Why do you need protein AND carbohydrates to build muscle?

If you want to build muscle, you have to eat protein, so far so good. And anyway, you should cut out carbohydrates, then your fat reserves will disappear more easily. This knowledge is well established in the collective memory. Protein-rich and low-carb diets have long been considered the gold standard in the fitness scene – whether you're a woman who wants to finally be able to do a few push-ups in a row or a man who wants to get and show off a six-pack.

However, strictly avoiding carbs is quite difficult for some people. It can even lead to symptoms such as fatigue, constipation, headaches, and more. In any case, it seems that this demonization of carbs may be exaggerated. On the contrary, they may even contribute significantly to muscle building and thus to achieving your desired figure. At least that's how bodybuilder and Mr. Universe 2023 in the over-45 category, Mark Taylor, sees it. In an interview, he said that the secret to his success is potatoes and porridge.

For years, Taylor adhered to a protein-rich, low-carb diet, as recommended for muscle building, with almost religious zeal. But he felt constantly tired, and his muscles looked “flat” instead of bulging nicely under the skin. At some point, he broke his strict diet, started eating carbs and more calories – and that's exactly what led him to success, he says.

And what does science think of this strategy, which goes against conventional norms? There are certainly some arguments in its favor—albeit indirect ones, writes Justin Roberts, a nutritionist at Anglia Ruskin University in the UK, on the science platform The Conversation.

How muscle building works

If you want to build muscle, you have to train—there's no way around it. The principle is relatively simple: muscle growth occurs through progressive overload training. There are two strategies for achieving this: you can gradually increase the weight you use to perform the exercises, or you can do more repetitions or sets of an exercise. If the training is strenuous enough, muscle adaptations occur during the recovery phase, which over time leads to more muscle mass.

More specifically, muscle growth occurs through a balance of two processes: muscle protein synthesis, in which new muscle tissue is formed or damaged tissue is repaired, and muscle protein breakdown, in which, as the name suggests, muscle tissue is broken down. These two processes are constantly taking place, so the extent and balance between the two influence the overall increase in muscle mass.

A targeted diet can help support this process. Proteins are an essential part of this, as they provide amino acids such as leucine, which are used to build muscles. There is now extensive evidence that daily protein consumption, combined with sufficient calorie intake, is a relevant component of muscle building.

Other building blocks include nutrients such as essential fatty acids, vitamins, and minerals. A calorie deficit, on the other hand, is only helpful to a limited extent. Eating fewer calories than the body metabolizes can have a negative effect on training.

There is also good evidence that consuming 20 to 40 grams of rapidly available proteins, such as whey protein, can accelerate muscle protein synthesis in the short term. Many fitness enthusiasts also rely on slow-release proteins such as casein protein before bedtime to meet their daily protein requirements or optimize their recovery phase.

What about carbohydrates?

And how do carbohydrates fit into this? They seem to contribute to indirect profitability. The study situation is not entirely clear. Some studies show that the combination of carbohydrates and protein after training can lead to increased muscle protein synthesis. Other studies find no evidence that this is better than consuming protein alone. This is understandable, as amino acids are the key component for growth, and carbohydrates simply cannot provide them. This means that they cannot directly drive muscle protein synthesis.

However, carbohydrates could have an impact on how much muscle protein is broken down. This is because they cause the body to produce the hormone insulin, which has been shown to reduce protein breakdown.

In which, proteins also influence insulin production, with a similar effect to carbohydrates. It is often argued that if you eat enough protein after training, there is no particular need for carbohydrates in terms of muscle building. So why did they make such a decisive difference for Mr. Universe Mark Taylor?

To understand this, it is worth taking a look at the practices of bodybuilders. When building muscle, many of them go through a “bulking” phase, in which they increase their daily calorie intake by 15 percent or more in order to produce more muscle mass. Once the desired level has been reached, a “cutting” phase follows, in which body fat is strategically reduced and the muscles become more visible. Avoiding carbohydrates can promote fat loss and lead to a slimmer physique. That is why this approach is quite popular.

Glycemic index

But in many cases, a low-carb diet also goes hand in hand with less energy. This can potentially lead to a reduced immune system capacity, increased fatigue, and decreased performance. Testosterone levels can also drop as a result, but this hormone is needed for muscle building. And for women, there is another problem: low-carb diets can disrupt the hormonal cycle, possibly even causing menstruation to stop. This low-carb strategy is therefore downright harmful for some people.

Carbohydrates also provide energy in the form of glucose, which is stored in the muscles as glycogen so that it is available later. During strenuous training, these glycogen stores are depleted because they provide quick energy. Carbohydrates thus enable more intensive training, which indirectly influences muscle protein synthesis. On the other hand, those who do not refuel with carbohydrates and constantly train in a low-glycogen state can undermine muscle growth and worsen their overall training results.

However, it is important to consider which carbohydrates you consume. Those with a low glycemic index are recommended. The glycemic index (GI) is a measure of how quickly the carbohydrates in a particular food raise blood sugar levels. Foods with a low GI have a slower release effect. This has a positive effect on mood and ensures that sufficient energy is available throughout the day. You feel less tired and it contributes to better overall health. Among other things, we know that a low GI helps to lower blood pressure.

Pasta is also fine

Occasionally, it can still be good to eat foods with a higher GI, such as pasta. Spread throughout the day, a low glycemic index is certainly better. However, studies show that pasta, bagels, and even muesli, which have a higher GI, help to quickly replenish glycogen stores and aid recovery after a long or hard workout. The ideal combination for training AND recovery therefore seems to be a mix of low and high GI foods spread throughout the day.

Carb loading not only makes sense for your next running competition, it can also make a decisive difference in strength training. And it's definitely good for your mood.