by the FDA are the following:
- Sibutramine (Meridia™) – a serotonin-norepinephrine reuptake inhibitor that works on receptors in the hypothalamus (the brain’s “satiety center”) to reduce appetite.
- Orlistat (Xenical™) – stops the action of gastrointestinal lipase (a fat-breakdown enzyme) and reduces fat absorption, resulting in increased fat loss in the feces. The popular over-the-counter weight loss drug Alli™ is a lower-dose version of Xenical.
The Science of Satiety
If (and until) leptin re-emerges as a practical weight-loss application, you can alter your diet to more naturally increase satiety. Satiety is the feeling of being full, and protein and fiber are the two nutrients that can help you accomplish this—which in turn, helps prevent overeating elsewhere in your diet.
Exactly how protein helps to promote satiety is not entirely known. It may serve to increase circulating levels of leptin, or increase in the level of cholecystokinin release that slows the emptying of food from the stomach during digestion.
Fiber works to keep you fuller because it also slows down the rate of digestion. You might notice that if you eat a piece of low-fiber white toast or white bagel, you get hungrier again more quickly than if you eat the same amount of calories of a 100% whole wheat bagel or piece of high-fiber bread. High fiber foods take longer to digest, meaning that there is more time until the next time when you get hungry again.
Some food manufacturers are starting to realize the importance of promoting satiety. One such company is LightFull Foods™, a San Francisco-based outlet that produces LightFull smoothies. These 11-oz. smoothies are low in calories (90 calories/serving) and have a good amount of fiber and protein (5-6 grams of both, depending on the flavor). While some nutrition professionals would argue that calories from drinks do not keep you as full as calories from foods, as far as satiety is concerned, a beverage that contains protein and fiber instead of high fructose corn syrup and high levels of refined carbohydrate, is definitely a step in the right nutritional direction.
The Protein-Fiber Combo
In order to promote optimal satiety throughout the day and in order to prevent overeating, keep these numbers in mind when it come to fiber and protein: Women need 25 grams of fiber per day and men need 38 grams. Most adults need somewhere between 75-125 grams of protein per day, depending upon your activity and calorie level. Scheduling an appointment with a registered dietitian is a good way to help determine what your optimal, personal calorie and protein needs are.
So while leptin as a supplement will not promote any substantial weight loss, and leptin as a prescription drug is probably years away, it does not hurt to focus on satiety in other food-based forms. Bump up your fiber and protein intake—without increasing calories—and you’ll have a safe, natural appetite control mechanism that really works to curb your food intake.
- A high-protein diet induces sustained reductions in appetite, ad libitum caloric intake, and body weight despite compensatory changes in diurnal plasma leptin and ghrelin concentrations. Weigle, et al. Am J Clin Nutr. 2005 Jul;82(1):41-8.
- Appetite Regulatory Hormone Responses to Various Dietary Proteins Differ by Body Mass Index Status Despite Similar Reductions in ad Libitum Energy Intake. Bowen, et al. J Clin Endocrinol Metab. 2006 Aug;91(8):2913-9.