Food is your body’s primary source of energy, and three main nutrients in foods supply your body with this energy. These are carbohydrates, fat, and protein. Typically after eating a meal, your body will first break down carbohydrates from foods, and then fat and protein. Ketosis is a natural metabolic state that occurs when your body doesn’t have enough carbs (or glucose) for energy, so it burns fat instead. 

Ketosis happens when your carbohydrate intake is low. As your body breaks down fat, it produces an acid called ketones or ketone bodies, which becomes your body and brain’s main source of energy.

Because ketosis shifts your metabolism and relies on fat for energy, your body can burn fat at a higher rate. Translation? You may reach your weight loss goal sooner than if you didn’t cut carbs at all.

Putting — and then keeping — your body in ketosis isn’t exactly easy. You’ll need to severely minimize your intake of carbohydrates, eating no more than 20 to 50 grams (g) of carbs per day to get there and stay there. A single medium pear, for example, contains 26 g of carbs, and even foods that aren’t generally considered high in carbs — such as nuts and non starchy veggies — contain a small amount of carbohydrates, and so will need to be limited or avoided on this plan.

If you’re following the keto diet, you will need protein, but you should limit your intake to about 20 percent of your total daily calories. (1) This is important because when you consume more protein than you need, your body converts the excess protein into carbs through a process called gluconeogenesis. This process pushes your body out of ketosis.

Another dietary approach that’s gaining popularity nowadays is called intermittent fasting and is based on skipping food for limited, planned periods of time. Intermittent fasting will not put you into ketosis on its own. Some people combine intermittent fasting with a keto diet — but you should know this approach hasn’t been studied or proven to work for weight loss.

In addition to following a keto diet, you can talk to your doctor about adding supplements, such as exogenous ketones, to put and help keep your body in ketosis, according to a study from 2017.

Checking your ketone level is one way to know if you’re in ketosis. This metabolic state usually kicks in after three or four days of restricting your carbohydrate intake. You don’t have to visit a doctor to measure your level. Pick up a ketone urine test from a nearby drug store, or use a blood sugar meter that’s capable of measuring ketones.

A normal blood ketone level is under 0.6 millimoles per liter (mmol/L). (2) Any level higher than this can indicate a state of ketosis.

Physical signs and symptoms of ketosis include:

• Weight loss
• Loss of appetite
• Increased energy, though energy may be decreased in the first few weeks on the diet
• Fruity-smelling breath (halitosis)
• Constipation or diarrhea

Many of these symptoms are associated with what people call the “keto flu.” Experts say symptoms should subside within two weeks.

The long-term effects of constant ketosis haven’t been thoroughly investigated. But it appears to be generally safe for most people, at least as a short-term weight-loss solution.

Again, it’s important to note that this state can cause a high level of ketones in the bloodstream, which can make the blood acidic, a dangerous medical state.

Everyone’s body responds differently to ketosis. So while some people are able to produce insulin during ketosis to slow down ketone production and avoid a toxic level, others can’t. Ketosis becomes dangerous when blood turns acid. Always speak with your healthcare provider before making any changes to your diet.

And keep in mind that diets based on putting your body into ketosis are no more effective for weight loss long term than conventional diets that have sound scientific backing.