Intermittent fasting has recently become popular as a weight-loss tool, thanks to the increased attention brought to the practice by best-selling diet books such as "The Fast Diet" by journalist Michael J. Mosley. And while fasting has been around for centuries, health experts are divided on its effectiveness as a tool for permanent weight loss.
"Small studies have suggested that regular intermittent fasting is effective at promoting weight loss and at lowering the body's resistance to insulin," according to a Sept. 24 U.S. News & World Report article.
In the trendy "Fast Diet," dieters are encouraged to eat what they want, as much as they want, for five days of the week, alternated by two days of a very-low-calorie diet (500 to 600 calories a day). Proponents claim the 5:2 diet has enabled thousands of people to lose weight effortlessly without feeling deprived or counting calories on a daily basis.
Proponents say the beauty of this type of intermittent fasting is the freedom it gives people to eat what they want most days of the week, while only restricting themselves for two days. Actor Hugh Jackman did a different type of intermittent fasting to rapidly lose and then gain weight for his roles in "Les Misérables" and "The Wolverine."
And while some diet experts say intermittent fasting can dramatically improve body-fat composition and overall health, others insist fasting of any type is a recipe for binge-eating and rebound weight gain.
"Fasting can cause people to think too much about food, and possibly overeat on the days when they're allowed to eat freely," Heather Mangieri, a rep for the American Dietetic Association, told LiveScience.
"If people eat lots of cake and cookies on their 'normal eating' days and don't think about their overall diet, it can potentially lead to nutrient deficiencies and poor eating habits."
While fasting (whether intermittent or longer-term) will result in weight loss because of the dramatic drop in calories consumed, experts say depriving oneself results only in temporary weight loss, and fuels overeating, obsessing about food and weight regain.
Fitness maven Tony Horton, creator of the best-selling workout regimen, P90X, isn't sold on the merits of any kind of fasting. He dismisses the notion that the body needs to fast in order to "cleanse itself" of toxins and impurities because that's what our internal organs and immune systems are for.
"Unless you've got major social issues and you're in prison, I recommend that you don't fast," Horton said on a SoundCloud broadcast. "That's just me. I'm gonna get all kinds of mail about it saying, 'Tony, fasting is good because it helps cleanse the body.' "
Horton, 55, who attributes his age-defying physique to a healthy diet, yoga and P90X workouts, says fasting doesn't make sense to him because the body needs nourishment from food to function properly. He pointed out that most people would never even dream of not feeding their dog for a day or two, so why would they starve themselves and expect optimal well-being?
"I can't imagine not putting nutrition and vitamins and fiber and things in your body that helps your body sleep, function and work out," he said. "You need fuel so your body and your brain can work properly. Think about it: How well does your car run when it's on fumes? Not too well."