At long last, one of your bucketlist which is participating on a marathon will be fulfilled. You and your friends signed up on a 16k marathon. One day at your training session for the preparation for the marathon, a friend of yours suggest to add proteins on your diet to perform better on your run. But another friend tells you to take more carbs for endurance.

Now you are confused. Which is right? Carbs or Protein?

Before answering that, let's discuss the science behind what happens inside a muscle during exercise.

To generate force when doing exercise like running, your muscle contracts and then it relaxes so that the cycle can repeat itself.

There are two long fibres called actin and myosin inside your muscle. The myosin hrabs the actin fibre to pull it so that it can contract and generate force.

This action happens on its own. To be able to do this, the muscle needs energy to be burned. When myosin pulls an actin fibre it burns the energy called Adenosine Triphosphate also known as ATP.

You can compare your muscle with a car engine. Your muscles contains a small store of ATP which is only enough to last for 3 seconds of muscle contraction. So, for muscle to able to this action, it needs a way to continously refuel and make a new ATP.

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

1. Creatine Phosphate

The muscle breakdowns rapidly Creatine to make new ATP. But Creatine can only generate enough ATP to power a muscle for about 20 seconds. Cratine is good for short burst of mus le power but not good for endurance.

2. Glycogen-Lactic Acid System

A from of stored carbohydrate. All body cells can store glycogen to some extent, but liver and muscle cells can store large amount.

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.

This system can power up muscles for about 1 and a half minutes so it is not good for endurance. The lactic acid also causes mus le fatigue.

3. Aerobic System

Glycogen is broken down into glucose,then futher to pyruvic acid. This is sent into mothocondria, a powerful place in the cell where it reacts with oxygen to produce enorkous amount 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.

Which type of diet performs best for endurance training: a high carbohydrate diet, a high fat diet or a mixed diet.

1. Mixed diet

All energy comes from carbs, but they are used up 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.

2. 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.

3. 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 a reseach, a cyclist was put on high protein/moderate carb diet for 7 days, and then test for a time trial. And after then, they were put on high carb/moderate protein and also test for time trial.

Cyclist with high protein diet took 20% longer to complete the time trial.

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:

When preparing for an endurance event like a marathon one can focus on :

1. High carb diet - 6-10grams of carbs per kilo of body weight per day

2. You shouldn't do any high intensity exercise for 2 days - muscles need about 48 hours to build up their glycogen even on high carb diet

3. Protein supplements - 0.25grams of prorein per kilo of body weight to help with recovery of muscle wasting.