Background

Broadly, we are discussing the interplay between lifespan (years lived) and healthspan (quality of life during the years lived). I don’t see any point in increasing our longevity if the quality is poor. So the goal isn’t to add more time to life, but to add more life to time. As we age, frailty becomes of greater concern. Simple facts like 22-58% patients experiencing a fragility fracture (e.g. hip fracture from a fall) are dead within 12 months, paint a bleak picture. A critical understanding of this discussion around healthspan/longevity/frailty is the role of protein as we age.

Protein is necessary for cellular growth, repair and normal function. It is essential for muscle development and immune function, with a minor role as an energy source. Protein’s basic building blocks are amino acids, of which nine are essential (our body can’t manufacture these, so we need to ingest them) and 11 that are non-essential. We still require them, but the body can synthesise them as needed. When it comes to muscle protein synthesis (MPS), the essential amino acid leucine is king.

The Problem

We face a growing problem as the proportion of older Australians increases. Those aged 65+ accounted for 12% in 1995 and 17% in 2024. Age-related decline in skeletal muscle mass and strength is called sarcopenia. Sarcopenia increases the risk of falls and fractures, dependent living, morbidity (likelihood of illness and injury), and mortality. The primary interventions to counteract sarcopenia are resistance training and protein intake. We discuss resistance training here; it’s now time to dive into protein.

In regard to sarcopenia, question(s) to consider include,

1. Is sarcopenia due to a lack of ingested protein?
2. Is sarcopenia due to a lack of utilisation of ingested protein?

Is sarcopenia due to a lack of protein ingested?

Protein recommendations daily allowance (RDA) based on nitrogen balance studies for adults in the USA are 0.8 g/kg of body weight, and in Australia are 0.75-1.0 g/kg body weight, depending on age, gender, and illness.

This recommended level is contested as too low for older individuals (Ref 1, Ref 2) for several reasons. Firstly, the nature of the research on which the recommendation is based (nitrogen balance studies) is regarded as insufficiently sensitive to measure MPS (the conversion of amino acids into muscle protein). Secondly, it does not account for age-related metabolic resistance. Finally, as we age, illness, inactivity, and injury lead to repeated periods during which muscle growth is retarded or halted, and regaining this lost muscle is more difficult in older individuals. Having a low baseline of protein intake, the RDA means that older individuals are more likely to undershoot their required level of protein intake to optimise muscle mass and function.

Using a more recent method to assess nitrogen requirements (the indicator amino acid oxidation approach), researchers calculated that the necessary protein intake is closer to 1.2 g/kg body weight in older males and females. There is ongoing debate that the RDA for protein intake should be increased for older individuals (Ref. 1 & Ref. 2 ), and I would see the 1.2 g/kg bodyweight level as a minimum for the average older adult.

Researchers in a prospective study compared two groups of healthy, older men (70+ years). One group consumed the RDA for protein (0.8 g/kg), and the other 2× the RDA (1.6 g/kg). Baseline body scans (DXA) and a leg power test (isotonic knee extension) were repeated after 10 weeks of consuming their allocated protein intake, and researchers reported that both leg power and whole-body lean mass increased in the 2*RDA group. In contrast, the RDA participants lost approximately 600 g of lean muscle in the arms and legs.

The researchers concluded ”the current dietary recommendation for protein was insufficient to maintain muscle mass and physical function in older men.”

Why is more than the RDA important?

An essential difference between fat, carbohydrate and amino acids is that while fat can be stored as triglycerides and carbohydrates can be stored as glycogen, essential amino acids (EAA) can’t be stored and so must be regularly available to cover periods of high demand (e.g. high stress situations – aging, injury, infection, training). Well, they can be stored, but as muscle. If amino acids are not available through ingestion, the body’s only other option is to catabolise (i.e., break down) skeletal muscle to obtain the necessary amino acids, which would be detrimental to the goal of maximising skeletal muscle mass as we age.

