We often take our muscles for granted, but from our forties onwards we start to lose muscle, and if muscle loss continues, it can have implications for our general health. Muscle strength is a key marker for overall health and reduced muscle mass and strength increases risk for disease and frailty. Reduced muscle strength also increases risk for metabolic diseases, such as Type 2 Diabetes. But muscle loss is not inevitable! We can take simple actions to maintain and build muscle. Good nutrition and exercise will reduce muscle loss and keep us healthier longer. Here we describe how muscles are built and lost, and provide four simple actions you can take to protect your muscles.
What is muscle and why does it matter?
Skeletal muscle makes up about 30-40% of our total body mass. These muscles connect to your bones and allow you to perform a wide range of movements and functions. Muscle mass and strength usually start to decline in our forties and by the time we reach around 80 years of age, we have often lost about 30% of our peak muscle mass. (1 ) Lower levels of muscle strength are linked to higher risk of cardiovascular disease, respiratory disease, cancer as well as all-cause mortality. (2) So it's very important to look after our muscles, to keep them strong.
How we build and maintain muscles
Muscle tissue is dynamic and in a constant state of turnover and remodelling with muscle proteins being both synthesised and broken down simultaneously throughout the day.
Muscle protein synthesis (MPS) - is a metabolic process in which amino acids are incorporated into muscle protein, supporting the maintenance or building of muscle mass
Muscle protein breakdown (MPB) – is the opposing process to MPS and involves the breakdown of muscle protein, which happens throughout the day and particularly during exercise.
The balance between MPS and MPB throughout the day will determine the health of our muscles as shown below:
Why we lose muscle as we age
As we get older MPB exceeds MPS leading to a loss of muscle mass and strength over time. There are many reasons for this including:
It may often be a combination of factors which lead to greater muscle loss at an earlier age. For example, a combination of inadequate nutrient intake combined with illness or injury may accelerate muscle loss as shown below:
Figure 1. Factors that accelerate muscle loss. Malnutrition, illness and injury are accelerators of muscle loss. However, the rate of muscle loss is greater (i.e., accelerated) when these factors are combined, leading to severe, more rapid muscle loss. (Prado et al 2022) (3.)
Muscles and metabolic health
Muscles also play a key role in blood glucose control and are critical to good metabolic health. Evidence shows that low muscle mass and function increases risk for insulin resistance and Type 2 Diabetes. (2) So why are muscles so important for metabolic health?
Normally, when glucose rises in the blood after eating, the hormone insulin is released to move glucose from the blood and into the cells, where it can be used for energy. Through the action of insulin, glucose leaves the blood to be taken up by cells in the liver, muscles and fat. However, the primary site for the disposal of glucose after a meal is muscle, and around 80% of glucose is taken up into cells in skeletal muscle. The health of the muscle and the ability of its cells to take up glucose is critical for effective blood glucose control. If muscle mass is low and muscle strength impaired, cells in the muscles can become insulin resistant and become less effective at taking up blood glucose.
Insulin resistance is a state in which the cells of the body fail to respond properly to insulin. In these circumstances higher and higher levels of insulin are needed to support the movement of glucose from the blood into the cells. As insulin resistance worsens, the body is unable to supply sufficient insulin to bring blood glucose down effectively – this is Type 2 Diabetes as shown below:
Development of Insulin Resistance and Type 2 Diabetes: Prof. Ben Bikman https://www.youtube.com/watch?v=XDVvQFgkP44
When muscle cells become Insulin resistant, MPS is reduced, leading to a reduction in muscle mass and strength. This in turn worsens insulin resistance – a vicious circle!
Insulin resistance in the muscles is considered the primary defect in insulin resistance. (4) Muscle glucose uptake is impaired in Type 2 Diabetes and is approximately 60% lower than in a non-diabetic population.
Four simple ways to protect your muscle mass and strength
We know the importance of maintaining and building muscle mass and strength, so what are the steps we can take to protect our muscles? Making changes to our diet and lifestyle can protect and build our muscles, and by doing so, improve insulin sensitivity and reduce future risk of disease. Here are four simple things you can do:
1. Eat plenty of high -quality protein
2. Regular resistance exercise
3. Eat fermented foods daily
4. Keep moving and sit down less!
We describe these in more detail below.
1. Eat plenty of high quality protein
Eating enough protein is essential for muscle protein synthesis (MPS). As we get older we need a higher level of protein to build and maintain muscle.(5). Whilst government guidelines (6) recommend we have 75g per kg of bodyweight, many nutrition experts (7) consider these levels too low and a higher intake of protein recommended, particularly for older people.
