We usually introduce a steady stream of this type of fuel into our bodies with each meal or snack, explains Pamela Nisevich Bede MS, RD, CSSD, LD. These carbohydrates are usually the body’s first choice when looking for an instant fix.
“When a carb is available, the body will naturally turn to this to make energy instead of dietary fat or stored body fat. However, when we remove carbohydrates from our diet, our bodies begin to break down fat and turn to a fuel source in the form of ketones, which is more efficient but generally underutilized,” explains Bede.
Ketones are a substance produced by the liver when the body breaks down fat for energy, which are then released into the blood. Your body’s cells use ketones to power everyday activities. When there’s a buildup of ketones in the blood and you’re switching gears into an ketogenic state, your body changes in some incredible ways.
1) YOUR INSULIN LEVELS DROP.
On a normal diet, after eating glucose-containing foods, your insulin levels will be higher. But when you’re in ketosis, your insulin levels will drop, says Steve Hertzler, PhD, RD, and chief scientific officer at EAS Sports Nutrition.
“With the lower insulin levels, it’s believed that the fatty acids are more readily released from the body’s fat tissue, freeing them up to be used for fuel,” he explains.
Because you’re using fat as the primary source for energy instead of carbs, you’re burning more fat, which means you can actually expect to lose some pounds quickly.
2) YOU’RE LESS HUNGRY DURING THE DAY.
Because you’re increasing protein consumption, you’re bound to fill up and feel satiated during the day. But beyond that, the ketogenic diet can also play a role in suppressing appetite, says Hertzler.
“One theory is that your body responds to a ketogenic diet like it would to a fasting state, as it adapts to burning fat as fuel, releasing ketones into the blood,” he explains. The elevated production of ketones is thought to suppress the appetite centers in the brain, he says.
3) YOU CAN START FEELING SICK.
Keto can have a few unfortunate side effects, one of which is known as the “Keto Flu,” or a group of symptoms experienced as one transitions from carbs to fat, says Bede. Possible side effects include headache, nausea, fogginess, muscle cramping, and fatigue. Call it Carb Withdrawal Syndrome.
4) YOUR BREATH MIGHT SMELL.
Be warned—you might need to carry some breath mints. “Some people may or may not have a change in breath odor on the ketogenic diet,” says Hertzler. Why? “One of the ketone bodies that is produced in liver is acetone—and it carries an odor,” Hertzler explains. That said, many people who are in nutritional ketosis won’t experience a significant change in breath odor, so it’s not a guaranteed side effect.
5) YOU MIGHT NOT BE ABLE TO POOP.
If you’re not being mindful of getting enough fiber and other nutrients,you might experience some digestive discomfort during the keto diet. “Keto dieters often cite constipation as a common experience, which is due to lower fiber intake on the regimen,” Hertzler says. Try adding a low-carb fiber supplement to ease symptoms, he suggests.
6) YOUR BODY MIGHT SLOW DOWN.
If you’re an athlete, you might be a bit slow during the early transition stage. While you’re adapting to the diet, you might feel a bit fatigued, even if you’re not an athlete—but once your body has adapted, you’ll have no issues cranking through a strength session, Bede says.
In fact, as your body settles into ketosis, your performance might be boosted. “Many athletes find that intense workouts equal better ketosis, and their improved body composition is totally worth those few brutal weeks,” she explains.
The takeaway? These symptoms don’t affect everyone, so if you’re interested in keto, give it a shot and see how you feel. But if you choose to say goodbye to keto, don’t jump back into a bowl of pesto penne right away.
“When going back to a ‘normal diet,’ carbs should increase slowly—no going back to old habits overnight, or else weight gain is likely to occur and you’re likely to feel terrible, with the influx of sugar that you are no longer accustomed to,” says Bede.
Read more: Why should you eat 6 small meals a day?