Why Some People Lose Weight and Get Fit Faster Than Others

New study examines how genetics may play a role in exercise adaptation


People lose weight and get in shape at different rates.

Likely you’ve learned this (sometimes infuriating) lesson directly through your own experience. While it’s not really nice to single them out (after all, they could have their own insecurities, too), many of us can name at least one friend or acquaintance that seems to easily maintain a slender physique without much effort at all.

Essentially, as you’ve probably gathered, this disparity, which so many of us view as unjust, comes down to genetics.

For instance, a recent study from researchers at the Phoenix Epidemiology and Clinical Research Branch (PECRB), part of the National Institutes of Health's National Institute of Diabetes and Digestive and Kidney Diseases, found that “certain physiologies” lose less weight than others when following reduced calorie diets.

This study analyzed the effects of a reduced-calorie diet on 12 obese men and women. The subjects were monitored for six weeks while they followed a 50 percent calorie reduction diet and the results showed that some of the participants metabolisms were characterized as “thrifty,” meaning their bodies held on to more weight, and others’ were characterized as “spendthrift,” meaning they tended to burn calories at faster rate.

Of course, this was just one small study and we know that exercise also plays an important role when it comes to weight loss, health and physical fitness.

To help paint a clearer picture of how genetics play a role in getting fit and possibly even losing weight, a more recent study sought to investigate how and why people respond differently to exercise, too.

“In the study, rats with a particular set of genes responded robustly to exercise, becoming much more fit after a few weeks of running, while rats born with other genes gained little cardiovascular benefit from the same exercise program, apparently because their heart muscles didn’t react as expected,” Gretchen Reynolds reports in The New York Times.

Published in The Journal of the American College of Cardiology, the study involved two strains of rats: one bred to respond well to exercise and another that would not.  All of the animals performed the same training program for two months, and by the end of the study the rats that were bred to respond well to exercise had increased the distance they could run before getting tired by 40 percent.

The other rats: on average they lost about two percent of their endurance during the training period.

Additionally, the researchers examined the rats’ hearts. The rats bred to respond well demonstrated structural changes within the cells of their left ventricles that indicate growth and strength while cells from the other group of rats looked like those from animals who hadn’t exercised at all.

“This cellular intractability likely explains why the animals lost fitness while training," Ulrik Wisloff, a professor at the Norwegian University of Science and Technology who led the new study told Reynolds. “If hearts don’t adapt to the demands of exercise, then workouts will sap bodies, not strengthen them.”

Likely the most important part of the study, though, was that the researchers were able to identify the specific genes associated with these adaptations.

“When they carefully assessed gene expression in the animals’ heart cells, they found more than 360 genes that were operating differently in the two groups of animals,” Reynolds reports. “Many of these genes are known to affect cell growth. In effect, these genes direct processes that should increase the size and strength of the heart. And they were not working as effectively in the animals bred to be resistant to exercise.”

Wisloff explained that these same genes exist in the heart cells of humans, but it’s impossible to know if human genes respond to exercise in the same way.

So then what can we learn from this research? Wisloff said it means that we should closely monitor our response to different types of exercise programs.

“If after months of training, someone is not able to run any farther than he or she could before, maybe it is time to change the intensity or frequency of the workouts or try something else, like weight training,” Wisloff told Reynolds. He explained that the genes controlling the body’s responses to the new activity are likely to be different from those involved in responses to aerobic exercise like running.

Basically, this research is a nice reminder of the fact that when it comes to health and fitness goals, there will never be a one-size-fits-all answer for everyone, and that it may take a few sessions of trial and error before you'll find out what exactly works best for you.

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