Losing Weight — Only to Regain It?
Written by Nancy Clark
Speaking at a webinar hosted by the American Physiological Society (April 14, 2022) Paul MacLean PhD, Professor of Medicine and Pathology at the University of Colorado School of Medicine, addressed the topic of weight regain. More specifically, the title of his talk was A dual tracer approach to measure the effect of exercise on energy expenditure and de novo lipogenesis during weight regain. This topic is relevant to athletes who struggle to stay at their desired competitive weight (as well as other clients, friends and relatives who struggle with yoyo dieting). While MacLean’s research was done with people with obesity, the results may also apply to athletes. Here’s a brief summary of what Dt. MacLean said.
• We have used restrictive diets, exercise, and behavior modification to lose weight, but when the diet stops, most people regain the weight within five years.
• Three reasons why dieters regain weight include biology, behavior, and environment:
1. Biology: The body has a strong biological drive to regain weight. The drive is created by an increased appetite and slowed metabolism. Adipose tissues take up extra energy and stores it very efficiently as fat.
2. Behavior: After 3 to 9 months, dieters tend to be less strict with their reduced-calorie diet and often report they have hit a weight plateau. Despite self-reported claims they are diligently dieting (yet are only maintaining weight), these dieters can become discouraged and less adherent when they see no weight loss. (Note: Dilgently dieting anecdotes are hard to verify in “real life” research.)
3. Environment: We live in an obesogenic environment with abundant food, easy access to ultra-processed foods, or on the other extreme, food scarcity. We also live in an environment that caters to physical inactivity.
• Exercise alone is an ineffective way to lose weight. When people add on exercise, some of the exercisers lose weight, but some gain weight. Among those who lose weight, the exercisers tend to keep the weight off if they stick with their exercise program.
• Randomized clinical trials that are well-controlled suggest exercise does little to curb weight regain. That said, even research subjects do not always comply with an exercise prescription. When these studies are re-analyzed and focus on subjects who do comply, higher levels of exercise are associated with greater success in keeping the weight off. Hence, questions arise:
1) Is weight maintenance more about being compliant to a restrictive eating plan than to exercise?
2) Do those who comply with the diet escape from regaining lost weight?
3) Are exercisers more likely to stay on their diet?
4) Does exercise create metabolic adaptations that favor weight maintenance?
Rodent research
Finding answers to these questions is hard to do in humans because of biology, behaviors, and environment, so MacLean turned to studying reduced-obese rodents who were allowed to eat as desired for 8 weeks during the regain process. Some weight-reduced rodents stayed sedentary while others got exercise.
• Fancy cages accurately measured the rodents’ energy intake and energy expenditure. MacLean was able to see how many calories the rodents burned and if they preferentially burned carb, protein, or fat for fuel.
• The exercised reduced-obese rodents ate less than the sedentary rodents who regained weight. Exercise seemed to curb the drive to overeat, meaning the rodents felt less biological pressure to go off the diet. With exercise, their appetites more closely matched their energy needs.
• Exercise promoted the burning of dietary fat for fuel. Hence, the rodents stored less dietary fat as body fat (adipose tissue). The rodents used carbohydrate to replenish depleted glycogen stores.
Carbohydrate is expensive to deposit as body fat. That is, converting carb and protein) into body fat uses ~25% of ingested calories to pay for that energy deposition. To convert dietary fat into body fat requires only ~2% of ingested calories. The metabolic cost of converting carbs into body fat, plus the calorie-burn of exercise, resulted in less weight gain.
• The sedentary rodents ate heartily and did very little exercise. Their bodies efficiently converted dietary fat into body fat; they used carb & protein to support their limited metabolic needs. They easily regained weight.
The depressing news for women
When followed over time, the longer the reduced-obese animals were weight-reduced, the stronger the appetite and drive to regain the weight. When allowed to eat as desired, they quickly regained the weight. “At least people, as compared to rodents, can be taught to change their eating behaviors to help counter those biological pressures” noted MacLean. For example, people who have lost weight can stop buying chips, store food out of sight, limit restaurant eating, etc.
Most of MacLean’s data is from reduced-obese male rodents. Exercised males got more weight management benefits than did the exercised females. Female rodents seemed to know they needed extra energy to exercise, so they ate more and regained weight. MacLean says we need more research to understand the clear differences in the biological drive to regain weight.
The bottom line:
Exercise is crucial for successful weight loss maintenance; it counters the biological adaptations that drive weight regain. Exercise suppresses appetite, increases energy expenditure, and makes weight regain energetically expensive. Keep moving!
Sports nutritionist Nancy Clark MS RD CSSD has a successful private practice in the Boston area. She is author of the best-selling Nancy Clark’s Sports Nutrition Guidebook. For more information, see www.NancyClarkRD.com
