We’ve long thought that exercising more helped us lose weight. It’s vital for overall health, but a new study has changed the way we think about fat burning.

A new study contradicts decades of popular advice when it comes to fat burning and weight loss.

Burn: New Research Blows the Lid Off How We Really Burn Calories, Lose Weight, and Stay Healthy by Dr. Herman Pontzer, an evolutionary anthropologist suggests that exercising doesn’t necessarily help you burn more calories because the body finds sneaky ways to adapt by cutting energy use elsewhere.

In the simplest of terms, the more you exercise, the more your body budgets its energy and in case you hadn’t noticed, working out makes you hungrier. It’s the body trying to replace the energy you just used up.

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“Exercise isn’t changing how many calories you spend, but how you spend them,” Dr. Pontzer told Insider.

“Diet and exercise are two different tools for two different jobs. Diet is the tool for weight loss. Exercise is your tool for everything else.”

In researching this book, Dr. Pontzer studied hunter-gatherer tribes that showed exercise doesn’t increase our metabolism and that humans, regardless of our activity level, burn about 3,000 calories a day. If you want to lose weight, you have to cut calories.

But there’s no point doing it with the aim to do it quickly, we know that fast weight loss and a drastic reduction in food (or cutting out a food group altogether) isn’t sustainable. Instead, it’s better in the long-term to make gentle adjustments.

“If you dramatically reduce your calorie intake, you’re likely to lose lean muscle mass, not the excess fat mass you’re trying to,” dietitian Melissa Meier previously told Body+Soul.

“That’s because when you don’t give your body the energy it needs to keep ticking, it starts to break down your muscle for energy in the form of protein.”

She says the ‘sweet spot’ for losing weight in a healthy way is to aim for about 1,500 calories a day.