Key takeaways:
Ketosis is a type of metabolism where your body uses fat instead of carbohydrates (glucose) for energy.
Starvation can cause ketosis. So can many different medical conditions.
Ketogenic diets aim to push your metabolism into ketosis to lose weight. One example of these diets is the keto diet, a high-fat, low-carb diet. But there are other ketogenic diets, such the paleo, South Beach, and Atkins diets.
There are certain signs that your body is in ketosis, including nausea, low energy, and bad breath.
If you’re on a ketogenic (keto) diet, the goal is to tip your body into a type of metabolism called ketosis. That’s when your body switches from burning glucose to burning fat for energy. The idea is that eating very few carbohydrates will get you there.
But how do you know when your body is in ketosis and burning fat instead of glucose? Read on to learn the signs that you’re in ketosis, along with how to help prevent other symptoms that you may experience.
What is ketosis?
Your body normally burns glucose for energy. Glucose comes from carbohydrates in your diet. When you restrict the amount of carbohydrates you eat, your body runs out of glucose to burn. So it turns to fat instead. Burning fat for energy generates ketones, molecules that can be used for energy. This metabolic shift is called ketosis.
Ketosis starts after your body has used up its stored glucose. Typically, this happens when you eat fewer than 50 g of carbohydrates per day. The keto diet has become a popular ketogenic diet. But other diets that restrict carbohydrates may also be ketogenic in some cases. Examples are the paleo diet, the South Beach diet, and the Atkins diet.
Of all of these, the keto diet is most likely to cause ketosis because it also restricts protein, another source of energy.
Good to know: Nutritional ketosis sounds similar to ketoacidosis, but they’re not the same thing. Ketoacidosis, like diabetic ketoacidosis (DKA), is a serious complication where ketone levels become extremely high and your blood becomes too acidic. This can be a life-threatening emergency that needs urgent medical treatment.
Symptoms of ketosis
When your body goes into ketosis, it may cause some side effects or symptoms. This usually occurs about 3 days into the diet.
Symptoms can be clues that you’ve reached ketosis and your body is burning fat. Keep in mind that not everyone gets symptoms. Most symptoms disappear within a few days. But a few can last longer. Here are the most common signs and symptoms of ketosis.
1. Flu symptoms
Flu-like symptoms are so common that they’ve been dubbed the “keto flu.” Flu-like symptoms tend to be much milder than an actual flu, and they only last the first few days of the diet. Scientists aren’t sure what causes the symptoms, but dehydration can make them worse.
Keto flu symptoms may include:
Upset stomach
Headache
Exhaustion
Dizziness
Nausea
Fever
2. Changes to your urine
You may pee more than usual during the first 1 to 2 weeks. Your urine may smell fruity as soon as 12 hours after starting a keto diet. This is caused by acetones — one of the types of ketones that are produced during ketosis.
3. Bad breath
It’s very common to have bad breath when you’re in ketosis, and it may be the first thing you notice. The higher levels of acetones can cause an unpleasant fruity odor, which you may notice soon after you reach ketosis. It’s been described as smelling like nail polish remover, pear drops, or overripe fruit. Unfortunately, bad breath can last while you’re on the diet.
4. Digestive issues
Stomach issues are a common side effect of low-carb diets, so you often feel them when you’re in ketosis. There are a few types of issues you might run into:
Constipation: Nearly 3 in 4 people on a keto diet get constipated. Some keto diets encourage low intake of grains, fruits, and vegetables. That means you’re getting less fiber, which is important for preventing constipation. The keto diet can also make you dehydrated, which can contribute to constipation.
Diarrhea: The keto diet typically encourages eating a lot of fat. Eating fatty foods can take its toll on your digestion. If your body can’t tolerate a high-fat diet, you could develop diarrhea.
Abdominal pain: A high-fat, low-fiber diet may also cause gas and bloating.
5. Weight loss
During the first 2 weeks on a ketogenic diet, it’s common to lose weight quickly. Much of this weight loss is from water. But after that, you may begin to lose fat. You may begin to feel less hungry, and you’ll likely eat fewer calories, which leads to weight loss.
How to reduce side effects and symptoms on a keto diet
Some signs and symptoms are a natural result of a ketogenic diet, but there are ways you can help ease them:
To help reduce flu-like symptoms, drink about 3 L of water daily. Staying hydrated can help ease symptoms.
Try to rest and limit your activity for the first couple of days on the diet.
To help prevent constipation, stay hydrated and choose low-carb, fiber-rich vegetables (like asparagus and broccoli). If you’re still constipated, you can try a low-carb laxative, like Miralax.
