The fastest way to get into ketosis is through a low-carb diet, intermittent fasting and exercise. Once you're in ketosis, your body burns fat instead of carbs for fuel. Endurance athletes may benefit from ketosis, but power and strength athletes may experience issues.
Along with following a low-carb diet, performing high-energy exercises, such as sprinting or HIIT, will use up your glucose stores so you can achieve ketosis more quickly. Once you have reached ketosis, high-intensity workouts can be difficult to maintain and may need to be swapped for less intense exercises.
The Keto Diet Overview
The ketogenic, or "keto," diet is a popular eating plan for those looking to lose weight. It actually started as a way to help control diabetes, as well as a treatment plan for children with epilepsy, says the Harvard T.H. Chan School of Public Health. It is used in monitored settings for conditions like cancer, Alzheimer's disease and polycystic ovary syndrome.
On the keto diet, you eat mostly low-carbohydrate and high-fat foods. This deprives your body of glucose, which is the main source of energy for the cells in your body. If your body doesn't have carbs for fuel, it first uses the glucose in your liver and breaks down muscle.
After three to four days, the stored glucose is gone. Your liver begins to produce ketones from stored fat and use them for fuel. When the ketones reach certain levels in your bloodstream, you achieve a metabolic state called ketosis.
For your body to go into this state, it's necessary to reduce your total carb intake to 20 to 50 grams a day. To put it into perspective, this is less than the amount of carbs found in a medium bagel, says Harvard T.H. Chan.
While on the keto diet, about 70 to 80 percent of your calories come from fat, 5 to 10 percent from carbs and 10 to 20 percent from protein. It's important to limit or avoid foods high in carbs, such as pasta, bread, fruits and even beans and starchy vegetables. The diet consists largely of meat, fish, butter, avocados, oils, nuts and seeds.
As an example, a 2,000-calorie diet would equate to 165 grams of fat, 40 grams of carbs and 75 grams of protein. The protein amount is lower than that associated with most low-carb diets, says Harvard T.H. Chan, as too much protein can kick you out of ketosis.
The Ketosis State
This eating pattern is designed to induce ketosis, causing your body to use stored fat for fuel instead of glucose. A summer 2017 study in the_ Journal of Special Operations Medicine_ reports that most people will achieve ketosis after two to four days of fasting for 72 hours or by eating 20 to 50 carbs per day. Extreme exercise has similar effects.
How fast your body goes into ketosis varies for each person and depends on several factors, including your body fat percentage and resting metabolic rate, says Harvard T.H. Chan. For some individuals, it can take longer than a week to be in a ketosis state, according to the above review.
Some symptoms may indicate that you are going into ketosis, but a blood test is the most accurate way to know for sure. For some people, dangerous levels of ketones can build up in the blood, causing ketoacidosis. It is important to talk to your doctor before starting the keto diet to make sure it's safe for you.
Ketoacidosis can be a concern for people with type I diabetes, but in rare cases, it has also occurred in healthy people who followed low-carbohydrate diets for a long time.
Read more: Benefits of Ketosis
Exercise and Ketosis
The fastest way to get into ketosis is through fasting — in addition to a low-carbohydrate diet and prolonged exercise, says the Cleveland Clinic. You can even go in a mild ketosis phase while sleeping at night. However, ketosis can be difficult to reach for some people.
Even though exercise and ketosis are linked, you may not feel like exercising during those first few days or weeks when starting the keto diet. Many people experience a number of side effects called the "keto flu" (more on that below), resulting in dizziness, fatigue and even nausea.
If you are following a low-carbohydrate diet and aren't reaching ketosis or having symptoms, high-energy activities like sprinting or high-intensity interval training (HIIT) will quickly use up your glucose stores so you reach ketosis quickly. It's important to listen to your body, however, and drink plenty of water to stay hydrated.
In addition to water, consider drinking a sports drink with electrolytes, including magnesium, potassium or salts. Because the keto diet cuts out foods that have a natural source of electrolytes, like some fruits and vegetables, you may be prone to cramps or nausea.
If you start feeling dizzy or nauseous, back off and do light exercises, like a restorative yoga class, says Intermountain Healthcare. Even simple activities exercises like walking, light jogging or light cycling are better than no exercise at all.
What Is the Keto Flu?
