When it comes to losing weight, experts agree eating right and exercising are key. But since healthy eating habits are hard to stick to, many people ditch the diet and try to exercise to the point that the benefits outweigh any effects of a bad diet. New research from the City University of New York, however, finds that exercise alone won’t cut it if you’re looking to drop unwanted pounds.

The study, published in Current Biology, shows that our bodies fail to progress once we reach a certain fitness level; they get used to grueling workouts, and stop burning extra calories. This finding led the researchers to suggest the best way for a person to lose weight is to add a diet plan to their exercise regimen.

"Exercise is really important for your health. That's the first thing I mention to anyone asking about the implications of this work for exercise. There is tons of evidence that exercise is important for keeping our bodies and minds healthy, and this work does nothing to change that message." said lead author Herman Pontzer, of the City University of New York, in a press release. "What our work adds is that we also need to focus on diet, particularly when it comes to managing our weight and preventing or reversing unhealthy weight gain."

Over a week, Ponzer and his colleagues analyzed the activity levels and number of calories burned in 300 people. Each participant received accelerometers to keep track of physical activity, and they all answered surveys meant to assess activity levels from occupations that required manual labor.

The researchers found daily physical activity had a weak effect on the number of calories a participant burned each day. This only applied to those who were most sedentary, however. Moderately active participants burned an average of 200 calories more per day than their sedentary counterparts. Those with the most physical activity, meanwhile, didn’t see a noticeable uptick in burned calories when compared to the moderately active group.

"The most physically active people expended the same amount of calories each day as people who were only moderately active," Pontzer said.

The study suggests we need to ditch the idea that more physical activity will burn more calories, the researchers said. If you’re not exercising enough, they said, you’ll find that weight gain is easy, and you’ll become unhealthy. Conversely, exercising too much results in what’s known as a fitness plateau — the point where an exercise routine no longer burns calories.

While there are ways to overcome a plateau, such as implementing new exercise techniques, the research supports the idea that dieting is just as important to weight loss. After all, you can workout all you want, but without changing your diet, the calories will continue to go into your body.

Source: Pontzer H, et al. Constrained Total Energy Expenditure and Metabolic Adaptation to Physical Activity in Adult Humans. Current Biology. 2016.