Fasting for your health: Harmful or helpful?

A woman raids the refrigerator late at night (2011 Christopher Boswell)

Depriving yourself of something you want is difficult enough, but fasting is more than simple self-denial: It goes against your physical needs and a lifetime of habits and mores. This self-denial is one reason why fasting is used in many of the world’s religions, but there is evidence that abstaining from food, at least temporarily, can bring a wealth of health benefits too.

Around the world and throughout time, fasting developed independently among different groups for its spiritual and physical benefits. Now, outside of religious context, some doctors consider fasting an effective method of reducing cholesterol, lowering the risk of heart disease and diabetes, and even extending life span. But this level of deprivation may not be healthy for everyone, and it certainly isn’t a good introduction to living well.

It’s not for everyone

“Fasting is an advanced technique,” says Dr. Joel Fuhrman, author of “The End of Dieting” and a fasting expert. “If someone isn’t already committed to eating healthy both before and after, it just isn’t realistic.”

Going from a strict fast back to a diet of unhealthy foods is more dangerous than skipping the fast altogether. This sort of yo-yo effect is hard on your body.

“Also, the fast itself will be more unpleasant, as your body will go through more intense withdrawal symptoms than if you were someone who was normally eating healthy foods,” Fuhrman says.

These unpleasant feelings— such as headaches, moodiness and difficulty concentrating— are often attributed to hunger by inexperienced fasters, and could give you reason to never fast again. But, several studies have identified that these symptoms stem from changes in the brain brought on by high-fat and high-sugar diets. When you cut out those types of foods suddenly and without warning, your body goes into crisis mode.

But for those already living healthfully, the potential benefits of fasting are many.

Increased longevity, heart benefits and more

When you fast, or go without food for a period lasting several hours to several days, your body turns from burning digested food for fuel to burning stored energy. Initially, this includes muscle But once the body realizes you are fasting, it goes into ketogenesis, sparing the muscle and instead relying on ketones, a byproduct of fat. This is called the catabolic phase and is when your body begins to reap the benefits of fasting.

“Lower caloric exposure and episodic fasting can extend the life span of all animals,” Fuhrman says. “The longer we spend in the catabolic state, the longer we live.”

Intermittent fasting has been found to increase life span in animals by as much as 42 percent and reduce the risk of cancer. Although research continues, these results have not been duplicated in human studies.

However, we do know for certain that fasting can have beneficial effects for the heart— significantly changing blood cholesterol levels and reducing the risks of heart disease. There is also evidence that it can combat obesity, lower blood pressure, lessen the symptoms of rheumatoid arthritis and reduce the risk of Type 2 diabetes. Anecdotally, some patients find fasting before chemotherapy lessens the negative effects of the powerful cancer drugs.

One study, which looked at fasting through several religious traditions, found varying results, mostly due to the differences in fast specifics from religion to religion. Still, lower body mass, reduced cholesterol and increased insulin sensitivity were among the positive findings.

Making fasting work for you

For most nonreligious fasters, alternate-day fasting or “intermittent fasting” seems to be the most well-studied and practiced forms of food deprivation. And although going one day without food can seem an insurmountable request, the knowledge that you’ll be eating again tomorrow may put your mind at ease.

If a full day is too long, Fuhrman suggests extending the catabolic phase overnight by eating dinner earlier and breakfast later.

As Fuhrman says, fasting should be a second step, not the first. Eating healthy and having control over your daily diet is the foundation of better health. If you can achieve this, fasting may be one way to level up.