As your body reaches ketosis, you may experience what is known as the keto flu in the first few days after drastically cutting the carbs in your diet. These flu-like symptoms may include, according to Intermountain Healthcare:
- Sugar cravings
- Brain fog and difficulty concentrating
- Stomach aches
- Stomach issues like diarrhea or constipation
- Trouble falling asleep
Some people won't experience any of these symptoms, while others will have them for less than a week. A small percentage may have symptoms for up to a month. Starting with a traditional low-carbohydrate diet before transitioning to a keto diet may help lessen the side effects.
Drink lots of water to ensure you stay hydrated. Sipping on chamomile tea at night can make it easier to increase your fluid intake and relax before sleep. This type of tea is recommended on the keto diet.
Make sure you eat enough fats from foods like avocados, fish and egg yolks, says Intermountain Healthcare. Not doing so may worsen your symptoms.
Taking an Epsom salt bath before bed will not only help relax your muscles but may also improve electrolyte absorption, so that's an option to consider.
Exercise and ketosis don't always mix at first. Give your body a chance to adjust before jumping into a workout routine. Talk to your doctor if you experience any signs of the keto flu to ensure your ketone levels are staying within a safe range.
Keto Diet Exercise Tips
In general, if you love high-energy exercises, then the keto diet may not be right for you in the long term. Even though high-energy activities like HIIT or sprinting can help achieve ketosis, once you are in that state, you may need to alter your exercise routine. You may feel like you fatigue more quickly than you used to while doing high-energy activities.
Those who prefer sprinting or playing tennis may experience a decrease in performance due to their carb intake. Endurance activities, such as cross-country running or biking, might be a better long-term match for those on the keto diet, says the Cleveland Clinic.
If you find that you can't do your normal high-energy workouts, switch to exercises like yoga or a low- to moderate-intensity training on a stair climber. In general, when starting the keto diet, it's better to aim for lower-intensity workouts as your body adjusts.
An April 2017 study in the Journal of Strength and Conditioning Research suggests that ketogenic diets are a good option for building lean muscle mass. The small study looked at 25 men enrolled in a resistance training program and divided them up between those on a keto diet and those on a traditional Western diet.
After 10 weeks, both groups gained lean body mass and lost body fat, but the keto group had more lean body mass gains.
Keto supplements claim to reduce sluggishness and suppress appetite. Unfortunately, most of them don't provide any nutrition or added metabolic health benefits, notes the Cleveland Clinic.
In some cases, ketogenic pre-workout supplements may help athletes train for longer by tapping into their fat reserves. But these products can also have the opposite effect and cause your body to store fat and increase insulin. A food-based ketogenic diet without supplements is recommended, especially for endurance athletes.
Pros and Cons of Keto
There are several factors to consider before starting a keto diet. This eating plan may provide short-term benefits, such as weight loss and improvements in blood pressure, blood sugar and total cholesterol, says Harvard T.H. Chan. However, more studies are needed to assess its effects in the long run.
Harvard T.H. Chan warns that potential risks of the diet may include kidney and liver problems because high fat intakes cause the liver to work harder. Deficiencies in vitamins B and C, phosphorus, magnesium and selenium can also be an issue.
Read more: 6 Reasons the Keto Diet Is Not for You
Additionally, many keto-friendly foods are high in saturated fats, such as those in red meat and bacon, and may affect your blood lipids. Make sure you talk with your doctor before starting this program.
Endurance athletes may benefit from this eating pattern, but the National Academy of Sports Medicine (NASM) reports that a keto diet can negatively affect your sports performance, especially activities that require short bursts of energy. They recommend a more balanced, well-rounded diet that includes carbohydrates for optimal sports performance.
One option to get the benefits of the keto diet while minimizing the negatives is to alternate between low- and high-carb days. This is called carb cycling.
The downside is that your body may come out of the ketosis state due to the increased carb intake, so you'll have to start all over. Consider these benefits and risks and talk to your doctor to see whether or not a keto diet is right for you.
- Harvard T.H. Chan School of Public Health: "Diet Review: Ketogenic Diet for Weight Loss"
- Journal of Special Operations Medicine: "Ketones and Human Performance"
- Cleveland Clinic: "Can Ketone Supplements Rev Up Your Workouts?"
- Intermountain Healthcare: "Beware the Keto Flu"
- Journal of Strength and Conditioning Research: "The Effects of Ketogenic Dieting on Body Composition, Strength, Power, and Hormonal Profiles in Resistance Training Males"
- National Academy of Sports Medicine: "What Is the Ketogenic Diet? Foods, Benefits, Risks"