What You Should Know About the 5:2 Diet and Intermittent Fasting

What to Know About the 5:2 Diet and Intermittent Fasting
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Diets designed for weight loss make big promises, like dropping pounds and boosting your health — without struggle or deprivation. And that’s one of the big draws of intermittent fasting diets, including the 5:2 Diet.

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What the 5:2 Diet Is All About

At its core, intermittent fasting involves going for short periods of time with much less food than normal, explains Michael Mosley, co-author of The FastDiet and author of The 8-Week Blood Sugar Diet. He, along with Mimi Spencer, created the 5:2 Fast Diet, a plan that includes eating your normal allotment of calories for five days, and then eating one-quarter of your calories (about 500 for women, and 600 for men) on the other two days.

“During this time when you’re eating far fewer calories than normal, your metabolic rate actually speeds up and your body also gets on with essential repairs. It’s a bit like doing a spring cleaning,” says Mosley. “Instead of having to spend time and energy digesting your food, your body works on repairing itself instead,” he adds. Not to mention, you’re cutting a total of 3,000 calories per week, which is significant enough to help people slim down. (Keep in mind, noticeable weight loss will be more likely in overweight individuals compared to already-fit folks, Mosley says.)

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How to Make 5:2 Work for You

That all sounds good, but you still have to work through the logistics of the 5:2 diet. On your “normal” eating days, the plan calls for women to eat about 2,000 calories. So you can’t necessarily chowing down on anything you want. Those days should still be healthy days. Mosely recommends following a Mediterranean-style diet containing fruits, vegetables, oily fish (like salmon), nuts, olive oil, yogurt, cheese, and even the occasional glass of wine.

Then, there are the working days — aka the days you fast. You get to choose when you do this. So it’s entirely up to you whether you do them spread out or back-to-back. During those days, aim to eat foods that keep you full, like fish, meat, and vegetables. For instance: three-ounces of chicken breast contains 142 calories. Put it on a bed of two cups of spinach (14 calories) for a meal that’s less than 200 calories. You can also choose whether you eat mini meals throughout the day or one meal total.

A common misconception is that your body enters into “starvation mode” during those two days, prompting your system to conserve fat and calories rather than burning them. “All the studies show the reverse is true,” says Mosely. “Only when you go without food for prolonged periods of time (weeks) do you go into ‘starvation mode,’” he says.

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The Drawbacks to Fasting

One of the main drivers of success of the 5:2 diet-style of fasting is that you only have to cut calories in the very short-term. However, that doesn’t mean the two low-cal days won’t get difficult. You might feel intense hunger — the type where it’s difficult to concentrate and you start fantasizing about food rather than focusing on, say, work or having fun. Though Mosely admits it can be tough the first few times, people get used to it, he says, and find it’s easier than cutting calories every single day.

Whether or not the diet is sustainable for everyone isn’t so clear. “If it works for you, then it’s completely fine,” says Philadelphia-based weight loss and fitness expert Charlie Seltzer, MD. It’s not inherently dangerous to your health, but you may find it hard to maintain. “Most people are not going to be able to eat 500 calories in a day,” he says. Hanger aside, there’s also the risk of overeating the next day, especially if you’re not tracking your calories and eating mindfully.

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Another downside? It can throw your social life for a loop, notes Amy Shapiro, MS, registered dietitian with Real Nutrition NYC. While she says that there’s good research to support intermittent fasting for fat burn and weight loss (though not every study is in agreement), it can be difficult in some real-life scenarios. For example, say a friend wants to grab lunch on a fasting day, that might mean you say no or opt for a small side salad (and suffer order envy). Or, maybe it’ll require you to make a separate dinner from what your family is having. Traveling might pose challenges, too, when you’re eating out more and it’s harder to track calories.

Consider all of those steps before deciding whether or not to jump into intermittent fasting. “If you attempt it, give it a real shot,” says Shapiro. The last thing you want to do is follow it for one week, then skip it the next. That’s one quick way to tank your results. “Give yourself time to adjust to it. And aim to turn it into a lifestyle instead of turning it into a fad,” she adds.

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