Is Fasting Healthy Or Dangerous? The Benefits And Problematic Risks Of The 'Fast Diet'

If you haven't heard of "fasting diets" or "the 5:2 Plan," here's the basic principle: Several days of eating normally, then a few days "fasting" (eating extremely minimally), rinse, repeat. The trend became big in the U.K. in 2013, and it's gradually getting more attention in the U.S. as the "fast diet". But calling fasting a "diet" is actually a misconception — fasting is, according to scientists, about a lot more than just stripping pounds. Obviously, the entire concept is potentially problematic: any fasting needs to be done carefully and healthily as part of a normal-calorie diet, otherwise fasters develop the risk of malnutrition. And if you've ever experienced disordered eating, fasting is absolutely not for you.

But as much as the idea of fasting sounds like a potential eating disorder trigger that makes us want to eat a sandwich, the appeal of fasting for people looking to improve their health or lose weight is kind of understandable. Rather than monitoring every mouthful, declaring certain foods as "bad," and constantly counting calories, the idea of occasional fasting is a lot simpler.

And now, the University of Southern California has just released details of a study that shows that a particular type of fasting is seriously helpful for overall health — including boosting stem cell levels. The real benefit of fasting, it seems, may actually be to your lifespan, not to your waistline. But before you go live on oat cakes and water for a week, hold up, and let's look at the science. What does fasting do to the body, what does the USC study mean, and is this really the future of living longer?

What Does Fasting Do To Your Body?

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I was first introduced to the idea of fasting for your health by a neuroscientist back in 2009. She told me over dinner (which she couldn't eat) about the research that showed intermittent fasting lowers the risk of Alzheimer's and Parkinson's as we age. Putting the brain in starvation mode prompts neuron activity, because the brain's under mild stress — and that keeps our grey matter healthier for longer.

Controlled fasting has also been shown to help reduce seizures in epileptic children. But we've known about the health benefits for a long time: studies in the 1930s and '40s across the U.S. showed that laboratory rats and mice, when fed on alternate days, lived longer and healthier lives than others. It's just that recent research has brought it back to the spotlight.

So what's fasting supposed to do? Let me count the ways. Intermittent fasting days are meant to help us increase our responsiveness to insulin, improve our immune systems, and reduce the risk of cardiovascular disease. But it's not for everybody: it's easy to overdo it or to slip into disordered attitudes about food and eating, particularly for people who've suffered eating disorders in the past. And we're still looking for proper human trials to confirm all the findings — which is why this USC study, which used yeast, mice, AND men was so important. Let's delve into it.

Can Fasting Ever Be Good For You?

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Most fasting diets are actually pretty hardcore — and, according to an expert interviewed by Science magazine, people who try them are prone to "failing miserably." The USC study is different in a number of ways, but the big one is that, frankly, the regime it suggests is a lot easier — and still gets good results for those who maintain a healthy attitude towards calories and food.

The USC devised a regime that was based on months, not weeks. For four days twice a month, mice were fed on low-calorie, low-protein diets — and the results were pretty stunning. Mice who fasted on the USC's regime lived longer, developed more stem cells, had lower cancer and inflammatory disease levels, and slowed the loss of density in bones. The fasting also improved brain and memory performance, and helped cells regenerate.

And when the scientists tried it on the 19 human subjects for three months, they discovered that the biological "markers" for diabetes, cancer, and cardiovascular disease dipped significantly compared to a control group.

For five days a month, the subjects ate between 34 percent and 54 percent of their normal daily calorie intake, and then went back to normal on the other days. The 54 percent of a daily calorie dose for women was around 1080 calories, which can mean homemade granola for breakfast, pulled chicken salad for lunch, and risotto for dinner. They weren't asked to live at the gym, steer clear of pastries, nothing. And the fasting still improved their body's chances of avoiding cancer and other diseases (and didn't wreck their metabolisms).

The real excitement in these results is the rejuvenation thing. The mice, who were all reasonably old (for mice), showed reversals in a lot of signs of aging. Their muscles didn't have as much aging-dependent decline, and their platelet and hemoglobin levels, which should have dipped as they got older, were boosted.

The fasting mice also lived about 11 percent longer than their non-fasting counterparts. But the scientists noted that, in very old or very weak mice, the extreme fasting wasn't actually good for them — and that fasting needs to be gentler with them so that they still get any benefit. So if you're not in a good state of health, physically or mentally, this is not your jam.

The Bottom Line

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The USC scientists finished their study by saying that a test group of 19 people was way too small to make any grand claims about fasting and aging. (Science also needs to figure out whether fasting affects the health of men and women differently.) But it's a good start.

The good news? This shows that we may be on the right track — but that getting it right may take a while. We know that calorie reduction in general is a good idea for human health, but developing that idea into something specific has taken a lot of trial and error. Two different studies on calorie reduction in rhesus monkeys back in 2011 showed completely different results; one showed that it significantly boosted lifespan, the other reported no change at all. No, somebody didn't mess up — it just shows that getting calorie reduction and fasting right can take a lot of experimenting.

And the bottom line? This is not for everybody, or even for most, until it becomes better understood. Any health benefits would be pretty easily outweighed by the potential development of an eating disorder or unhealthy fasting habits — so unless you're being closely supervised by a doctor or a nutrition scientist, be wary of this diet trend.

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