This Is What Happens to Your Body When You Stop Eating Carbs

Low-carb diets are as popular as ever, but the jury's still out on how effectiveโ€”and safeโ€”they are.

The lowdown on low-carb diets

Ever since Atkins, most people think that cutting carbs is healthy and a great way to lose weight. According to a survey by the International Food Information Council Foundation, consumers rank sugar and carbs as the top reasons for weight gainโ€”the highest ranking since 2011. Not surprisingly, diets that restrict carbohydrates, including ketogenic, paleo, and Whole30, are among the most popular in the country today. This makes recent research in the European Heart Journal linking the absence of carbs in the diet to an increased risk of an earlier death all the more shocking. Confused? You’re not alone.

Overhead view of traditional italian handmade ravioli on cutting board
Asya Nurullina/Shutterstock

To carbโ€”or not?

The research, which was presented at the annual meeting for the European Society of Cardiology, looked at data on 25,000 people over an 11-year span and found that individuals whose diets were lowest in carbs had a 32 percent higher risk of a premature deathโ€”including from heart disease and cancerโ€”compared with those who ate a higher-carb diet. This wasn’t even the first finding of its kind: A separate study in The Lancetย revealed that low-carb dietersโ€”people who got less than 40 percent of their daily calories from carbsโ€”had a higher mortality risk during the study than did moderate carb consumers whose diets were 50 to 55 percent carbs. (Check out these 7 science-backed reasons to put bread back on the menu.)

Buckwheat tray dieting clean eating food concept overhead
casanisa/Shutterstock

Not all carbs are created equal

Experts believe that the recent findings might have something to do with the kinds of carbs you’re eating and what you’re replacing them with. “The quality of the food on a low-carb diet matters,” says registered dietitian Julie Stefanski RD, a spokesperson for the Academy of Nutrition and Dietetics. “The effects of a menu of pork rinds and beef jerky can’t be directly compared to the impact of eggs with spinach and avocado.” But as more evidence of the long-term effects of these diets emerges, it’s good to bone up on some of the other effects that passing on the bread basket can have on your body. (Learn more aboutย nutritionist-approved carbs here.)

Woman sleeping, woman sleeping on the bed, young woman sleeping
ViChizh/Shutterstock

You’re getting sleepy

“Carbohydrates are our number one source of energy,” says Gina Sam, MD, a New York City-based gastroenterologist. Compared with protein and fat, they are broken down most quickly into glucose, the stuff our bodies run on. So skimp on them and you might find yourself feeling lethargic. (Check out these 16 low-carb diet mistakes you should never make.)

Dirty and empty diss, plate left after finished breakfast, lunch or dinner. Plate with pieces of crumbs and pieces. Kitchenware concept for restaurants and cafes.
Viktor Kochetkov/Shutterstock

You may feel more full

Lots of people report feeling less hungry on low-carb diets despite eating fewer calories. Reason: If you’re eating high-quality sources of lean protein and healthy fats (the mono- and polyunsaturated kinds), your body takes longer to break down those nutrients than it takes with carbs. When you down a big bunch of carbs like a bagel, your pancreas dumps tons of insulin into your blood in response to the sudden carb glut. This can cause extreme blood sugar spikes and drops that can lead to sudden, intense hunger or cravings. Filling up on protein and fat helps keep your blood sugar levels steady. The problem, says registered dietitian Jessica Crandall, a certified diabetes educator, is that these kinds of diets are rarely sustainable, especially at extremes where you’re only eating 120 grams of carbohydrates or less a day.

Asian woman measuring waist size
Rawpixel.com/Shutterstock

You may lose weight

People who stick to low-carb diets do tend to drop poundsโ€”for a while, anyway. Some is water weight, says Crandall, and the rest comes from the fact that you’re decreasing the amounts of a significant source of calories in your diet. Carbs include grains, starchy vegetables, fruits, and sweets, and that makes up a lot of what we eat. Butโ€”insert sad trombone hereโ€”the weight will likely come back, she says. She regularly sees clients who lose 30 to 40 pounds on a low-carb plan, but when they come back in a year, they’ve regained 50. (Learn about the many ways to have your cake and keep blood sugar levels steady, too.)

girl covers her face with her hands
file404/Shutterstock

You may have morning breathโ€”all day

Keto dieters may be familiar with this side effect: When you deny your body carbs for energy, it must burn fat in a process known as ketosis. Sounds good, but experts debate just how safe it is for long periods. And one odd outcome of ketosis is bad breath: A by-product of the process is the production of ketones, and they can put a sour note in your breath. Some people describe it as fruity or metallic or even like nail polish remover (acetone, the main ingredient, is a by-product of ketosis). Generally, the odor will subside as your body adjusts to the diet.

