The subject of eating and hormone deficiencies is on my mind. I read about it in a Wall Street Journal article last month which concluded that appetite—no surprise—may be more about biology and biochemistry than previously thought. Days later a nutritionist colleague referred me to a website promoting a replacement for an appetite-regulating hormone some overeaters may lack. Interesting, but scary stuff, reminiscent of the nature-nurture debate—that is, how much power do we really have over our bodies?

The WSJ article explains that a lack of leptin, a hormone secreted by fat cells, is one of the reasons that people regain lost weight. Leptin plays a key role in fat metabolism because its levels decrease when we lose weight, generating a host of physiological changes which promote pounds creeping back on. In studies, it doesn’t matter if people were lean or obese before losing weight. Whatever their body mass, after losing weight, brain activity (measured by blood flow) increased in areas that focus on sensory responsiveness to food and decreased in areas of control. Translated, that means that decreased leptin makes food more attractive while lessening our ability to govern impulses around it, a double whammy. But, voilá, when subjects were given replacement leptin, brain activity returned to its pre-weight loss levels.

For decades we’ve heard that weight loss triggers the body to go into survival mode to conserve calories and now we have a better understanding of how that happens on a cellular level. There is a biologically determined need for our species to regain lost weight in order to keep on keeping on. Although this may make overweight overeaters feel better on the one hand—it’s not about will power and self-discipline after all—it may make them feel worse on the other—how can you fight biology and evolution?

Enter the email from my colleague about leptin replacement. I went to the website she referred me to, wondering about its legitimacy and whether the product is something I should recommend to clients who struggle with weight. How would I know which clients have a leptin deficiency? For that matter, unless they’re tested, how would they? The website raised more questions than it answered. How much double-blind research has been done and who are the study funders (ie, the makers of the product?)? Where are the long-term results and what about side effects?

If you suspect you have a leptin deficiency, talk to your doctor. Ask if there are tests you can have to find out and about the latest research into leptin replacement.