Nutrition, Training

Carbs vs Fat for Endurance and Performance

There’s so much science that goes into human nutrition and performance that it’s almost impossible to find a starting point.  I guess the best place would be that which has the biggest impact for the smallest investment.  Or more simply, that which underpins the whole thing: energy production.

Some of you will know the three macronutrients and how they provide energy, but what can sometimes be hard is deciding how much of each to have, and perhaps less importantly, when to have them.  This piece will quickly outline what macronutrients are, and attempt to briefly answer the “quantity” and “timing” questions.

A Quick Overview of Macronutrients

The term “macronutrient” refers to the three larger (macro) nutrients that provide the body with energy: protein, carbohydrate, and fat.  Outside of being a fuel source, each macronutrient plays a different role in the body.

For example, protein is essential for the replication of all cells, important in this case for its crucial role in muscle growth and repair.  Fat plays many roles including a key part in hormone regulation, as well as being a vital part of cell structure.

Carbohydrate is different to fat and protein in that it is the only one of three of the macronutrients where its intake is not critical to survival.  However, if we’re talking about maximising sports performance, it seems to be essential (keto advocates hold back the rage momentarily).

The Impact of Low-Carb

Carbohydrate and fat provide almost all of our fuel during physical activity.  Protein does provide a minimal amount, but this is only during longer duration endurance activity.

Given that fat contains more calories than carbohydrate, coupled with the fact that exercise performance is severely hampered when carbohydrate stores (glycogen) are depleted, it should make sense that switching to fat as a fuel source would improve performance; primarily by increasing fat oxidation and preserving muscle glycogen stores.

However despite the increased fat oxidation, performance appears to be hampered not improved, when switching to fat as a primary dietary source for fuel.  The main factor affecting performance differences, appears to be the increased usage of oxygen that fat requires to produce an equivalent amount of ATP (energy) as carbohydrate [1].

Understanding the mechanism behind the difference in oxygen efficiency of fat and carbohydrate oxidation requires a solid base knowledge of human metabolism, so an explanation of such is perhaps not warranted here.  However, the data for such has been well established for decades and appears somewhat indisputable.

Beyond oxygen efficiency, other possible differences in performance rates may be due to subjective experience and perceived rates of exertion.  However it is worth noting that this is of secondary interest.

Training Low, Competing High

Whilst carbohydrate intake is therefore crucial to peak performance, recent scientific research is suggesting that old protocols of continual high carbohydrate consumption are sub-optimal.  Lower carbohydrate consumption around training appears to offer improved biological adaptations to training [2-4].

Given that a low level of stored glycogen and circulating glucose impairs performance, the concept of “training low, competing high” has been widely used in recent years.  This is a protocol where low-carbohydrate consumption around training is used to maximise training-induced adaptations, and carbohydrate refeeding is then employed prior to competition to restore glycogen levels in the muscle and liver [3].

Pre-Event Nutrition

Basic recommendations of pre-event fuel have often centred on a “light” meal rich in carbohydrates 2-4 hours prior to an event, and foods such as fruit or low-fat muesli bars 1-2 hours prior to exercise.  More recent research is suggesting that it may be more beneficial to load carbohydrates and restore glycogen levels in the days leading up to an event.

Some research has also shown that a high fat meal four hours prior to an event, had a significantly better impact on performance than a high carbohydrate meal at the same time.  This was after three days of carbohydrate loading prior to the event.  Benefits of the high fat meal were improved further when maltodextrin (a carbohydrate) was consumed immediately prior to the exercise [5].

Whilst more research is needed, it suggests that the following may be beneficial:

When What
For 3 days leading up to event Carbohydrate loading.
4 hours prior to event High fat meal (55g FAT, 75g CHO, 37.5g PRO) [5]

 

Within 1 hour of event Simple carbohydrate fuel e.g. maltodextrin.

 

Whether alternative protocols are used or not, the main rule is to ensure that you aren’t going into an event with low glycogen stores.

