Recently I led the most comprehensive review to date on how many carbs strength trainees need to optimize performance. Now a new review by King et al. has performed a meta-analysis of studies on the effect of pre-workout carbs on acute strength training performance. The new review effectively zooms in on our review’s section on acute performance and bolsters its findings with a statistical meta-analysis. Some of their conclusions disagree with our analysis, so let’s take a deep dive into the data to find the truth. Below are the new review’s main conclusions.
The new review’s conclusions
“Carbohydrate ingestion has an ergogenic effect on resistance training performance by enhancing volume performance, which is more likely to occur when sessions exceed 45 min and where the fast duration is at least 8 hours. Further, the effect is moderated by the number of maximal effort resistance training sets completed, but not the load used or carbohydrate dose.”
“Collectively, the findings of the current review demonstrate an ergogenic effect of carbohydrate ingestion for enhancing volume performance during resistance training.”
“Our overall recommendations reflect the position that carbohydrate ingestion is an efficacious nutrition strategy for enhancing volume.”
Our review’s conclusions
In contrast, we concluded pre-workout carbs generally won’t influence strength training performance in practical settings: “In conclusion, carbohydrate intake per se, independent of energy intake, is mechanistically and statistically unlikely to acutely affect resistance training performance in a fed state for workouts up to 10 sets per muscle group. Higher-volume workouts may require higher carbohydrate intakes to optimize performance, but there is a clear need for more isocaloric research with realistic placebos. However, given the uncertainty in the literature, based on Lynch and Krings et al., strength trainees may be advised to consume at least 15 g net carbohydrate and 0.3 g/kg protein within 3 hours pre-workout to optimize performance. If the workout involves more than 10 sets per muscle group, higher carbohydrate intakes might be warranted.”
The key difference between positions is that their overall conclusion says carbs benefit performance, whereas our overall conclusion says they generally do not. Their conclusion is supported by their overall analysis result that when grouping all studies together, total training volume was significantly higher in the groups consuming carbs than those did not. However, there are 3 huge caveats to the conclusion that this means carbs universally improve our performance in the gym.
Caveat 1: Do you train fasted?
In the subgroup analysis of the new meta-analysis, the results showed that pre-workout carbs only significantly affected performance when the participants had been fasting for at least 8 hours. There was no significant effect in studies in which the subjects had not been fasting for at least 8 hours prior to their test workout. The evidence thus only supports consuming pre-workout carbs if you’d otherwise train fasted. Our findings agree with this. We recommended not training fasted. Concretely, we recommended consuming at least 15 g net carbohydrate and 0.3 g/kg protein within 3 hours pre-workout. Higher intakes do not provide further benefits according to both our analysis and the new meta-analysis. Formally put, there was no dose-response effect of carbohydrate intake.
Caveat 2: Do you perform more than 10 sets per muscle group?
Similarly, subgroup analysis in the meta-analysis showed pre-workout carbs only significantly improved performance in training sessions over 45 minutes. There was no significant effect of carbohydrate intake on sessions shorter than 45 min.
In my view, it makes little sense to measure session length rather than the number of sets per muscle group. In 45 minutes you could do 20 sets of squats with a 1-minute rest interval or you could do a ‘full-body’ workout with bench presses, chin-ups and squats for 3 sets each with 5 minute rest intervals. Both are 45 minutes, but you do either 20 or 3 sets of squats. Clearly these workouts will have different effects on glycogen depletion and energy availability to the quads. As a concrete example of a study in the analysis that influenced the results, the new study authors included Wax et al. (2012) in their analysis, whereas we excluded it for not meeting our criteria of a representative strength training protocol. The effect size favoring pre-workout carbohydrate intake in this paper was over 4 times greater than that of the average in the literature of its section, making it the largest effect size in this sub-analysis by almost factor 2. The reason for the huge effect size in this study was that they did not use a conventional strength training protocol. They performed 20-second maximal quadriceps contractions with periodically superimposed electrical muscle stimulation to ‘super stimulate’ the quads and the rest intervals between sets were only 40 seconds. They continued until they couldn’t hold the contraction anymore for at least 5 seconds, which took about 15 minutes even in the placebo group. So despite it being a very short workout in total, they were doing around 15 sets to failure for the quads with electrical muscle stimulation to boot. The duration in time per se should be largely irrelevant. What matters is the training for the muscle in question.
The authors performed a moderator analysis and it indeed showed the number of sets influenced how big the effect of carbohydrate intake on performance was. The authors seemed to have used total set volume though, which is still not a good marker in my view, because muscle glycogen can only be used by that specific muscle. Training your biceps does not deplete glycogen stores in, say, your quads. So the most logical measure in my view is sets per muscle group. This is what we used for our analysis and the results are in agreement that pre-workout carbohydrate intake only becomes relevant when you’re doing a bro-split type workout with 10+ sets per muscle group. To quote myself:
“In studies with performance tests consisting of more than 10 sets per muscle group, significant positive effects of higher carbohydrate intakes or a trend thereof were observed in 3 studies, whereas only 1 study found no significant effects. Again though, none of the studies favoring higher carb intakes were isocaloric. Out of 14 studies with lower-volume performance tests (up to 7 sets per muscle group), 3 studies significantly favored the carbohydrate conditions, yet 2 favored the lower-carbohydrate conditions. In other words, if you do up to 7 sets per muscle group, it’s very unlikely you need more than 15 grams of carbs pre-workout, but if you go up to 11+ sets, you may benefit somewhat from higher intakes. You’ll benefit more from designing a higher-frequency training program though.”
