Diet and exercise are both crucial in maintaining a healthy weight, but one is far more critical than the other. If you want to lose weight, your best bet is to pay attention to what you eat.
A recent study in the journal Systematic Reviews found that people who only changed their diets lost more weight than those who only increased physical activity. In fact, another recent study in the journal PeerJ found that over three years, people who got 30 minutes or more of physical activity a day actually had higher rates of weight gain than those who exercised less.
Nolan Cohn, a registered dietitian nutritionist and spokesperson for the Academy of Nutrition and Dietetics, says that it's much easier to avoid calories in the first place rather than to try to burn them off. Working off a 100-calorie cookie is one thing, but it would take hours at the gym to negate 1,200 calories from a hamburger and fries.
Additionally, if you don't pay attention to portion sizes, you may overeat after starting a new workout routine, says Nolan Cohn. Not only will your hunger increase naturally due to the energy burn, but you may also slack off on healthy food choices. "There's this idea that you've earned it to eat something because you worked out," says Nolan Cohn. "It winds up holding people back."
While it is true that muscle weighs more than fat, this does not mean that you can use this as an excuse to justify your weight increase. "That's a few pounds, not 20 or 30 pounds," says Nolan Cohn. "It's not a justification for the weight gain."
Dieting alone isn't enough to lose weight, according to a study published in the Systematic Reviews journal. Adding exercise to a healthy diet boosts endorphins, which "improves feelings of positivity or accomplishment," says Nolan Cohn. "When you combine those forces [of diet and exercise], it reinforces losing the weight and keeping the weight off."
It's important to exercise for many reasons beyond just keeping a healthy weight; research shows that regular physical activity has a positive impact on everything from heart health and immune system function to mental health and sleep quality.