All About Intermittent Fasting

Intermittent fasting (IF) is the name some nutrition experts give to the practice of occasionally going for extended periods without eating. This fancy name implies that IF is the exclusive domain of the nutritional elite. It’s not. In fact, we all do some form of IF every single day, except we don’t call it that. We call it sleeping" (Berardi, J.).

People do this because there are some that suggest you can maintain a higher percentage of muscle mass when losing weight or losing body fat. If you ARE dieting and it works within your schedule, intermittent fasting is actually a great tool to use because even though you are in a caloric deficit, your feeding window is shorter. Rather than eating 2000kcal over a span of 12 hours, you might eat that in a span of 7 hours. This would leave you feeling more satisfied (if you feel like your stomach is a black hole) and mentally you wouldn't feel like you are dieting.

Studies shows that IF, when done correctly might help extend life, regulate blood glucose, control blood lipids, manage body weight, gain (or maintain) lean mass, and more. Most people during sleep are experiencing the benefits of this because you ARE fasting. Current research shows that some of these benefits might only be realized after longer fasts around 24 hours.

Is it beneficial for athletes?

If an athlete trains early in the AM, would it be beneficial to train fasted? Are 24 hour fasts doing any benefit for athletic performance? A lot of this is going to depend on the athlete and what type of training is being done. If you train like a bodybuilder, you might feel great waking up early and training fasted because you don't like training on an empty stomach.

A CrossFitter might feel sick and nauseas doing a lifting session and a hard metcon in the AM without some sort of calories beforehand because of the glycolytic nature of the sport. Some athletes might be able to train fasted and still lift heavy and crush metcons. It's really up to the individual, but are there any benefits to it?

There are LOTS of studies that have been done, unfortunately most of those done on animals in controlled environments, so it really isn't comparable. If you are an athlete that likes to train in the morning fasted and not eat until lunch time and that works for you, great! Do that. With performance athletes, the biggest problem that could come up is not having a big enough eating window to get your calories in. If a 200lb male is trying to eat 4000kcals+ per day, but only has an 8 hour eating window, that might cause some stomach distress. 

From the research I've done, it doesn't seem like there's really any evidence to support an *increase* in athletic performance because of doing IF or periods of fasting. There are health benefits of fasting for sure, but an increased 1RM back squat? A little unlikely.

Other benefits of fasting (not just IF)..


  • blood lipids (including decreased triglycerides and LDL cholesterol)

  • blood pressure (perhaps through changes in sympathetic/parasympathetic activity)

  • markers of inflammation (including CRP<, IL-6, TNF, BDNF, and more)

  • oxidative stress (using markers of protein, lipid, and DNA damage)

  • risk of cancer (through a host of proposed mechanisms; we’ll save them for another review)


  • cellular turnover and repair (called autophagocytosis)

  • fat burning (increase in fatty acid oxidation later in the fast)

  • growth hormone release later in the fast (hormonally mediated)

  • metabolic rate later in the fast (stimulated by epinephrine and norepinephrine release)


  • appetite control (perhaps through changes in PPY and ghrelin)

  • blood sugar control (by lowering blood glucose and increasing insulin sensitivity)

  • cardiovascular function (by offering protection against ischemic injury to the heart)

  • effectiveness of chemotherapy (by allowing for higher doses more frequently)

  • neurogenesis and neuronal plasticity (by offering protection against neurotoxins)

"Luckily, intermittent fasting gives your hard-working gut microbes a break from their digestion duties, so they can focus on cleaning house and keeping their populations intact. Fasting can also increase the diversity of your gut bacteria—important for your immune and overall health—and boost your body’s resistance to bad guy bacteria" (Zarrinpar, A.).

"Researchers are discovering that daily fasting activates a gene that strengthens the gut barrier, which protects us from harmful microbes, toxins, and other substances that can leak into the bloodstream and trigger immune reactions" (Shen, R.)


Part 1:

I don't personally believe you could gain an athletic advantage in terms of actual performance from doing IF or fasting. From a health and gut health perspective, trying some fasting or even experimenting with a 24 hour fast might be beneficial for your digestion. If my clients are experiencing some gut issues, I usually recommend them try a 24 hour fast and see how they feel. In most cases (with my clients), the ones experiencing GI issues feel a lot better when there are prolonged fasting periods to give their body a break from digesting. 

If you wanted to try a 24 hour fast, you could go from 5pm-5pm so that it doesn't feel like you're going a WHOLE day without food. If you do give it a try, let me know how it goes for you and if you experienced any GI or cognitive benefits!

Part 2:

DO WHAT WORKS FOR YOU. If intermittent fasting works great with your daily schedule and life, go for it! If it doesn't, I think research shows you'll be just fine eating like a normal human throughout the day. :-)


“All About Intermittent Fasting, Chapter 3.” Precision Nutrition,

Shen, R., Wang, B., Giribaldi, M. G., Ayres, J., Thomas, J. B., & Montminy, M. (2016). Neuronal energy-sensing pathway promotes energy balance by modulating disease tolerance. Proceedings of the National Academy of Sciences, 113(23). doi:10.1073/pnas.1606106113

Zarrinpar, A., Chaix, A., Yooseph, S., & Panda, S. (2014). Diet and Feeding Pattern Affect the Diurnal Dynamics of the Gut Microbiome. Cell Metabolism, 20(6), 1006-1017. doi:10.1016/j.cmet.2014.11.008

Lauren Bordelon