Is Fasted Training the Ultimate Workout Hack?

One major controversy in exercise is whether you’re better off working out in a fasted state. When I went to the gym fasted for the first time, I was shocked how much better I felt: quicker, lighter, stronger. Since I now exercise at 5 am, I also don’t have a choice — it’s not like I’m going to make breakfast at 3 am and give myself time to digest. My training is so much better in a fasted state I have wondered whether Olympic athletes compete fasted, and if pro athletes have tried it before games.

Additionally, the evolutionary biology of training fasted makes sense. Since the beginning of time, the order has been: first you hunt, then you eat.

My point of view got me into a kerfuffle recently on Twitter. A health guru wrote a post attacking fasted workouts, and I told him he was wrong. My comment generated two replies: 1) a brusque response from the health guru telling me that evolution is just “a shit theory,” and 2) a more thoughtful, lengthy reply from a member of the Open Longevity Project telling me I misunderstand energy systems.

I did some research on both of these viewpoints.

Is evolution a shit theory?

About 65 million years ago a giant asteroid struck near Mexico in an explosion known as the KT event. The impact caused dense clouds of debris and aerosols to circle the planet, blocking sunlight for several decades. While particles in the atmosphere absorbed almost all UV light, some blue light was able to penetrate due to its longer wavelength.

The animals that survived this decade of low light, like birds and small nocturnal animals, had blue-light sensitive proteins (opsins) in their eyes. In modern times, humans and other mammals have retained these opsins, like melanopsin, that respond to blue light and help regulate sleep and other circadian processes.

In fact, this blue-light adaptation now creates enormous problems. Excess blue light in our environment, besides causing all manner of metabolic problems, is also driving us insane.

Is evolution a shit theory? You can literally see that it is not.

Do I misunderstand energy systems?

Actually, it depends.

I was right about our ancestors hunting fasted, but … ancestral hunting was oriented around lengthy walks for persistence hunting, combined with sprinting in short bursts. Under these conditions, fasted exercise works.

I was wrong about the typical gym bro being able to train fasted because … maximal exertion like deadlifts or squats drain glycogen with an intensity unlike anything our ancestors did. Pre-exercise food intake is likely helpful if you’re pumping iron with the goal of hypertrophy — particularly if you’re doing many sets per body part.  

The reality of the gym, however, is that the best strategy for overall health is to exercise like our ancestors. Excessive muscle growth reduces lifespan because the mitochondria that belong in your brain and heart populate muscles instead. Large muscles are also not necessary for healthspan beyond a moderate layer of protective armor. Furthermore, you can infer what nature prefers by observing what women find attractive — and it’s not Mr. Olympia. Bodybuilding fans are mostly men, who mistakenly think they are following a regimen useful in attracting women.

How can I explain my personal success with fasted weight training?

My lifestyle has created adaptations in my body that make it work:

• With consistent fasted training, mitochondria become more efficient at oxidizing fat for fuel, even during exercise.
• Over time, the body upregulates enzymes involved in fat metabolism, allowing the body to use fat as a primary fuel source at higher intensities, sparing glycogen stores.
• In a fasted, fat-adapted athlete, the body also upregulates gluconeogenesis pathways, increasing the liver’s ability to create glucose and provide extra glucose during intense activity.

It’s all a light story anyway

Truth be told, the entire argument about food and exercise probably misses the point.

Sunlight — especially exposure to red, infrared, and ultraviolet light — would have played a crucial role in supporting our ancestors’ energy production and overall metabolic health. Second, regular exposure to natural light would have optimized our ancestors’ ​hormonal health​. Finally, sunlight also delivers photonic energy that could have contributed to exercise intensity. In short, for our ancestors living in nature, exercising while fasted would have felt completely different.