Intermittent Fasting: Does It Work?

Ask Healthy Living: Should I Try Intermittent Fasting?

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So, what's the deal with intermittent fasting? Does it work and is it safe?

-- Allie

We've been getting some version of this question quite a bit: Does this new trend in intermittent fasting -- which entails drastically restricting calories on one or two days per week and then eating normally on others -- actually lead to sustained weight loss and better health?

One reason intermittent fasting has received so much attention lately is because of books like Dr. Michael Mosley's "The Fast Diet" and Dr. Caroline Apovian's "The Overnight Diet." These books tout scientific research that shows how calorie restriction from partial fasts could help maintain a healthy weight. For Mosley, a personal tipping point was the impetus to find a useful diet.

"My start point was: Ugh, my blood sugar is terrible, I’m basically diabetic, [I have] high cholesterol. I’m a bit overweigtht. What am i going to do about it?" he tells HuffPost Healthy Living. "I started off by looking at calorie restriction. And I saw that that’s the only thing that’s ever been found to extend life. The problem is, it just is impossible to do -- I cannot imagine myself doing it. I went from that to look at more four-day fasts and, subsequently, fewer day fasts -- and that seemed to work."

In total, Mosley reports losing 19 pounds of fat, restoring healthy cholesterol levels and returning his fasting glucose (a measure of pre-diabetes) to normal.

"Any time you lose weight, you see improvements in glucose metabolism," says Scott Isaacs, M.D., author of "Hormonal Balance" and a clinical instructor of medicine at Emory School of Medicine. "And anytime you restrict calories, you get weight loss. But if you do something unsustaniable you get fatigue after a while and ultimately gain the weight back."

The problem with that? Regained weight following a very restricted diet is typically comprised of fat, whereas lost weight from the diet is a combination of fat and lean tissues. What's more, weight gain might follow a different pattern after such a diet. Extreme calorie restriction in which the body no longer is fueled by sugars, but is instead fueled by fat reserves (a process known as ketosis) can lead to both weight loss and appetite suppression.

"During a fast, a person can go into starvation ketosis, which reduces appetite. They won't be hungry because of the ketones -- a byproduct of fat -- that masks hunger. But as soon as they do something where they are no longer ketotic, there's a rebound appetite, which can be hard to control," Isaacs says.

That contrasts with the experiences of many 'The Fast Diet' devotees (it's a bestseller in the U.K.) who have lost weight on the program -- and some of the physicians who think it may be worth a shot.

"The first question you want to ask with a diet is: Is this dangerous?" says Dr. Aaron Cypess, assistant professor of medicine at Harvard and staff physician at Joslin Diabetes Center. "And the second question is: Can you do this for more than a few months? It seems to me that it is not dangerous and that for some people, it may be easier than a global calorie restriction."

That said, fasting can be considered dangerous for those with underlying conditions. In her question to Ask Healthy Living, Allie went on to specify her concerns:

I've heard a lot lately about various kinds intermittent fasting, and I am interested in trying it. However, I am prone to hypoglycemia, and we're not just talking about the "hangries" (hungry+angry): we're talking migraines, confusion, inability to focus, etc. Not eating breakfast can seriously impact my work, and I do not get days off right now. Is there a safe version of this regime that I can try?

In this context, a fasting diet would be inappropriate, according to Cypess, who says that those who take certain medications, such as beta blockers or diabetes medications, should also not fast.

So does it work? Possibly. "It’s an emerging area -- let’s see how things turn out. This is early days and the people who are interested in it and have looked into it are all kind of convinced there’s something there and the question is: How a big a something is it?" Mosley told HuffPost Healthy Living during an earlier interview.

Should you check with a doctor before starting? Definitely.

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Should I Try Intermittent Fasting?

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