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Should you really be fasting? 3 diet myths get busted

 / Updated  / Source: TODAY

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The trend of feast-or-fast as an eating habit promises you can eat what you want most days.

The idea is you have to cut calories and watch what you eat, but not all the time. You can eat virtually anything you want on some days, so long as you drastically restrict your calories on others.

The two most popular forms of intermittent fasting are the 5:2 diet — which allows you to eat what you want five days of the week, but just 500 hundred calories the other two — and an every-other-day diet, where you feast one day, but limit to 500 calories the next.

The basic concept calls for eating your normal caloric intake on the “feast” days (which would be somewhere around 2,000 calories depending on your weight, gender and activity level), then 25 percent of that on the “fast” days. The calories on your fast day can be spread out or eaten in one meal, but it’s recommended to opt for high protein and high fiber foods since those take longer to digest and will help you feel fuller, longer.

But is fasting really a good idea? Dr. Natalie Azar busts some common myths about feast-and-fast calorie counting.

Myth 1: Human beings aren’t built to fast.

Not true. Eating three meals a day might be the norm but some say it’s not what we’re designed to do. The theory is evolution prepared us to fast.

After fasting for 12 to 16 hours, there’s a shift in energy metabolism, and fats become the primary source of fuel, according to Mark Mattson, Ph.D., chief of the Laboratory of Neurosciences at the National Institute on Aging in Baltimore who has been studying the effects of intermittent fasting—in animal models and humans—for many years. That accounts for intermittent fasting’s popularity as a weight-loss plan, but also contributes to other health benefits, such as reduced cholesterol, lower blood pressure, improved insulin resistance.

Myth 2: Intermittent fasting allows you to eat whatever you want.

Not true. It might sound like a dream come true for dieters tired of calorie counting. But it’s not an excuse to gorge on junk food.

“You still have to pick mostly healthy, whole foods in order to affect weight loss,” says Alissa Rumsey, R.D. and spokeswoman for the Academy of Nutrition and Dietetics. “And on the fasting days you may experience mood swings, loss of energy and hunger pains.”

Myth 3: Cutting calories may help you live longer.

Maybe!

“Fasting produces oxidative stress in the body, and that stress triggers protective pathways,” says Michael Guo, a researcher at the University of Florida. “These pathways then help protect the body from further stress and extend lifespan.”

Levels of a protective protein called SIRT 3, which is activated by oxidative stress and has been shown in mice to increase lifespan, increased in subjects after they’d been fasting. Guo is heading research on a study exploring calorie restriction and longevity, which will appear in the journal Rejuvenation Research.

--TODAY contributor Sally Wadyka contributed to this report

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