Low-Carb Or High-Carb Diet For Resistance Training

There is a common question that pops up rather frequently, and it centres around whether you should eat a low-carb or high-carb diet for resistance training. To answer this question, we need to explore how the crossover between exercise physiology and nutrition (e.g. low or high-carbohydrate diet) might impact your resistance training outcomes. By the end of this article, we hope to answer 3 primary questions:

1. What type of diet is best for resistance training performance?
2. What type of diet is best for resistance training recovery?
3. What type of diet is best for resistance training adaptations?

 

Performance, recovery, and adaptations may indeed be interlinked, but by splitting them up and exploring them separately, you will hopefully gain a deeper appreciation for some of the nuances at play.

 

Resistance Training Energetics

To take a step back, it is worth considering exactly what we are dealing with when it comes to resistance training. If we take a moderate repetition range working set, then we are producing high muscle forces for ~8 repetitions, each of which might last 2-4 seconds. Therefore, the length of the working period is going to be ~24 seconds.

 

 

As we know from research on exercise energetics, such a bout of resistance training will primarily involve 1) intracellular ATP stores, 2) creatine phosphate, and 3) glycolysis. The longer the set goes on, the more we will be relying on glycolysis for ATP, while also recognising that it is not an on/off switch and aerobic metabolism will be ticking away in the background, especially during rest periods.

Therefore, based on the high-intensity efforts, and short duration working periods, we would expect resistance training to rely heavily on carbohydrate metabolism for energy production, since fat oxidation is a much slower process and is insufficient for high-intensity exercise (Van Loon et al. 2004). This is observed in resistance training studies, with increasing RER (i.e. more carbohydrate metabolism) during resistance training sets, further increasing through subsequent sets (Farinatti et al. 2016).

Having said that, it is important to note that while this is the norm, the body is adaptable and can adapt its substrate utilisation patterns in response to changes in diet. Therefore, while this foundational information would push us toward concluding that low carbohydrate diets may not be a great idea, it’s worth maintaining an open mind before we explore further questions.

 

Muscle Glycogen, Carbohydrate Availability & Supplementation

It has been demonstrated that resistance training can reduce muscle glycogen content by 24-40%, with greater decreases seen with higher repetition protocols (Knuiman et al. 2015). However, interestingly, a lot of the research looking at the resulting fatigue from low glycogen status in resistance training tends to look at this question from the perspective of pre-exercise carbohydrate restriction. I don’t think it is fair to consider those two things the same; glycogen depletion during exercise vs pre-exercise glycogen status achieved via nutritional changes.

There is mechanistic evidence suggesting that low glycogen availability did not attenuate the increases in ERK1/2 or p90 ribosomal S6 kinase phosphorylation (pathways involved in muscle growth) following 3 x 10 leg extensions with 70% 1RM (Creer et al. 1995). They did find an attenuated response in Akt phosphorylation and a non-significant attenuation of mTOR phosphorylation, both of which are also involved in the anabolic response. However, another study which demonstrated a similar attenuation of mTOR phosphorylation showed that this effect did not lead to a reduction in muscle protein synthesis (MPS), which is really what we wish to affect, as opposed to just mTOR in isolation (Camera et al. 2012). It is important to note, however, that there are methodological issues in that the study designs do not really reflect resistance training volumes used in the real world, which may be more likely to highlight the negative effects of low glycogen availability.

One would think that protection against glycogen losses via carbohydrate supplementation may have positive effects. We do have limited evidence to suggest that carbohydrate ingestion prior to resistance exercise can enhance performance, but this effect was shown in the context of two sessions performed on the same day (with the performance boosted during the second session), but it would be an extrapolation to say that is purely a glycogen availability related effect, as we do have evidence from the same author to suggest that even in the presence of greater depletion of muscle glycogen (up to 49% less), there are no differences in isokinetic muscle strength (Haff et al. 1999; Haff et al. 2000). However, it may have implications for those of you training twice per day, or for multiple sports/activities.

Furthermore, there is conflicting evidence that would suggest no benefit to carbohydrate (CHO) supplementation during resistance exercise, with one of the multiple studies assessing this effect during squats at 85% 1RM performed to volitional failure with 0.3g/kg CHO showing no significant increase in repetitions performed, volume load or total work (Kulik et al. 2008). Other studies show similar outcomes, and some show signs of positive effects (Lambert et al. 1991; Conley and Stone 1996; Haff et al. 2000; Smith et al. 2018). This tells us that, while there may be benefits to a high carbohydrate diet (if our theory related to resistance training energetics leads us in the right direction), this may not necessitate acute consumption of carbohydrates within the workout period.

