Carbs vs Protein For Endurance - Which Is Better?

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Transcript

Completing a half marathon has been on your bucket list for ages. You finally round up a bunch of friends and sign up for a charity run in 6 months. After one of your training sessions, a friend suggests that you should add protein to your diet to perform better on your run. But another friend tells you that loading up on carbs is better for endurance.

So who’s right? If you’re into endurance training like cycling or long distance running, should you focus on carbs or protein?

First let’s have a look at what happens inside a muscle during exercise.

All dynamic forms of exercise like running require contraction of your muscle to generate force, and then relaxation so that the cycle can repeat itself.

Deep down inside a muscle are two long fibres called actin and myosin. For a muscle to contract and generate force, myosin needs to grab the actin fibre and pull it.

Of course, all of this doesn’t happen on its own. Muscles need energy to make the magic happen. When myosin pulls an actin fibre, the main fuel being burned is called Adenosine Triphosphate, also known as ATP.

Think of a muscle like an engine of a petrol thirsty car. Each muscle contains a small store of ATP, which is only enough to last for about 3 seconds of muscle contraction. So muscles need a way to continuously re-fuel and make new ATP.

Well the body has three energy storage tanks that it draws upon to power this ATP guzzling machine.

First is Creatine Phosphate. Muscles breakdown Creatine to rapidly make new ATP. But Creatine can only generate enough ATP to power a muscle for about 10 seconds. So creatine is good for short bursts of muscle power like when lifting weights, but not so good for endurance.

Then there’s the second tank – the glycogen-lactic acid system. Glycogen is a stored form of carbohydrates. When you eat a slice of bread, the carbs that your body doesn’t use immediately is stored in the form of glycogen. All body cells can store glycogen to some extent, but your liver and muscle cells can store especially large amounts.

When muscles sense that ATP and Creatine stores are running low, muscles start breaking down glycogen into glucose. When there isn’t a lot of oxygen available, this glucose is converted into lactic acid, which leads to the production of ATP.

The Glycogen-Lactic acid system can power muscles for about one and a half minutes, which is much better than the 10 seconds of the Creatine system, but not enough to get you through a half marathon. Also, lactic acid causes extreme muscle fatigue.

The final trick up the body’s sleeve is the Aerobic system. Here, glycogen is broken down into glucose, then to pyruvic acid. But rather than being converted into lactic acid, pyruvic acid is instead sent to a powerful place in the cell called the mitochondria. In the mitochondria, pyruvic acid reacts with oxygen to produce enormous amounts of ATP.

So to recap, stored ATP and Creatine can power a muscle for about 10 seconds, the Glycogen-lactic acid system powers the body for about one and a half minutes. But what about the Aerobic system? Well it is essentially unlimited. As long as there are enough nutrients, the aerobic system will continue to pump out ATP.

But what happens when the body runs low on glycogen?

Well fat stores can be broken down to make significant amounts of ATP. And it can also convert protein into glucose, but this process is not very efficient. So in order of priority, the body likes to use glycogen first, then fats, and protein only as a last resort.

So now that we know that the body likes to use carbs and fats for energy, let’s see which type of diet performs best for endurance training: a high carbohydrate diet, a high fat diet or a mixed diet.
On the left is the percentage of energy coming from carbs, with 0% on the bottom and 100% on the top. On the right is the percentage of energy sourced from fats, with 0% on the top, and 100% on the bottom.
For an athlete on a mixed diet, initially all the energy comes from carbs, but they are used up fairly quickly.

At 4 minutes of activity, about 75% of energy is from carbs, and 25% is from fats. At 2 hours, the athlete reaches exhaustion. At that point, fats are providing most of the energy, with only 35% coming from carbs.
What about a high fat diet? Even at the start of the event, only 80% of energy is from carbs, with fats providing the remaining 20%, mainly due to low glycogen stores. The athlete reaches exhaustion at about one and a half hours into the event.

But the story is very different for a high-carb diet. The glycogen stores are so abundant, that even at 1 hour into the event, around three quarters of energy is from carbs and the remaining 25% from fats. The athlete reaches exhaustion at the 4 hour mark, which is about 2 hours longer than a mixed diet.

When recovering after an event, an athlete on a fat and protein diet takes a long time to recover their muscle glycogen stores. But an athlete on a high carb diet can rapidly regain their muscle glycogen stores over the first 40 hours of recovery. So high carb diets easily outperform a mixed or high-fat diet.

But is there still a role for protein?

In one study, cyclists were put on a high protein/moderate carb diet for 7 days, and then completed a time trial. They were then put on a high carb/moderate protein diet for 7 days and completed another time trial. The sequence of the two diets was randomized.

The results showed that cyclists on a high protein diet took about 20% longer to complete the time trial compared to the cyclists on a high carb diet.

But some studies do show that adding protein can reduce blood markers of muscle damage, and improve feelings of muscle soreness after a grueling event. So it is thought that adding protein to a high carb diet can assist with recovery and help offset muscle damage.

There are three take home points:

If you’re training for an endurance event like a half marathon, you should focus on a high carb diet. One study recommends getting 6 to 10 grams of carbohydrates per kilo of body weight, per day

Second, muscles need about 48 hours to build up their glycogen stores even on a high carb diet, which means that you shouldn’t do any high intensity exercise for 2 days before a big event.

And finally, protein supplementation can be added to help with recovery. One study recommends an intake of 0.25 grams of protein per kilo of body weight, per hour of endurance exercise.

Thanks for watching and I’ll see you in the next one.

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Key References

Guyton and Hall Textbook of Medical Physiology 13ed (2015), chapter 85 (p1085-89)
International Society of Sports Nutrition Position Stand 2017: https://jissn.biomedcentral.com/articles/10.1186/s12970-017-0177-8
Macdermid et al. 2006: https://www.ncbi.nlm.nih.gov/pubmed/16676704?dopt=Abstract
Burke et al. 2011: https://pubmed.ncbi.nlm.nih.gov/21660838-carbohydrates-for-training-and-competition/
Saunders et al. 2007: https://pubmed.ncbi.nlm.nih.gov/17685703-consumption-of-an-oral-carbohydrate-protein-gel-improves-cycling-endurance-and-prevents-postexercise-muscle-damage/
Saunders et al. 2004: https://pubmed.ncbi.nlm.nih.gov/15235331-effects-of-a-carbohydrate-protein-beverage-on-cycling-endurance-and-muscle-damage/

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