Is leptin why the lost weight creeps back on?You might have seen news stories this past week about leptin, reporting that the hormone helps to explain why it's often harder to keep weight off than to lose it in the first place. Named after leptos, the Greek term for "thin," leptin is a hormone released by your fat cells. Although it has a number of functions, one of leptin's main roles is to let your brain know how fat you are. When you lose fat, leptin levels drop. When you gain fat, leptin levels go up.As well as being affected by total body fat levels, leptin levels will rise and fall quite rapidly in response to both overfeeding and underfeeding. After the initial drop in response to underfeeding, leptin declines at a rate that's linked more closely to the loss of fat. So, does this research reveal any new information that's going to make it easier for you to lose fat or build muscle? Let's see... The news reports were based on a study published by researchers at New York's Columbia University [1]. The researchers gave leptin injections to lean and obese volunteers who had recently lost weight. The team, led by Dr. Michael Rosenbaum, found that most of the metabolic and hormonal changes which mean people have a hard time keeping the weight from creeping back on were reversed once leptin levels were restored to pre-weight loss levels. The study, though interesting, doesn't really tell us much that we didn't know already. Rosenbaum and his team reported similar results several years ago in a study published in the Journal of Clinical Endocrinology and Metabolism, where a low-dose course of "replacement" leptin reversed some of the metabolic changes that occur during weight loss [2]. In the study, four subjects (2 men and 2 women) were fed 800 calories per day until they'd lost 10% of their initial weight. This led to a drop in both leptin and thyroid hormone concentrations, along with a reduction in the metabolic rate. For the next five weeks, subjects received low-dose leptin injections twice a day to bring leptin back to pre-diet levels. These "replacement doses" of leptin reversed the drop in energy expenditure and thyroid hormone levels. The participants also continued to lose fat while preserving muscle tissue. It looks like a drop in leptin production acts as a signal of negative energy balance (you're burning more calories than you're taking in) and low energy reserves, rather than indicating a positive energy balance and increased energy reserves. What's more, a drop in leptin concentrations seems to have a bigger impact on your body than increasing leptin levels above the normal physiological range. "The primary functional role of leptin is apparently to defend — not reduce — body fat by increasing food seeking and decreasing energy expenditure when fat stores are insufficient," writes Dr. Rosenbaum in the Journal of Clinical Investigation. "Physiological responses to concentrations of leptin below and above this threshold are very asymmetrical: decreased concentrations of leptin trigger full-strength counterregulation to what is "perceived" as a threat to survival; concentrations of leptin above the threshold — signaling "sufficient" or excess fat stores — are not responded to vigorously, or at all." In other words , your body will fight harder against losing fat than it will against gaining fat. That's why most people find it a whole lot easier to get fat than they do to get lean. So, while some have referred to leptin as an "anti-obesity hormone," it's probably more accurate to label it as an "anti-starvation" hormone that tells your brain what to do when energy is in short supply. Unfortunately, you can't just take a leptin pill and hope that your weight problems will be solved forever. For one thing, leptin can't be taken orally because your stomach will break it down. For leptin to be effective, you need to inject it. Every day. For life. This is not only very inconvenient but also very expensive. An easier and cheaper solution is to follow a diet that involves cycling your calorie and carbohydrate intake over the course of a week. A day or two of controlled overfeeding will raise leptin levels and can help you avoid some of the metabolic adaptations inherent with any type of restricted-calorie diet. I don't recommend so-called "cheat days," not as they're usually described anyway, as they have the potential to do undo all of the good work you've done during the previous six days. Instead, it's my opinion that most people who are dieting will benefit from some kind of planned break once or twice a week. A planned break can come in many forms. The two I recommend are the free meal and the one-day re-feed. Whether you choose a free meal or a one-day re-feed depends on how low your calorie intake is, how lean you are, and your current rate of fat loss (instructions on how to plan a free meal or a one-day re-feed in How to Beat a Weight Loss Plateau by Cheating on Your Diet).
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