Is Fasting Good for You?

Most people who stick to a regular fasting routine find they are less hungry on days they fast. But is fasting good for you? Here's what you should know.

Americans aren’t used to the idea of fasting. But there’s quite a bit of evidence that it can be good for your health. It’s one way to lose weight and regulate blood sugar levels. It may possibly fight a variety of illnesses, too. 

An argument for specific fasting times being normal for human bodies goes like this: Back in our hunter-gatherer days, human beings frequently went hungry. Our ancestors didn’t snack all day, that’s for sure. As a result, humans evolved to store sustenance in muscles and fat tissues to stay alive for relatively long periods with little food. That is the same process predators in the wild follow today.

Some people have likened the benefits of fasting to those of exercise. Short-term wear and tear on your body can potentially make it healthier. 

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Fasting is not new for some people with certain religious beliefs. Fasting is required for specific periods in Judaism, Catholicism, and Islam, and many people have found these times of fasting to be difficult.

Fasting for a religious holiday, however, isn’t the same as keeping to a regular fasting regime over weeks or months. The human body usually gets used to going without food for a spell when it’s an ordinary occurrence. 

People who do well on low-carb, high-fat diets may be good candidates, since fasting has a similar effect, forcing your body to burn fat for fuel.  

The fasting weight loss regimes with known results are strict. One approach, called the 5:2 diet, is to eat whatever you want for five days and only 500 calories — about one light meal — the other two days of the week. Some people eat 500 calories every other day and then eat normally on the other days. Some fast most of every day, eating within only a window of hours.

None of these regimes would be advisable without first talking to your doctor, especially for pregnant women or people taking medication for high blood pressure, diabetes, or heart problems. 

University of Illinois nutrition professor Krista Varady, PhD, whose research focuses on the efficacy of intermittent fasting not only to control weight but also potentially lower the risk of certain diseases, notes that most people gradually become less hungry on their fasting days and don’t gorge on their eating days.

Evidence from decades of animal and human studies points to potentially wide-ranging health benefits of intermittent fasting, according to an extensive review of the research conducted by the National Institute on Aging (NIA) and published in the New England Journal of Medicine.

When it comes to animal studies, more research has been done on calorie restriction — limiting how much food animals eat during a day — than fasting for a specific time. The NIA points out, however, that in some studies lab animals are put on a type of intermittent fast because they consume all their daily allotted food within certain hours and go many more hours without food.

In many of these studies, rodents and other animals were fed 10 to 40 percent fewer calories but more nutrients than their usual diets. Many of the animals had extended lifespans and a reduced rate of several illness, in particular fewer cancers.

A mouse study established that two to five days of fasting each month reduced biomarkers for cancer and heart disease. Other data from animal studies suggest that intermittent fasting could possibly counteract multiple sclerosis, lupus erythematosus, and type 1 diabetes.

Based on these results in animals, researchers are zeroing in how fasting might benefit human health and even increase lifespan. Many studies have documented how obese and overweight people who diet to lose weight can improve their health. Research indicates intermittent fasting may have more benefits than just cutting back on calories.

Research has shown that obese people using alternate-day intermittent fasting weight loss regimes have lost weight even if they ate a high-fat diet on the days they ate normally and up to 500 calories on their fasting days.

In fasting studies, 10 to 20 percent of people usually drop out but, after several weeks, the others adjust.

In a study of 107 overweight and obese women ages 30 to 45, half were put on the 5:2 program and half on a low-calorie diet with no timing requirements. After six months, the women on the 5:2 program lost more weight and belly fat, retained more muscle, and saw more improvements in their blood sugar regulation than the women on low-calorie diets.

People on fasting weight loss routines have also seen some relief from symptoms of asthma and arthritis, possibly because breaks from peak consumption reduce inflammation and give your body a chance to rejuvenate and repair. Fasting lowers insulin and another hormone called insulin-like growth factor, or IGF-1, making the body stop pushing for new cell growth, which could in effect slow aging.

Mark Mattson, PhD, a professor of neuroscience at Johns Hopkins University and the former chief of the Laboratory of Neurosciences at the NIA’s Intramural Research Program, believes fasting may slow cognitive decline. He has chosen for years to eat meals later in the day.

Blogger James Clear reports that he eats one meal at 1 p.m. and another at 8 p.m. each day and doesn’t eat again until 1 p.m. the next day. After his first year on this regime, he decreased his body fat even though he cut his training time at the gym from 7.5 hours to 2.5. The internet abounds in similar anecdotal reports.

While these personal tales can be inspiring, before you try regular fasting talk to your healthcare provider, especially if you have any chronic health problem or special dietary needs. If you opt to fast intermittently, be prepared to be uncomfortable for at least two weeks, but the results may motivate you to stick with it.   

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