It may seem harmful to restrict your body of food, however it’s actually a part of human nature—and comes with certain benefits. Nutritionists love the idea of intermittent fasting. It’s not technically a diet; it falls squarely into the “lifestyle change” category, plus it brings us back to our ancestral roots. While evidence proves that it can help you lose weight, you may be wondering how it actually does so. What happens to your body when you fast?
1. Your Insulin Lowers
Danielle Schaub, MS, RD, CDN, a registered dietitian at New York-Presbyterian/Weill Cornell Medical Center offers a quick biology lesson: after you eat, carbs are digested into sugars, then those sugars enter your bloodstream and trigger a release of insulin. Insulin’s job is to move sugar from the bloodstream to your cells. But insulin also blocks fat cells from releasing fat, which means your body can’t burn fat when insulin levels are high. It’s only when the sugar is relocated into the cells that insulin levels drop again.
2. Your Metabolism Speeds Up
“Short-term fasting can increase metabolic rate, since levels of [the hormone] norepinephrine increase during a fast,” says Erin Palinski-Wade, RD, CDE, author of Belly Fat Diet For Dummies. Since metabolism is the rate at which your body burns calories—and that rate is mostly fixed, unfortunately, by your unique composition—being able to kick your metabolism into high gear through fasting might allow you to burn more calories. Just be mindful of how long you fast, though.
3. Fasting Retrains Your Body
Thanks to our hunter-gatherer ancestors, our bodies are made for intermittent fasting. But thanks to our modern way of eating, our bodies have totally forgotten this fact. If we retrain our bodies to adapt to periodic fasting again—or get better at shifting between carb-burning mode and fat-burning mode, as Schaub puts it—we can reap some serious benefits, including weight loss.
4. You Burn More Fat
On a normal diet that includes carbs, your body will usually burn glucose from those carbs instead of burning fat, but Thurlow says this isn’t the best way. “While fasting, your body is given the opportunity to utilize fat stores for energy, a process signaled by lowered insulin levels,” she says. “This is a great thing. It’s incredibly efficient and it is how our bodies are designed to work.”
5. Your Digestive Function Improves
Are you giving your digestive system the rest it needs to do its job? If you’re eating frequently over the course of a 16- or 18-hour day, maybe not. “Digestion is the most taxing system in our body…it takes a lot of work!” says nutrition coach Megan Kober, RDN. “When you allow your digestive system to rest, your body can go to work on breaking down not only fat cells but also unwanted immune cells in the body.”
6. You Might Lose Weights
Be honest: you’re considering doing intermittent fasting because you want to lose some weight. Hey, we’ve all been there! Thankfully, there is a lot of emerging research on fasting that suggests it could be a scientifically-backed way to lose weight, right along with calorie reduction. According to Palinski-Wade, fasting not only promotes a calorie deficit but also increases your metabolism (which we’ve already told you!). But that’s a real one-two punch for weight loss.
7. You Maintain Muscle Mass
Trying to build muscle and lose weight? Traditional dieting could make that hard to accomplish. Kober says fasting has shown itself to be more effective at preserving lean muscle mass than calorie restriction. What’s more, muscle mass is directly correlated with metabolic rate—meaning the more lean muscle you have, the more calories you burn at rest. “Losing weight via fasting versus losing weight via calorie restriction means that you will be more likely to lose actual fat, not fat and muscle mass,” Kober says.
8. You Eat Less Overall
Generally speaking, practicing intermittent fasting means you don’t have to count calories (you can, but it’s not required). Why? Because there’s only so much food most people can eat within a limited time frame, so counting—or restricting—calories isn’t necessary. “Restricting calories to a certain eating window helps reduce overall intake, further helping with weight loss,” says Schaub.