The popular diet has come under scrutiny by some people in the health and wellness community.

Originally designed in the 1920s to treat epilepsy, the ketogenic — or “keto” — diet has become one of the most popular weight loss trends over the past couple of years.

Everyone, from celebrities to tech influencers and bloggers, has become obsessed with the low-carb, high-fat diet that works by sending the body into ketosis, which is the metabolic state where your body burns fat instead of glucose for energy.

However, some fitness experts aren’t so keen on the keto diet. Last week, fitness trainer Jillian Michaels blasted the diet, saying it’s a bad idea for a million different reasons.

“Your cells, your macro molecules, are literally made up of protein, fat, carbohydrates, nucleic acids,” Michaels recently told Women’s Health. “When you do not eat one of the three macronutrients, those three things I just mentioned, you’re starving yourselves. Those macronutrients serve a very important purpose for your overall health and well-being. Each and every one of them.”

With all the opinions being thrown around about the eating plan, it can be difficult to keep up with what’s factual and what’s not. Here’s what we know about the keto diet, thanks to science.

You run the risk of putting your body into starvation mode on any diet, but it all comes down to the quality of the foods you’re eating, many health experts argue.

For example, the keto diet requires dieters to get approximately 75 percent of their calories from fat, 20 percent from protein, and the remaining 5 percent from carbohydrates.

We’re used to getting about 45 to 65 percent of our calories from carbs, so that’s a big change for your body to get used to, but we aren’t starving our bodies of them.

Rather than eliminating carbs from your diet, you should be more intentional about the type of carbs you eat. Swap out the simple, refined carbs for more complex carbs that are high in fiber, such as non-starchy vegetables and legumes. These take longer to digest, so they don’t spike your blood sugar levels like simple carbs do.

“It is a stretch to say we are starving ourselves on a low carb diet,” Alvin Berger, PhD, a lipid biochemist and adjunct professor of nutrition at University of Minnesota, told Healthline. “On a low-carb diet, or a low-carb diet combined with intermittent fasting, there is a ‘metabolic fasted state.’ That is, the body thinks it is fasted, so fats are burned off and other fasted metabolic pathways are active, but we are not obviously really fasted.”

The keto diet alone shouldn’t deprive your body of key vitamins and minerals. However, if you get clumsy with it and restrict too much or, say, overdo it with the fats or red meat, you might run into trouble.

“If you’re not eating a wide variety of vegetables, fruits, and grains, you may be at risk for deficiencies in micronutrients, including selenium, magnesium, phosphorus, and vitamins B and C,” Dr. Morton Tavel, a clinical professor emeritus of medicine at the Indiana University School of Medicine, said.

A lot of keto dieters don’t eat enough fiber, for example, which leads to digestive issues like constipation. Others struggle with getting enough magnesium — which may trigger muscle cramps and fatigue — and vitamin D, which can cause brittle bones and fractures.

It’s crucial to include a healthy mix of foods in your diet — fish, meats, nuts, seeds, veggies, fruits — to hit your daily nutritional needs. If you suspect you’re developing a deficiency, it’s worth asking your doctor or a dietitian about supplements.

Previous research has shown that the keto diet — or any low-carb diet — helps dieters lose weight faster than they would if they followed a low-fat diet. That’s been the main draw of it, after all.

This happens for two reasons.

  • When you hit ketosis, your body stores less fat because it’s using it for fuel.
  • The keto diet suppresses your appetite, according to previous research. The less hungry you are, the fewer calories you’ll eat.

All that being said, it’s difficult to adhere to the keto diet for a long time because of how restrictive it is. As soon as you start eating carbs again, you’re likely to gain the pounds back right away.

Adhering to a strict diet can also put you at risk for yo-yo dieting. This type of weight cycling can put you at a higher risk for heart disease, stroke, and early death, recent research suggests.

If you have any liver issues, you’ll want to avoid the keto diet. Because the body has to metabolize so much fat on this eating plan, it could worsen existing liver issues.

“In a high-fat diet, there is more metabolic burden on the liver to convert the fatty acids to their two fates: the fatty acids are oxidized to energy or converted to ketone bodies via the process of ketogenesis,” said Berger. “Thus, if there is liver disease, there could be an issue to properly metabolize the ingested triglycerides and their released fatty acids.”

The same goes for those with kidney problems, health experts believe. One of the kidneys’ main jobs is to break down protein. Keto dieters tend to eat larger amounts of meat and fish, which can increase uric acid and calcium levels and lead to kidney stones and gout.

We don’t have much evidence regarding the long-term side effects of the keto diet. That being said, most dietitians don’t recommend adhering to the keto diet for months on end, as it’s not a well-balanced eating plan.

If you’re thinking of going on a high-fat, low-carb diet, always consult your doctor first.

The keto diet isn’t right for everyone. Yes, it could be a quick and effective weight loss plan for certain healthy individuals, but it could put others seriously in danger.

The keto diet can help healthy individuals lose weight fast, but some may be at risk for developing nutritional deficiencies, liver damage, and harmful yo-yo dieting habits.