Intermittent Fasting

I guess we’ll start at the beginning. I first came across intermittent fasting (IF) in college. I found a conversation about it on a bodybuilding forum that led me to Martin Berkhan’s Leangains website. He had been implementing daily 12 hour fasts with 8 hour feeding windows to keep him lean during his bodybuilding training. I believe credit is owed to him for introducing IF to the general resistance training community. It looked enticing, but wasn’t something I began following.

Until I started working for my friend the summer before nursing school. I spent 8+ hours a day driving to houses and changing their floral arrangements. Light physical activity, on my feet all day. For whatever reason, I dove into IF. I found that I felt quicker physically and clearer mentally when I fasted until about 11am or noon. I noticed I started losing weight. But, that’s because I decreased the amount of hours I could eat, therefore I ate less. No breakfast, and no late night food after 8pm.

In nursing school when I went deep into the ketogenic and fasting physiology research, I came across time-restricted feeding (TRF, another term used in the literature). Majority of the literature on fasting is in animal models, so caution must be used when extrapolating results to humans. Lots of these studies fast the mice intermittently (every other day) followed by days of normal feeding. General conclusions usually display improved weight loss, blood pressure, fasting blood sugar, fasting insulin, and other biomarkers.

As far as human evidence, studies are few and far between. Many of them use different feeding windows, different calorie goals, have populations with varying training experience, and different populations with varying health backgrounds. Therefore, you must decide if those findings really relate to your health and background. Some human studies show similar improvements in inflammatory and metabolic biomarkers to the animal studies, but not all of them. The improvement of those markers is also likely coming from the caloric deficit, not the time spent fasting.

Lots of people like to talk about autophagy and fasting. Autophagy is basically the recycling process of dead or defected cells. Its happening all the time. It happens when you train. Intermittent fasting isn’t magic and doesn’t upregulate this process like so many people claim. Longer, extended fasts of 48+ hours will, but that topic is for another day.

A cool and applicable study published in 2020 in the journal Nutrients, titled “Four Weeks of Time-Restricted Feeding Combined with Resistance Training Does Not Differentially Influence Measures of Body Composition, Muscle Performance, Resting Energy Expenditure, and Blood Biomarkers” examined IF’s impacts on fat mass in a recreationally active young male population (average age 22). Both groups had the same full body resistance training program, the same protein goal of 1.8g/kg BW, and the same caloric deficit of 25%. Only difference is the intervention group maintained an 8 hour feeding window. Their conclusion after 4 weeks … “a TRF style of eating does not enhance reductions in FM over caloric restriction alone during a 4-week hypocaloric diet.” The IF group didn’t lose more fat than the control group, and all the differences in improvements of strength/muscle mass between groups were insignificant. PMID 32316561 if you want to review the study yourself.

BIRDS EYE VIEW:

Intermittent fasting isn’t magic. It’s simply a way to decrease calorie intake throughout the day. If you went about eating the same foods as you usually do, but limited the window in which you could eat them, you would likely consume less calories and lose weight. Some people, myself included, feel clearer and more alert when fasted. I will still do intermittent fasting on days that it makes sense, but I personally won’t do it very consistently. My current goal is to maintain my muscle mass, so spending more time fasted each day than fueled will not optimize my body’s ability to retain that mass. But, as I aim to lose some weight, I will use IF as a tool to help me control my calorie intake.

If it works for you, and gets you closer to your goals, that’s all that matters.