What to Know About Ketosis

Medically Reviewed by Shruthi N, MD on July 11, 2024
Written by Shawna Seed
7 min read

Ketosis is a process that happens when your body doesn't have enough carbohydrates to burn for energy. Instead, it burns fat and makes things called ketones, which it can use for fuel.

Ketosis is a word you'll probably see when you're looking for information on diabetes or weight loss. Is it a good thing or a bad thing? That depends.

"Keto" diets are popular weight loss programs that promote ketosis. In addition to helping you burn fat, ketosis can make you feel less hungry. It also helps you keep muscle.

For healthy people who don't have diabetes and aren't pregnant, ketosis usually kicks in after 3 or 4 days of eating fewer than 50 grams of carbohydrates per day. That's about three slices of bread, a cup of low-fat fruit yogurt, or two small bananas. You can start ketosis by fasting, too.

A diet high in fat and protein but very low in carbs is called a ketogenic or "keto" diet.

A keto meal plan doesn't completely cut out carbs, but you should limit yourself to 50 grams per day. You may think of carbs as things such as bread and pasta, but fruits are high in carbs, too.

Vegetables

Every day, you should eat five servings of non-starchy vegetables. (A serving is about 1/2 cup of cooked veggies or one cup of raw veggies.) Non-starchy vegetables you can find easily include:

  • Artichokes
  • Asparagus
  • Green and wax beans
  • Beets
  • Broccoli
  • Brussels sprouts
  • Cabbage
  • Cauliflower
  • Celery
  • Cucumbers
  • Eggplant
  • Greens such as collard, mustard, kale, and turnip
  • Mushrooms
  • Okra
  • Peppers
  • Radishes
  • Salad greens such as endive, escarole, lettuce, romaine, spinach, arugula, radicchio, and watercress
  • Squash
  • Tomato
  • Turnips

Protein

Aim for at least 60 grams of protein every day. Good sources include:

  • Poultry
  • Lean meat
  • Fish
  • Plant-based proteins

You might not be as hungry as usual when you're aiming for ketosis. Try eating the protein part of your meal first to make sure you meet your protein goals.

Healthy fats

These are a good source of calorie-dense nutrition. They also can lower your "bad" cholesterol. Examples include:

  • Avocados
  • Canola oil
  • Olive oil
  • Safflower oil
  • Nuts such as peanuts, cashews, almonds, pecans, and walnuts
  • Peanut butter and peanut oil
  • Oily fish such as salmon, mackerel, and tuna
  • Tofu
  • Flaxseed and flaxseed oil
  • Eggs
  • Sunflower seeds

Fruits

You'll want to limit fruit because it's high in carbohydrates. Aim for one cup per day. Berries are a good choice because they have fewer carbs than other fruits.

Liquids

Avoid drinks that are sweetened with sugar. But try to get 64 ounces of fluid each day to stay hydrated. This will help keep your electrolytes in the right range.

Calcium

You need this nutrient to keep your bones strong. Aim for 1,200 milligrams a day. You can take calcium supplements, but good food sources include:

  • Milk, yogurt, and cheese
  • Leafy greens such as bok choy, kale, and collards
  • Broccoli and broccoli rabe
  • Seafood
  • Soybeans, beans, and lentils

Ketosis can have some benefits beyond weight loss. Doctors may put children who have epilepsy on a keto diet because it can help prevent seizures. Adults who have epilepsy sometimes eat modified Atkins diets.

Some research suggests that ketogenic diets might help lower your risk of heart disease. Other studies show that specific diets very low in carbs help people who have diseases such as:

Researchers are also studying the effects of these diets on conditions including:

  • Acne
  • Cancer
  • Polycystic ovary syndrome (PCOS)
  • Nervous system diseases such as Alzheimer's, Parkinson's, and Lou Gehrig's disease

During the first week of a keto diet, you might start to feel bad. Some people call this the "keto flu," but it isn’t an official medical condition. Some doctors think this is due to sugar and carbohydrate withdrawal. Or it could be because of changes to your gut bacteria or an immune system reaction. You might notice temporary side effects such as:

  • Headache
  • Fatigue
  • Brain fog
  • Irritability
  • Constipation
  • Trouble sleeping
  • Nausea
  • Stomachache
  • Dizziness
  • Sugar cravings
  • Cramps
  • Sore muscles
  • Bad breath, also known as ketosis breath

Drinking plenty of water can ease or prevent some of these symptoms.

