Experts say the diet can be difficult to stick with in the long run.

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Halle Berry talked about her diet and fitness regimen on Instagram. Getty Images

Can giving yourself cheat days help you stay on the keto diet, like actress Halle Berry swears by?

On her Friday #PHITTalks Instagram Stories, Berry said cheating is important, and falling off the wagon is okay, as long as you “jump right back on” after indulging.

“Sometimes you just have to eat what you want. You have to satisfy that craving, and that’s how you can come back better and stronger,” she said. Her trainer, Peter Lee Thomas, agreed that rewarding yourself is important.

But is cheating a good idea on a diet as strict as keto, which relies on putting your body into a different metabolic state?

Experts aren’t sure due to the lack of research on long-term keto dieting.

A small study published in March 2019 in the journal Nutrientsfound even the slightest cheating can cause blood vessel damage. Nine males who were on a keto diet for seven days were given a glucose drink and their response was evaluated.

“Even though these were otherwise healthy young males, when we looked at their blood vessel health after consuming the glucose drink, the results looked like they might have come from someone with poor cardiovascular health,” Jonathan Little, PhD, associate professor in the School of Health and Exercise Sciences at the University of British Columbia and study senior author, said in a statement. “It was somewhat alarming.”

“My concern is that many of the people going on a keto diet — whether it’s to lose weight, to treat type 2 diabetes, or some other health reason — may be undoing some of the positive impacts on their blood vessels if they suddenly blast them with glucose,” Little said. “Especially if these people are at a higher risk for cardiovascular disease in the first place.”

When following a keto diet, a person must deprive the body of carbohydrates and glucose for energy so it instead burns stored fats. During ketosis, the body uses ketone bodies in the blood as opposed to blood glucose. The diet has had proven health benefits for people with certain conditions such as epilepsy.

Diana Lehner-Gulotta, a registered dietitian in the neurology department at the University of Virginia Health System, treats people with medical conditions that have been shown to improve using the keto diet.

“Studies looking at this diet solely for weight loss do seem to indicate that it’s helpful. However, there aren’t any studies about what happens when you come off the diet or examining the side effects of the diet,” she told Healthline.

In her experience and based on research she has done in people with multiple sclerosis, the diet is difficult to stick with in the long run. Also, people gain back a lot of weight if they no longer follow the diet.

People who stick to the diet well are at increased risk for nutritional deficiencies, high cholesterol and triglyceride levels, osteoporosis, kidney stones, and acidosis, she said.

“These side effects are a big concern about the mainstream keto craze, so I don’t endorse anyone following this diet without medical supervision,” Lehner-Gulotta said.

Sharon Palmer, RDN, a nutritionist from California, noted that it is hard to achieve ketosis to begin with.

So on cheat days, a person would definitely fall short of achieving ketosis. This may affect the body differently than if you cheated on another diet. Other diets may be about eating a lower amount of calories or restricting a certain food group, but cheating may not affect the way the body operates as it does on the keto diet.

“It’s not clear if ketosis is a healthful state to be in for average, disease-free people,” Palmer said.

“Weight loss and healthy eating are two different things,” she explained. “You can lose weight with a tapeworm, but that’s not a healthful endeavor. There are far healthier ways to lose weight than a keto diet.”

Palmer pointed out that it’s best to follow a diet that can help you be healthy in the long term, not one that results in rapid weight loss that can lead to yo-yoing weight.

Palmer notes that for some people cheating is the only way they can “stick” to the keto diet.

That’s because keto forces people to sacrifice healthy foods such as fruits, vegetables, and whole grains that are linked with lower inflammation and long-term health.

Keto also has an impact on the social facets of eating.

“With a keto diet, it’s hard to go out to eat or enjoy food with family and friends,” she said. Food traditions are treasured human interactions we hand down to the next generation. Sharing family meals together is good for children and families, too.

Palmer believes the concept of cheat days isn’t a positive health message because it adds guilt to going off a diet.

People can resort to binges when they fall “off their diet wagon,” and cheating reinforces that behavior. Research has pointed to health risks with yo-yo dieting, she added.

“It’s much healthier physically and mentally to eat a diet that’s sustainable, one you can follow as part of a healthful eating pattern long term,” she told Healthline.