Fasting is hardly a new idea.  Ritualistic fasting has long been a part of various religious traditions, and during our hunter-gatherer days, our bodies were optimized to go for brief periods without eating.

More recently, many fad diets have sprung up around the idea of periodic fasting, and the proponents of such diets claim a whole raft of health benefits including rapid weight loss, a reduction in risk factors for both heart and kidney diseases, and even as a ward against cancer.  The question is, are those claims backed up by science, or is it mostly hype and marketing?

It’s a fair question, and the answer isn’t as straightforward as it might first seem.  Let’s start by talking a bit about what happens when you fast.  First and foremost, you’re changing the focus away from what you eat to a focus on when you eat, and that’s an important distinction.

When you don’t eat, the supply of glucose in your body begins to decrease.  Glucose is fuel for your cells and every cell in your body needs it to function properly. So as the supply begins to dry up, your body starts looking for other sources of glucose, which is stored in both muscle and fat as glycogen.

After a few days without eating, your body will kick into “Ketosis Mode,” which means that it starts to burn fat as its primary source of glycogen to preserve your muscle mass.  That’s a good thing and you will lose weight as this begins to happen, but it’s got some downsides, including halitosis (bad breath) and constant fatigue.  This is your body rebelling against the idea of going without food for so long, and at this point, the longer you continue to fast, the more you risk things like kidney and liver damage.

The short answer then is yes, fasting does have some real, tangible benefits, although many of the claims about protecting your heart, kidneys, and warding you against cancer aren’t yet backed by a sufficient body of evidence to say them with any real certainty.

If you decide it’s something you want to do, you should consult with your doctor and let him or her know how any why you’re planning to.  Be sure to let them  know every type of medication you’re on, and any supplements you might be taking because these things will affect how well fasting will work for you.