From a perceived exertion perspective, it has been noted that during a 2-hour session, supplementation with a 10ml/kg CHO solution (6% CHO) produced no attenuation of RPE, other than for whole body RPE during the back squat and upright row (Utter et al. 2005).

As a summary of this, the ISSN 2017 position stand suggests:

“Carbohydrate ingestion throughout resistance exercise (e.g., 3-6 sets of 8-12 repetition maximum [RM] using multiple exercises targeting all major muscle groups) has been shown to promote euglycemia and higher glycogen stores. Consuming carbohydrate solely or in combination with protein during resistance exercise increases muscle glycogen stores, ameliorates muscle damage, and facilitates greater acute and chronic training adaptations.”

However, I would just add that this conclusion seems to be somewhat confusing to me, as there did not seem to be evidence discussed in their position stand that would lead to such a clear-cut conclusion, although there is evidence to suggest that CHO and essential amino acid (EAA) supplementation combined can reduce markers of muscle damage and increase muscle cross-sectional area (CSA) (Bird et al. 2006). But, it remains to be elucidated whether this is an effect that could be attained purely through EAAs. We have discussed intra-workout carbohydrate supplementation before, and we must always refer back to the overall diet pattern and we can’t just assume that the diet is set up correctly.

 

Recovery & Adaptations

In the absence of sufficient carbohydrate intake (e.g. a very low carbohydrate diet), blood glucose levels still need to be maintained. The process of gluconeogenesis can enable this, which may involve the conversion of one’s beloved amino acids to glucose. Considering the fact that these amino acids are the building blocks of proteins, which are the building blocks of your muscles, this may be of interest, due to the potential for suboptimal muscle hypertrophy on a low carbohydrate diet (due to increased protein breakdown). Along with this, insulin tends to confer a strong net positive effect on muscle protein balance, affecting muscle protein synthesis (context-specific – dependent on amino acid availability and blood flow), but mainly [reducing] muscle protein breakdown, which may have implications for carbohydrate availability in the diet (Fujita et al. 2006; Everman et al. 2016; Abdulla et al. 2016). If we are eating low/no carbohydrates, then we may be breaking down more protein than someone on an isocaloric diet, (which may explain observed changes in nitrogen balance in some studies, which can sometimes be misinterpreted as muscle loss itself), which may simply drive up your protein needs. This is corroborated by evidence that endurance athletes who train in a state of low carbohydrate availability may require higher protein intakes to support muscle protein synthesis (Gillen et al. 2019).

Furthermore, it is also worth considering how this relates to muscle glycogen status and the cell signalling associated with exercise adaptations. Despite it being common practice for bodybuilders and resistance trainees to prioritise maintaining full glycogen stores, the evidence does not suggest that low muscle glycogen impairs resistance training signalling (Camera et al. 2012). This is a good lesson for those who fear feeling “flat”, as some bodybuilders and hypertrophy-focused trainees interpret such a feeling as being a signal to refeed as soon as possible in order to fill up their glycogen stores, which may limit one’s rate of fat loss (which may be desirable at times, but not all of the time).

Along with this, it does not seem to be the case that the ingestion of large boluses of carbohydrates after training are necessary to augment the muscle protein synthesis response. It is often suggested that these large carbohydrate boluses are necessary, since they spike insulin, which, as discussed previously, confers net anabolic benefits. While there is an element of truth to this, in that insulin does play a role in augmenting the anabolic response, these benefits can be yielded from a post-training protein feeding alone (Staples et al. 2011; Figuireido and Cameron-Smith 2013). Therefore, from a muscle hypertrophy perspective, it does not appear to be necessary to consume carbohydrates post-workout in an attempt to rapidly replenish muscle glycogen, although this will be more of a priority for individuals who need to recover quickly to perform again. Examples would include 1) training the same muscle groups within 24 hours, or 2) using those muscles for sport and not simply isolated gym training (e.g. 10km run the day after lower body resistance training) (Figuireido and Cameron-Smith 2013).

