Even if I’m not expressly fasting, I gravitate towards working out on an empty-ish stomach. It just feels right to me to run on empty or, at the most, a couple eggs or a handful of nuts. Lifting heavy things while picturing the pounds of meat to come is, for lack of a better word, kinda Primal. The hunger fuels my performance – at least it seems to – while a brick of food sitting in my belly is a subjective burden. Look around the blogosphere (especially at Leangains and Free the Animal, where Martin Berkhan and Richard Nikoley have been doing some great work together charting Richard’s Leangains journey) and you’ll see that plenty of others are feeling the same.
This particular study took lean, active young 20-something men and broke them up into three groups: a fasted training group, a fed training group, and a non-training control group. The fed and fasted groups ate the same meals made up of the same foods, just at different times relative to the workout. They both trained in the morning, a mix of hard endurance stuff, lots of glycolytic work. No weights. The fasted group destroyed the fed group. All groups were eating an isocaloric high-fat, high-carb (50/40/10 F/C/P) diet well above maintenance, but the fasted group gained the least weight and the least amount of body fat. Most importantly, glucose tolerance and insulin sensitivity improved in the fasted group and suffered in the fed group (you don’t even wanna know about the poor control group), meaning the fasted folks were better able to shuttle nutrients into their muscles and handle both carbs and fat together. I can’t imagine the food quality was doing them any favors, either; Martin notes that subjects were supplied with take home meals, which I read as processed, boxed crap full of frankenfats and refined grains.
There’s more, of course. A study released earlier this month describes the beneficial effect of fasted endurance training on post-workout eEF2 activity. eEF2, or elongation factor 2, is a crucial factor in muscle protein synthesis. eEF2 is subject to either dephosphorylation (generally good for protein synthesis) or phosphorylation (generally inhibitory of protein synthesis). Subjects were split into two groups: CHO, who received a carb-rich breakfast before and carb-rich drinks throughout an endurance training session; and a fasted group, who received only water. Training was 3x a week for 2-hours at 70% VO2 max for both groups (not my cup of tea, personally). The CHO and fasted groups both had comparable eEF2 phosphorylation pre workout, but post workout, CHO group phosphorylation doubled and dephosphorylation was largely negated, while fasted group dephosphorylation was maintained and phosphorylation remained stable. Remember: dephosphorylation good for muscle maintenance, phosphorylation not so good. As I’ve said before, this type of endurance training can be fairly catabolic, and I myself had trouble maintaining weight, let alone actual muscle mass, as a runner.
Another study seems a bit more mixed. It looked at sprinting athletes, either fed (24g whey protein, 4.8g leucine, 50g maltodextrin/glucose) or fasted and then told to sprint. Power output and performance were similar, but fed athletes displayed greater muscle protein synthesis and muscle cell signaling. From what I can tell, though, the fasted athletes were never fed, not even after the sprinting. This is definitely interesting, but I’d like to see what happens to fasted athletes who eat right after training. The study’s authors even conclude that the important thing is ingestion of carb/protein in “close proximity” to time of training irrespective of chronological order.
The takeaway? It’s just more fuel for the fire. Fasted training improves metabolic performance and helps maintain muscle after endurance exercise, and, as long as you eat soon after, can jibe with intense sprint work. I’ll continue covering this topic as new research is unveiled. Stay tuned.
About the Author
Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.