CNN  — 

America is in the midst of a keto craze. The trendy diet – which bans carbs to make your body burn fat for fuel – has kicked Weight Watchers’ derrière on the stock market, captured the endorsement of celebrities such as Kourtney Kardashian and Halle Berry, and deluged the internet with recipes and copious social media chatter about pounds lost.

Now the popular diet even has a day named after it. The Vitamin Shoppe, which wants to sell you a ton of keto-based products, has named the first Sunday of this new decade “National Keto Day.”

“What on Earth justifies granting a day to memorialize a fad diet?” said Dr. David Katz, founding director of the Yale University Prevention Research Center. “The grapefruit diet surely warrants its own day too!”

Katz is no fan of keto, or any other diet that restricts entire food groups, calling them unhealthy and unsustainable.

“Losing weight fast by using a severely restricted, silly, unbalanced diet inevitably leads to even faster weight regain,” said Katz, who is the president of the True Health Initiative, a non-profit organization dedicated to health promotion and disease prevention.

“Absent ketosis, keto is just a false label for some kind of diet that presumably restricts added sugar and refined carbohydrate – which, frankly, any good diet does,” Katz said.

Katz’s low opinion of keto is echoed by many nutritional specialists across the country. Katz joined 24 other top names in the field to rank 35 popular weight loss programs for 2020 recently put out by U.S. News and World Report.

The popular keto diet flunked, coming in next to last – which it has done for several years now. Only the highly restrictive protein-only Dukan Diet ranks lower.

“Most health professionals are concerned that the degree of carb restriction requires someone to cut out many of the foods that have been consistently recommended as being healthy: fruits, beans/legumes and whole intact grains,” said Stanford professor Christopher Gardner, who conducts research on low-carb diets at Stanford Prevention Research Center.

With such negative reviews, just how did keto capture such a faithful following? Experts say it’s because its legions of fans are focusing on the short-term benefits of fast weight loss, without factoring in possible long-term risks.

What is keto?

Keto is short for ketosis, a metabolic state that occurs when your liver begins to use stored fat to produce ketones for energy. The liver is programmed to do that when your body loses access to its preferred fuel – carbohydrates – and thinks it’s starving.

The diet has actually been around since the 1920s, when a doctor stumbled on it as a way of controlling seizures in children with epilepsy who didn’t respond to other treatment methods.