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It’s not you. You’re not imagining it. It really, actually, legitimately is harder to keep weight off than it is to lose it in the first place. You really do feel hungrier than you used to, and still the pounds keep creeping back on. This is the conclusion that Dr. Joseph Proietto and his colleagues at the University of Melbourne just published in the New England Journal of Medicine .
Dr. Proietto runs a weight-loss clinic. In this most recent study, he recruited fifty obese individuals without diabetes or other serious illnesses into an intensive ten week weight loss program. After weight loss was achieved — study participants were required to lose ten percent of their body weight — they received dietary counseling to help them maintain their new weight. Dr. Proietto measured levels of a variety of hormones known to mediate appetite and got subjective ratings of appetite before the program began, immediately after it ended, and then again a year later.
Of the fifty people recruited, thirty-four were able to complete the study. Perhaps not surprisingly, Dr. Proietto found that the participants reported their “desire and urge to eat” as higher immediately after the weight loss regimen than it was before they had started. But distressingly, it was just as high a year later. What’s more, they reported being more preoccupied with thoughts of food, and less full, after a year than they had been just coming off of the diet.
The levels of nine different hormones were measured. Of these, leptin might be the best known. It is made by body fat, and thus functions as an indicator of energy stores. It acts in the brain to suppress hunger and increase metabolism. Leptin levels plummeted by 64% over the ten weeks that the study participants were dieting, and although they recovered somewhat over the course of the next year, they were still 35% lower than when the study began. The researchers noticed that as study participants put weight back on, their leptin levels rose. Ghrelin can be thought of as the opposite of leptin — whereas leptin suppresses feelings of hunger, ghrelin promotes them. And as such its levels were the opposite of leptin’s — for the ten weeks of the diet the participants’ ghrelin levels steadily rose, and although they fell over the course of the year, they ended up significantly higher than they were at the beginning of the study. The other hormones followed the same pattern established by these representatives; those that suppress appetite were reduced, while those that stimulate appetite were increased.
These hormonal changes indicate that a full year after these people lost weight, their bodies were trying to put it back on. Their bodies regarded this leaner state as akin to starvation, and treated their heavier body weights as normal. Their metabolism was not at all the same as that of someone who had always weighed this lower amount rather than achieving it by dieting.
A number of other studies have borne out this idea, that a weight-reduced body is quite different than one of the same size that had always been that way.
Last month, Tara Parker Pope expanded upon Dr. Proietto’s study in the in The New York Times Magazine. Ms. Parker Pope highlights some studies being done at Columbia University confirming that after people lose weight their muscles are more efficient — meaning that when doing the same activity as people who were always at that lower weight, they burn 20-25% fewer calories. And using brain scans, neuroscientists at Columbia have shown that images of food activate regions of the brain associated with reward more strongly in people after they have lost weight, while regions associated with control did not respond as strongly in these post dieters. Their brains are actively making food look more appealing, and undermining their will power, to get them to eat more — to get them back to their original weight.
The National Weight Control Registry tracks 10,000 people who have lost at least thirty pounds and kept it off for at least a year. Analysis of their habits reveals that to maintain their new lower weights, these individuals must in fact eat less, and exercise more, than those who naturally weigh the same amount. And that’s not really surprising: if you want to lose weight and keep it off, you have to permanently change your lifestyle. The lifestyle that you adopt to lose weight has to be one you’re prepared to maintain for the rest of your life. So as Ms. Parker-Pope notes in her article, it is not hopeless. It is not impossible to lose weight and then keep it off. It’s just really, really hard.
Sumithran P et al. Long-term persistence of hormonal adaptations to weight loss. N Engl J Med. 2011 Oct 27; 365(17):1597-604.
Rosenbaum M, Kissileff HR, Mayer LE, Hirsch J, Leibel RL. Energy intake in weight-reduced humans. Brain Res. 2010 Sep 2; 1350:95-102. Epub 2010 Jun 2.