Our muscles are constantly breaking down and building up: every two to three months the proteins in our muscle are completely renewed. In order to make muscle proteins, we need protein from food, for example from animal sources such as meat, cheese and yoghurt, or from plant products such as beans, nuts and soymilk. Previous research on protein powders showed that animal proteins have better muscle-building properties than plant proteins. 'But in reality, we do not get our proteins in powder form, but through complete meals,' says PhD student Philippe Pinckaers. 'Those meals contain different types of protein and other nutrients such as fibers, fats and carbohydrates. These nutrients affect how proteins are released from the diet and influences the making of muscle proteins'. To investigate how muscles respond after eating a complete meal, Pinckaers asked 16 participants aged over 65 to come to the lab twice for a dinner meal.

Dining in the lab

On one of the test days, quinoa with chickpeas, broad beans, soy beans and soy sauce was on the menu, while on the other test day participants were served with a beef tartlet, potatoes, green beans, apple sauce and herb butter. Both meals had similar amounts of protein, fat, carbohydrates and calories. Prior to the meals, participants were administered an infusion of special amino acids. Amino acids are the building blocks of proteins, which in turn are essential for muscle building. 'The amino acids administered via the infusion were marked, as it were with a flag,' Pinckaers explains. 'We took small pieces of muscle tissue from the participants and were able to measure the amount of 'flags' in them. If more flags are measured, it means that muscle proteins are built up faster, which is beneficial for muscles. In this way, we found that after eating a meal with animal protein, muscle protein was built up faster than after eating a vegan meal. This means that a vegan meal does not have the same capacity to make muscle proteins as a meal that includes animal proteins.' This difference arises partly because plant-based foods are harder to digest, and because they naturally contain fewer essential amino acids.

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The results do not mean that everyone should eat meat or other animal products, clarifies professor of exercise science and lead researcher Luc van Loon. 'Healthy people can very well compensate for the lower quality of plant proteins by eating more of them.' For elderly or frail patients it is a bit more complicated. 'Elderly people actually need more protein in order to reach the same level of muscle protein synthesis, when compared to young individuals. However, they actually eat less. Also, patients with reduced appetite or who do not exercise much, for example during hospitalisation, may have trouble consuming a sufficient amount of protein. For them, it is therefore important to choose protein sources that stimulate the making of muscle proteins as much as possible. The best sources in this situation would be proteins from animal products".