As a physician who specializes in muscle-centric medicine, I see individuals who want to optimize their body composition. Optimal body composition is achieved by decreasing adipose tissue and increasing lean muscle mass. Dietary protein is the limiting factor that determines diet quality. This is because the body requires essential amino acids that high-quality protein provides. These amino acids are necessary for the growth, repair and creation of new tissues in the body.
The organ of longevity
Treatment strategies for each may differ, but the key concept I convey to all my patients, and one which is critical to understand, is that muscle is the largest and an extremely important organ system (just as the heart is an organ so, too, is skeletal muscle). And the healthier muscle is, the healthier (and potentially longer) a person’s life may be.
Regulation of blood glucose and fat in the body are vital to our well-being and survival. And muscle is the metabolic regulator of the body. For example, it is the largest unit for glucose disposal, which relates to dietary carbohydrates. In fact, skeletal muscle is responsible for 80% of insulin-dependent glucose metabolism. Thus, the more muscle you have, the more carbohydrates you burn. In addition, muscle is the largest site for fat oxidation. So those with elevated levels of cholesterol don’t require more drug therapy. Instead, they require more muscle to target fat utilization.
Stimulating muscle synthesis
There are two ways to achieve and maintain healthy muscles. One is to stimulate muscle protein synthesis through resistance training. Another is through dietary interventions via dietary protein. Each meal is a feeding opportunity to augment skeletal muscle. It is necessary to get the correct amount of protein at each meal to stimulate muscle protein synthesis. The required amount is 30 grams of high-quality protein, which is roughly 4 oz. The reason for this amount is the role of the essential amino acid leucine. And thirty grams of such protein contains around 2.5 grams of leucine. Leucine at this dose is needed to switch on synthesis. If one eats below this amount there are still benefits, but muscle protein synthesis is not one of them.
For older populations, understanding how these two mechanisms work, both individually and in concert, is the key to resisting the tendency of muscle to deteriorate and become infiltrated with fat as the tissue ages. This debilitating condition is known as sarcopenia, and it’s a challenge all individuals will face. Therefore, taking steps to maintaining quality muscle tissue is key.
Sarcopenia is usually considered to start in the 40s and 50s, but these days, possibly because people in more affluent parts of the world are becoming so inactive, it may be starting even earlier. In young people, muscle synthesis is primarily driven by insulin and growth hormones. Protein supplements, therefore, aren’t really needed in the diet. Older people, however, gradually become more resistant to these stimuli. And that leaves them with just two ways to stimulate muscle synthesis: Exercise or diet.
The first part of the equation, exercise, isn’t the focus of this post. More confusing to athletes and consumers alike is the question of protein supplements in the diet. To use supplements appropriately, they need to manage the amount of protein ingested at each meal, the timing, and the quality of the protein source itself.
It’s useful to gain some understanding of the underlying mechanisms. First, an individual needs to ingest around 100 grams of protein during each day for basic health maintenance and tissue protection. While the amount will vary depending on body weight, activity levels and other factors, most Americans consume somewhat less than this, replacing protein with carbohydrate-heavy meals.
To make the task more difficult, research has revealed that, as people age, they require more protein at once. From 65 years and up, in fact, they need around 40-50 grams in one serving to stimulate the same kind of muscle turnover. Individuals find this to be quite a bit of protein, particularly when we consider that appetite tends to reduce with age.
So all we need to do is to eat more protein? Not exactly. To get the right effect from dietary protein, it’s necessary to activate an anabolic signalling protein called mTOR, which is a key driver for muscle health. mTOR responses to leucine, which is present in many food types, but in differing amounts. Many people taking protein supplements fail to realize is that it takes about 2.5 grams of leucine to trigger mTOR, kick-starting a cascade of events that enable muscle to be synthesized. And this is where the type and quantity of protein ingested really makes a difference.
The data is very clear. If you compare animal-based proteins (which includes dairy proteins) with plant-based proteins, the ability to stimulate muscle is different – and this difference is based on the difference in leucine content. For example, more than 40 grams of soy and wheat proteins are needed to activate mTOR signalling. And it would take 6 cups of quinoa to equal the same amount of leucine in one chicken breast. Whey protein supplements, by comparison, are very high in leucine, requiring just 25 grams to achieve the same effect.
This brings me to an important point: The leucine content in plant-based proteins isn’t just very low – it’s not very digestible, either, primarily because it’s bound by fiber. In fact, plant-based proteins should be counted more as calories, or as something that’s useful for gut health, but not as something that is good for the organ of longevity: the muscle.
For athletes and others who engage in exercise designed to support muscle synthesis, I do have a particular piece of advice that seems to come as a surprise for many: On the days where you train, you are actually stimulating your muscle to make maximum use of any protein you consume, which means you need less protein to achieve the same amount of synthesis. Your muscle is simply primed for the task. On the days where you don’t train, that’s exactly where you need to increase your protein intake. It may seem counter-intuitive, but that’s the reality!
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