How Long Does It Take for the Ketosis Diet to Work?

If you've read or done a cursory search about dieting over the past few years, you've probably come across the keto diet. The ​ketosis, ketogenic or "keto" diet​ is a low-carbohydrate, high-fat diet. First used at Mayo Clinic in the 1920s as an effective treatment for pediatric epilepsy, the diet has grown into what CNN has dubbed the "keto craze," particularly as a weight-loss and lifestyle regimen.

There have been a number of testimonials in support of the diet that claim "better focus," "more energy," and other positive effects based on subjective experience with the diet. The metabolic state known as ​ketosis​ is key to this experience and is worthy of further exploration, most notably the time and processes required to induce and maintain this state.

The keto diet is included within the spectrum of low-carbohydrate diets, of which there are two types: very low-carbohydrate and low-carbohydrate. The keto diet falls within the former — in which less than 10 percent of calories come from carbs, amounting to less than 50 grams per day. The energy difference is made up with increased consumption of fats.

The diet is a specific version of low-carb consumption that seeks to induce and maintain nutritional ketosis. By restricting carbs to less than 50 grams per day, glycogen reserves (your store of carbs) become depleted and the body produces ketones. These are used as the body's primary fuel source rather than glucose that would otherwise come from the breakdown of available carbs. For this reason, the creation of ketones, the diet is often said to be "ketogenic" (i.e., ketone-producing).

Fasting, the total restriction of all foods including carbs, can also cause a state of ketosis, but the keto diet can maintain this state of ketosis while also providing a steady supply of nutritional energy — thereby allowing you, in theory, to lead a relatively normal and productive life. A 2015 review published in Frontiers in Psychology compared the keto diet to fasting, drawing similarities between the metabolic and neuro-psychological changes that result from ketosis, which is likely an evolutionary adaptation to food and carbohydrate scarcity. Many other low-carb diets, do not, by necessity, require maintenance of ketosis, particularly beyond the early stages.

The keto diet has a number of proven health benefits, particularly in the short to medium term. These include treating obesity, lowering glucose levels in patients with diabetes, lowering high cholesterol, restoring fertility in polycystic ovarian syndrome, reducing some cardiovascular risk factors and reducing hunger. However, the long-term effects of the diet are still under investigation.

Based on the laws of thermodynamics, it is often accepted in medicine that a "calorie is a calorie" but it is also observed that low-carb diets lead to more weight loss than low-fat diets when calories are equal. Though total energy expenditure may be the same, the additional weight loss may be due to changes in how energy is metabolized within the body.

According to the Harvard T.H. Chan School of Public Health, a number of theories may explain why the ketogenic diet promotes weight loss:

• High-fat content of the diet leads to greater satiety and lower food cravings.
• Decreased carbs leads to lower appetite, stimulating hormones like insulin and ghrelin.
• Ketones directly reduce hunger.
• The metabolic effects of converting fat and protein to glucose increases energy burned off.
• Decreased insulin promotes fat loss rather than lean body mass.

​Read more:​ The Benefits of Ketosis

There are a number of ketogenic diet strategies and meal plans to help you achieve a state of ketosis. Although fat and protein intake must certainly be considered, minimizing carbs is key. As shown by a study published in Obesity Reviews in 2014, less than 50 grams of carbs per day will induce a state of ketosis. The ketones produced can then be measured.

Clincally, ketosis is measured by levels of ketones in urine or serum, of which there are three types: acetoacetate, acetone and beta-hydroxybutyrate (BHB). Nutritional ketosis generally increases serum ketones to seven times normal levels but there are inconsistencies in the medical literature when it comes to measuring a state of ketosis.

Therefore, when trying to achieve ketosis, it's important to keep your carbs under 50 grams — less than the amount found in a medium plain bagel — and measure your ketone levels. In actual practice, however, most people do not clinically measure their ketone levels but rather look for signs, symptoms and tests observable at home.

