What Nutrition Experts Really Think About the Keto Diet

Find out what subtleties of the trendy diet may be cause for concern.

Controversies about the keto diet

People seem to be relying on the keto diet's popularity, but not all nutritionists support it. We spoke with 10 nutritionists from across America to get their thoughts on this high-fat, moderate-protein, and very low-carb diet.

It excludes most fruits.

"I'm not a fan of the keto diet because it excludes most fruits, which are sources of many micro- and macronutrients, as well as vitamins," says Jonathan Valdez, owner of Genki Nutrition and spokesperson for the New York State Academy of Nutrition and Dietetics. "Nutrients found primarily in fruits include magnesium, potassium, folate, and vitamins A, E, and C. Research has established a direct link between adequate fruit consumption and a reduced risk of cardiovascular disease, cancer, obesity, osteoporosis, hypertension, depression, respiratory disease, and gastrointestinal disease. While you're on the keto diet, your risk of heart disease and stroke increases. Who needs that?"

She is too strict

"To enter and maintain true ketosis, people must count carbohydrates, abstain from many food categories, monitor protein intake, and even limit their choices to specific foods within approved categories," says Malina Malkani, MS, RD, RD, spokesperson for the American Academy of Nutrition and Dietetics, and founder of Wholitarian Lifestyle. "For many, following such strict rules over a long period of time can be quite challenging, especially when factoring in social life (entertainment, work, social gatherings, etc.). We have strong evidence that the keto diet is effective in the short term, but there is less data on its health effects and long-term effectiveness. Without a long-term solution, the likelihood of returning to previous eating habits and regaining weight increases."

She only allows full-fat dairy products.

"I recommend consuming all dairy products, regardless of fat content," says Kate Ayoub, RD, RD, RD, and associate professor of pediatrics at Albert Einstein College of Medicine. "Whether it's milk, cheese, or yogurt, the protein, vitamins, and minerals are the same; these foods are very nutrient-dense. I know that full-fat dairy products have no advantage over low-fat or fat-free ones. There's no reason to avoid either." Ayoub explains that an inverse relationship has been established between milk and dairy consumption and obesity. But we're talking about full-fat and low-fat products—high-fat dairy products will contain more calories, which you'll need to cut back on elsewhere to prevent weight gain.

It encourages the consumption of unhealthy fats.

"I'm concerned that the consumption of fats like palm oil, coconut oil, cocoa butter, butter, and lard is encouraged in large quantities," says Carolyn O'Neill, MS, RD, a registered dietitian nutritionist. "These foods contain unhealthy saturated fats, which raise levels of 'bad' cholesterol (LDL), a risk factor for heart disease."

This is a low fiber diet.

Elizabeth Ward, MS, a registered dietitian with Better Is the New Perfect, is concerned about the long-term impact of inadequate fiber intake on the keto diet. "Research shows that higher-fiber diets are beneficial in reducing the risk of chronic diseases such as cardiovascular disease, type 2 diabetes, and diverticulitis," Ward explains. "Furthermore, consuming fiber from fruits, vegetables, and whole grains enriches the gut microbiome, promoting health."

You may experience keto flu.

Switching to a severely restricted carbohydrate intake can be a dramatic change for your body, and it may take some time to adapt. Kristen Smith, MS, RD, RD, a spokesperson for the Academy of Nutrition and Dietetics, explains, "For a few days at the beginning of the keto diet, some people may experience a combination of symptoms commonly referred to as the 'keto flu,' which can include nausea, headache, constipation, abdominal pain, and weakness. Because of these side effects when transitioning to a new diet, many people give up and return to their previous eating habits. It's important to stay hydrated and limit physical activity when transitioning to a keto diet." Not everyone will experience these symptoms when starting a keto diet, but anyone changing their eating habits should be aware of them.

It's not targeted at athletes correctly.

The keto diet is often targeted at athletes and active individuals, promising to improve their performance or body composition. "You'll see compelling reviews and a negative portrayal of carbohydrates. But athletes need carbohydrates to perform well," says Marisa Michael, MS, RD, RD, owner of Real Nutrition, LLC. "In studies of low-carb diets, athletes didn't perform better. They either performed worse than usual or the same, and their subjective ratings of physical performance were higher than when they ate enough carbohydrates. This means they could perform the same exercises, but they felt much worse during the workout. Additionally, athletes on the keto diet weren't able to reach high intensities." Your body uses carbohydrates during high-intensity exercise, such as intense bursts of speed, jumping, or any fast, intense movement. A keto diet can hinder your ability to achieve that winning sprint.

It contains a lot of coconut oil.

Coconut oil contains stearic acid, a saturated fatty acid that doesn't affect blood cholesterol levels, but unfortunately, the 60 percent saturated fatty acids in coconut oil significantly raise cholesterol levels, according to Joan Salge Blake, RD, a registered dietitian nutritionist, professor of nutrition at Boston University, and host of the SpotOn! podcast about nutrition and health. However, as Blake says, there's good news: "Coconut oil is an excellent skin moisturizer and hair conditioner. In other words, coconut oil is better applied topically than internally."

You can develop an unhealthy relationship with food.

"As a mother, I want to continually promote healthy relationships with food and healthy habits," says Jennifer Hunt, a registered dietitian and nutritionist with Healthy Inspiration. "Some adults or children may have medical reasons for following the keto diet, but I'm concerned about the mental image a child will have of their parents following this diet for weight loss. Because it severely limits fruits and vegetables, which contain beneficial vitamins, minerals, antioxidants, and fiber, I don't consider keto a healthy diet for families."

It is unsustainable in the long term.

"Strict diets that restrict all food categories, like keto, force people to choose: all or nothing," says Zoe Griffiths, a registered dietitian and CEO of Nutrition at WW. "Research shows that people achieve better results when a diet has structure and (at the same time) flexibility and applicability to everyday life, rather than just strict rules." Griffiths suggests a test for the diet's applicability in everyday life: ask yourself if you can live with it long-term. For example, can you eat your favorite foods and enjoy spending time with family and friends?" A healthy approach to eating results in a balanced diet with a flexible structure that fits easily into your life and helps you develop healthy habits," explains Griffiths.