Vitality

More Than Willpower: Weight Loss Makes Us Hungrier — Even When We Don't Know It's Happening

Our battle against the bulge may be futile, new research sponsored by the National Institutes of Health suggests, thanks to a treacherous traitor  — our very own bodies.

Researchers reexamined data from an earlier randomized placebo-controlled clinical trial of patients with Type 2 diabetes. The patients in the treatment group had been given an experimental drug that caused them to urinate out more glucose than normal, meaning they took in fewer calories even as their diets remained the same. Over the course of six months, the treatment group first experienced drastic weight loss followed by steady weight regain, according to the study. 

Using a newly devised mathematical model, the researchers found it was the patients’ proportionately growing appetites that largely fueled this regain, not the small changes in metabolism commonly seen with weight loss. They calculated that for every pound lost, and despite not being consciously aware they were eating less, the patients ate an average 50 calories a day more than they did before the study began — over 3 times the amount of calories saved by a shifting metabolism.

“While energy expenditure adaptations are often thought to be the main reason for slowing of weight loss and subsequent regain,” they concluded in the study, it’s the feedback loop of increased hunger that “plays an even larger role and helps explain why long-term maintenance of a reduced body weight is so difficult.”

Though the findings are currently available on BioRxiv, a prepublication journal, they will be eventually published in the journal Obesity later this month during Obesity Week 2016. 

Plate of food New research pinpoints the role that increased hunger plays in keeping us from losing weight. Photo by Mario Tama/Getty Images

Scientists have long theorized that increased hunger is a major contributing factor to weight loss failure. People on conventional weight loss programs have elevated levels of hormones known to regulate hunger, research has shown. And people who lose weight via surgery — the only treatment that reliably leads to long-term weight loss — experience a permanent reduction of their hunger hormone levels. To say nothing of the numerous weight loss tips that warn against hunger pangs.

But finding definitive proof of this link has been hard, namely because losing weight typically requires a lot of conscious effort and is hard to track accurately. For instance, asking people to count how many calories they’ve eaten in a day often ends in failure since most underestimate their tally. Similarly, the ways we try to lose weight can affect our behavior, even from one day to the next. There’s some evidence that exercise helps mitigate the slower metabolism seen during weight loss attempts (though not as much as we assume), but other research finds that many overcompensate for a workout by eating more than they normally would. And so-called starvation diets can trigger binging episodes, eventually leading to eating disorders.

By looking at real-world people who weren’t losing weight via lifestyle changes and whose daily calorie intake was assessed rigorously, the researchers were able to directly measure how the human body fights off weight loss via hunger for the first time, they said.

Less encouraging is the possibility that there might be not anything we can do currently to fight back.

There’s no evidence that the hunger feedback loop gets any weaker the longer someone keeps their weight off, the researchers noted, adding that a similar effect can be seen with permanently slower metabolisms. In other words, there’s never a point when the body stops wanting to regain weight. So even long-term weight losers have to try harder than everyone else to stay thin, likely for life. And without a “heroic and vigilant effort to maintain behavior changes in the face of an omnipresent obesogenic environment,” the researchers concluded, weight regain is practically inevitable.

Sadly, for the vast majority of people, that effort will almost certainly fall short.

Source: Polidori D, Sanghvi A, Seely R, et al. How Strongly Does Appetite Counter Weight Loss? Quantification Of The Homeostatic Control Of Human Energy Intake. BioRxiv. 2016.

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