The Athlete's Kitchen – Weight: Is It a Matter of Willpower?

by Nancy Clark MS RD CSSD

Is weight simply a matter of willpower? You might think so, given the number of runners who add on miles, subtract food, and expect excess fat to melt away. But it does not always happen that way. Older runners notice the fat that creeps on year after year seems harder to lose. And others who have slimmed down complain how easily they regain lost body fat.

The Endocrine Society ( took a close look at why we can too easily accumulate excess body fat, as well as why it's so easy for dieters to regain lost fat. (1) They describe fat-gain as a disorder of the body's energy balance system, not just a passive accumulation of excess calories. They highlight many factors other than food and exercise that influence body fatness, including genetics, the environment, and evolution.

If you are frustrated by your seeming inability to easily shed a few pounds, here are some facts to ponder.

  • Studies with identical twins, as well as adopted children, suggest 25% to 50% of the risk for becoming obese is genetic. Identical twins who are raised in different homes tend to weigh the same, despite eating different foods.
  • Some people might have a "thrifty gene" that conserves calories and resists fat loss. In terms of evolution, this would be important for surviving famines (a.k.a. diets).
  • Genetic factors alone fail to explain the rapid increase in obesity during the past 40 years. Genetic factors get influenced by the environment. We need to learn more about the combined impact of genes plus: environmental toxins, highly processed foods, a sedentary lifestyle, antibiotics, the microbiome, maternal obesity, and fetal exposure to a mother's obesity-promoting diet.
  • Some "experts" say sugar/carbs are inherently fattening. They claim carbs trigger an insulin spike which drives sugar into fat cells, creates hypoglycemia (low blood sugar) and stimulates the urge to overeat. The Endocrine Society does not support this controversial hypothesis. They say eating too many calories of any type is the problem.
  • Respected research shows no differences in fatness when subjects ate the same number of calories from carbohydrate, protein, or fat. A calorie is a calorie; 100 excess calories from fat and carbohydrate are no more fattening than 100 excess calories from protein. That said, some calories are yummier and less satiating than others; they are easier to overeat. For example, most runners could easily devour a lot more calories from ice cream than from boiled eggs!
  • We need to learn more about the brain's role in body fatness. What is the metabolic impact of carbs, protein and fat on the brain, and the psychological impact of enjoying rewarding foods? Does the brain-on-a-diet get signals about the amount of fat stored in adipose tissue and, in response, trigger the body to want to eat more and move less, in order to thwart fat loss and survive a perceived famine (diet)?
  • Social situations can promote fat gain. At parties, the presence of a lot of people, as well as a wide variety of foods, triggers overeating. In contrast, a repetitive daily diet with the same breakfasts and lunches every day can trigger sensory-specific satiety and curb food intake.
  • Dieting/restricting calories to lose fat increases the desire to eat, as well as reduces the metabolism. In comparison, forcing weight gain by over-eating increases spontaneous activity (fidgeting) and curbs hunger. That's why genetically skinny athletes have a hard time maintaining the weight they have forced their bodies to gain.
  • The rise in childhood obesity might be linked to endocrine disrupting chemicals (EDCs) such as bisphenol A (BPA), perflourinated chemicals (PFCs) and pthalates. EDCs pass from mother to fetus across the placenta, and later, to the infant via breast milk. They alter the signals given by estrogen, testosterone and thyroid hormone. Some research suggests they stimulate fat deposition.
  • BPA is used in hard plastic bottles, food-can linings, and food packaging. BPA is thought to promote the creation of new fat cells and change metabolism at the cellular level. To determine the obesogenic effects of BPA, we need more comprehensive research that looks at men vs. women, and younger vs. older people. Some studies indicate BPA may be linked to behavioral problems in boys. To be wise, limit your use of plastic containers with the number 7 in the recycling symbol on the container.
  • The types of bacteria that live in your gut, your microbiome, likely impact weight. Hence, the microbiome is becoming a target for obesity research. Your best bet is to cultivate a healthy microbiome by regularly eating fruits and vegetables—and limiting processed foods with little fiber.
  • Exercise plays a role in weight management—but less than you might think. Exercise alone is largely ineffective as a means to lose weight, even though it contributes to a calorie deficit. For some runners, exercise triggers the urge to eat more. Hence, you want to be sure your reason to exercise is to enhance health and performance, not burn calories to lose weight. Once you've lost weight, exercise does help maintain the loss.
  • After reading this information, you may be left wondering if you will ever be able to reach your desired weight. Perhaps yes, if you can take these positive steps:

    1) Enjoy a hearty breakfast, early lunch, and a later "second lunch" (or hearty snack), to negate hunger and a perceived daytime famine. Consume a lighter dinner, to enhance fat-loss at night, when you are sleeping.

    2) Focus meals and snacks on satiating whole foods with protein, fiber: apple + cheese, Greek yogurt + granola, peanut butter + crackers.

    Above all, be grateful for your healthy body. Give it the fuel it needs, and trust it will perform best when it is appropriately trained and well fueled on a daily basis. The best athlete is not the lightest athlete, but rather the genetically gifted athlete. If you trying to force your body into a too-lean physique, think again. Weight is more than a matter of will power.

    Sports nutritionist Nancy Clark MS RD CSSD has a private practice in the Boston-area (Newton; 617-795-1875), where she helps both fitness exercisers and competitive athletes create winning food plans. Her best-selling Sports Nutrition Guidebook and Food Guide for Marathoners are available at For workshops, see


    Schwartz M et al. Obesity Pathogenesis: An Endocrine Society Scientific Statement. Endocrine Reviews 38 (4):267-296, 2017

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