Researchers at the University of Alabama at Birmingham took 72 women aged 60-74 and split them into 3 groups: 1 day/week of aerobic exercise and 1 day/week of resistance exercise (1+1); 2 days of aerobic/2 days resistance (2+2); or 3 days aerobic and 3 days resistance (3+3).
Researchers supervised participants over 4 months and at the study’s end found that (emphasis mine):
all of the women had gained endurance and strength and shed body fat, although weight loss was not the point of the study. …
There were, remarkably, almost no differences in fitness gains among the groups. The women working out twice a week had become as powerful and aerobically fit as those who had worked out six times a week.
But the researchers also looked at how much energy the women were expending outside of their formal exercise efforts:
the women exercising four times per week … were burning about 225 additional calories each day, beyond what they expended while exercising …
But the women who had been assigned to exercise six times per week were now expending considerably less daily energy than they had been at the experiment’s start, the equivalent of almost 200 fewer calories each day, even though they were exercising so assiduously.
Hmmm! That’s a 425 calorie swing/day between the two groups. Over the course of a week (or a month), think that might make a difference to weight loss efforts?
Now before you say, hey, these were all menopausal women, researchers at the University of Copenhagen found a similar compensation to exercise in younger, sedentary men (emphasis mine):
Although the exercise-induced energy expenditure in [the group exercising 600 cals/day] was twice that of [the group exercising 300 cals/day], the resulting accumulated energy balance, calculated from changes in body composition, was not different … No statistically significant changes were found in energy intake or non-exercise physical activity that could explain the different compensatory responses associated with 30 vs. 60 min of daily aerobic exercise. In conclusion, a similar body fat loss was obtained regardless of exercise dose. A moderate dose of exercise induced a markedly greater than expected negative energy balance, while a higher dose induced a small but quantifiable degree of compensation.
Now this doesn’t mean folks who like to exercise more shouldn’t. Both studies were relatively small and motivation to exercise certainly can vary indvidually (just like tolerance to macronutrients and/or preference for a plant- or meat-based diet). [On the plus side for exercise fans, researchers measured participants' cytokine levels and found that those exercising 6x a week did not show higher levels of this stress-related chemical.]
But this does suggest (to me anyways) that if you are exercising daily, you may want to pay attention to whether you are compensating during the day. And if you aren’t a daily exerciser, it looks like a little exercise can go a long way … good news for people who don’t have the time or the inclination for doing lots more!