About 1 in 20 children who have epilepsy and are on the keto diet get kidney stones. A supplement called potassium citrate can help prevent them. Talk to your doctor about the kidney stone risk if your child is on the keto diet.

If you’re a new mom and don’t get enough calories or fluids, ketosis could affect your breast milk supply. Doctors generally recommend that you wait until you’re done breastfeeding if you want to start the keto diet.

Not everyone loses weight in ketosis. There are several possible reasons for this.

One is that some foods considered keto-friendly -- avocados, for instance -- are high in calories. Eating too much of these foods will make it hard to lose weight.

Some research suggests that your genetic makeup can affect how well your body responds to a keto diet.

If you're not losing weight, you might have an underlying medical issue, or the medicine you take could be interfering with weight loss. Some key factors may include:

  • Thyroid issues
  • PCOS
  • Hormonal birth control
  • Medications such as beta-blockers and antidepressants 

Certain things hold true about all weight-loss programs: You have to stick to it, and you need to burn calories. So if you eat foods that aren't recommended or don't exercise, that can affect your outcome.

Other factors that can make it hard to lose weight include:

  • Not getting enough sleep
  • Shift work and other things that disrupt your body's natural sleep/wake rhythms
  • Not getting enough fluids
  • Drinking alcohol

Some over-the-counter supplements claim to raise your ketone levels. They come as pills, powders, oils, and other forms. There isn’t much research on whether they work or if they’re safe. Talk to your doctor before you start taking any supplements.

If you're healthy and eating a balanced diet, your body controls how much fat it burns so you don't usually make or use ketones. But when you cut way back on your calories or carbs, your body will switch to ketosis for energy. It can also happen after you exercise for a long time and during pregnancy.

If you have diabetes that isn’t under control, ketosis can become dangerous when ketones build up. High levels lead to dehydration and change the chemical balance of your blood. It becomes acidic and can cause a coma or death.

People who have diabetes can get ketoacidosis, or diabetic ketoacidosis (DKA), when they don't take enough insulin. They can also get DKA when they're sick or injured or when they don't get enough fluids and become dehydrated.

Some people who don’t have diabetes can get ketoacidosis, too. It's caused by alcoholism, starvation, or an overactive thyroid. A healthy low-carb diet shouldn't cause a problem.

If you have these symptoms, call your doctor:

  • Thirstiness or a dry mouth
  • Peeing a lot
  • Feeling tired
  • Dry or flushed skin
  • Upset stomach
  • Throwing up
  • Trouble breathing
  • Confusion
  • Fruity-smelling breath
  • Pain in your belly

When you have diabetes, throwing up can be especially dangerous. Although DKA usually starts off slowly, throwing up can speed up the process so that it happens in just a few hours. Call your doctor if you've been throwing up for 2 hours or more.

Ketosis isn't harmful in an otherwise healthy person and requires no treatment.

If you progress to ketoacidosis, however, you'll need quick medical attention.

You can find out how much ketosis is going on in your body by testing for ketones in your blood or urine. You can buy test strips to check your pee at home. Some blood sugar meters can measure ketones in your blood.

If you don't know how and when to test your ketones, talk to your doctor or diabetes instructor. High levels of ketones are dangerous.

Ketosis levels

Here are some guidelines on ketones readings: 

  • Nutritional ketosis: Between 0.5 and 3.0 (mmol/L)
  • High risk for ketoacidosis: Above 3.0 (mmol/L)

If you're diabetic, a reading between 1.6 and 3 (mmol/L) indicates some risk for ketoacidosis, and you should check with your doctor.

When you're in ketosis, your body doesn't have enough carbohydrates, so it turns to burning fat for fuel. The fat is turned into a substance called ketones. You can achieve ketosis by following a low-carb, high-protein diet, sometimes called a keto diet. Some research shows that keto diets can help people lose weight. They also might have benefits for people with type 2 diabetes, insulin resistance, and metabolic syndrome. When you're in ketosis, you may have headaches, fatigue, stomach upset, and irritability, among other side effects. Some people develop an odd smell to their breath. If your level of ketones gets too high, you're in danger of ketoacidosis, a condition that requires immediate medical attention.

How do I know if I'm in ketosis?

You can measure the level of ketones in your body. If the level is between 0.5 and 3.0 (mmol/L), you're in nutritional ketosis. 

Is ketosis good for the body?

Several studies have found that keto diets can help people lose weight. It's sometimes recommended for kids with epilepsy.

What happens when you're in ketosis?

Because your body doesn't have enough carbohydrates, it turns to fat for fuel.