Consuming cauldrons of cabbage soup or reducing their carnivorous leanings weren’t likely the top health choices for Socrates, Plato and other Greek philosophers—they preferred intermittent fasting. It wasn’t considered a fad diet but a lifestyle, a practice described 3,000 years ago as “the physician within.”

Intermittent fasting—a diet, in general terms, focused not on what’s eaten but when—is often grouped with other weight-loss fads. It’s usually practiced by limiting eating to a specific number of hours each day, which may range from a 4- to 12-hour time window within a 24-hour period. When the body depletes its sugars, fat is burned.

Intermittent fasting is as controversial as any diet. Part of spiritual healing and purification in many faiths, it can be practiced successfully with medical supervision, or unwisely as a quick-fix diet.

Glenn Burkett, a longtime dietitian and wellness expert in Naples, doesn’t ascribe to its practices—for any reason.

“People are going to get into a program where they say, ‘I am only going to eat between 12 and 8,’” says Burkett, who owns a vitamin company and is a former host of a wellness television program in Southwest Florida. “They are going to become even more nutrient deficient. What they will choose to eat between 12 and 8 will be the wrong nutritional choices.

“Therefore, they are going to have heart issues and other problems—brain, liver, kidney, joints. I have studied the pros and cons, and I would not recommend it to someone because they are still focusing on weight loss and not nutrition.”

Approaching 100 years ago, intermittent fasting reached one of its modern-day popularity peaks via the beliefs of Herbert McGolfin Shelton, a Texas-based naturopath. He was an alternative medicine advocate who supported rawism and fasting. Shelton in 1928 self-published the first of seven books, An Introduction to Natural Hygiene. Shelton also began publishing Hygienic Review magazine, which gained a substantial following during its four-decade tenure.

In 1942, Shelton was charged with negligent homicide and “treating and offering to treat a human being without a state medical license” for starving a patient to death. The case was never tried, and the charges were dropped.

Six years later, Shelton founded the American Natural Hygiene Society, with intermittent fasting among its many principles. It was renamed the National Health Association in 1998.

Despite his prominence, Shelton, who died in 1985, also was repeatedly discredited. He was arrested, jailed and fined multiple times for practicing medicine without a license. In 1932, he served 30 days at Rikers Island, the infamous prison in New York.

After another patient died at one of his schools in 1978, Shelton lost a two-year battle against a lawsuit for negligence. He was bankrupted and forced to close his schools.

Intermittent fasting remains simultaneously praised and criticized, en vogue and dismissed. It’s been prescribed to “break the habits of gluttony.” It also was recently severely scrutinized by the American Heart Association. The Dallas-based national nonprofit heart disease and stroke prevention organization announced in March the results of a 20,000-person study. It detailed that people who limited their eating across fewer than eight hours per day, a time-restricted eating plan, were more likely to die from cardiovascular disease compared to people who ate across 12-16 hours per day. The AHA also believes that there is no good evidence of heart health benefits from intermittent fasting.

Several other prominent national health organizations, including the American Diabetes Association in Arlington, Virginia, and the National Institute on Aging in Gaithersburg, Maryland, also have reservations about the benefits of intermittent fasting.

The ADA found “limited evidence about the safety and effects of intermittent fasting on Type 1 diabetes.” The NIA acknowledges intermittent fasting shows weight loss success in several studies on obese or overweight individuals. However, it does not recommend intermittent fasting for nonoverweight individuals because of uncertainties about its effectiveness and safety, especially for older adults.

Mark P. Mattson, an adjunct professor of neuroscience at Johns Hopkins School of Medicine in Baltimore, has studied intermittent fasting for three decades. He defines what happens to the body after several hours as its stored sugars are depleted and fat burning begins as a “metabolic switching.”

“Intermittent fasting contrasts with the normal eating pattern for most Americans, who eat throughout their waking hours,” Mattson says. “If someone is eating three meals a day, plus snacks, and they’re not exercising, then every time they eat, they’re running on those calories and not burning their fat stores.”

Another popularity surge occurred in 2012 with the broadcast of the BBC documentary “Eat, Fast and Live Longer.” The trend grew quickly, and in 2018 intermittent fasting was the most popular diet in the United States, according to a survey by the International Food Information Council in Washington, D.C.

“People are grasping,” says Burkett. “What is the next thing to grasp onto? They all choose the easiest way out. If there was a pill that worked, everyone would be on the pill. It doesn’t work, and that’s what we found out over the years.”