Overall, it would generally be considered suboptimal to consume a very low carbohydrate diet when trying to gain muscle or maximise muscle retention in a caloric deficit. However, there is unlikely to be a night and day difference, so if that is your preferred diet, you can still achieve great outcomes, and it is likely a fine strategy for short periods of time (e.g. quick 4-6 week fat loss phase). It is likely that the detriments of low carbohydrate diets have been overstated. While the evidence suggests that low carbohydrate diets tend to result in greater losses of lean body mass (of which muscle is a part) during caloric restriction, it is difficult to ascertain the specific difference since muscle thickness may simply be reduced due to a loss of water/glycogen within the muscle, making it a little more difficult to tease out whether or not there is truly more muscle mass lost (Tinsley and Willoughby 2016; Greene et al. 2018; Kephart et al. 2018). This also confounds evidence finding lower increases in both body and muscle mass on a [supposedly] hyperenergetic low carbohydrate diet, the interpretation of which may also be limited by changes in energy intake as a result of satiety differences between dieting conditions (Vargas et al. 2018). Along with this, the evidence would suggest some individual differences in outcomes on a low carbohydrate diet, therefore your personal response is not necessarily predictable (Chatterton et al. 2017).  

 

Low-Carb or High-Carb Diet For Resistance Training Performance

We have discussed adaptations, along with recovery, but what about performance? We have made the basic physiological case for carbohydrates likely being useful to support performance, but it is worth looking to see what evidence we have on controlled trials investigating performance.

Chatterton et al. (2017) investigated the effect of an 8-week low carbohydrate high fat (LCHF) diet in sub-elite Olympic weightlifters and powerlifters on strength, body composition, mental state and adherence. This was a small study, containing 5 lifters (3 sub-elite weightlifters, 2 sub-elite powerlifters), in which the subjects consumed a low carbohydrate, high-fat diet for an 8 week period, with 4 weeks of monitoring at each end of the intervention (16 weeks total). Carbohydrate intake was set at 1g/kg of body weight. 4 of the 5 lifters showed maintenance or slight increases in absolute or relative strength, one participant experienced a decrease in strength. This participant also happened to consume the highest carbohydrate intake at baseline, which may explain the discrepancy (greater perturbation to normal diet), along with some normal variation in performance over such a period of time, as suggested by the authors. What this study mostly highlights is the potential benefit of a low carbohydrate diet, since participants were able to spontaneously reduce caloric intake through reducing carbohydrates, while mostly maintaining (or slightly increasing) performance. Likewise, Greene et al. (2018) conducted a similar study in intermediate-elite lifters (weightlifters and powerlifters), demonstrating no difference in performance following 3 months on a low carbohydrate ketogenic diet. Again, this reinforces the previous points that this may be a viable strategy for short periods of time, despite the fact that such practices may not lead to optimal outcomes in the long term.

Paoli et al. (2012) conducted a similar study in elite gymnasts, with similar outcomes over a 30-day period. Despite consuming a very low carbohydrate diet, the gymnasts experienced no performance deficits on the hanging straight leg raise, ground push-up, parallel bar dips, pull-up, squat jump, countermovement jump, or 30-sec continuous jumps. This, again, is good news for anyone considering the consumption of a low-carb diet over a short period of time. This study also brings us a little closer to some of the training practices we may be interested in from the perspective of what hypertrophy training might look like. The previous two studies discussed both used 1RM as their means of assessment, which is useful, but may not be generalisable to multi-set, moderate-high rep resistance training performance.

When we consider that 1) it is generally this moderate-high rep, multi-set training that tends to be carried out with the goal of maximising muscle hypertrophy, and 2) we would expect carbohydrate/glycogen availability to be of greater relevance to these longer bouts (vs single rep performance which), we certainly shouldn’t close the coffin on the potential for lower carbohydrate diets to compromise resistance training performance. This gymnast study certainly provides hope, but our conclusions are limited by the fact that a single set may not reflect the outcomes across multiple sets (or a whole workout), and also due to the use of bodyweight movements, meaning the results could be confounded by the fact that the participants also reduced their body mass by ~5%. Moderate doses of resistance training can lead to considerable losses of muscle glycogen and hence it would be most interesting and useful to see the performance pattern over multiple sets at moderate repetitions (e.g. 4 sets of 12 repetitions) (Robergs et al. 1991; Tesch et al. 1998; MacDougall et al. 1999).

Unfortunately, there does not appear to be much evidence [that I can find] comparing multi-set resistance training performance between individuals on a low carbohydrate vs high carbohydrate diet. While there is a body of evidence on peri-workout carbohydrate supplementation, it would be unfair to infer from this, since the mechanisms of action may not relate directly to those relevant to chronic dietary patterns (e.g. acute glucose supplementation does not allow us to infer the effects of muscle glycogen status and/or differences in substrate utilisation on performance). There is potential for carbohydrate restriction to affect your performance (Leveretti and Abernethy 1999), but again, if a lower carbohydrate diet is your preferred approach, it probably isn’t too problematic, especially if maximum performance/hypertrophy is not your goal.

