A new wave of evidence challenges exercise’s supposed effect on weight loss. While regular fitness undoubtedly improves and supports mood, brain, bone and heart health, researchers say it can’t be viewed as the main driver of weight loss.
Experts in metabolic physiology concluded last year the amount of exercise required to burn off the calories we eat is beyond what most people can achieve in a day. Surprisingly, the body’s use of calories appears to plateau no matter how much you move, or as the researchers in one study put it: “Individuals tend to adapt metabolically to increased physical activity, muting the expected increase in daily energy [expenditure].” In general, exercise burns off less than 10 to 30 percent of the energy we take in from food.
Sixteen healthy, fit, young men were put into two exercise groups: one group focused on intensity in exercise; the second group focused on duration or length of exercise. During the workouts, the scientists measured the blood for levels of acylated ghrelin, a hormone thought to influence hunger. In general, when acylated ghrelin levels rise, so does hunger. High levels of ghrelin usually mean higher levels of hunger.
What was observed: vigorous and longer periods of exercise reduced hunger more than gentle and shorter episodes of exercise. The longer and more vigorous the exercise, the longer the lack of hunger lasted. Seems counterintuitive but the more energy you expend, the less hunger the study participants experienced. They also noticed greater feelings of hunger after sitting around and taking breaks. This study suggests that if you want to reduce your feelings of hunger, you can try increasing the intensity and/or duration of each workout.
“This evidence and other studies lead me to believe that if some one initiates an increase in exercise and experiences weight loss it is likely the effect the appetite dampening effects rather than the calories burned,” says Dr. David Macklin, Director, Weight Management. “If exercise was a pill I would give it to everyone but very few overy few would lose any weight.”
While the results can’t be conclusive because of the small sample size, they may explain why sometimes you’re famished following a workout, while at other times, food is the furthest thing from your mind. It may also shed some insight into why you’re gaining weight even if you’re working out regularly. As they say, you can’t outrun a bad diet.