If you’ve missed a meal before—and it happens to the best of us—then you’ve probably wondered to yourself, what happens when you don’t eat?
Maybe you got sucked into an endless to-do list (or particularly enthralling Netflix series). Perhaps you didn’t eat or lunch because your well-intentioned plans to meal prep did not, well, go according to plan. Or you may have jumped on the buzzy intermittent fasting (IF) bandwagon and foregone breakfast on purpose. Whatever the reason, before you know it, it’s somehow been six hours since you’ve eaten.
What actually happens when you skip a meal? While it’s not a huge deal to fall short of three square meals every once in a while, you’re definitely going to feel the impact. Generally speaking, for most people, skipping meals can absolutely have significant effects on your brain and body.
First, your blood sugar and energy levels may drop.
Food is fuel. And when you go about your day without food in your system, you’re basically running on empty. That’s why, while you know best how to time your eating, experts generally do recommend people aim to nosh on something every few hours. “Eating regularly throughout the day…prevents dips in your energy [and] keeps you alert and focused,” Brigitte Zeitlin, M.P.H., R.D., C.D.N., founder of the New York-based BZ Nutrition. It’s not like if you don’t eat often enough on one day, all your systems will immediately go haywire. But your body will react to the dearth of fuel in various ways.
The primary one you’ll notice is low blood sugar. “The main fuel for your brain is glucose, which you get from eating foods—predominantly carb-rich ones,” Rachele Pojednic, Ph.D., assistant professor in the nutrition department at Simmons College and professor at the Harvard Extension School, tells SELF. (Complex carbohydrates, like fruits, vegetables, and whole grains, are especially great for energy because the fiber they contain helps keep blood sugar levels steadier.)
When you skip a meal, your body starts to run low on its immediate glucose supply. Low blood sugar can zap your energy, making you feel sluggish and weak, Zeitlin says. It can also make it hard to concentrate because your brain doesn’t have the fuel it needs to think straight. Other low blood sugar symptoms can include shakiness, sweatiness, and irritability. Hello, hangriness.
Soon, your growling stomach becomes all-consuming. When you don’t eat often enough, “The feeling that you need to have something to eat takes over,” Lauren Harris-Pincus, M.S., R.D.N., owner of Nutrition Starring You, tells SELF. Your body starts sending signals telling you, “Hey, it’s time to eat! “Hormones like ghrelin, which is appetite-inducing, and leptin, which is appetite-suppressing, will change to indicate you’re hungry,” says Pojednic. It can be hard to think about anything but food when your brain and body are starved for energy. Not great for things like productivity at work, socializing with friends, or being a generally comfortable, content, and OK human being.
Skipping meals can also make healthy choices harder.
Not eating for an extended period of time can impact the food choices you make when you finally do sit down to eat. “When people are super hungry, they tend to go for the carbs and sweets because those will raise their blood sugar,” says Harris-Pincus. That will probably make you feel better quickly. The problem is that the boost can be temporary if you load up on carbs alone. Without fat, protein, or fiber to temper the rise in glucose, your blood sugar can spike, and then dip all over again, leading to a vicious cycle. You’re also liable to be hungry again soon.
Beyond that, when you wait till you’re absolutely ravenous to eat, it’s easy to eat past the point of fullness or even comfort. “You are likely to overeat to make up for the lack of calories you took in throughout the day,” says Zeitlin. “That can cause nausea, constipation, bloating, and exhaustion.” Overeating usually happens because you’re taking food in way too quickly and ignoring your body’s satiety cues, says Pojednic.
Then there’s physical activity. “Skipping meals doesn’t only affect the nutrients you consume, but your ability to exercise and lead a healthy life,” says Harris-Pincus. Some people prefer working out on an empty stomach, which is usually just fine. But many people will do best with at least a light snack. It can be difficult to rev yourself up for a workout when you’re low-energy and food-focused. Plus, if you don’t properly fuel yourself before exercising (and after), you may not be able to exert yourself as much as you might otherwise, so you get less out of your workout. Finally, if you don’t refuel after a workout, your body can’t restore its glycogen levels (which requires carbs) and repair your muscles (which requires protein).
All in all, it’s usually not a smart move to skip a meal or go much longer than you usually do without eating. If you’re interested in trying IF, talk to a doctor or R.D. who can help you decide if that’s a smart eating plan for you.