 

Real-World Observations & Guidelines For Carbs and Resistance Training

While the general consensus of trainees shouldn’t be viewed as a reliable source of evidence, it is worth considering what heavily-muscled people tend to do. If this corroborates with the theory presented, then it would increase our confidence in the conclusion that higher carbohydrate diets are likely a good strategy for resistance trainees.

Bodybuilding is the sport most likely to give us insights into the nutrition practices of those seeking to gain/maintain the most muscle. Chappell et al. (2018) conducted a cross-sectional study to examine the nutritional practices of 51 natural bodybuilders (35 male, 16 female) who were competing in the British Natural Bodybuilding Federation (BNBF) finals. Interestingly, the male bodybuilders who placed (i.e. the better bodybuilders) had a higher carbohydrate diet at the beginning and end of the contest preparation period when compared with those who did not place. This observation suggests that, at least in male competitors, higher carbohydrate diets may confer benefits to natural bodybuilders. However, it is also worth noting that this difference in carbohydrate intake is confounded by the fact that there was also a difference in energy intake at the start and end between those who did and did not place [in the top 5]. Along with this, it is not clear whether the competitive advantage, in this case, was the result of actual muscle size, or other factors (e.g. muscle fullness, body fat level). Therefore, this observation is likely of more relevance to the competitive physique athlete than it is to the general trainee at this point in time.

Furthermore, other dietary survey literature and a systematic review of 18 studies suggests that bodybuilders tend to consume somewhere in the range of 4-7g carbohydrate per kg of body weight, and other strength/power/speed athletes (weightlifters, throwers, sprinters) who would be engaging in somewhat similar activities (shorter bursts vs endurance athletes) consume 3-5g/kg (Slater and Phillips 2011; Spendlove et al. 2015). For these reasons, guidelines for bodybuilders include recommendations of carbohydrate intakes as high as feasible (once protein and fat requirements are taken care of (refer to our article on setting up the diet if you are unsure of what these requirements are)), and broader guidelines for strength sports, in general, suggest intakes of 4-7g/kg (Slater and Phillips 2011; Helms et al. 2014).

 

Application: Low-Carb or High-Carb Diets For Resistance Training

When examining these types of questions, it is nice to start at the basic science level (i.e. exercise metabolism) and zoom out to what we see working in controlled studies, and even to what we see working in a free-living environment. Having taken all that into consideration, it would seem that low carbohydrate diets are unlikely to be the best option for an individual looking to maximise their strength or muscle size. If you take your resistance training seriously, but really find that a low-carb, high-fat (LCHF) diet is best for you, then increasing protein intake slightly beyond standard recommendations may be useful to mitigate any negative effects of low carbohydrate availability on muscle protein balance (however, you must also be aware of the potential pitfalls to a LCHF diet).

For those seeking general health or body composition outcomes, it’s really up to your preferences more than anything else, since the difference in outcomes long term is likely to be insufficient to drive such nuanced decisions. If a diet allows you to consume the foods you enjoy, that are most accessible and convenient for you, then that is likely your best bet, provided you meet your basic nutritional needs (appropriate calories, sufficient protein, fibre, fruits, vegetables, etc.). At the end of the day, long-term adherence is what is most important, and if a low-carb diet facilitates adherence for you, then that is fantastic.

Overall, we have established that carbohydrate availability in the diet is likely to be permissive of better performance, recovery, and adaptations for the resistance training athlete. However, this effect is likely to be more pronounced in those who are training to support performance in another sport (e.g. GAA, soccer, rugby, martial arts), or to maximise muscle mass (e.g. bodybuilding, involving multi-set, higher rep resistance training). In the short term, lower carbohydrate diets are unlikely to have detrimental effects, and could be used effectively for athletes looking to cut weight without losing strength (e.g. powerlifting, weightlifting, Brazilian Jiu-Jitsu).

Hopefully, future evidence will fill in some of the knowledge gaps related to 1) the chronic effects of low-carbohydrate diets on muscle hypertrophy outcomes, and 2) the effect of low carbohydrate availability on multi-set, moderate/high rep resistance training performance.

If you need help with dialling in your diet, and figuring out exactly what kind of carb intake would be most beneficial for you, then you may benefit from online coaching. However, if you want to learn how to coach someone to better nutrition, then you may be interested in getting certified as a nutrition coach.