What is intermittent fasting and can it boost testosterone levels? Here's what to know

Regular readers of my column know that I have been very bullish on intermittent fasting, and I regularly receive notes from others who have tried intermittent fasting and benefited greatly.

Here is a recent note: "I read your article on intermittent fasting and I have achieved benefits far greater than I imagined at my present age of 75. I am a female, and like you, I was already a healthy eater, not overweight, and doing regular exercise but still had belly fat. With intermittent fasting, I dropped 10 pounds of belly fat in a heartbeat. This is the simplest thing I have ever done, and I am convinced it will add many years to my life!"

What is intermittent fasting?

Intermittent fasting is a revised eating pattern in which you go for extended periods of time in a truly fasted state.

This means you consume water, black coffee, or unsweetened tea only, and nothing that triggers an insulin response. Keeping insulin levels low is the key to success when it comes to managing your weight. Why? A primary job of insulin is to feed fat cells (cells that store fat in the body) with glucose, and much of that glucose is converted to fat and stored. What’s more, if you keep feeding fat cells throughout the day, they never get a chance to unload fat. This means things are always moving in the direction of fat gain, and that’s why we get fatter year after year.

A popular approach to intermittent fasting is the 16/8 method in which you eat only during an 8-hour period, fasting the other 16 hours. Studies show this is somewhat effective, but a longer fast accomplishes so much more. In my case, I started with a 16-hour daily fast and worked consistently toward a goal of fasting at least 20 hours per day. I wanted to investigate the impact of a longer fast on keeping my insulin levels as low as possible for as long as possible. In addition, research suggests that the longer the daily fast the greater the production of human growth hormone (HGH).

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HGH is made by the pituitary gland. Unfortunately, with age, production declines and when it does, levels of body fat are likely to increase along with the loss of muscle mass and bone mass. I am convinced that reclaiming my “six pack” waistline and being more muscular now at age 76 than I was 15 years ago is due to intermittent fasting contributing to a much lower insulin level throughout the day, plus an increase in HGH.

What should I eat when intermittent fasting?

Typically, I consume everything I will eat for the day between about 6 and 9 p.m. Ironically, I eat more now than I used to eat in order to keep my weight up. Yes, you read that right. I eat more just to keep my weight at 190 pounds, what I weighed in high school. After I consume a full dinner, I drink large glasses of a tasty blend loaded with fruits, vegetables, protein powder, etc. I also gorge on handfuls of raw nuts (cashews and walnuts), trail mix, high-protein bars, natural peanut butter on whole-grain bread, etc. In addition, I am not as strict in my diet as I used to be.

Another benefit of fasting is that the body is not preoccupied with hours of digestion after meals and it can turn its attention to other important tasks. This includes not only the production of HGH, but also healthful immune cells, plus cleansing the body of older, malfunctioning cells (autophagy) and replacing them with new, vibrant cells.

In addition, there is evidence that testosterone production may increase as well.

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Does intermittent fasting increase testosterone levels?

Intermittent fasting boosts HGH, which in turn, may promote increased testosterone production. Although not firmly established, considerable supportive research data has been found on male rats and more recently on humans. In addition, my personal experience may be instructive.

I have been on a minimal dose of testosterone for the past four years. Before I started, I noticed I was having trouble sleeping, an unusual problem for me, plus my energy level was low. What’s more, even though I regularly engage in demanding resistance training, it was getting harder and harder to hold onto muscle mass. I thought I should have my testosterone level checked, and sure enough, it was low. So low, in fact, it was below the normal range of about 250 to 1000 ng/dl (nanograms per deciliter). I started giving myself weekly testosterone shots that brought my level up to midrange, where it is supposed to be, and I was sleeping well again and feeling good.

Then as I got serious about intermittent fasting, things changed dramatically. In my regular checkup with my urologist, my serum testosterone level leaped up substantially.  Was this a one-off anomaly? Hard to tell. I didn’t mention my intermittent fasting, because at the time I didn’t see a connection, and over the years my testosterone level had jumped around a bit, but not nearly this much. I was scheduled for a retest several months later, and in anticipation, I researched the possible connection between increased testosterone and intermittent fasting. 

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My test results showed the same very high level. At this point, I discussed my intermittent fasting theory with the doctor, and I presented some reprints of research studies supporting the effect of raising testosterone levels. We agreed to cut my testosterone dosage by 60% and see what happens. The latest test results show that I’m back to midrange despite a much lower dosage, supporting the positive impact of intermittent fasting. And like most folks, I don’t like taking medications, so I’m delighted to take much less and still achieve the same good results.

Reach Bryant Stamford, a professor of kinesiology and integrative physiology at Hanover College, at stamford@hanover.edu.