The Keto Carb Limit: Exactly How Much Sugar Kicks You Out of Ketosis?

How Ketosis Works

Originally used to treat epilepsy, the keto diet is now a popular weight loss plan, in part because its focus on fat consumption can leave you feeling fuller and more satisfied than other diets.

When your body depletes the stores of glucose (provided by carbohydrates) that it typically burns for fuel, it starts burning ketones, a form of energy made from fat. It takes a few days to fully enter a ketogenic state, during which a majority of the energy your body uses comes from ketones instead of carbohydrates.

As your body enters ketosis, you may experience side effects collectively referred to as “keto flu.” These symptoms include fatigue, upset stomach, headache, and dizziness, and they’re most common when a person is first entering ketosis. They usually subside once the body has adjusted to burning ketones instead of carbohydrates.

The most accurate way to know if you’re in a ketogenic state is to test your blood or urine using test strips, available at drug stores and online. Handheld breathalyzers can also be used to check ketone levels, but this newer technology isn’t necessarily accurate.

Some people say they feel differently when they’re in ketosis. “You can usually tell,” says Florida-based registered dietitian nutritionist Franziska Spritzler, author of ‌The Low-Carb Dietitian’s Guide to Health and Beauty‌. “You’re not as hungry.”

Falling Out of Ketosis and Getting Back In

Many keto diet plans recommend getting only about 5 to 10 percent of your daily calories from carbohydrates, which translates to between 20 and 50 grams of carbohydrates a day for most people. Exceeding that daily limit by consuming foods or beverages that are high in sugars or starches sends your body out of ketosis, as it returns to burning carbohydrates, which are its preferred source of fuel.

However, falling out of ketosis doesn’t mean starting from scratch. Though it can take several days to enter ketosis during the initial stage of the keto diet, it doesn’t take as long to return to ketosis after a slip, says David Bridges, PhD, assistant professor of nutritional sciences at the University of Michigan School of Public Health.

“Yes, if you go to your mother’s house and she made these delicious cinnamon rolls and you just have to have one, it will probably stop the process of generating ketones and take you out of ketosis temporarily,” he says. “But if it’s just one meal, and you go right back to your [keto] diet, you should be able to get back into ketosis fairly quickly.”

How Eating Sugar May Make You Feel on the Keto Diet

Eating sugar while in ketosis may cause side effects too. “You may experience some gastrointestinal distress,” says Dr. Bridges. “If you’ve been in ketosis for a while, your body may no longer be equipped to digest high-carbohydrate foods in the same manner it used to be.”

You may also experience symptoms of keto flu as you get yourself back into ketosis. And if you stop following the low-carb diet for more than just a meal or two, you’re likely to gain back some of the water weight you lost initially, says Bridges.

Eating sugar while in ketosis may also trigger a setback psychologically for some people, according to Spritzler. “I recommend staying low carb as much as you can, because when you get used to eating a certain way, you can get to the point where you really don’t crave sugar,” she says. “But if you go ahead and have a cheat day or a cheat meal, it can stimulate those pleasure centers in the brain. It can be difficult to get back on track without wanting that sweet treat again.”

Bridges and Spritzler agree that eating a starchy meal or sugary dessert certainly could throw your body out of ketosis, and it might make you feel pretty lousy for a short time as well. But as long as you’re not indulging in high-carbohydrate foods regularly, the occasional treat shouldn’t derail your long-term plans for losing excess weight or keeping it off with the keto diet.