WE ALL KNOW the most basic principle of weight loss: You need to burn more calories than you consume. And you have a long road of weight loss ahead of you, it can easily seem like the best way to fast-track this journey is to simply consume a whole lot less calories. That way, you’re not adding any new fat to your body, right?

Actually, it’s not that simple. What’s more, cutting too many calories can actually have the opposite effect, completely stalling your weight loss efforts.

RMR: Or, why you still need to fuel the fire

To understand why, it’s important to understand resting metabolic rate (RMR), or the number of calories your body burns at rest. Let’s say you decide to cut your intake from 3,000 calories down to 1,000. The first thing that’ll happen if you drop your energy intake too low or too quickly is that your RMR will also drop.

“Your body basically says, ‘Okay, no calories coming in? I’m going into ‘sleep’ mode to save energy,’” Talbott explains. Evolutionarily, your body doesn’t know how long that calorie deprivation is going to last, so it puts you in energy-saving mode to optimize survival.

This drop in RMR can be substantial—as much as 10%, Talbott says. In a larger guy, that’s about 250 calories less your body is burning naturally—which may not sound like a lot, but can make a ton of difference in weight loss over time, he points out.