Exercise and appetite: does type and intensity matter?

Exercise burns calories — but doesn’t necessarily help you lose weight

Exercise is a cornerstone of wellness, and is independently important. Exercise is also used as a tool to control weight, but it isn’t a very effective weight loss plan when applied without a weight-loss diet. Exercise’s less than expected influence on weight loss is attributed to our body’s tendency to compensate for energy loss by increasing appetite and intake, or energy conservation and a reduction in energy expenditure. But although exercise by itself (without calorie control) doesn’t result in significant weight loss, regular exercise is linked with lower risk of gaining weight over the years. 

Does when you exercise matter?

Does the timing of exercise matter? The study of our circadian rhythm – our internal clocks that run a ~24 hour cycle related to the sun’s activity – is showing that many of our processes, including hormonal secretion, appetite, and metabolic pathways, fluctuate with the time of day. 

A new study in the current issue of the journal Appetite looks at the effect of morning vs. evening exercise on appetite, food intake and voluntary performance.

The healthy volunteers undertook two trials, in one they exercised at 10:30 am, and in the other at 10:30 pm. They ate a standardized meal 2 hours before exercise (intense cycling), and were offered a meal after exercise in which they could eat as much as they wished.

And the results: Although the participants reported similar appetite regardless of the time of day they exercised, they ate on average 150 calories more when they exercised in the evening.

This is a small study, and bear in mind that many people, especially in the US and in Europe, tend to eat more food in the evening as it is. Also, when to exercise isn’t necessarily a choice – time constraints arise throughout the day, and it’s hard enough to fit exercise as it is.

If you do have the flexibility you can experiment with timing your exercise and seeing if it helps you better control your appetite and intake. 

High or low intensity

Another method that could supposedly help with appetite control through exercise is increasing the intensity of the workout. High intensity exercise may suppress hunger more than low intensity exercise.

High intensity interval training – short intermissions of high effort sprints, interspersed with recovery periods – is rising in popularity and is sold as a time-saving and more efficient way to train than moderate intensity continuous exercise.

A new review study in Appetite collected 13 randomized controlled studies compares high and medium intensity exercise.

The researchers found that both types of exercise suppressed appetite for a period of about ½- 1½  hours, high intensity exercise to a greater extent. Which makes sense: during times of acute exercise the body diverts its resources to muscles, and puts the digestive system on hold. We also know that appetite hormones like ghrelin are suppressed during exercise.

The diminished appetite does not last however. Hunger bounces back and the post-exercise disinterest in food is short lived, regardless of exercise intensity.

Does swimming really make you ravenous?

Is there any evidence supporting the notion that swimming dials up your appetite? A study looking to see if swimming can help obese women with lose weight had women walk fast, ride a stationary bike, or swim laps in a pool. All the women worked their way up to exercising for 60 minutes a day. After 6 months, the walkers lost 10% of their starting weight, the cyclists lost 12%, but the swimmers didn't lose any weight at all. The walkers and cyclists lost some fat but the swimmers didn't lose any. The reason swimming might not do the trick is because it stimulates appetite — perhaps due to the cold water effect.

The habit you can keep

The most important thing is to exercise – time and type of exercise matter less – and even if there’s no effect on weight whatsoever.

The best exercise is the one you can do, the activity that you enjoy, that’s accessible to you, that fits your schedule, that doesn’t cause you discomfort, the one that doesn’t require equipment you don’t readily have or an ill-afforded membership. 

If you still haven’t mastered an exercise habit the most important parameter is sustainability – pick a plan that you could keep and adopt as second nature, one that you can stick to.

Dr. Ayala