Fasting Is in Our Blood. Here's How to Do It Right.

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If you don’t know me, Spartans, it's nice to meet you. People call me Dr. Geo — short for Geovanni, not George — and I like to call myself the natural urology doc. In my practice in New York, I help men and women to create lifestyle plans to prevent and manage all illnesses that have anything to do with the urinary tract. 

My method, as you may have guessed, is natural. “Naturopathic,” to be precise. And that means that I take all of the body’s systems into account for a holistic, big-picture story of what is going on in your body.

I have been reading books on therapeutic fasting for over 20 years — way before it was gaining popularity as it now — and I have been fascinated with its history. The first few books I engaged in were Rational Fasting by Arnold Ehret and The Miracle of Fasting by Patricia and Paul Bragg. While the mechanism by which fasting worked to heal human bodies was not clear, the results reported in those books were compelling. Now, a simple search through online scientific journals yields hundreds of research articles on the health benefits of fasting.

What Is Fasting?

To define it broadly, fasting is the strategic, periodic limiting of food intake for health benefits. People have engaged in fasting since recorded history, but they mostly did it for religious reasons or as part of a ritual. Today, people fast as a way to heal or cleanse their bodies.

Fasting does not mean that a person gives up all food or drink for days on end, or subsists entirely on mustard packets for a week. (Who thought of that?) That would most likely do more harm than good as a result of a dip in blood sugar.

There are different ways to fast. One is called calorie restriction (CR) — reducing caloric intake without pushing yourself to the point of malnutrition. The other type is called Intermittent Fasting (IF). This usually means eating for a period of time and abstaining from food for another period of time, as opposed to a constant calorie restriction. One kind of IF is a 12/12 IF approach: eat for 12 hours and fast for another 12 hours, drinking only water. Other approaches to IF include fasting for two to three days of the week.

Related: Top 10 Things Athletes Should Know About Intermittent Fasting

What’s the Evidence?

There is a large amount of research on the health benefits of fasting. A review of several studies found that just a 15-40% decrease in caloric intake had many benefits, including:

  • improved glucose tolerance
  • made the body more sensitive to insulin
  • reduced blood pressure and heart rate
  • reduced oxidative stress
  • reduced the incidence of “spontaneous cancers”
  • preserved the brain
  • protected the kidneys
  • prolonged reproductive function

And that’s just for constant calorie restriction. What can intermittent fasting (IF) do for you? An article published in a German journal reports that supervised, intermittent fasting for seven to 21 days helps both rheumatoid arthritis and quality of life.

Why Does This Happen?

Although scientists are not sure exactly how fasting works, we know that it does have benefits. I think that it might have something to do with the fact that human beings, for hundreds of thousands of years as hunter gatherers, dealt with scarcity on a daily or almost daily basis. But that’s something we can never really know.

You could say our bodies are adapted to it. And when we suddenly drop human bodies into a world of abundance and sitting (and in terms of evolution, the past 500 years of industrialization have been pretty sudden), they just don’t know what to do — they get diabetes, they become overweight, they develop disease — all sorts of problems. Then again, this is just my theory.

What Should You Do?

I know that Joe De Sena has a saying with you Spartans: If you’re not hungry, you’re eating too much. Well, normally I'd think that that's a little extreme, but in the case of moderate calorie restriction, it makes some sense.

My recommendation is this:

First, if you are not already keeping a food journal, start one and stick to it. Being aware of your food intake will do your body more good than anything you eat. Also, more important than counting calories is counting nutrients and food groups. For example, are you getting enough protein? Enough vitamin K? Enough dark leafy greens?

Related: 10 Signs You’re Not Getting Enough Protein

Once you have kept a food journal for at least two weeks, start your first fasting experiment. Keep in mind that you have a real, non-superficial goal: preventing disease and staying alive longer.

How to Get Started

It is best to ease into a fast.

For your first fast, start by fasting for 12 hours a day, every day for three weeks. It is best to do this at night between 8 p.m. and 8 a.m.

Then, add another three hours to your daily fast — 8 a.m. to 12 p.m. Return to your standard 12-hour daily fast on one to two days of the week.

You can then experiment with fasting for 24 hours a day, once a week for three weeks.

What Should You Eat While Fasting?

When you are on the fast, eat whole foods, lean meats and chicken, fish, vegetables, and low-glycemic fruits. Drink six glasses of lemon water every day, and emphasize vegetable smoothies.

Related: What Is the Best Fasting Diet for Fat Burning & Performance?

In the fast that I described above, you should keep exercising. Just stay well hydrated — coconut water is my favorite.

Be Careful.

I want you to be very careful with fasting, because it is not hard to slip into an unhealthy relationship with food, especially for people who are driven and ambitious like yourselves. Food is good; it’s not a reward; it’s fuel for the activities that you love to do. If you have an eating disorder, are pregnant, have untreated hyperthyroidism, or are malnourished, I would not recommend fasting.

Geo Espinosa is director and founder of the Integrative and Functional Urology Center at NYU. He is a husband and proud father of three. He also writes frequently for his blog,

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