Intra-Workout Refueling

Carbohydrate consumption during exercise lasting longer than an hour has been shown to improve performance [6].  This is likely due to its benefit on maintaining blood glucose and sparing glycogen stores [7].

Weirdly enough, even rinsing the mouth with a carbohydrate solution (think swishing Gatorade and spitting it out) has been shown to benefit performance in some studies.  This has sometimes been in the case of short duration high intensity exercise; where intra-workout carbohydrate supplementation is not needed [8].  How does it improve performance if the carbohydrate isn’t ingested and the body doesn’t need it?  Possibly by stimulating reward centres in the brain but more research is needed to establish the exact mechanism.

As a general rule, aim for around 30-45g/hour of carbohydrate during all activity lasting longer than an hour.  For endurance events lasting longer than an hour, replace 5-10g/hour with protein.  Choose complex carbohydrates where possible.

Recovery Nutrition

It is well-established that consuming protein post-workout improves muscle protein synthesis.  Although the immediacy of that consumption following a workout seems to be far less important than was once thought [9].

As a general rule, look to consume around 20-40g (dependant on lean body mass) of protein following activity [10].

Carbohydrate intake of around 1.2g/kg body weight seems to have a desirable effect on glycogen resynthesis following a workout [11].  However consuming both protein and carbohydrate has the greatest effect on muscle protein synthesis [11].

For example, an 85kg male with good lean mass would benefit from a post-workout supplement or meal with around 30g protein and 100g carbohydrate.

A Quick Note on Hydration

The importance of adequate hydration cannot be overstated.  Regardless of whether you nail your intake of macronutrients, even in a state of mild hydration, performance will suffer.

 

  1. Burke, L.M., et al., Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. J Physiol, 2017. 595(9): p. 2785-2807.
  2. Marquet, L.A., et al., Enhanced Endurance Performance by Periodization of Carbohydrate Intake: “Sleep Low” Strategy. Med Sci Sports Exerc, 2016. 48(4): p. 663-72.
  3. Bartlett, J.D., J.A. Hawley, and J.P. Morton, Carbohydrate availability and exercise training adaptation: too much of a good thing? Eur J Sport Sci, 2015. 15(1): p. 3-12.
  4. McCleave, E.L., et al., A low carbohydrate-protein supplement improves endurance performance in female athletes. J Strength Cond Res, 2011. 25(4): p. 879-88.
  5. Murakami, I., et al., Significant effect of a pre-exercise high-fat meal after a 3-day high-carbohydrate diet on endurance performance. Nutrients, 2012. 4(7): p. 625-37.
  6. Jeukendrup, A.E., Carbohydrate intake during exercise and performance. Nutrition, 2004. 20(7-8): p. 669-77.
  7. Too, B.W., et al., Natural versus commercial carbohydrate supplementation and endurance running performance. J Int Soc Sports Nutr, 2012. 9(1): p. 27.
  8. Rollo, I. and C. Williams, Effect of mouth-rinsing carbohydrate solutions on endurance performance. Sports Med, 2011. 41(6): p. 449-61.
  9. Aragon, A.A. and B.J. Schoenfeld, Nutrient timing revisited: is there a post-exercise anabolic window? J Int Soc Sports Nutr, 2013. 10(1): p. 5.
  10. Macnaughton, L.S.W., S.L.; Witard, O.C.; McGlory, C.; Hamilton, D.L.; Jeromson, S.; Lawrence, C.E.; Wallis, G.A.; Tipton, K.D., The response of muscle protein synthesis following whole-body resistance exercise is greater following 40 g than 20 g of ingested whey protein. Physiol Rep., 2016. 15.
  11. Howarth, K.R., et al., Coingestion of protein with carbohydrate during recovery from endurance exercise stimulates skeletal muscle protein synthesis in humans. J Appl Physiol (1985), 2009. 106(4): p. 1394-402.

Leave a Reply