Why do we lose muscle mass as we age and what can we do to mitigate this?

What do we mean by muscle mass and quality?

Muscle mass refers to the total amount of muscle in the body, while quality refers to the functional characteristics of the muscle tissue itself, including strength, endurance and its ability to generate force.

The first point to make is that muscle mass plays an underappreciated role in improved metabolic health and reduced disease risk. It’s a key aspect to our health because firstly, we need it to maintain our locomotion – walk around, be mobile and have an independent lifestyle – but secondly because it’s integral to our metabolism.

Skeletal muscle is our main reservoir for the uptake of glucose, allowing us to regulate glucose levels. This has an important role in mitigating risk of type 2 diabetes. Obesity levels are also impacted, because the more muscle we have, the higher our resting metabolic rate. Therefore, maintaining muscle mass/quality is important across the lifespan and in terms of extending our healthspan.  

Why do we use muscle mass/quality as we age?

There are many factors that contribute to muscle loss as we age. One factor is a reduction in muscle protein synthesis which describes the rate by which amino acids from protein get incorporated into new muscle protein and is called anabolic resistance.

So, anabolic resistance is when someone receives an anabolic stimulus, such as by eating some protein or conducting a bout of resistance training, but their muscles don’t respond with maximum efficiency. 

An important part of anabolic resistance is the body’s response to leucine, which is one of the three branched chain amino acids found in protein. Leucine switches on the muscle protein synthesis machinery, but as you get older, you need more leucine to be able to switch on that machinery.

The age-related loss of muscle mass can begin when someone is in their 40s. By their 60s, people start losing muscle mass on average around 1% per year. There are lots of factors that contribute to this, but anabolic resistance is a key one.  

What causes anabolic resistance?

This is the Holy Grail question in our field, and the answer is very complex.

Imagine you ingest some protein. The gut has to digest the protein and then absorb that protein into the blood stream. Then it needs to take up the amino acids from the protein into the muscle itself. Now these need to be transported across your body to the target muscle cell, which could be in your leg, for example. They need to be taken into the muscle cell and start up this machine, which is called the mTOR pathway, which is essentially a cascade of little proteins inside the muscle.

With ageing, each step of the pathway can be impacted. Simply looking at digestion in the above example, there's evidence that - as we get older - amino acids can get stuck in the gut rather than being transported to the small intestine. This is called a splanchnic retention of amino acids.

A more practical issue is that the chewing of protein can be impacted as we lose teeth due to ageing. As you can see, there are many parts of a long chain of mechanisms and interactions that stop working as effectively. How these processes all relate to each other is described by the term 'integrative physiology'.

What are some of the detrimental effects of muscle loss as we age?

There are many detrimental effects, such as increased risk of falls. You could also lose your independence, such as being able to do your own shopping, get out of the chair by yourself, bend down and get back up again, play with your grandkids, and so on.

There's also the metabolic health aspect. In theory, if you maintain your muscle mass, you should be able to increase your basal metabolic rate. This is a factor in terms of weight management and reducing obesity risk, but also type 2 diabetes in terms of glucose uptake and controlling blood glucose levels.

What sorts of interventions are you researching?

We're primarily interested in non-pharmacological interventions. This has been said many times, but exercise is like a miracle pill that is able to benefit almost every aspect of our biology. It also doesn't have any side effects, within reason.

We don't necessarily recommend that older adults go and lift really heavy weights . There's evidence that we can ask older adults to lift a much lower weight but do more reps of it. It's safer and you're more likely to get older adults in the gym that way.

I'd also like to emphasise that it doesn't need to be resistance training in a gym. It could be any kind of exercise or movement at home, such as doing the gardening or doing household chores. I'm often trying to help my parents lift heavy items, but sometimes it's best to let them try and do it, again within reason.

Along with researching protein nutrition, I also study other nutritional interventions, such as Omega 3s. Evidence suggests that Omega 3s can interact with protein in a beneficial way, stimulating muscle and leading to better health outcomes.

Olly’s top tips for keeping your muscles in shape as you get older:

1. Use it or lose it. Any physical activity, whether it be completing those weekly household tasks (e.g., gardening, carrying groceries), walking rather than driving to the shop, or lifting some light weights at the local gym, will help keep your muscles big and strong. 
   
   
2. Follow the official recommended intake of one portion of oily fish per week and consider supplementing your diet with fish oil capsules. Accumulating evidence suggests that omega-3s may protect against muscle loss with ageing.