jenk

One of the side affects of weight loss is that your body becomes more efficient. AKA, losing weight? Must not be enough food! Must conserve fuel! Or as Gina Kolata wrote in the NY Times:

When people lose substantial amounts of weight, their physiology changes so that, although they may look normal, they have all the hallmarks of starvation. Their metabolism slows down, they expend fewer calories when they exercise because their muscles become much more efficient, and their thyroid hormone and adrenaline levels drop. They also have much lower levels of the fat hormone, leptin.

This, naturally, causes the weight to come back. Repeated diet-and-regain is called "yo-yoing". I've read that yo-yoing has been intentionally used as a treatment for underweight. For most of us, tho, yo-yoing is unintentional. It's how I "dieted up" to my adult weight.

A group of researchers at Columbia University devised an experiment to see whether if they could prevent these changes that occur with weight loss. Leptin, they reasoned, tells the brain how much fat is on the body. But what if the researchers put people - fat and thin - on weight-reducing diets and gave them enough leptin to make their bodies think that they were still fat. The leptin would then serve as a sort of virtual fat. Would the subjects still show the metabolic changes of starvation?

The answer, published in the current issue of The Journal of Clinical Investigation, was that the leptin trick worked. [...]

At low levels of exertion, comparable to normal daily activities, they burned 23 percent fewer calories. When they took leptin, their calorie burning increased to pre-diet levels.

They also measured thyroid hormone concentrations in the blood and found that leptin reversed the declines in those levels that occurred with weight loss. And the scientists measured the effects of weight loss on the sympathetic nervous system, documenting lower levels of adrenaline in urine. Leptin reversed that, too.

Dr. Michael Rosenbaum, the lead investigator, said the 10-week study was too short and too small to determine whether continuous leptin treatments could allow dieters to keep off their weight permanently and effortlessly. But, Dr. Rosenbaum said, it established a proof of principle.

"Obesity is the one disease I can think of where your body fights the cure," he said.

Interesting....