In the column 'A conversation with...', experts from Maastricht UMC+ discuss one of the questions submitted for the Dutch National Research Agenda. This time Professor in Human Movement Sciences Luc van Loon discusses the question:
"It is actually a miracle that we are still walking around, because essentially we are totally different people than we were two months ago. Your body is constantly breaking down muscle tissue and producing it again. Roughly one to two percent of all your muscles are replaced with new material every day. In other words, after roughly two months you consist of entirely new muscles. That process continues throughout your life, but sometimes the breakdown occurs more quickly than the production of new muscle as you grow older. Consequently, older people experience problems with mobility more often.It is therefore important to devote sufficient attention to preserving the muscles, and not just as you become older. When you are lying in hospital with a broken leg, for example, within five days your muscles already lose a substantial volume of their mass and strength. But patients with diabetes and cardiovascular diseases also suffer muscle problems. And cachexia (severe weight loss) is a very common problem among cancer patients. In Maastricht we are searching for methods to minimise the loss and promote the retention and growth of muscle mass and strength.
Two factors are particularly important for maintaining or even enhancing healthy muscle growth: protein and physical activity. It therefore seems a straightforward matter of ingesting enough protein and taking enough exercise. And that is certainly true, but a lot more is needed to achieve an optimal result. Timing is important, as are the types of protein, the pattern of exercise and so on. Not so long ago we demonstrated that you literally are what you have just eaten. We found labelled amino acids (the building blocks of proteins) that had been injected in a cow fully replicated in human guinea pigs who had drunk the milk from the cow. Five hours after the volunteers drank the cow’s milk, around ten percent of the labelled amino acids were found to have been incorporated directly in the new muscle tissue. In other words, you are, literally, what you eat.
It appears that you can influence the intake of protein in various ways. For example, muscle absorb protein from crushed meat (such as mince) better than protein from a steak. And muscles absorb more so-called 'fast’ proteins (such as whey protein) than 'slow' proteins (such as casein). Apart from the fact that these proteins are digested more quickly, more of them are used in muscle tissue. An important point to realise is that you should actually never consume only proteins. Foodstuffs also contain carbohydrates, fats and other substances. That can also play a role in protein intake. But we can do even more to optimise muscle building.
Everyone knows that sufficient exercise is important for a healthy physique. What constitutes sufficient exercise to retain muscle mass and strength differs from one person to another. It is naturally different for a top athlete than a person over the age of 65. But exercise also has an interesting effect on protein intake, because when a person engages in physical exercise before a meal, more of the protein that is consumed, up to about twenty percent, is converted into muscle tissue. For older people in particular, it is advisable to go shopping themselves and to be active before eating a meal. This is also a useful tip for patients. Ahead of a scheduled operation or an intensive session of chemotherapy, for example, it can make sense to train the muscles to withstand periods of bed-ridden immobility. But of course everyone can benefit from a conscious combination of a good diet and exercise. A final piece of advice, which is no less important for being frequently repeated, is this: vary your diet, eat healthily, chew your food thoroughly and take enough exercise."