The ketogenic diet—also known as the keto diet—has gained traction in the past decade or so due to its alleged positive effect on weight management.

The diet has been popular among celebrities including Gwyneth Paltrow. The Hollywood actress previously faced backlash from health experts who said there was a lack of evidence to support her suggested “healing” remedies, which included a keto and plant-based diet.

But what are the pros and cons of a ketogenic diet and is it safe? Newsweek spoke to experts to find out.

What Is a Keto Diet?

A ketogenic diet is defined as a diet high in fat and low in carbohydrates (sugars), which causes the body to break down fat into molecules known as ketones.

“Ketones circulate in the blood and become the main source of energy for many cells in the body,” the U.S. National Institutes of Health (NIH) explains.

The nutritional breakdown of a keto diet includes the following (according to the book Ketogenic Diet by Wajeed Masood, Pavan Annamaraju and Kalyan R. Uppaluri, shared at the NIH website):

  • Fat: Around 55 to 60 percent of the diet.
  • Protein: Around 30 to 35 percent.
  • Carbohydrates: Around 5 to 10 percent (Note: For a 2,000 kcal per day diet, carbohydrate intake would amount up to 20 to 50 g per day).

Speaking to Newsweek, Dr. Kevin Hall, senior investigator at the NIH’s National Institute of Diabetes and Digestive and Kidney Diseases, noted it’s important to clarify that there are several versions of the “keto diet” and the health effects of these various types may be quite different.

Some people follow a plant-based keto diet with no animal products that entails consuming lots of fiber from non-starchy vegetables but very little starch or sugar, while other keto diets include a lot of animal products but very few non-starchy vegetables.

Some versions of the diet contain less red meat and processed meat, less saturated fat as well as more fish and plant-based fats that have lower levels of saturated fat.

But the commonality of all these keto diets is that “they are all sufficiently low in dietary carbohydrates that the body increases its production of ketones, resulting in elevated blood levels of ketones,” Hall said.

Ketones are substances produced by your body if your cells don’t get enough blood sugar (glucose). Glucose is the main energy source for your body.

Grilled chicken and vegetables on a table.
A bowl of grilled chicken meat and fresh vegetable salad of tomato, avocado, lettuce and spinach.
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What Happens to the Body on a Keto Diet?

Due to there being a low level of carbohydrates available for energy, your body breaks down fat into ketones, which become the primary source of fuel for the body. Ketones provide energy for the heart, kidneys and other muscles such as the brain.

A ketogenic diet is essentially considered “a partial fast,” explains the Academy of Nutrition and Dietetics.

“During a total fast or starvation state, the body has no source of energy. Thus, it breaks down lean muscle mass for fuel. With the keto diet, the ketones provide an alternative source of energy. Unlike a full fast, the keto diet helps to maintain lean muscle mass,” the academy says.

Pros of a Keto Diet

1. Helps Treat Epilepsy, Reduces Seizures

Speaking to Newsweek, Roxana Ehsani, registered dietitian nutritionist and spokesperson for the Academy of Nutrition and Dietetics, said: “The ketogenic diet was originally created and to be followed by people suffering from epilepsy. It has shown to be effective at reducing and preventing seizures.”

A keto diet helps reduce seizures in pediatric patients with epilepsy, the ASN’s Psota added.

Dr. Russel Wilder of the Mayo Clinic was the first to coin the term “ketogenic diet,” using the diet to treat epilepsy in 1921.

For nearly a decade, the ketogenic diet was considered a “therapeutic diet” for pediatric epilepsy and was widely used until the introduction of antiepileptic agents, which led to the decline of the diet’s popularity, the Ketogenic Diet book says.

2. Weight Loss

According to the Ketogenic Diet: “The resurgence of the ketogenic diet as a rapid weight loss formula is a relatively new concept that has shown to be quite effective, at least in the short run.”

Speaking to Newsweek, Dr. Tricia Psota, a registered dietitian nutritionist and member of the American Society for Nutrition (ASN), said: “A keto diet elicits weight loss in most people, and some people report being less hungry while they are in ketosis.”

The NIH’s Hall noted: “It’s also important to consider a diet’s benefits and risks in the context of the comparison diet.”

For example, compared to a typical Western diet that’s high in ultra-processed foods, which contains lots of sugar and fat but are low in fiber, a ketogenic diet can result in weight loss, he explained.

3. Blood Sugar Control

According to the ASN’s Psota, research suggests a keto diet may present potential benefits related to blood glucose (sugar) control, such as improving insulin sensitivity.

The NIH’s Hall said a keto diet may lower glucose and insulin levels in the blood, which may be beneficial for people with type 2 diabetes or pre-diabetes.

