10 Real Benefits of Fasting

Medically reviewed by Natalie Olsen, RD, LD, ACSM EP-C on June 19, 2017Written by Ashley Marcin on June 19, 2017

What is fasting?

You’ve likely heard of a number diets that have you eating fewer calories or limiting yourself to specific foods. But what about a diet focused on eating no food at all?

This is called fasting. Of course, you may be familiar with fasting before blood tests or for religious purposes. But is it bad for your health? Possibly.

Types of fasting

First, it’s important to point out that there are a few different ways to fast. Most people who try this type of diet don’t go without food for long periods of time. Instead, they practice what is called intermittent fasting.

Intermittent fasting

Intermittent fasting is when you fast for periods of time, whether during the day or throughout the week. The 5:2 diet, for example, has people eating normally five days a week and fasting two days. On the fasting days, you consume 500 calories, maybe 200 calories for breakfast and 300 calories for dinner.

Alternate-day fasting

Alternate-day fasting, or ADF, is a type of intermittent fasting. The every-other-day diet is an example of alternate-day fasting in which you eat as much food as you want every other day. On the fasting days, you should consume less than 500 calories. On feast days, there are no limits. You can eat any foods your heart desires.

Time-restricted fasting

Time-restricted fasting is when you, for example, try eating all your meals within eight hours and don’t eat the rest of the day.

Are there any benefits of fasting?

People who follow various fasting diets say it can do anything from shed pounds to improve overall health.

What does the science say? Some of these claims may have merit. Others are more complicated. The majority of the studies conducted on this topic have been on mice, and no solid conclusions have been made on human populations. More research is required, but here’s a compilation of what current studies have shown.

1. Lose weight

Simply put: Eating fewer meals throughout the week means you’ll generally consume fewer calories. One review reveals that intermittent fasting or alternate-day fasting may be good options for losing weight and keeping it off.

However, many people may have trouble ignoring hunger on the fasting days. This may make these diets difficult to follow in the long term. Not only that, but there aren’t many studies on the effects of fasting on humans over long periods of time.

In studies about fasting periods for religious reasons, researchers actually found that any weight loss was transient. This means that the weight would return after the period of fasting was over.

2. Look trim

Still, fasting may help you look trimmer. Mice who were put on intermittent fasting diets had less body fat and retained more lean muscle mass.

Up to 52 percent of the mice had lower body fat percentages at the end of the study. Not only that, but around 13 percent of the mice also increased their lean mass.

However, the researchers admit in their conclusion that the study doesn’t prove that fasting has any added benefit beyond simple calorie restriction.

3. Reduce bad cholesterol

One study shows that alternate-day fasting may do more than just help with weight loss. Researchers had 16 people who were obese undergo a 10-week fasting period.

The participants had not only lost weight and fat by the end of the trial, but also lowered their LDL (bad) cholesterol levels, total cholesterol levels, and even triglycerides. With such a small sample size, however, it’s hard to know if these results would apply to a larger population.

4. Lower blood pressure

In the same study, the individuals also saw their systolic blood pressure decrease from 124 +/- 5 to 116 +/- 3 millimeters of mercury (mm Hg). A normal reading of systolic blood pressure is anything between 90 and 120 mm Hg.

Fasting brought the group’s numbers down from a high level to a more normal range in just 10 weeks. Again, it’s important to understand that this was a relatively short trial with only 16 participants.

5. Repair cells

Autophagy is a process where your body removes waste from cells. Fasting may actually promote this process, especially in the liver, according to a study. Young mice fasted in the lab for 24 to 48 hours. After that, researchers looked at their cells for signs of autophagy.

While research in the past suggested that the brain didn’t get the same benefits as the liver, this study shows the reverse to be true. The brains of the mice showed dramatic signs of this cellular cleansing. The researchers conclude that fasting is a simple and safe way to get this benefit, though more research should be done on humans.

6. Reduce insulin resistance

A study published in Translational Research examines fasting and its potential to help with the prevention of type 2 diabetes. While traditional calorie restriction diets have typically been the focus of research in the past, this study shows that fasting may be a solid option for reducing diabetes risk in both overweight and obese populations.

This is because fasting can decrease body weight, lower insulin resistance, and reduce blood sugar levels. The authors of the study concluded that more research is needed surrounding this approach before it can be widely recommended.

7. Fight disease

One review of studies found that existing research has shown a positive association with fasting and the possibility to reduce risk of diseases related to obesity. This can include fatty liver disease, type 2 diabetes, and cancer. That said, the researchers later explain that there is little data on humans and how fasting might help with these diseases or others, like Alzheimer’s. The potential is there, but more study is needed on human subjects.

8. Reduce inflammation

At the same time, some studies show that fasting may help reduce inflammation in the body, which is often related to many diseases. One study examined 40 people observing Ramadan along with 28 people eating a normal diet. Ramadan is a religious month for Muslims, during which time they don’t eat or drink between sunrise and sunset — about 12 hours a day.

Blood test results between the two groups showed that a longer period of intermittent fasting may reduce inflammation, as well as help with risk factors for heart disease. Of course, it’s important to note that this was a small study performed only over the course of a month.

9. Increase brain power

One six-month animal study found that diets like the 5:2 diet are challenging to the brain. According to the results, when the brain is tasked with things like physical exertion or calorie restriction, like with fasting, its neural connections strengthen.

Not only that, but it may also have an antidepressive effect. However, human studies still need to be done.

10. Increase longevity

In a recent study, researchers examined the link between fasting and living a longer life. In fact, fasting just a few days each month may be all you need to do to see a change. The idea is that animals, including people, have often lived in environments where food isn’t always available.

Fasting may slow different diseases of aging and even slow bone density loss. The team developed a diet called the fasting mimicking diet (FMD) that was first tested on lab mice. In a pilot human trial, people went through three cycles of the FMD. These subjects showed a decrease in a hormone called IGF-I, a marker for aging.

Risks and considerations

You should always speak with your doctor before making any big changes in your diet. While controlled studies have shown some benefits to fasting, going without food or with severely limited amounts of food for several days each week may have an impact on your nutrition. Fasting can cause anything from fatigue in the short term to vitamin and mineral deficiencies over time.

As well, certain groups of people shouldn’t try fasting. Children and adolescents who’re still growing shouldn’t fast, for example. Low-calorie diets high in protein may not be a good idea for women, as it may increase the risk of gallstones. People who have diabetes may also want to be careful with fasting — especially if they’re being treated with insulin, metformin, or other drugs. Last, anyone with a body mass index of less than 18 likely shouldn’t try a fasting diet.

The takeaway

More research is needed to prove fasting leads to many health benefits for humans. Fasting is not recommended as the magic fix for weight loss and disease prevention just yet. In the meantime, remember the standard advice of eating balanced diet and exercising regularly for good health.

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