To ease nausea, try eating more frequent, small meals rather than 3 large meals.
For bad breath, try sugar-free chewing gum or mints.
Benefits of ketosis
There are some claims that ketogenic diets may have other health benefits beyond weight loss. But the research is still limited. And there are plenty of potential risks associated with a ketogenic diet that may not outweigh the reported benefits.
Some possible benefits may include:
Better cardiovascular health: There’s some evidence a keto diet could improve your levels of cholesterol and fat in your blood. This evidence is mixed though. And it’s important to know that some studies actually show that a keto diet could increase your cholesterol levels.
Blood sugar management: There’s some evidence a low-carb diet could help people with diabetes manage their blood sugar. This could lessen the need for insulin and other medications. But it’s not clear whether these benefits last over time.
Improved cognitive skills: Some animal studies suggest the keto diet could help improve memory and attention. But the research in humans is too limited to draw any conclusions.
Potential risks of keto diets
The keto diet is difficult to follow over the long term. There are risks to rapid weight loss and rebounding with weight gain. The typical keto diet tends to be high in saturated fats (often animal fats). It’s also low in carbs that are important sources of nutrients, like:
Grains
Legumes
Fruits
Vegetables
These dietary changes may increase the risk of certain conditions, including:
Kidney stones or disease
Severe low blood sugar in people with diabetes
Nutrient deficiencies
Liver abnormalities
Risk of disordered eating from any restrictive diet
Impaired gut health from a low-fiber diet
Increased risk of colorectal cancer
Certain groups may have special concerns or risks. Talk with a healthcare professional before trying a keto diet if you have any of these conditions:
You’re pregnant or breastfeeding.
You have Type 1 diabetes.
You have liver, kidney, or respiratory issues.
You’re taking the anti-seizure medication lamotrigine. The keto diet can make this medication less effective and lead to more seizures.
Frequently asked questions
On the keto diet, your pee might darken or become more yellow if you’re dehydrated. It’s common to be dehydrated when you enter ketosis.
Yes, fasting causes ketosis. When you don’t eat at all, your body runs out of glucose (from carbohydrates) to burn for energy. So, it burns your fat stores instead. When your body switches from burning glucose to burning fat, it enters ketosis.
Your poop might look greener. That’s because high-fat diets can lead to more bile, a digestive fluid. Bile is green and can change the color of your poop.
You may have heard reports of “keto insomnia,” or people having trouble sleeping shortly after starting a keto diet. Scientists are still working to understand why sleep changes may occur on keto diets. It may have to do with changes to sleep-regulating chemicals, like melatonin, that happen when your body enters a different metabolic state. Usually, your body adjusts to the new metabolic state and sleep patterns go back to normal.
After starting a keto diet, you may experience symptoms of ketosis in about 3 to 4 days. But not everyone notices symptoms, and they often go away in a few days.
There’s no specific number of carbs that will take you out of ketosis. But most people need to consume fewer 50 g of carbs per day to stay in ketosis. The exact number of carbs will vary because other factors influence your metabolic state, like your activity level, insulin sensitivity, and metabolism.
On the keto diet, your pee might darken or become more yellow if you’re dehydrated. It’s common to be dehydrated when you enter ketosis.
Yes, fasting causes ketosis. When you don’t eat at all, your body runs out of glucose (from carbohydrates) to burn for energy. So, it burns your fat stores instead. When your body switches from burning glucose to burning fat, it enters ketosis.
Your poop might look greener. That’s because high-fat diets can lead to more bile, a digestive fluid. Bile is green and can change the color of your poop.
You may have heard reports of “keto insomnia,” or people having trouble sleeping shortly after starting a keto diet. Scientists are still working to understand why sleep changes may occur on keto diets. It may have to do with changes to sleep-regulating chemicals, like melatonin, that happen when your body enters a different metabolic state. Usually, your body adjusts to the new metabolic state and sleep patterns go back to normal.
After starting a keto diet, you may experience symptoms of ketosis in about 3 to 4 days. But not everyone notices symptoms, and they often go away in a few days.
There’s no specific number of carbs that will take you out of ketosis. But most people need to consume fewer 50 g of carbs per day to stay in ketosis. The exact number of carbs will vary because other factors influence your metabolic state, like your activity level, insulin sensitivity, and metabolism.
The bottom line
When you first enter ketosis, you’ll likely experience some noticeable symptoms. The most obvious symptoms are flu-like symptoms, like nausea, dizziness, and fatigue. These will go away in a few days. Other symptoms, like constipation or fruity-smelling breath or urine, could last while you’re on the diet. Lastly, you’ll likely lose weight if you’re following the keto diet.
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