The ability to build muscle declines with age and a higher level of protein is needed to reduce MPB and increase MPS. (7) As we get older we need a higher level of protein to support good health, promote recovery from illness, and maintain functionality (8)
Recommended intake of protein
Daily intake of 1.2 – 1.5 g of protein per kg of ideal bodyweight with older adults aiming for at least 1.5g per kg of bodyweight
A woman of average weight (9.5 stone) will need approximately 75 - 90g protein per day, with older women aiming for 90g/day
A man of average weight (11stone) will need approximately 80-112g of protein per day, with older men aiming for 112g/day
Minimum amount of protein needed at each meal
A minimum amount of protein is needed to stimulate MPS, and it is the post-prandial availability of essential amino acids that determines MPS. The minimum amount of protein needed to generate MPS is far greater for older adults than for younger adults. Younger adults need a minimum of 0.24g protein per kg of bodyweight at a meal whilst older adults need 0.4g/kg bodyweight or more at each meal in order to stimulate MPS (9).
Minimum intake of protein at each meal for older adults
It’s also important to spread protein intake out evenly across the day as far as possible. Many people skew their protein intake, often having insufficient protein at breakfast and with the bulk eaten during an evening meal. Increasing protein intake at breakfast is a good way to increase intake and distribution of protein.
Protein quality
Protein quality is determined by the digestibility and bioavailability of the amino acids in the protein, which are measured using specific indices. Animal-based proteins are highly bio-available and contain all nine essential amino acids in good quantities, including leucine, which is important for MPS. Plants generally have a lower digestibility score than animal foods, and anti-nutrients in plant foods may reduce amino acid availability. For example, studies have consistently shown that whey supplements (from milk) increase MPS more than soy protein supplements.(10)
Getting enough protein as a vegetarian or vegan
It is certainly possible to meet daily protein intake requirements with plant sources of protein alone, but higher levels of protein are needed. Soy, used to make foods such as tofu, is a good choice as it contains all nine essential amino acids, although low in methionine. Another good choice is Quorn or mycoprotein, a fungal protein that has a high protein density and a similar amino acid profile to dairy foods.(11 ) Pairing plant sources of protein can also ensure that a meal contains all nine essential amino acids – for example, pairing legumes with grains or legumes with nuts or seeds.
2. Resistance exercise at least twice a week
Resistance training requires our muscles to contract to lift a heavy object against the pull of gravity. This type of exercise provides the most effective stimulus for muscle tissue growth in healthy adults (12) and it also improves body fat mass, muscle strength and muscle performance in healthy older people with sarcopenia (13). Resistance exercise is also the most effective strategy for increasing muscle mass and function in people with Type 2 Diabetes.
A bout of resistance exercise stimulates MPS and MPB, both of which are good for muscle health. However adequate protein is required alongside resistance exercise otherwise muscle protein balance will remain negative. Higher levels of protein taken after exercise will result in greater levels of MPS than lower levels of protein, particularly in older adults.(14)
Resistance training has been found to increase muscle mass by 2.3% over 6 weeks in people with Type 2 Diabetes, whilst simultaneously increasing glucose clearance by around 20%.
We recommend you take some form of resistance exercise twice every week
Photo from U.S. Department of Health & Human Services (HHS) NIH National Institute on Aging
3. Eat Fermented foods regularly
It may seem strange but the health of our gut has an impact on the health or our muscles. The diversity of the gut microbiome reduces as we age, and this dysbiosis can generate low-grade systemic inflammation which leads to a reduction in muscle protein synthesis (15).
To keep you gut healthy we recommend that you regularly eat fermented foods, such as kefir, live yoghurt, sauerkraut, kimchi, cider apple vinegar, kombucha or by taking probiotic supplements.
4. Keep moving and sit down less!
Getting up and keeping busy will reduce your risk of muscle loss. Just reducing the number of hours you spend sitting each day will reduce your risk of muscle loss whatever activities you are doing. Studies have shown a clear link showing more sedentary time in the day and the risk of muscle loss and weakness:
One study found that older women who were sedentary for 8-11 hours per day had lower muscle functionality than women of the same age who were sedentary for 6 hours or less every day (16).
Another study found that for every sedentary hour, the risk of sarcopenia (muscle loss) increased by 33% in people aged 60-86 years. (17)
A third study showed that people who perform a small number of daily steps (<1000–1500 daily steps, for 14 days) show a reduction of 14–26% in MPS when compared to subjects who practice ≥6000 steps daily (18)
We recommend you stay active and keep sedentary activities to a minimum - ideally 6 hours or less per day
In Summary
Looking after your muscles is so important, but it doesn't need to be difficult. By taking action and making a few changes to your normal habits, you can maintain healthy muscles as you get older and reduce your chance of metabolic and other diseases.
In summary, we recommend:
