For a long time I did all my workouts in a fasted state; usually they were in the morning and I didn’t feel terribly hungry, so a cup of coffee sufficed to get me into the gym. I put on 35 pounds of muscle doing this, albeit I was pretty skinny when I started, so that was from a low base. I no longer workout fasted, the reason for which I’ll describe below.
The basis for fasted workouts is usually given as greater fat loss. The idea is that with no fuel added right before the workout, your body will need to burn fat to supply the workout with energy. There’s some basis for this – it’s not all broscience – since any protein or carbohydrate in food raises insulin levels. Even small increases in the level of insulin all but abolish lipolysis, the process of fat breakdown. When one is fasting, insulin levels are low, and lipolysis proceeds apace.
This is all very well in theory, but does it work in real life? Some researchers recently tried to answer that question: Body composition changes associated with fasted versus non-fasted aerobic exercise. From the abstract:
It has been hypothesized that performing aerobic exercise after an overnight fast accelerates the loss of body fat. The purpose of this study was to investigate changes in fat mass and fat-free mass following four weeks of volume-equated fasted versus fed aerobic exercise in young women adhering to a hypocaloric diet. Twenty healthy young female volunteers were randomly assigned to 1 of 2 experimental groups: a fasted training (FASTED) group that performed exercise after an overnight fast (n = 10) or a post-prandial training (FED) group that consumed a meal prior to exercise (n = 10). Training consisted of 1 hour of steady-state aerobic exercise performed 3 days per week. … A meal replacement shake was provided either immediately prior to exercise for the FED group or immediately following exercise for the FASTED group, with this nutritional provision carried out under the supervision of a research assistant. Both groups showed a significant loss of weight (P = 0.0005) and fat mass (P = 0.02) from baseline, but no significant between-group differences were noted in any outcome measure. These findings indicate that body composition changes associated with aerobic exercise in conjunction with a hypocaloric diet are similar regardless whether or not an individual is fasted prior to training.
Result: no difference in body composition between fed or fasted workouts. The participants ate a hypocaloric diet, designed for them to lose weight, which they did.
What I wonder is what the effect would be on those not eating a low-calorie diet. That is, bodybuilders are interested in fat loss and muscle gain, not necessarily in losing weight per se. It seems possible to me that fasted workouts would help shed fat, and a post workout meal would help put on muscle, but I have to remain agnostic on that. Another wrinkle is whether resistance training might see different results from aerobic exercise. Also, participants ate a high-carbohydrate diet, and it seems possible that their insulin levels never got low enough, even in the fasted state, to get lost of lipolysis going. Those on a lower carb diet might see different results.
I mentioned above that I no longer work out fasted. One reason is the simple one that the weights are now heavier, the sessions more difficult, and having some food ahead of time seems a good idea. The other reason is the ambiguity of whether a dose of protein such as whey taken around the workout, either before or after, increases muscle protein synthesis and hence hypertrophy. There’s been a ton of research on pre- vs. post-workout protein and how it affects muscle protein synthesis. For example: Timing of postexercise protein intake is important for muscle hypertrophy with resistance training in elderly humans, which found that “early intake of an oral protein supplement after resistance training is important for the development of hypertrophy in skeletal muscle of elderly men in response to resistance training.” Here’s another: Timing of amino acid-carbohydrate ingestion alters anabolic response of muscle to resistance exercise, which concludes that taking protein before a workout increases muscle protein synthesis.
The ambiguity of protein timing was discussed in a recent review: Nutrient timing revisited: is there a post-exercise anabolic window? The authors question whether protein timing is a real effect, or whether just adding more protein to the diet without regard for timing is the real reason for greater hypertrophy.
However, when one is in the process of weightlifting, muscle is broken down, and all the more so if there are no amino acids from protein circulating in the bloodstream. So, to protect my muscles from breakdown, and to encourage hypertrophy, I take my protein before my workouts. There’s no guarantee that this will increase hypertrophy – at least that’s what the science says – but it seems to me a particularly good form of insurance that I’m not damaging my muscles to no avail while lifting weights.
That’s what I believe: you should take protein before a workout.