The new best-selling book “The Keto Reset Diet” says it can fix a sluggish metabolism and train your body to be a fat-burning machine. Experts are skeptical.

It isn’t just you. Dieting is an endless pursuit for many Americans.

Around 45 million Americans go on a diet each year.

And the weight eventually comes back for 33 to 66 percent of people who’ve dieted.

In the New York Times best-seller “The Keto Reset Diet: Reboot Your Metabolism in 21 Days and Burn Fat Forever,” author and keto diet enthusiast Mark Sissonwrites that “yo-yo dieting is severely destructive to your metabolism.” He claims that following a low-carb, high-fat diet will help turn you into a ‘fat-burning beast’ and stay this way for the rest of your life.”

The book explains that the three-week keto reset diet does this by reprograming your genes into a state of “metabolic efficiency” — which he considers burning fat, rather than being “dependent upon regular high-carbohydrate meals to sustain your energy, mood, or cognitive focus.”

Critics say the science doesn’t support these claims.

A person’sresting metabolic rate (RMR) is largely based on their weight, but factors like age and genetics also play a role. When someone significantly restricts calories to lose weight, their body can also enter starvation mode. Their metabolism slows down considerably to conserve energy.

Extremely low-calorie diets make it easier to regain weight after a diet is over. If someone with a slowed metabolism hits their target weight and celebrates by eating the same amount of daily calories a person with a typical RMR and of their same weight and age would eat, they could gain weight rapidly.

Case in point: contestants from the TV show “The Biggest Loser.” Contestants in the 30-week competition aimed to drop weight quickly. They ate as little as 800 calories a day and exercised for hours daily. A study of 14 contestants found that six years after the show, 13 had regained considerable weight.

More shockingly, their metabolisms hadn’t recovered. On average before the show, the group burned 2,607 calories a day. At the end of the competition, they burned 2,000 calories a day. Six years later, they only burned 1,900 calories a day.

That’s an extreme case, according toLara Dugas, PhD, a physiologist who studies metabolism at Loyola University Chicago.

“If you are significantly restricting your calories in the short term, you are going to dampen your resting metabolic rate (RMR), but studies show that once you stop restricting food, your RMR will return to the expected for your body weight,” Dugas told Healthline.

That means most people who diet regularly don’t face lastly metabolic damage. In a study of postmenopausal women with a history of chronic dieting, researchers found the same thing: Yo-yo dieting doesn’t hurt weight loss or permanently damage the metabolism.

Also, a damaged metabolism may not be the problem when a person regains some weight. People often feel like their body fights to maintain a certain set weight. That’s exactly what it’s doing.

“The body has homeostatic mechanisms to try to preserve what’s in place. Otherwise, the weather changes, or you go on a trip — your body would be fluctuating all over the place,” explained Dr. Bruce Lee, the executive director of the Global Obesity Prevention Center at Johns Hopkins Bloomberg School of Public Health.

While science says your metabolism probably doesn’t need resetting, some studies show that low-carb diets like the keto diet can help people lose weight more quickly.

Whether the keto diet helps people keep the weight off isn’t known yet.

What happens many times — like with the similar Atkins diet — is that a diet becomes a fad, but then people start to regain the weight, Lee told Healthline. The fad diet passes because people figure out its benefits are short term.

“The short-term reaction doesn’t mean you’re resetting your metabolism for the longer term,” Lee pointed out.

Dr. Joe Feuerstein, an associate professor of clinical medicine at Columbia University and director of integrative medicine at Stamford Hospital, treats thousands of patients for weight loss a year through his consultation service. He’s used the ketogenic diet with several patients.

“I have found that the ketogenic diet works very well in clinical practice. I have one patient who lost nearly 100 pounds using this plan. The keto diet isn’t better for all things — it is just quite effective for weight loss,” he clarified.

Feuerstein doesn’t recommend using the diet over the long term.

In “The Keto Reset Diet,” Sisson aims for “a reprograming of your genes and a long-term recalibration of your appetite and metabolic hormones in the direction of fat- and ketone-burning and away from carbohydrate dependency.”

According to proponents of the keto diet, it’s effective because restricting carbs causes the body to seek energy in stored fat, or ketone bodies, which it breaks down in a process called ketosis. The body then relies on ketones for energy until you start eating carbs again.

But, according to a post by Will Little for KetoSchool, during the first three weeks of ketosis, the body rapidly adapts, and “all the other tissues in the body use a decreasing amount of ketones for energy, eventually using mostly fat… So, contrary to popular opinion, shortly into the diet you are not producing or burning very many ketone bodies.”

Dugas doesn’t see much of an advantage to burning carbs versus fat for energy.

“Our bodies are so flexible, and our brains tightly regulate our blood glucose. Your body will use what’s available,” she explained. “You can get your calories from carbs, fat, or protein — all of them are broken down to maintain our blood sugar.”

A two-year study of different weight loss strategies found that in the long run, people eating diets with various proportions of macronutrients catch up to the keto group.

That’s likely because, ultimately, the keto diet works the same way as other diets: You burn more calories than you consume.

The main difference is that fat and protein, compared to carbs, makes people feel full for longer.

“Excluding food groups is a mechanism to get you to eat less food,” Dugas explained. “When you cut a major food group from your diet, you’re going to eat less. Research studies indicate that some people do better on a low-carb diet, others on a low-fat diet.”

“The macronutrient breakdown is less important than the fact that people are sticking to the diet,” Dugas explained. “It’s about finding the right fit for yourself.”

Pick a diet that you can stick to and “aim for no more than one to two pounds of weight loss a week,” Lee recommended. When you drastically change the conditions in your body, it can shock your metabolism or mood, he explained.

“As a physiologist, I’m not a fan of the keto diet, but I do believe that our diets today have too much sugar, and that we can really benefit from eating a more moderate contribution from carbohydrates,” Dugas said.

We need more research to know how the keto diet effects weight loss long term.

However, Lee pointed out, there are studies that show the consistent factors behind proven, healthy diets are moderation and variability.

It seems like you may not have to give up carbs to reset your metabolism or lose weight after all.