Cookie Studio/Shutterstock

Your brain can get fuzzy

You may not realize it, but just thinking requires energy. “Your brain needs a minimum of 120 grams of carbs a day to function,” Crandall says. When you enter ketosis, you’re cutting off the main energy source for both your body and your brain. That can lead to dizziness, headaches, lightheadedness, and an inability to think clearly until your brain adjusts. Combined with the fatigue you feel, these symptoms are collectively known as the “keto flu.” (Check out some common reasons people fail when attempting the keto diet.)

Signs bathroom on brick wall
Pongsatorn Singnoy/Shutterstock

You can’t, um, go

“People tend to forget that some carbs can be a good source of fiber, and fiber helps move food through your digestive system,” says Dr. Sam. Not eating enough fiber can clog up the system, especially if you’re eating a lot of animal protein. You could find yourself constipated.

Hand picks a white toilet paper that hangs on the wall in the bathroom
Ihar Krents/Shutterstock

Or you can’t stop going

If you’re replacing all those carbs you cut out with fat, even healthy fat, it can have the opposite effect on your bathroom habits, according to Dr. Sam. “Some people may experience bloating, diarrhea, or excessive flatulence,” she says. Maintaining a balance of nutrients in your diet is critical. (Check out these 30 ways to bulk up on fiber.)

Young woman having a menstruation pain in gray concrete background
Bignai/Shutterstock

You might get indigestion

Watch for acid reflux, heartburn, and lots of belching when you up the fat quotient in your diet. “You have a valve called the lower esophageal sphincter, which prevents stomach acid from entering the esophagus,” says Dr. Sam. “Too much fat in your stomach can cause that sphincter to open, allowing acid to flow back up.”

Exercise
GaudiLab /Shutterstock

Your workout could suffer

“You can perform without carbs,” says Crandall, who is also a personal trainer, “but you won’t perform as well.” Because carbohydrates are your body’s preferred energy source, forcing it to rely on fat for fuel will take extra effort. So if you’re looking to gain strength or improve your endurance time, getting enough carbs is essential. (Check out these 10 foods that will get your workout results right.)

Spoon with cod liver oil pills on table, closeup
New Africa/Shutterstock

You could develop a vitamin deficiency

In extreme cases of carb-cutting, you may be skimping on the basic nutrients your body needs to function. Sure, sugar and refined grains are carbs, but so are whole grains and certain fruits and vegetables. Eliminating those foods entirely can make it tough to get vitamins B and C, antioxidants, and fiber, says Crandall. Research suggests that those nutrients can be a big help in preventing chronic conditions like cancer and heart disease. If you’re not mindful of getting your nutritional needs met in other waysโ€”say, through supplementsโ€”cutting carbs could backfire in a big way. It’s always a good idea to talk to your health-care practitioner before you make any major diet decisions. Next, check out the 12 silent signs that you need more carbs.

Sources
  • International Food Information Council: "One-Third of Americans Are Dieting, Including One in 10 Who Fast โ€ฆ While Consumers Also Hunger for Organic, โ€œNaturalโ€ and Sustainable"
  • European Heart Journal: "Lower carbohydrate diets and all-cause and cause-specific mortality: a population-based cohort study and pooling of prospective studies"
  • The Lancet: "Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis"
  • Julie Stefanski RD, a spokesperson for the Academy of Nutrition and Dietetics
  • Gina Sam, MD, MPH, a New York Cityโ€“based gastroenterologist
  • Jessica Crandall, RD, a certified diabetes educator
Medically reviewed by Elisabetta Politi, CDE, MPH, RD, on March 08, 2021