The Facts about Fasted-State Training, Part I
Is exercise with an empty belly a panacea for weight loss and improved endurance? Let's find out!
At first blush, fasted-state training seems like a silver bullet leading to all kinds of physiological adaptive goodness. The idea is that you exercise without food in your system— typically in the morning when your last meal was dinner. In this scenario, blood sugar and glycogen levels are compromised, so you’re more likely to burn body fat as fuel.
Proponents of the practice feel—among other things—this can lead to sustained weight loss and a shift in your metabolism allowing you to exercise harder for longer amounts of time.
I’d love for this third paragraph to simply read, “This is all true! The end. There will be no Marvel movie post-credits teaser. Please exit the theatre in an orderly fashion.”
Sadly, this is not the case. While fasted-state training may have some benefits, research is mixed. In the words of The Dude, “This is a very complicated case. You know, a lotta ins, a lotta outs, a lotta what-have-yous.”
With that in mind, let’s break it down with a two-parter. Today, we’ll look at fasted-state training for weight loss. Next week, we’ll look at fasted-state training for improved endurance.
But first, a PSA regarding immunity.
Moderate exercise promotes the release of immune system-boosting proteins called cytokines. It also promotes the circulation of white blood cells called lymphocytes, making it easier for them to find bad things (antigens) to attack. Experts even say that regular exercise can be a valuable weapon in fighting COVID.
However, prolonged, intense exercise such as cycling or distance running may have an opposite effect. It can suppress your immune system, especially when it comes to upper respiratory tract infections—“catching a cold” as the hoi polloi call it.
To combat this, the Journal Sports Sciences explains that 30g to 60g an hour of carbs during prolonged exercise may help support your immune system. A sports gel every 45 minutes should cover that. A large banana or five dates every hour should also work. As for how to cram four or five large bananas into your jersey pockets, you’re on your own.
In other words, fasted-state training for longer periods doesn’t do your immune system any favors, so if it’s cold and flu season or you’re at higher risk of COVID, think it over.
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Now, the weight loss thing.
Yes, exercising in a fasted state does push your body to utilize fat stores acutely. However, if you’re doing it to lose weight, you need to consider your entire day of eating and activity.
At this point, we know that weight loss isn’t necessarily as simple as calories in, calories out. Herman Pontzer’s book Burn: New Research Blows the Lid Off How We Really Burn Calories, Stay Healthy, and Lose Weight does an amazing job of explaining and exploring this concept.
That said, it does apply in the context of this article. Since we brought up the Marvel Cinematic Universe a moment ago, let’s split the timeline, creating a multiverse to illustrate this point.
Across the entire multiverse, let’s say Ant-Man burns 1,800 calories during his day of normal activity, plus 600 bonus calories fighting Yellowjacket, for a total of 2,400 calories.
However, on Earth 1, Ant-Man wakes up, fights Yellowjacket in a fasted state, then eats 1,900 calories over the course of his day. 2,400 (daily burn plus exercise) minus 1,900 equals a 500-calorie deficit that day. He’ll probably lose a little weight.
Yet, on Earth 2, Ant-Man wakes up, eats a 300-calorie breakfast, then fights Yellowjacket non-fasted, then eats an additional 1,600 calories over the rest of his day. In both universes, he ate 1,900 calories and had a 500-calorie deficit. Weight loss will most likely be the same. Yes, he “mobilized fat stores in a fasted state” on Earth 1—but then he replenished those fat stores later in the day.
A study in the Journal of the International Society of Sports Nutrition backs up this math. It divided 20 women into two groups. They all ate a similar diet (around 1,300 calories), but half of them did a cardio workout in a fasted state while the other half drank a 250-calorie shake prior to exercise. Everyone had similar results with regards to weight loss.
Here’s another study featuring high-intensity interval training that came to the same conclusion.
Power math and comic book metaphysics aside…
Here’s a caveat. Fasted-state training may be a useful weight loss tool if you use it as a distraction to skip breakfast and therefore eat less over all. A 2016 study on young men showed that those who skipped breakfast before running for an hour ate less over the following 24-hour period than those who ate breakfast before running.
Generally, I don’t really advocate skipping meals, especially in light of the immunity issues we just reviewed, but I thought you should know.
No matter which corner of the multiverse you live in, the takeaway is that fasted-state training on its own doesn’t lead to weight loss, but it can be used as a tool in a bigger weight loss strategy.
Next week we’ll look at how—and if—fasted-state training can improve your metabolism so that you can exercise and/or fight crime longer without blowing up.