Which is Better: Carbs or Protein for Endurance

Nutrition supports sports performance by providing your body with the energy required to operate, and different sports – depending on their intensity and duration – are fuelled by different energy systems.

It should not come as a surprise, then, that what you feed your body will impact your training and results.

Endurance sports such as running, cycling or rowing usually require a big amount of energy for long periods of time. Is there a way to optimise your diet to support this kind of exercise?

In short, there is. The answer, however, isn’t as simple as “eat this then” and we should add a word of caution before we dive into the science recommendations: please remember that these are only guidelines.

Nutrition is incredibly personal and emotional, and your nutrition plan should reflect this. There’s no such thing as a general perfect diet, so try out an approach that works for you and your goals.

Food is Fuel, But How?

Why does nutrition for endurance sport matter? A big aspect of performance is energy; how much of it you have available and how to create new when you deplete your primary sources. Therefore, it’s useful to understand what’s going on in your body when you exercise.

The fuel part

All dynamic forms of exercise require the repetitive process of contraction and relaxation of your muscles to generate force, and muscles need energy to contract and relax.

The body has three energy storage systems to power the muscles:

• Creatine phosphate. This system creates ATP (energy) fast but can only create enough energy to power a muscle for about 10 seconds. It is perfect for short bursts of muscle power, such as when you’re attempting a weightlifting 1RM, but isn’t as useful for endurance events.
• Glycogen lactic acid. Glycogen is a stored form of carbohydrate, meaning that when you consume carbs, the ones that are not used immediately get stored as glycogen mostly in your liver and muscles. In short, when you need more energy, muscles break down glycogen into glucose, which in turn becomes lactic acid when there’s a shortage of oxygen. Lactic acid leads to the production of ATP but creates big muscle fatigue and only supports efforts of around a minute to a minute and a half, which isn’t sustainable for endurance.
• Aerobic system. This system uses oxygen to produce energy. This works by breaking glycogen down into glucose, which is further broken down to hydrogen ions, which react with the oxygen stored in mitochondria to produce ATP. This process is slower but creates the most energy. As long as you have enough nutrients, the aerobic system can continue to work almost indefinitely.

When your activity is of relatively low intensity or when your body runs out of glycogen, you can access your fat stores to create ATP. It is also possible to convert protein into glucose, but the process isn’t very efficient and so your body will only use this as a last resource.

Summed up: to create energy efficiently for exercise, your body will use up glycogen (stored forms of carbohydrates) first, then fat, and protein as a last resource. You only really use protein for energy when you’re in a calorie deficit.

The food part

Having enough stores of muscle glycogen and fatty acids means you have readily available energy to perform.

Filling up your muscle glycogen stores to support your endurance activities thus becomes of understated importance. Carbohydrates are the main source of energy for endurance sport, but carbohydrate stores are limited to the liver and the muscles.

This means you should replenish carbohydrates daily, especially for athletes regularly doing high volumes of training at moderate to high intensities.

Day to Day carbohydrate intake

What’s the ideal number of carbs you should eat daily?

According to a 2019 Nutrition Review for Endurance Athletes, which assessed inputs from the Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine, the recommendation for daily carbohydrate intake looks as follows:

What does this mean? If, for example, you weight 70kg and exercise around 1 hour per day, your diet should include anywhere between 350g (5 grams x 70 kilogram of bodyweight) and 490g (7 x 70) of carbohydrates per day.

The science on whether you should consume a set number of carbs per day or change your intake based on the intensity of your exercise and rest days is still heavily contested. Until there’s a clear answer, we recommend you do whatever feels best; some people like consistency whereas others like mixing things up, both approaches are fine.

Where does protein come in?

Even if your body only uses protein as a source of energy as a last resource, there is space for protein in your day-to-day nutrition. In fact, protein intake is pretty important and plays a big part in your endurance nutrition plan.

While protein won’t necessarily support you during exercise, it can assist with recovery. Studies have found that including protein in your diet can reduce blood markers of muscle damage and improve feelings of muscle soreness after hard exercise.

Additionally, the benefits of consuming a balanced diet cannot be understated.

Summed up: this means that while you shouldn’t necessarily worry too much about having a high protein intake for endurance, you should definitely include it in your diet.

Pre competition carb consumption (loading)

Muscles need about 48 hours to replenish glycogen stores (even on a high-carb diet), so you should start fuelling up earlier than the night before.

For races that are less than 90 minutes long your body is unlikely to run out of glycogen, so you don’t need to worry too much about super-loading. For longer endurance events, carbohydrate stores can become a limiting factor to performance, so “carb loading” is advised.

This should be done 36-48 hours before a competition and is believed to boost performance by 2-3%.

Eating 1-4g of carbohydrates per kilogram of bodyweight 1 to 4 hours before your event is also recommended to top off liver glycogen stores, as many competitions take place in the morning, directly following an overnight fast which depletes liver glycogen.

It’s recommended you train this, as many people can experience stomach issues during exercise from eating beforehand if they’re not used to it.

During competition fuelling is an incredibly interesting and intricate topic, and as such deserves its own article. The short answer as to how much you should consume during a race, as with most training advice, depends on the duration and intensity of your event.

Which is Better: Carbs or Protein for Endurance

Ultimately, from a physiological standpoint, a balanced diet high in carbohydrates is likely to be the best diet you could follow to support your performance. There is place for both carbohydrates and protein – as well as fat – in your diet.

Following healthy nutritional habits, a balanced diet, and a sustainable approach to nutrition should get you most of the way to achieving your goals from a fuelling standpoint.

Disclaimer: Any recommendations made are not intended to diagnose, treat, cure, or prevent any disease. The content in the article is intended for educational and informational purposes only and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional.

Always consult a qualified dietitian before making big changes to your diet.