Apparently, since for most of human history, famine was a bigger concern than feast, our bodies have evolved to maintain a certain weight, making losing weight more difficult than simple caloric reduction and/or exercise, and making it much harder to lose weight once you’ve gained it. Anecdotally, we’ve known this to be true, but now there is some scientific data to support what our bodies have been telling us.
“Loosely put, after you’ve lost weight, you have more of an emotional response to food and less ability to control that response,” says Michael Rosenbaum, lead author of the study in this month’s Journal of Clinical Investigation.
The key driver of this system is leptin, a hormone secreted by fat cells. When humans… lose 10% or more of their body weight, leptin falls rapidly and sets off a cascade of physiological changes that act to put weight back on. Skeletal muscles work more efficiently, thyroid and other hormones are reduced — all so the body burns 15% to 20% fewer calories, enough to put back 25 pounds or more a year.
This mechanism kicks in whether people are obese or relatively lean before losing weight — and researchers believe the effect can last for years. In previous studies, giving subjects replacement leptin reversed the metabolic changes, in effect tricking the body into ignoring the weight loss.
The latest study shows that these metabolic changes are mirrored in altered brain activity when people lose weight. The Columbia researchers put six obese subjects on liquid diets and reduced their weight by 10%, then gave them replacement leptin or a placebo. At each stage, researchers observed their brain activity using functional MRIs when they were shown food and non-food items.
The scans showed that in the weight-reduced state, the subjects had more blood flow in areas of the brain that govern emotional and sensory responses to food and less in areas involving control of food intake. When the subjects were given replacement leptin, brain activity returned to what it had been before they lost weight.
Not that keeping weight off is impossible, just it takes more willpower than you’d think.
[You don’t win friends with salad, unless it is really good, like this from Cafe Suron, on Pratt, Rogers Park, Chicago]
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