Carbs and Resistance Training

This week a study was released that has the potential to be quite revolutionary in the resistance training world. It was conducted by Menno Henselmans and co-authors and showed there that is no high-quality evidence that carbohydrates should be the preferred choice of fuel for resistance training performance [1]. This is very much against the grain of the prevailing wisdom over the last few years that has endorsed the idea that carbohydrates should be biased over fats on the rationale that resistance training workouts deplete glycogen and that refueling glycogen is anabolic and aids recovery.. Here, I will discuss the findings of the study and then share my thoughts on implications this can have in relation to how you structure your diet for bodybuilding success.

The Study

People often place way too much emphasis on single studies and this appears to happen a lot in the training and nutrition world (though maybe that’s just my experience bias because it’s the world I’m in). However, what’s different about this single study is that it’s a systematic literature review (SLR). This strengthens its integrity quite significantly. In a SLR you state the databases you are searching, your search terms, and your inclusion and exclusion criteria. In this way, other researchers should be able to replicate your SLR and get exactly the same findings. This is in contrast to a standard literature review where a researcher can select articles as they please, meaning — subconsciously or otherwise — they can pick those that support their hypothesis or bias.

Another advantage of the SLR is it is (theoretically) comprehensive. It’s unlikely you’re going to cover every single article relevant to your topic due to differences between search databases, search terminology, time constraints, human error (i.e., missing a paper whilst flicking through the search results) and language differences. However, you’re covering a decent amount of ground and so the chance of an article — especially one with important results relevant to your research question — slipping through the net is small.

We also mentioned that the search terms and inclusion/exclusion criteria are relevant. On this note, I see nothing wrong with their approach in the methodology. The search terms seem comprehensive enough and probably didn’t much miss. The inclusion criteria were:

(1) acute carbohydrate manipulation (up to 24 h) or supplementation prior to strength tests

(2) exercise-induced glycogen depletion and carbohydrate manipulation prior to strength tests

(3) short-term carbohydrate manipulation of at least a day and up to a week prior to strength tests

(4) long-term changes in strength performance after more than a week of carbohydrate manipulation and strength training.

Included articles underwent a quality assessment designed specifically for grading sports science literature (TESTEX) and, although I didn’t check all of the articles, most are in peer-reviewed journals.

The Findings

In short, the findings show that there was basically no support for prioritizing carbohydrate intake over other macronutrients for enhancing resistance training performance purposes in any of four categories investigated. Whilst some of the studies were confounded by the fact that they were not isocaloric (calories were not matched when investigating the effect of macronutrients on performance, meaning differences could be due to calories rather than macronutrient ratios) the authors also put forward some reasoning as to why these findings might be the case.

Primarily, they refute the notion that carbohydrates should be consumed for glycogen replenishment after resistance training because glycogen is not really depleted so much. Resistance training consists of performing exercises at a moderate/high intensity for a short duration of time, after which trainees spend large amounts of time resting until they are ready to perform the next set. Unlike exercises with a higher cardiovascular component, during resistance training we spend more time resting than actually working. During the rest times the aerobic system (fueled by fatty acids, and not glycogen) can supply the necessary energy. Additionally, there is also the contribution of the creatine phosphate system during the lifting itself. If we combine the contribution of these systems and look at the energy expenditure we can expect during a resistance training session, we don’t really get close to a level of glycogen depletion that would necessitate high levels of carbohydrates as something like running or playing football might. One exception of this could be those performing very high volume training sessions of long durations, but given that the literature is not very supportive of this as an effective training approach, this style is diminishing in popularity.

Interpretation

It’s first worth pointing out that this does not mean we should just abandon the idea that macronutrient ratios matter at all. Although it is an SLR, it is still only one study. It could be that that studies in the SLR didn’t have enough power or that higher sensitivity techniques yet to be developed will find different results in the future. I’m not trying to argue for or against the results here, but I’m just trying to convey that we should always look at studies as a piece of the puzzle of evidence and never place too much weight on one or another.

Having said that, I think one takeaway from this is that maybe we don’t have to place too much effort on maximizing carb intake, and instead can eat a little more freely in ways that, for some people, might better suit their needs or routines. I know quite a few people in the bodybuilding community who account for their protein, place fats at a minimum of around 0.5g/kg bodyweight/day, and then eat as many carbs as possible to make up the remainder of the calorie quota. Indeed, I basically do the same with myself and encourage most clients to do the same. In light of this evidence, such an extreme approach may not be necessary.

I’ve had discussions over the years with many people, some of which have been clients, who’ve claimed they feel they perform much better with higher fat diets instead of carbs. In this scenarios, I’ve always encouraged them to reconsider this on the physiological rationale for the performance enhancement effects of carbs presented at the start of the article. Thus, such people may now be more inclined to stand their ground and bias fat intake, which indeed for them may actually be the better option. And since there’s a physiological rationale for anabolic effects of higher fat intakes in the form of higher testosterone production and hypertrophic signalling (in the case of omega-3s [2]), there may even be some benefits to be gained from doing so (although the SLR probably would have noticed if there was). Thus, I think the results of the study (if reflective of the true situation) are great news; it means need not worry too much about macronutrient ratios and, as long as you hit your calorie targets, performance won’t take a hit.

Exceptions

Apart from the situation of high-volume training we discussed above, others who may also want to maintain a carb-bias in their diet would be those who also engage in other sports with a much higher cardiovascular element, for example, if you also play football, do HIIT training, cross-fit, etc. In these circumstances, glycogen will be much more depleted and so you will want to maintain carb intake to replenish depleted stores.

Additionally, I think biasing carbs when in a calorie deficit is still wise for hunger management purposes. Fatty foods tend to have a higher calorie density and, whilst some people claim their hunger is much lower with a higher fat intake, foods with a high volume: calorie ratio often tend to be rich in carbohydrates (think of fruits and vegetables). So, in this scenario, although you’re not setting up your diet to bias carbohydrate intake per se, by focusing on fruit and veg intake for satiation purposes your diet will end up being carb dominant. I mention this only because some people may limit their carb intake to bias fats in light of these findings, which could have the impact that dieting becomes more difficult if not accounted for.

Conclusion

As often happens when research is released that goes against the dogmatic grain of the bodybuilding world, there will probably be some pushback to these results. Whilst it is good to maintain a healthy skepticism, we should also utilize science to facilitate our progress. Although the results of Henselmans et al. may not providing us with some cutting edge trick to enhance performance, they do give us more flexibility to set up our diet in a way that best suits us on an individual level and, if nothing else, give us one less thing to worry about. Having the knowledge that you don’t have to be so precise about how you distribute your macronutrients should be welcomed news and should allow you an extra degree of freedom with which to enjoy your life.

References:

[1] https://doi.org/10.3390/nu14040856

[2] https://dx.doi.org/10.3389%2Ffnut.2019.00144

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Dan Kirk

Dan Kirk

Researcher at Wageningen University Research; MSc Nutrition & Health and BSc Biochemistry; practicing data science; and lifetime natural bodybuilder