Can fasting support immune health? It’s complicated.

Can fasting support immune health? It's complicated.

New research from the Yale School of Medicine found that dieting and fasting may help our immune systems fight disease, but that’s not the whole story when it comes to calorie restriction and our health.

The researchers found that restricting calories through dieting or short-term fasting may help our bodies fight inflammatory diseases like type 2 diabetes, atherosclerosis, and Alzheimer’s disease.

When we fast, our bodies produce a compound called β-hydroxybutyrate (BHB), which blocks inflammation. Intense exercise and low-carb diets also stimulate BHB production.

This isn’t the first study to find that fasting (within reason) can support immune health. Valter Longo, PhD looked into how caloric restriction may help our bodies fight cancer. In an interview with Natural Medicine Journal editor Tina Kaczor, he explained that fasting creates a hostile environment for cancer cells in our bodies without causing much harm to patients.

Longo cautioned in the interview that fasting to help your body fight cancer is all about finding a balance. “I don’t think severe calorie restriction is appropriate since, in addition to many beneficial effects, it also causes severe weight loss,” Longo tells Kaczor. “I believe that for now, a high micronourishment, mostly plant-based diet with some fish that allows a BMI of 21–23 and low waist circumference is the ideal diet. Brief periods of fasting followed by refeeding to remain at a steady weight may also be recommended.”

A 2014 study found that fasting for two to four days stimulated particpants’ immune systems and even reversed some signs of aging.

The Dangers of Fasting

Before you hop on the 5:2 Diet bandwagon, though, let’s take a look at the dangers of frequent fasting.

Not all fasting is created equal. Alternate day fasting, where you only eat every other day, can impair your glucose tolerance, according to an article in The American Journal of Clinical Nutrition. Restricting yourself to one meal a day did help participants in another study maintain body weight. Along with the benefits, though, the participants reported feeling hungry, and researchers saw an increase in their blood pressure, cholesterol, and the stress hormone cortisol.

We need food to live. Calories feed our muscles and our brains. According to a recent report in The Telegraph, fasting for more than six hours starts to mess with our decision-making. And fasting for 72 hours or more can be very dangerous.

It’s around that 72 hour mark that your body starts breaking down muscle. At this point, you also see the exact opposite of the effect you’re going for: your immune system becomes compromised.

Fasting also messes with your stomach. When you don’t eat, your stomach slows acid production, since there’s no food to break down, but the smell of food can trick your gut into thinking it’s about to have some work to do. The result? Acid reflux.

Another lesser-known side effect of fasting is dehydration. We actually eat a good portion of our daily water intake. When you cut out food, it’s easy to get severely dehydrated.

So, should you fast to boost your immune system? Like so many things health-related, it’s complicated. If you are looking at a fast to help improve your immune health or to fight disease, you should definitely talk to your doctor first.

What about Juice Fasts?

Juice fasts are not a good solution for a quick health fix. Fruit juices – even unsweetened ones – contain a lot of sugar. You can potentially drink as many calories in a day as you would eat, so in the context that we’re talking about (calorie restriction), juice fasts don’t deliver the same results as true fasting.

I love a juice shot as much as the next person, but juicing strips fruits and veggies of one of their most beneficial elements: healthy fiber. What’s left after you run your produce through a juicer is a glass of water, vitamins, and lots of sugar. Specifically, lots of fructose. Fiber helps your body digest the natural sugar in fruits and veggies. Without that fiber, fructose is bad news. In fact, there’s research linking added fructose in our diets to type 2 diabetes.

Image Credit: fasting photo via Shutterstock

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About the Author

My name is Becky Striepe (rhymes with “sleepy”), and I am a crafts and food writer from Atlanta, Georgia with a passion for making our planet a healthier, happier, and more compassionate place to live. My mission is to make vegan food and crafts accessible to everyone!. If you like my work, you can also find me on Twitter, Facebook, and .