Late last month marked the start of the annual eat-too-much and move-too-little holiday season, with its attendant declining health and surging regrets. But a well-timed study suggests that a daily bout of exercise should erase or lessen many of the injurious effects, even if you otherwise lounge all day on the couch and load up on pie.
To undertake this valuable experiment, which was published online in October in the Journal of Physiology, scientists at the University of Bath in England rounded up a group of 26 healthy young men. All exercised regularly. None were obese. Base-line health assessments, including biopsies of fat tissue, confirmed that each had a normal metabolism and blood sugar control, with no symptoms of incipient diabetes.
The scientists then asked their volunteers to impair their laudable health by doing a lot of sitting and gorging themselves.
An energy surplus is what people have when they consume more energy, in the form of calories, than they burn. If unchecked, an energy surplus contributes, as we all know, to various types of poor health, including insulin resistance – often the first step toward diabetes – and other metabolic problems.
Overeating and inactivity can each produce an energy surplus. Together, their ill effects are exacerbated, often in a very short period of time. Earlier studies have found that even a few days of inactivity and overeating spark detrimental changes in previously healthy bodies.
Some of these experiments have also found that exercise blunts the ill effects of these behaviors, in large part, it has been assumed, by reducing the energy surplus. It burns some of the excess calories. But a few scientists have suspected that exercise might do more; it might have physiological effects that extend beyond just incinerating surplus energy.
To test that possibility, it would be necessary to maintain an energy surplus, even with exercise. So that is what the University of Bath researchers asked their subjects to do.
Their method was simple. They randomly divided their volunteers into two groups, one of which was assigned to run every day on a treadmill at a moderately intense pace for 45 minutes. The other group did not exercise.
The men in both groups also were told to generally stop moving as much, decreasing the number of steps they took each day from more than 10,000 on average to fewer than 4,000, as gauged by pedometers. The exercising group’s treadmill workouts were not included in their step counts. Except when running, they were as inactive as the other group.
Both groups also were directed to start substantially overeating. The subjects who were not exercising increased their daily caloric intake by 50 percent, compared with what it had been, while the exercising group consumed almost 75 percent more calories, with the additional 25 percent replacing the energy burned during training.
Overall, the two groups’ net daily energy surplus was the same.
The experiment continued for seven days. Then both groups returned to the lab for additional testing, including new insulin measurements and another biopsy of fat tissue.
The results were striking. After only a week, the young men who had not exercised displayed a significant and unhealthy decline in their blood sugar control and, equally worrying, their biopsied fat cells seemed to have developed a malicious streak. Those cells, examined using sophisticated genetic testing techniques, were now overexpressing various genes that may contribute to unhealthy metabolic changes and underexpressing other genes potentially important for a well-functioning metabolism.
But the volunteers who had exercised once a day, despite comparable energy surpluses, were not similarly afflicted. Their blood sugar control remained robust, and their fat cells exhibited far fewer of the potentially undesirable alterations in gene expression than among the sedentary men.
“Exercise seemed to completely cancel out many of the changes induced by overfeeding and reduced activity,” said Dylan Thompson, a professor of health sciences at the University of Bath and senior author of the study. And where exercise did not countermand the negative results, he added, it “softened” them, leaving the exercise group “better off than the non-exercise group.”
From a scientific standpoint, this finding hints that the metabolic effects of overeating and inactivity are multifaceted, Thompson said, with an energy surplus sparking genetic as well as other physiological changes. But just how exercise reverses those effects is impossible to say based on the recent experiment, Thompson said.
Differences in how each group’s metabolism used fats and carbohydrates could have played a role, he said, as could the release of certain molecules from exercising muscles, which only occurred among the men who ran.
Of more pressing interest, though, is the study’s practical message that “if you are facing a period of overconsumption and inactivity” – also known as the holidays – “a daily bout of exercise will prevent many of the negative changes, at least in the short term,” Thompson said. Of course, his study involved young, fit men and a relatively prolonged period of exercise. But the findings are likely to apply, he said, to other groups, such as older adults and women and perhaps to lower levels of training.