After the Diet – Is Regaining Weight Avoidable?

by Nancy Clark, MS, RD, CSSD

“I lost 10 pounds and vowed to keep them off, but no such luck. I’m so discouraged.”

“I got to my desired racing weight, then BOOM, I regained all the lost pounds after the marathon.”

“This is my third time losing 40 pounds...”

If any of those stories sound familiar, you are not alone. Research suggests dieters tend to regain lost weight within five years, if not much sooner. This includes many joggers, runners and elite marathoners alike who struggle to stay at a goal weight.

If you are fearful of regaining your hard-lost weight, this article will help you understand why maintaining lost weight takes effort. Paul MacLean PhD, Professor of Medicine & Pathology at the University of Colorado School of Medicine, has carefully studied weight regain.

He notes three reasons why dieters regain weight: biology, behavior, and environment:

1. Biology: The body has a strong biological drive to regain lost weight, as noted with increased appetite and a slowed metabolic rate. As backlash from dieting, the body learns to store fuel very efficiently as fat.

2. Behavior: After three to nine months, dieters tend to be less strict with their low-calorie diets; they often report they have hit a weight plateau. Despite self-reported claims they are diligently dieting (yet only maintaining weight), these dieters can become discouraged and less adherent. (Note: Diligently dieting anecdotes are hard to verify.)

3. Environment: We live in an obesogenic environment with easy access to ultra-processed foods, a sedentary lifestyle, and chemicals that contribute to weight gain including those found in upholstered furniture, pesticides, cosmetics, and who knows what else. Weight is far more complex than self-induced over-eating and under-exercising. You should not blame yourself for 100% of your excess body fat!

When adding on exercise, some people lose weight and some gain weight. Daily runs do not guarantee fat loss. Runners who lose weight tend to keep the weight off if they stick with their exercise program. High levels of exercise are linked with greater success.

That’s good news for runners who train regularly! That said, a fine line exists between compulsive runners (who exercise to burn off calories) and dedicated runners (who train to improve their performance). Fear of weight gain can impact both groups.

Questions arise:

  1. Is weight maintenance more about being compliant to a restrictive eating plan than to exercise?
  2. Do those who comply with a strict diet escape weight-regain?
  3. Are people who exercise more likely to stay on their diet?
  4. Does exercise create metabolic adaptations that favor maintaining lost weight?
Picture from Scientific American

Research with Rodents

Finding answers to these questions is hard to do in humans because of biology, behaviors, and environment. So, MacLean turned to studying formerly obese rodents who had lost weight then were allowed to eat as desired for 8 weeks (the regain phase). Some weight-reduced rodents happily stayed sedentary while others got exercised.

  • 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 carbohydrate, protein, or fat for fuel.
  • The exercised reduced-obese rodents ate less than the sedentary rodents and they regained less weight. Exercise seemed to curb their drive to overeat, meaning they 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 exercised rodents converted less dietary fat into body fat. They used carbohydrate to replenish depleted glycogen stores. Note: Carbohydrate inefficiently converts into body fat. That is, converting carb (and also 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. Given the calorie-burn of exercise plus the metabolic cost of converting carbs into body fat, exercised rodents gained less weight.
  • The sedentary rodents ate heartily and were content to be inactive. Their bodies efficiently converted dietary fat into body fat; they used carb & protein to support their limited energy needs. They easily regained weight.

The Depressing News

When followed over time, the longer the formerly obese rodents were weight-reduced, the stronger their appetites and drive to regain 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.

More depressing news for women: most of MacLean’s data is from reduced-obese male rodents. Exercised females showed more weight regain than did exercised males. The female rodents seemed to know they needed extra energy to exercise, so they ate more and regained weight. MacLean states we need more research to understand the clear differences in the biological drive to regain weight.

From Harvard Health

A Glimmer of Hope

 The best way to maintain weight is to not gain it in the first place. Yes, easier said than done (as stated upfront), but at least runners who maintain a consistent exercise program can curb weight regain. We can also change our behaviors to minimize weight regain by prioritizing sleep, curbing mindless eating, choosing minimally processed foods, etc.

Can the running culture change, so that runners can focus less on weight and more on performance? Runners, like dogs, come in many sizes and shapes. Some runners are like St. Bernards, others are like Greyhounds. A starved St. Bernard does not become a Greyhound, but rather a miserable St. Bernard.

By fueling your genetic body type and focusing on how well you can perform, you can enjoy running stronger, being more powerful—and meeting your time goals. If being leaner means a life-long sentence to Food & Exercise Jail to maintain the lost weight, you might want to think again?


Sports Nutritionist Nancy Clark, MS, RD counsels both casual and competitive athletes in Newton MA (617-795-1875). Her best-selling Sports Nutrition Guidebook is a popular resource, as is her online workshop and books. For more information visit

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