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July 25, 2023

Why do dieters so often regain weight? Drexel, Penn researchers join national study to find better answers

Researchers want to develop a better picture of the biological and behavioral reasons people put back on the pounds they've lost

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Diet Weight Gain Source/Image licensed from Ingram Image

A study funded by the National Institutes of Health seeks to better understand why so many people who lose weight from dieting end up regaining the pounds they lost. Philadelphia is one of the cities where people are being enrolled in the study.

In recent years, research has presented a discouraging picture of the long-term success dieters have in keeping off the weight they've worked hard to lose.

Upwards of 80% of dieters end up regaining most or all of their lost weight — often within a period of five years or less, according to a national analysis of long-term weight loss studies. One prominent study of 14 contestants who had appeared on the reality TV series "The Biggest Loser" — each having lost at least 50 pounds, and some more than 200 pounds — found that they had regained about two-thirds of the weight they lost within six years, on average. Some ended up heavier than they were before appearing on the show. 

As the U.S. faces rising rates of obesity, diabetes and high blood pressure, especially among younger people, there's a growing push to better understand what causes diets to fail and how to help those who are overweight make changes.

Researchers from Drexel University and the University of Pennsylvania will participate in a new study led by the National Institutes of Health to discover the biological and behavioral influences that prompt people to regain weight. The POWERS study will track the initial weight loss of its participants for about 1 1/2 years and then follow them over a longer weight maintenance period. 

"Current research and societal beliefs have some dieters believing it's a futile exercise," said Michael Lowe, a Drexel professor and clinical psychologist who has served as a long-term consultant to Weight Watchers. "By conducting this research, we hope to explain why some people regain weight and that dieting is not self-defeating when effective approaches to weight maintenance are taken."

More than a decade ago, Lowe developed the now widely-used Power of Food Scale to offer a more complete behavioral measure explaining why some people are more vulnerable to overeating than others. It has been used in hundreds of studies worldwide to analyze self-reported emotional responses to food, as well as physical reactions like salivation when food is present. 

Lowe's research builds on and challenges earlier theories that have suggested restraint from food — particularly chronic dieting that fails — makes people more susceptible to overeating. The Power of Food Scale helps individualize how appetites and levels of food motivation differ among people.

One idea frequently used to explain the long-term ineffectiveness of dieting is called "set point theory," an evolutionary principle that people each have individual weights that their bodies adjust to and target over time as a survival mechanism.

According to the theory, the more people lose weight through dieting and lifestyle changes, like regular exercise, the more their bodies "fight back" to return to their set points. This includes metabolism slowing down in response to weight loss — meaning fewer calories get burned each day — and hormonal changes that can make people feel more hungry, or less full after eating. A number of other biological factors, from inherited traits to changes in gut bacteria and fat tissue among overweight people, also influence the ways weight is lost, maintained and gained. 

"What we see all the time is that people will change their diet and exercise to lose weight, and maybe they will lose some weight at first. But then their weight will hit a plateau and get stuck there," Marcio Griebeler, an endocrinologist and obesity specialist at the Cleveland Clinic, said earlier this year. "That's because there's a difference between losing weight and changing your set point. If you're going to have lasting weight loss, you need to change the set point."

To successfully lower one's set point, it's often recommended to take a longer-term, steady and strategic approach to weight loss. This requires conscious behavioral and dietary changes that enable the body and mind to adjust to more healthy patterns. 

Over time, embracing those changes and goals may help people avoid feeling that keeping off weight is beyond their control — which can prevent them from taking helpful steps to slow weight gain. Some people may use weight loss surgeries and drugs to help establish new set points, yet dietary choices and well-planned exercise habits remain crucial to maintaining a healthy weight after shedding pounds. 

The POWERS study intends to look beyond set point theory as a general model to better understand why certain people are prone to regain weight, while others are able to maintain a reduced weight after dieting.

Lowe will be joined in the NIH-funded study by colleague Kelly Allison, the director of the Center for Weight and Eating Disorders at Penn Medicine, and Penn psychiatry professor Matthew Hayes. Tufts University professor Susan Roberts, a nutrition scientist, also will contribute to the study along with clinical researchers at the Columbia University Irving Medical Center.

The study specifically will examine how diet-induced weight loss affects psychological, metabolic and neurological measures. Participants in the study will be evaluated for food intake and appetite drive, metabolic rate and physical activity. The researchers will then use this data to determine whether it's possible to predict future weight regain and tailor the approach of dieters to have long-lasting weight maintenance.

"This study is unique because of the comprehensive and rigorous measures we're taking," Allison said. "We're chasing down every possible influence on weight regain, from behavior down to the cellular and molecular level."

The POWERS study currently is enrolling volunteers in Philadelphia who want to take part in a weight loss intervention program that will require regular follow-up visits. Those interested must be ages 25 to 60 and may not have type 1 or type 2 diabetes, or be taking a medication for diabetes. Volunteers must have obesity as measured by body mass index within a certain range. A survey is available to determine eligibility to enroll.

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