A recent study shows fasted training affects the post-workout anabolic response to weight training more favorably than fed-state training.

This study is very interesting to say the least, since it lends scientific support to explain the beneficial effects from both fasted-training and Leangains-style intermittent fasting. Let me give you the lowdown on this study in layman’s terms.

Weight training activates enzymes and switches on genes that up regulates protein synthesis in muscles. Out of these signalling mechanisms, the phosphorylation, “activity” plainly speaking, of p70s6 kinase may serve as an indicator of muscle growth, along with other myogenic transcription factors. Myogenic meaning from within the muscle. Nutrition no doubt affects the myogenic signaling mechanisms, but it’s still not fully understood to what degree.

In this study, subjects were split into two groups that were trained on two occasions separated by three weeks. The three-week rest period between sessions served as a “washout” period, in order to make sure that the prior session didn’t interfere with the results obtained during the second test.

The workouts were fairly basic whole-body sessions: 3 x 8 in seven movements such as bench press, overhead press, curls and leg press.

One of the sessions (F) were performed on an empty stomach after an overnight fast.

The other session (B) was performed in the fed state. Subjects were given a breakfast of 722 kcal composed of 85% carbs, 11% protein and 4% fat, and training was initiated 90 minutes after the meal.

After the weight training session, both groups rested for 4 hours. At the one- and four-hour marks, muscle biopsies and blood tests were obtained . Participants were also also given a recovery drink to sip each hour during the rest period.

Results revealed that the F session had twice as high levels of p70s6k in comparison to the B when measured at the one-hour mark post-workout. Other myogenic transcription factors were also higher at this point, though not quite as pronounced as p70s6k. At the four-hour mark, the differences between the two groups had evened out.

Why may fasted training be beneficial for the post-workout anabolic response?

The researchers concluded that “Our results indicate that prior fasting may stimulate the intramyocellular anabolic response to ingestion of a carbohydrate/protein/leucine mixture following a heavy resistance training session. ”

Among other things, increased levels of p70s6k may lead to a faster transport of amino acids into the muscle cell membranes, which should lead to a more rapid and potent anabolic response to post-workout nutrient ingestion. The effects seen on the other myogenic signaling mechanisms could also affect muscle growth through other pathways.

It seems that the increased anabolic activity seen post-workout is a compensatory response to the increased catabolism that occurs during fasted state training. Very interesting. The big question is if there would be a net difference in muscle growth at the end of the day. Training on an empty stomach will cause greater catabolism in the short run, but will it yield greater gains in the long run? Do we make a small sacrifice in order to receive a greater reward?

Well, I think we can leverage the results of this study to our benefit and sidestep the negatives if we ask ourselves why, relative to the fasted group, p70s6k and the other myogenic transcription factors were inhibited after a pre-workout meal. Or rather the highly insulinogenic pre-workout meal served in the study — a whopping 153 g high glycemic index carbs.

There’s no clear answer here, but other studies have suggested that carb intake during an endurance training can blunt the expression of several metabolic genes post-exercise. Insulin may play a role here, for sure.

Another way to think of it is that by providing nutrients to the body, exercise is experienced by the body as less of a stressor compared to fasted-state training. No need to adapt or compensate when all is provided for you. A similar phenomenon can be seen with antioxidant intake, where recent studies show that ingesting antioxidants from supplements weakens the body’s own response to deal with free radicals created by training. We are making it easy for the body and that may be a suboptimal way to train.

So do I suggest everyone start training fasted from now on? Of course not. Remember, it is still not known if the net effect of fasted state training will lead to more favorable results in the long run.

However, I do suggest the following:

  • Make sure that the great majority of your daily allotment of calories and carbs are ingested in the post-workout period, and not before.
  • The immediate pre-workout meal should contain no more than a moderate amount of low glycemic index carbs. The exact amount would depend on many factors, total workout volume being the biggest one to consider, but a good guideline for a moderate volume weight training session is approximately 0.6 – 0.8 g carb per kilogram body weight or 0.3 – 0.4 g per pound of body weight. Have this meal 1.5 – 2.5 hours before your training session.
  • For fasted sessions, ingest 10 g branched chain amino acids (BCAA) shortly prior (5-15 mins) to your training session. This does not count towards the 8-hour feeding window that I advocate post-workout; that starts with your post-workout meal. By ingesting BCAA pre-workout, we can sidestep the increased protein breakdown of fasted training while still reaping the benefits of the increased anabolic response as seen in this study. Not only that, BCAAs actually increase phosphorylation of p70s6k when ingested in the fasted state prior to training. So by training fasted, with BCAA intake prior to sessions, we get a double whammy of increased p70s6k phosphorylation that should create a very favorable environment for muscle growth in the post-workout period.
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