When your body’s blood sugar levels rise, it releases insulin, which lets the glucose into your body’s cells to be used as energy.

Diabetes patients either don’t produce enough insulin or their bodies can’t utilize the insulin as well as it should and too much blood sugar stays in their bloodstream.

When you’re on a keto diet, the body is deprived of carbohydrates and insulin secretion is significantly reduced.

“When glucose availability drops further, the endogenous production of glucose is not able to keep up with the needs of the body” and a process known as ketogenesis begins, according to the Ketogenic Diet book.

Ketogenesis provides the body with an alternate source of energy in the form of ketone bodies, replacing glucose as a primary source of energy.

“During ketogenesis due to low blood glucose feedback, the stimulus for insulin secretion is also low, which sharply reduces the stimulus for fat and glucose storage,” the book explains.

According to the Academy of Nutrition and Dietetics, research findings on the benefits of the keto diet for health conditions including obesity and diabetes are “extremely limited.”

A diabetic person checking blood sugar levels.
A diabetic person checking blood sugar levels.
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Cons of a Keto Diet

4. Flu-Like Symptoms

Among the short term health risks of keto diets are flu-like symptoms, referred to as the “keto flu.” These may include upset stomach, headache, fatigue and dizzy spells, while some have also reported trouble sleeping, according to the Academy of Nutrition and Dietetics.

5. Nutrient Deficiency

The keto diet requires either “cutting out or drastically reducing” many nutrient-dense foods, such as fruits, vegetables, and grains. This can lead to micronutrient (i.e. vitamin and mineral) deficiencies over time, said the ASN’s Psota.

Ehsani from the Academy of Nutrition and Dietetics said the diet “eliminates nutrient dense foods essential to your overall health and well-being.”

Keto diets limit your intake of grains, starchy veggies, beans, lentils, fruits, vegetables and dairy products. All of these foods are loaded with essential vitamins, minerals, antioxidants and dietary fiber, the registered dietitian nutritionist said.

The ASN’s Psota said one way to avoid these “micronutrient deficiencies” while on a keto diet would be to take a multivitamin supplement. “However, supplements do not provide the fiber that whole foods like fruits, vegetables, whole grains, and beans contain,” she warned.

6. Constipation

The low intake of dietary fiber may cause constipation, Ehsani said. Those on a keto diet are often required to take a fiber supplement to maintain regular bowel movement.

Bowls of fresh fruit.
Bowls of fresh fruit on a table. Keto dieters have a low intake of fiber, which you can get from fruit.
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7. High Cholesterol

The NIH’s Hall said another concern is that some people may experience “a substantial increase in blood LDL cholesterol and Apolipoprotein B [a protein that forms the backbone of LDL]” due to the high fat content of keto diets.

These concerns may be mitigated by decreasing the saturated fat content of the diet and replacing it with sources of monounsaturated fats, but more research is needed on this topic, he said.

According to Hall, there are also medical interventions that can help decrease blood LDL cholesterol levels and Apolipoprotein B to consider, “but the efficacy of such medications also needs more research.”

A doctor checking cholesterol level test results.
A doctor checking cholesterol level test results.
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8. Heart Disease

The potential for high levels of LDL cholesterol (“bad” cholesterol) raises the risk of heart disease in keto dieters, the ASN’s Psota said.

According to the Academy of Nutrition and Dietetics, a “considerable body of research” has shown diets high in saturated fat may increase the risk for heart disease and other chronic health problems.

“The risk that keto dieters might be taking with regards to their long-term cardiovascular health has not been fully studied,” the academy said.

9. Kidney Stones and Other Risks

Kidney stones and liver disease are among the other long-term health risks of a keto diet. The diet is also not recommended for those who suffer from the following conditions, according to the Academy of Nutrition and Dietetics:

  • Pancreatic disease
  • Liver conditions
  • Thyroid problems
  • Eating disorders or a history of eating disorders
  • Gallbladder disease or those who have had their gallbladders removed

10. It’s Too Restrictive

Ehsani from the Academy of Nutrition and Dietetics said the keto diet is by nature very restrictive and therefore not sustainable. “Most people have a very hard time following such a rigid diet that cuts out major food groups,” she said.

11. It’s a Temporary Solution

Ehsani explained: “The keto diet is a fad diet, meaning it works until it doesn’t. You may experience rapid weight loss, but it’s not a healthy solution towards attaining weight loss.

“If you’re looking for a healthy way to lose weight, instead work with a registered dietitian nutritionist (RDN),” who can create a personalized plan based on your unique health and nutrition needs and goals, she added.

A spread of proteins including fish.
A spread of various sources of protein, including fish, eggs and nuts.
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