Ketosis is the result of following the ketogenic diet, which is why it's also sometimes called “the ketosis diet.” Ketosis takes place when glucose from carbohydrate foods (like grains and all sources of sugar or fruit) is drastically reduced, which forces the body to find an alternative fuel source: fat. Although dietary fat often gets a bad name, provoking fear of weight gain and heart disease, it's also your body's second preferred source of energy when carbohydrates are not easily accessible. Because it also requires drastic carbohydrate restriction, studies show that complete or intermittent fasting can also induce states of ketosis. However, total fasting, which would result in a level of ketosis comparable to the ketogenic diet, isn't easy to maintain beyond a few days. In addition, total fasting will also metabolize muscle tissue. Ketosis cannot begin until there's an absence of glucose in your body. Glucose is normally used by cells as a quick source of energy — without it, the body starts to burn fat and produces ketones instead. Once ketone levels in the blood rise to a certain point, you enter into a state of ketosis. This state usually results in quick and consistent weight loss until you reach a healthy, stable body weight.

Here's how ketosis works:

Consumption of glucose from carbohydrate foods — grains, starchy vegetables, fruit, etc. — is cut way down. This forces your body to find an alternative fuel source: fat (think avocados, coconut oil, salmon). Meanwhile, in the absence of glucose, the body also starts to burn fat and produces ketones instead. Once ketone levels in the blood rise to a certain point, you enter into a state of ketosis. This state results in quick and consistent weight loss until you reach a healthy, stable body weight. To sum up a complex process, ketosis happens when the liver breaks down fat into fatty acids and glycerol, through a process called beta-oxidation. There are three primary types of ketone bodies that are water-soluble molecules produced in the liver: acetoacetate, beta-hydroxybutyrate, and acetone. The body then further breaks down these fatty acids into an energy-rich substance called ketones that circulate through the bloodstream. Fatty acid molecules are broken down through the process called ketogenesis, and a specific ketone body called acetoacetate is formed which supplies energy. The end result is staying fueled off of circulating ketones (which are also sometimes called ketone bodies) — which is what's responsible for altering your metabolism in a way that some people like to say turns you into a “fat-burning machine.” The goal of the ketogenic diet is to keep you in this fat-burning metabolic state of ketosis. This is achieved by following a very low-carbohydrate, high-fat diet that includes only moderate amounts of protein. Foods like bread, cereal, processed snacks, and sugary drinks are therefore off the table, while fattier foods like butter, grass-fed beef, fish, and also non-starchy veggies take center stage, providing the majority of daily calories (as much as 70–80 percent).