Is Fasting Actually Healthy? What Science Can Tell Us

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We're currently in the season of Lent, a practice in the Christian tradition that includes periods of abstinence and the denial of many foods and beverages.

Fasting isn't limited to the Christian tradition. Other examples include Ramadan (a month of fasting), and the Greek Orthodox tradition in which the faithful sometimes give up not only meat but also dairy products, fish, wine, and the use of oil in cooking. And the Daniel Fast is another religious-based fast that includes a 10- or 21-day avoidance of foods declared unclean in the Book of Daniel.

Research suggests that fasting is healthy when part of a spiritual, emotional, or physical cleansing — not a hard-core diet plan.
 

Of course, fasting isn't just associated with religion these days. Many popular diets now include a component of intermittent fasting. Coldplay's Chris Martin, for example, recently revealed that he follows the "6:1 diet," in which he doesn't eat at all one day a week.

But what does the science actually say about the benefits of fasting? Let's take a look at when it can promote health — and when it only hurts.

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Is Fasting Good for You? The Pros and Cons

The notion that the absence of eating might be healthy may seem counterintuitive at first, given that food contains nutrients, and you need them to survive. On the other hand, with 69 percent of Americans overweight or obese, it certainly seems that many of us could stand to rein it in a bit.

Still, the question of whether fasting is actually good for you isn't settled yet, and there are supporting studies on both sides.

And, interestingly, the answer to whether fasting is healthy or not depends on more than just the number of calories you consume or when you eat. It turns out that the context in which you fast also has a big impact on the outcome.

Calorie Restriction

It looks like Benjamin Franklin was correct when he stated: “To lengthen thy life, lessen thy meals.” Research suggests that cutting calories overall can mimic the effect of healthy antioxidants to decrease age-related deterioration in your body and brain.

In other words, one of the strongest indicators of longevity is not just what you eat but how much of it you eat. Those who eat smaller tend to live longer.

However, if you take this to an extreme, go cold turkey, and severely clamp down on calories, your body can interpret the situation as a stressor. In one study, experimental animals put on a two-week fast showed spikes in their stress hormones along with decreases in their cardiac muscle volume and output. That form of caloric restriction was terribly unhealthy.

Likewise in humans, fasting for a full two days led to symptoms of insulin resistance and, as you might predict from this result, induced diabetes in some cases. Along with increased stress hormones and insulin resistance, your systems can go into what is commonly called “starvation mode," in which your metabolism slows down (you’re burning fewer calories). Even worse, your body can hold on to the fat it does have, essentially frustrating the very point of the fast in the first place.

Intermittent Fasting

Intermittent fasting refers to a diet that involves periods of fasting and nonfasting, as opposed to overall calorie restriction.

Research suggests that intermittent fasting can be healthy for your body and weight. In a study of religious fasts, such as Ramadan, Lent and the Daniel Fast, researchers found that those who engaged in voluntary, controlled restriction in this context didn't tend to suffer the metabolic ill effects.

Here's what other research on these practices found:

Of course, more research needs to be done to determine just what it is about particular fasts that make them healthy or unhealthy.

But one critical element seems to be how your body interprets the context. It’s not about the calorie count alone or the religious element. In the cases above, healthy fasting seemed to occur within the mental context of a spiritual, emotional, or physical cleansing. It’s taken by your mind — and so your body — as a positive means to a healthier end.

By contrast, unhealthy fasting seems to be focused on deprivation alone — whether externally imposed by some arbitrary program or internally imposed as through a deprivation diet.

The Bottom Line

Fasting isn't good or bad for you on its own. It can depend on how you frame it. If you use fasting as a hard-core diet technique to lose weight quickly and punish yourself for your past dietary "sins," your body will work against your efforts.

On the other hand, if you use fasting as a part of a meditative, purposeful cleansing of the body, mind, and spirit, it will be taken that way. That’s because diet is more than just what you put in your mouth — it’s also the context of that consumption.

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