Elizabeth Pegg Frates, M.D. Harvard

If you’re trying to lose weight, you’ve surely heard that you need to “eat less and exercise more.” The more you move, the more calories you’ll burn – and you’ll lose weight. But as it turns out, the effect of physical activity on human physiology may be a lot more complicated than that.

In a report recently published in Current Biology, researchers explored the relationship between exercise and “energy expenditure” (calories burned). This study monitored the physical activity and corresponding total energy expenditure in 322 men and women in North America and Africa.

What the researchers found was a little surprising. Physical activity did increase energy expenditure as expected, but only up to a point. Physical activity was monitored by accelerometers, which measure counts (units of “motion”) per minute per day, taking into account motion and velocity. At lower levels of activity, increasing the counts per minute per day did increase energy expenditure. However, with higher mean counts per minute per day, increasing counts did not increase energy expenditure, indicating a ceiling effect. So in this study, after a certain point, more exercise did not equal more energy used.

Based on their findings, the study investigators encourage that we reconsider current public health messages that state more exercise equals more energy expended, as this is not always the case.

These study results notwithstanding, whether you’ve yet to get in gear on an exercise resolution or you’re already an inveterate exerciser, it’s important to know that the benefits of regular physical activity go beyond burning calories. For example, 150 minutes of moderate to vigorous intensity physical activity per week can significantly decrease the risk of dying prematurely. How? By lowering blood pressure and resting heart rate, and increasing nitric oxide levels, which serves to open up blood vessels. It also increases levels of beneficial HDL cholesterol and lowers levels of damaging LDL cholesterol. In addition, regular physical activity increases insulin sensitivity. This is especially important for people with diabetes – and it can also help you avoid the disease in the first place.

Exercise can also help enhance cognitive skills – it’s true that what is good for the heart is good for the brain. Research demonstrates that regular exercise can actually increase the size of the hippocampus, an area of the brain involved with memory. There are important mental health benefits to be gained as well. Studies suggest that for some people with depression, exercise may improve mood and symptoms just as well as medication can. In addition, a five-minute bout of exercise has been demonstrated to reduce a person’s state of anxiety.

If you’re trying to slim down, exercise is an important part of a healthy way to lose pounds. Moderate physical activity can help you burn more calories. And the good news is you don’t need to train for a marathon to get in shape. But perhaps more importantly, regular exercise does so much more than that – no matter the size of your waistline. It would take almost 10 medications to replicate all the benefits encapsulated in the “exercise pill.” That should be good motivation to help you get moving.

Elizabeth Pegg Frates, M.D. is an award-winning teacher at Harvard Medical School as well as Harvard Extension School.