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VERIFY: Is fasting good for you?

Fasting diets have become a popular choice among people looking to shed a few pounds.

MINNEAPOLIS - Fasting has been around for centuries, often as a religious custom, but it's now become the buzzword behind several of the latest diet trends.

Intermittent Fasting is the umbrella term for a variety of diets that involve fasting. Alternate-day fasting is one version, where a person eats a normal amount of calories one day, and then doesn't eat, or sharply limits their calories the next day. The 5:2 diet is a variation on alternate-day fasting, where a person eats normally five days of the week, then limits calories the other two (often to 500 calories or less). There's also the Warrior Diet, which involves eating only in a scheduled window every day, like 8 hours in the afternoon and evening, followed by 16 hours of fasting.

"Our body is always either in a fasted state, or in a fed state," said Paul Kriegler, Registered Dietician and Program Manager for Nutritional Products at Life Time. "People get attracted to kind of the trendiness of fasting, but they don't realize that if you're living a healthy lifestyle, you're probably spending 12-16 hours every day in a fasted state."

"I think there's a strong belief that if I fast, I'll lose weight, and it may work in the short term," said Renee Korczak, Ph.D., who's also a Registered Dietician, as well as a nutrition professor at the University of Minnesota, and lead sports dietician for Minnesota United FC. "But trying to really teach people, what are the long term health consequences of this is very important."

Korczak has concerns about fasting as a diet choice, particularly surrounding the long-term consequences.

"From a nutritional standpoint, when you're cutting calories, you can become deficient in certain nutrients, and that's so important, especially in certain populations," Korczak said. She suggesting fasting should never be a diet option for children, pregnant women, the elderly, or anyone who's already malnourished.

"The various types of fasting protocols are quite advanced eating strategies, I would call it. It's definitely not something I would send a beginner off to try to experiment with," Kriegler added. However, he does believe fasting can be done safely. "They need to look at their relationship with food, they have to a good strong healthy relationship with food, they should probably have an understanding of how healthy their metabolism is to begin with, and what kind of benefit they're looking for out of the fasting protocol they choose."

Korczak, however, does not recommend fasting.

"I'm just not there yet to say it's beneficial," she said, noting that fasting can cause changes with your metabolism. "When you're fasting, especially for long periods of time, you lower your resting metabolic rate, meaning that your baseline calories is now much lower, so you're already putting yourself in deficit."

But Kriegler believes fasting can be safe, if you include healthy choices.

"If you have a healthy metabolism and an overall healthy diet, then introducing periods of time where you skip a meal here and there doesn't send your metabolism wildly off course," Kriegler said.

The differing opinions of the dieticians mirrors the differing conclusions found online, and even in medical journals.

A 2017 study in the Journal of the American Medical Association reported that fasting wasn't necessarily any more effective than calorie counting, concluding: "Alternate-day fasting did not produce superior adherence, weight loss, weight maintenance, or cardioprotection vs daily calorie restriction." The study also found participants in the fasting group were more likely to quit the diet program early, compared to those on daily calorie restrictions.

However, another study published by the National Institutes of Health a year earlier found the opposite to be true, stating, "Our results from both the systematic review and the meta‐analysis suggest that (Alternate-day fasting) is an efficacious dietary method, and may be superior to (very-low-calorie dieting) for some patients because of ease of compliance, greater fat‐mass loss and relative preservation of fat‐free mass." The study did suggest that further clinical trials were needed.

The bottom line, our sources agree, is that fasting, or any diet plan, should start with a visit to a doctor's office.

"I would say consult your physician, because the physician might have a different opinion as to, if you do have a specific medical condition or a disease state," Korczak said.

"What I would do is check with your doctor, or get your health evaluated, understand your baseline level of metabolic health," Kriegler said.

Kriegler has penned several blog posts on the subject of dieting for Life Time, including "Should You Try Intermittent Fasting" and "Why Meal Frequency Matters."

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