Grilled fish and vegetables make for a healthy, easy keto meal. Image Credit: GooDween123/iStock/Getty Images

The ketogenic or keto diet promises quick weight loss, improved metabolism and the ability to eat foods that are often off-limits for people trying to slim down, like cheese and fatty meats.

Keto meal plans have become extremely popular — but are they safe?

Doctors first developed the ketogenic diet in the 1920s as a treatment for epilepsy in children. But it's since gone mainstream, with an explosion of keto diet books, online recipes and blogs, and celebrities and influencers touting its "transformative" powers.

Health and nutrition experts, however, are more cautious about going keto, for several reasons. Here are a few of the potential risks of going keto, and how to decide for yourself if it's the right diet for you.

1. Keto Flu

It's quite common for people to experience unpleasant side effects when first starting a keto diet. These symptoms — which can include fatigue, irritability, sleep issues, headache and digestive issues — are sometimes called "keto flu."

Keto flu often goes away once the body adjusts to burning fat instead of carbohydrates, says Jim White, RD, a nutritionist and personal trainer in Virginia Beach. But it's not uncommon for people to feel weak on the keto diet, even if they've been following it for a while.

"We know that low-carb diets can have effects on energy levels and can reduce exercise performance, which in an extreme state could become dangerous," White says.

People may want to limit their high-intensity workouts while following a keto diet, he says, especially during the first few weeks.

Related Reading Negative Side Effects of a Low-Carb Diet

2. Long-Term Health Concerns

More concerning, says White, is research suggesting that diets high in saturated fats may increase the risk for lasting health problems.

"There aren't really any long-term studies on keto in adults, since it's fairly new as a weight-loss diet," says White. "But we know that high levels of saturated fat are associated with things like high blood pressure and cholesterol, which can increase the risk of heart disease."

A 2017 review published in Nutrients echos White's point about the dearth of large low-carb diet studies in humans. But in animals, the review points out, keto-style diets have been associated with liver disease and insulin resistance.

In some human studies, ketogenic diets have actually been associated with decreases in cholesterol levels and blood pressure, the review notes.

"But these effects are usually limited in time," the authors write, and results have varied depending on the specifics of the diet and the demographics of the study participants. "As [ketogenic diets] are often rich in fats, some negative effects could happen," according to the review.

Those negative effects could even be life-threatening, some studies suggest. A large meta-analysis published in 2018 in The Lancet found that diets that are very low in carbs, compared to balanced diets, are associated with early death.

The review also suggests, however, that the keto diet doesn't have to be hazardous to one's health. When the researchers looked at what people were eating instead of carbs, they found that eating plant-based protein and fat was linked to a decreased risk of dying.

3. There's Potential to Go Overboard

What seems to be nutritionists' biggest concern about the keto diet is that people will use it as an excuse to eat lots of cheese and bacon, but will ignore the advice to eat lots of vegetables and other plant-based foods.

In fact, a major concern of the keto diet is that it allows plenty of saturated fats and animal products, which increase risk for heart and kidney diseases as well as cancer, a June 2020 study in The American Journal of Medicine notes. That's why the researchers state that this diet is not for people who aren't meticulous about making the right food choices.

"The keto diet is not supposed to be super high in saturated fat," says Amy Goss, PhD, a registered dietitian and assistant professor of nutrition sciences at the University of Alabama at Birmingham.

"It's really supposed to be a mix of plants and some animal sources of fat — including foods like avocado, olive oil, nuts and seeds — and smaller portions, because they're so calorically dense."

Another worry is that people often embark on keto diets without the guidance of a health professional. "When the diet was designed for children with epilepsy, the idea was that it was monitored very closely," says White.

"I tell people that if they want to try keto, they should work with a nutritionist or doctor to make sure they're getting the nutrients they need and avoiding possible health risks."

Related Reading 6 Keto Diet Mistakes to Avoid at All Costs

4. Nutrient Deficiencies

White also worries about keto dieters missing out on important vitamins, minerals and other micronutrients. "For example," he says, "when you take away whole food groups — like whole grains and a large percentage of fruits and vegetables — it's a lot harder to get enough fiber."

Fiber helps regulate cholesterol levels and aids in digestion, and inadequate levels can cause constipation. For those reasons, people on a keto diet may want to consider taking a fiber supplement.

People following a keto diet should also make sure they're getting enough magnesium, potassium, and B vitamins, he adds. Making sure to eat plenty of non-starchy vegetables — like dark, leafy greens — is a good way to boost your intake of micronutrients while still following a keto-friendly meal plan.

5. Weight Regain

One of the main reasons people are interested in ketosis is because they want to lose weight and keep it off — and if that's the case, they may be disappointed with the long-term results of a keto diet, says White.

"This diet is very restrictive, and most people cannot stay on it for very long," he says. "And when they go off it and go back to normal eating, they have a rebound effect which leads them to gain back the weight."

Not only can this be frustrating, he says, but it can also lead to an unhealthy relationship — both physically and mentally — with food and dieting.