Researchers conducting a systematic review examined the effects of dietary protein supplementation and resistance training. They identified in healthy adults a significant increase in muscle mass (1.1kg) due to resistance training, plus an additional 0.3kg (27%) increase when combined with dietary protein supplementation and a significant increase in strength (1 Rep Max test increased by 27kg), plus an additional 2.5kg (9%) when combined with dietary protein supplementation. They found that dietary protein supplementation greater than 1.6 g/kg body weight did not yield further gains in muscle mass or strength.

The authors concluded, “Dietary protein supplementation significantly enhanced changes in muscle strength and
size during prolonged resistance exercise training in healthy adults.

Is sarcopenia due to a lack of utilisation of ingested protein?

Researchers have demonstrated that with increasing age, individuals are less able to convert ingested protein into muscle mass. This is termed age-related anabolic resistance and is thought to result from a reduced sensitivity to leucine (the key essential amino acid in muscle protein synthesis), leading to a higher threshold that must be exceeded before MPS begins in older individuals.

Researchers used a unilateral exercise protocol (to compare the exercised leg with the non-exercised leg within the same individual) in combination with variable amounts of whey protein ingestion (0, 10, 20, or 40 g) in a group of healthy older men (n=37). They identified several helpful facts;

1. 20g of protein optimised MPS in the non-exercised limb. So, for the non-exercising, healthy older male, consuming additional amounts of protein above 20gms won’t improve muscle protein synthesis
2. At least 20 g of protein ingestion was required for MPS in the exercise leg, to be greater than MPS due to resistance training in isolation
3. At all levels of protein intake (10/20 & 40g), added resistance training increased MPS more than just protein ingestion
4. Protein ingestion (10/20 & 40g), in addition to resistance training, increases MPS by 13%, 44% and 91% compared to training by itself
5. 40g of protein optimised MPS in the exercised leg, which was 32% greater than when 20 g of whey protein was ingested.

They reported that older men in their study required twice the protein intake (40g protein) compared with younger men in other studies to optimise post-exercise MPS. These results concur with other research.

On a practical note, the researchers recommended distributing total daily protein intake throughout the day to provide multiple stimulatory events for MPS.

My Protein Goal & Source Considerations

I think the RDA of 0.8g/kg is too low, and 1.6g/kg appears ideal.

So 1.6g/kg is my baseline, spread throughout the day, in, say, four lots of 35 grams (my body weight is 85kg).

However, my goal is 2.0g/kg, and here are my reasons.

Firstly, undershooting protein intake is detrimental to my goal of maximising muscle mass production. It is tough to make up for what is lost, so bank what you can when you can.

Secondly, older adults require approximately twice the protein intake of younger adults due to anabolic resistance and reduced leucine sensitivity; therefore, we should be aware of age-related protein requirements when interpreting research.

Thirdly, so what if I consume too much protein? There is no research indicating that consuming more than 2g/kg body weight is harmful to health. In fact, as a group, elite/Olympic athletes consume whey (malaproprism) north 2g/kg of protein and they live longer than the average person.

If I aim for 2.0 g/kg and overshoot, no problem; but if I undershoot, it is unlikely that I would drop below my desired baseline minimum of 1.6 g/kg.

Like most supplements, you need to be comparing ‘apples with apples’. Here are a few things to consider.

• If you are using whey protein (WP) powder, there are two basic types. Standard WP and WP isolate (WPI). Once milk is separated into curds and whey (WP; care of the chief protein brewer, Little Miss Muffet and her assistant, Spider), it can be further refined into WPI, which is less abundant. WPI is said to be absorbed faster, and because it is a smaller fraction, it is more expensive.
• Where is the source of your protein? I want to make sure my protein comes from healthy, happy cows. So I source my protein powder from New Zealand cattle, not just ‘packed’ in NZ. Watch out for that con.
• Read the label. You are paying for protein (WP or WPI), so check the % of protein on the label per 100 g. A common brand claims 90 g of protein when its powder is mixed with 1/2 glass of milk. Durrrrr. The milk is bumping up its protein claim. Upon examination of the label, it was found to contain only 60% protein. Aim for approximately 80% or compare prices based on protein content.