Not Exercise, But Dieting Makes You Hungry: Beneficial or No Effects on Appetite of Exercise in Lean & Obese. (Ab-) using Exercise to Make Up For Messy Diets Still a Bad Idea!

Will working out make you cheat on your diet, 'cause it leaves you drained and ravenous? Or is it even a stand-alone weight loss tool with satieting and anti-depressive effects?

As a SuppVersity reader you will probably be aware of the fact that the purported "appetite increasing" effects of exercise are non-existent. Against that background, you won't be surprised to hear that scientists from the Norwegian University of Science and Technology have recently been able to show that the alleged hunger-inducing effects of exercise didn't occur, in twelve overweight/obese volunteers who had to perform moderate or high intensity exercise, either.

The exercise sessions, which were spaced 1-week apart and to which the subjects were randomly assigned in a counter-balanced fashion lasted 1 hour and were - and this may be an important fact - performed after a standard breakfast.

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After the subjects had been sweating in the gy, an ad libitum test lunch was served (that's 3h after breakfast) and fasting/postprandial plasma samples of insulin, acylated ghrelin (AG), polypeptide YY3-36 (PYY3-36) and glucagon-like peptide 1 (GLP-1) and subjective feelings of appetite were measured every 30 minutes for 3h. Nutrient and taste preferences were measured at the beginning and end of each condition using the Leeds Food Preference Questionnaire. In contrast to the "increased appetite" hypothesis, but much in line with what any sane individual would expect, the "[i]nsulin levels were significantly reduced while the GLP-1 levels increased during all exercise bouts".

Figure 1: Consumed and expended energy (in kcal) before and after the workout / laziness (Martins. 2014). Both exercise modalities induced a caloric deficit because the energy expenditure was not compensated for - In the course of the rest of the 24h this advantage vanished and the total energy balance no longer significantly negative in the exercise groups.

The effects on acelyted ghrelin depended on the exercise intensity and duration and was significant only in the MICC and HIIC, but not shorter S-HIIC, compared with control. Practically relevant effects on hunger or fullness ratings, the energy intake at the subsequent ad libitum meal and the food reward the obese subjects experienced were yet not observed.

And what about the lean guys? Does exercise make lean guys hungrier?

In general the results reseachers from the Loughborough University are about to present in a soon-to-be-published paper in the scientific journal "Appetite" clearly support the results Martins et al. observed in significantly heavier subjects.

Figure 2: PYY3-36 satiety hormone levels (pg/ml) after doing nothing (diet or control) or exercise (=pre-prandial) before, during and after ad libitum test meals (Deighton. 2014)

The weight (1) was yet not the only of a total of four differences: (2) The total amount of energy the subjects expended during their standardized exercise bout was higher 40% (350kcal for the lean guys vs. 250kcal for the obese guys in the Martins study), (3) the satiety hormone PYY3-36 increased significantly in response to exercise, and (4) the study had a second, a diet arm, in which skipping breakfast (163kcal) and skipping lunch (190kcal) both lead to significant increases in appetite and corresponding reductions in PYY3-36.

Losing weight does not have to ruin your metabolism if you follow this simple set of rules.

Bottom line: The fact that exercise didn't develop any appetite increasing effects in either the obese or the lean subjects in the Martins or Deighton study, respectively probably won't be convincing enough to shut all the critics of my recommendation to use exercise as an adjunct to dietary restriction in order to lose weight.

That's something I don't care about, anyway. What I do care about, though, is the fact that there are thousands of people out there who may read the message "burn 350kcal from exercise, don't get hungry and lose 1lbs of fat in 10 days" ... yeah, I know: No SuppVersity student would ever be so stupid, but just to make sure that none of the newbies get confused and end up in the black whole some people call the "athlete's triad", although, it befalls more weekend warriors than athletes these days: Do not work out to burn calories! Work out to steer the weight loss away from muscle and towards fat and (re-)read the rules you have to follow to make sure this strategy works.

Reference: 

• Martins, Catia, et al. "Effect of Moderate-and High-Intensity Acute Exercise on Appetite in Obese Individuals." Medicine and science in sports and exercise (2014).