One common way to test for ketosis is to smell your breath. Acetone, the active ingredient in nail polish remover, is given off as you exhale when you are actively in ketosis. It has a fruity odor that is similarly exhibited in patients with diabetes, in ketoacidosis. If you're healthy and you notice this fruity smell after starting the keto diet, you're likely in ketosis.

Additionally, you can purchase over-the-counter urine strips like those produced by Ketostix. The strips work by indicating the presence of acetoacetate. To perform the test, simply pass urine over the end of the strip, wait for the color to change (roughly 15 seconds) and compare the strip to the provided color chart. The best time to conduct the test is either early in the morning or after dinner.

Appetite suppression is also a notable change.

Given the inconsistencies in measuring ketones and defining an official quantitative threshold for ketosis, the time required to reach a state of ketosis, explains a 2018 review in Journal of Life and Environmental Sciences, ranges from one to 10 days. Despite this wide range, you can use an understanding of metabolism to help better predict where on this spectrum you will land once you start the keto diet.

When you either fast or limit your carbs to 50 grams per day, your body is deprived of adequate nutritional glucose to energize its cells. In response, the body begins to break down glycogen, a reserve supply of glucose in your liver, in order to meet its energy demands. The size of glycogen reserves are variable and dependent on a number of diet and lifestyle factors, including recent exercise patterns, metabolism and energy expenditure.

Glycogen eventually runs out, and your body begins to break down fats to be released into the bloodstream to meet energy demands. Though most of the cells in your body can use this energy source, your brain cannot because fatty acids do not cross the blood-brain barrier. As a result, the oversupply of fat in the blood is broken down into ketones in the liver, which can then cross the blood-brain barrier and be used as brain fuel.

Using ketones as fuel for the brain often leads to neuropsychological changes, including dampened hyperactivity, reduced cravings, improved memory and learning, and a host of other changes. These are things that, though subjective, can perhaps be felt and perceived as you enter a state of ketosis. By understanding this process, you may not only better discern whether you are in ketosis but also learn to tweak your diet and lifestyle to improve your chances of entering and maintaining ketosis.

In light of physiology, there are a few things you can do to induce ketosis quicker and limit the side effects in the early stages of the diet — often called the "keto flu" — which include nausea, vomiting, headache, fatigue, dizziness, insomnia, difficulty in exercise tolerance and constipation. These interventions include the following: limiting carbohydrates, consuming medium-chain triglycerides and increasing fat while limiting protein.

Although less than 50 grams is required to enter ketosis, it may be necessary to restrict carbs even more to decrease the time it takes to enter that state. By limiting carbs, your glycogen depletion, fatty acid breakdown and ketone production can kick in faster. Less than 20 grams of carbs per day for a few days (until ketosis induction is completed) can help with depletion of glucose reserves.

In fact, starting the ketogenic diet in a fasted and carb-deprived state improves the chances. Those who struggle with entering ketosis may want to consider limiting carbs to 20 grams. However, note that long-term carb restriction of less than 20 carbs can be dangerous, because the brain requires some carbs in order to operate and cannot rely entirely on ketones alone.

Medium-chain triglycerides (MCTs) help to promote the production of ketones. Unlike other long-chain fats, MCTs do not require the actions of bile and absorption into your lymphatic system before they enter the blood and are preferentially converted into bio-available ketones. Coconut oil is a great source of MCTs.

According to the Harvard T.H. Chan School of Public Health, ketogenic diets suggest an average of 70 to 80 percent of calories from fat, 5 to 10 percent from carbs and 10 to 20 percent from protein. For a 2,000-calorie diet, this amounts to about 165 grams of fat, 40 grams of carbs and 75 grams of protein.

With the keto diet, protein should be kept moderate in comparison with other low-carb high-protein diets, because eating too much protein can prevent ketosis. Protein can be converted by the body into glucose and can interfere in the glucose depletion required to induce ketone production. Still, some minimal level of protein is required to limit the breakdown of lean muscle mass.

​Read more:​ How to Increase Fat Burning During Ketosis