Physical activity is often considered a futile form of weight control because of the possible concomitant compensation of food intake. However, it should be noted that some studies have shown that exercise induces a brief suppression of appetite (hunger), even if this doesnot necessarily translate into a decrease in subsequent food intake.Evidence shows that only 19% of the intervention studies report an increase in energy intake after exercise, and 65% show no change. Whenthe physical activity level decreases, food intake does not seem to be down-regulated in the same way. In fact, compensation is observed when the deficit is created by a meal omission, which is not seen when the deficit is induced by exercise. These observations highlight the weak coupling between energy intake and expenditure. The present study was performed to investigate acute and short-term effects of exercise intensity on energy intake, macronutrient preferences, and appetite in women. The researchers hypothesized that high-intensity exercise would exert a brief, acute suppression of appetite and energy intake and that exercise-induced EE would trigger a partial compensation over the day, which would be more apparent after low-intensity exercise.
Seventeen young women were recruited through advertisements on the University of Ottawa campus. Of these participants, 13 completed allthree experimental sessions, the results of which are presented in this study. All participants took part in a screening session to ensure that they met the following inclusion criteria: age between 18 yr and 30 yr, not pregnant, free of any diseases or food allergies, weight stable for e"6 mo before their enrollment in the study ([+ or -] 2 kg), or not following a special diet or taking any medications that could influence food intake. All women were moderately active (30 to 45 min of continuous exercise performed 3 to 5 times/wk).
The 13 moderately active women [body mass index (in kg/[m.sup.2]):22.2 [+ or -] 2.4; age: 22.2 [+ or -] 2.0 y] were subjected to a crossover study in which subjects were randomly assigned to one of threeexperimental conditions: 1) control, in which the subjects remained seated and were allowed to read or write quietly in the laboratory for 1 hr and 15 rain; 2) low-intensity exercise (LIE), in which the subjects walked on a treadmill at a target exercise intensity of 40% of VO2 peak; and 3) high-intensity exercise (HIE), in which the subjectswalked on a treadmill at a target exercise intensity of 70% of VO2 peak. For the LIE and HIE conditions, the subjects exercised for a duration that allowed an EE of ~350 kcal. After each session, the participants ate ad libitum from buffet-type meals at lunch and dinner and ate snacks during the afternoon and evening. Visual analogue scales were used to rate appetite.
The findings of this study were two-fold. First, energy intake at lunch after the HIE session was greater than that observed during thecontrol session (878 [+ or -] 309 and 751 [+ or -] 230 kcal, respectively). Second, exercise-induced EE was almost entirely compensated by the subsequent energy intake during the HIE day. Relative energy intake (postexercise energy intake corrected for the energy cost of exercise above the resting level) at lunch was lower after the LIE session than after the control session (530 [+ or -] 233 and 751 [+ or -] 230 kcal, respectively) and was lower after the HIE session than after the control session (565 [+ or -] 301 and 751 [+ or -] 230 kcal, respectively). Similarly, daily energy intake tended to increase duringthe HIE session relative to that during the control session. No treatment effect was found for appetite scores throughout the experiment.In summary, the results from this study show that increasing exercise intensity in young women leads to an increase in energy intake during the meal that follows the exercise session. Moreover, the increasein energy intake on the day of the HIE bout is sufficient to almost completely compensate for the exercise-induced EE.
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