The above 2 caveats are of course major and the authors recognized them. Indeed, despite their categorical statements in a few parts of the paper that carbohydrate improve performance without any qualifying conditions, in other parts of the paper the authors do provide these qualifications: “Carbohydrate ingestion has ergogenic effects on resistance training performance where session duration was longer than 45 min and the fast duration was at least 8 hours. Conversely, carbohydrate ingestion did not significantly affect performance when session durations were shorter than 45 min or fast durations shorter than 8 hours.” (One could nitpick about the use of ‘or’ in this sentence, because technically no interaction effect between the 2 conditions was tested, but I think this is a moot point.) In other parts of the paper, the authors converted the duration of 45 minutes to “at least 8–10 sets”. Although the authors did not provide any support for this conversion and they should have specified it was sets per muscle group, these findings perfectly agree with our review’s findings. Pre-workout carbs are likely only beneficial when doing more than 10 sets per muscle group or if you’d otherwise be training fasted.
Caveat 3: Carbs aren’t the only energy source
All control groups in the new meta-analysis were technically training fasted. Yes, really. The authors only included studies comparing pre-workout carbohydrates to virtually calorie-free placebos, water or nothing at all. I guess the authors were trying to study a homogenous data set, but this of course massively limits the practical validity of the results. In our analysis, energy intake proved to be a decisive factor in explaining the different study findings in the literature. When we looked specifically at studies in which energy intake was equal between groups, “none of the isocaloric comparisons found the higher carbohydrate condition had greater performance than the lower carbohydrate condition.”
By only looking at carbohydrate intake and not accounting for the consumption of anything else, the authors also included a few dubious papers in their analysis. The biggest outlier in the analysis was clearly Bird et al. (2013). It showed a positive effect of ‘carbohydrate intake’ that was over 4 times greater than the average of the total included literature. I put ‘carbohydrate intake’ in between parentheses here, because the higher-carbohydrate group in this study also consumed *takes a deep breath* protein (EAAs), creatine, micronutrients, beta-alanine and caffeine(!) Assuming it was the carbs that improved performance in this study and not any of the multitude of other substances known to improve performance is questionable to say the least. In our analysis we did not include this paper.
The authors also included Naharudin et al. (2020) as evidence of a positive effect of pre-workout carbs. This is what we wrote about that study in our paper: “These researchers found that a high-carbohydrate breakfast (1.5 g/kg) improved resistance training performance compared to drinking only water after an overnight fast; however, a flavor- and texture-matched placebo breakfast with only 29 kcal improved performance similarly. The sham breakfast also reduced hunger similarly. Thus, the feeling of having consumed something can be more important than carbohydrate intake per se.” We then discussed multiple other studies showing that the perception of having consumed something, especially something with energy or a pleasant taste, can improve our motivation to push ourselves in the gym. The new meta-analysis’s authors do devote 1 line in the limitations section to this literature, but I think it deserves spotlight emphasis, as it completely undermines the idea that any of the observed benefits of pre-workout meals are really due to carbohydrates. Any other meal seems to be equally beneficial, which of course completely changes the practical application of these findings: it changes “you need carbs” to “just don’t train completely fasted and you’re fine”.
With the above caveats in mind, all the new meta-analysis really found is that consuming carbs is better than not consuming anything if and only if you’ve been fasting for 8+ hours and/or you’re training with a very high volume per session (per muscle group). The meta-analysis’s results are thus actually perfectly in line with our findings and they are a far cry from a categorical “pre-workout carbs improve your performance.” I feel the authors would agree on most of these matters, and they discuss all of these points at some point to some degree in their paper, but they failed to provide these crucial qualifications for their statements in some parts of the paper, making it seem like there were more relevant effects of pre-workout carbs than the data really supported. In my view, the new findings only strengthen our practical recommendations:
“Overall, our findings indicate conventional high-carbohydrate intake recommendations of 4–10 g/kg/day may be excessive for the performance of strength trainees, such as bodybuilders, powerlifters and Olympic weightlifters. Based on the inconclusive evidence and potential for benefits but not harm, strength trainees are advised to consume at least 15 g carbohydrates and 0.3 g/kg protein within 3 hours of their training sessions. If the workout contains eleven or more sets per muscle group or there is another high-intensity workout planned that day for the same musculature, higher carbohydrate intakes up to 1.2 g/kg/h may be warranted to maximize glycogen resynthesis in between workouts.”
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