How do fast and slow digesting proteins complement each other in seniors’ metabolism?
The World Health Organization has declared healthy ageing a global priority. Life expectancy for the elderly is continuing to increase around the world. By 2050, it is expected that the population aged 60 and above will have reached 2 billion worldwide, compared with 841 million currently 1.
From a biological point of view, ageing comprises all the physiological and psychological processes that lead to the progressive deterioration of the structures and functions of the organism. The main signs of ageing are vision and hearing loss, memory impairment and loss of muscle mass, known as sarcopenia.
However, this decline is not as linear and predictable as might be imagined. Each individual has their own ageing trajectory that varies in accordance with the events of their life. While some people still enjoy good health and solid functional capability at 70, others of the same age are fragile and dependent. The aim for everyone, therefore, should be to not accelerate their ageing trajectory. It is with this objective in mind that the WHO has launched its “Healthy Ageing” program in which maintaining mobility is an essential factor.
WHO has launched its “Healthy Ageing” program in which maintaining mobility is an essential factor
How can we maintain or increase mobility during ageing?
Mobility is key to healthy ageing as it ensures the ability to carry out one’s daily tasks and therefore lose as little autonomy as possible. From a physiological point of view, what allows us to keep our mobility is muscle maintenance. Ageing causes loss of muscle mass from the age of 40 onwards 2. Regular physical activity and adequate dietary protein intake are the two essential factors in preventing this loss of muscle mass.
Maintaining muscle mass is dependent on the balance between protein synthesis and its degradation in muscle. A dietary intake of proteins that are rich in essential amino acids is what, in part, regulates this balance. The ability to synthesize new muscle proteins is lower in an elderly person than a in younger adult, which is why protein needs are higher 3. The specific needs depend on the age and physical condition of each elderly person.
The protein needs of the elderly are higher than in a younger adult
The protein needs of the elderly are higher than in a younger adult. Achieving the right intake is a significant challenge for people suffering a loss of appetite, with around 20% frequently having difficulty chewing or dental problems such as tooth loss 6. Consequently, their food consumption, and their protein intake, is compromised through the course of each day 7. There are two aspects to an increase in daily protein intake: the quality of the proteins ingested and how that protein intake is spread across the day.
A good starting point to increase protein consumption in an elderly person is to spread the intake more evenly throughout the day. Scientific studies show that the threshold to trigger muscle synthesis in an elderly person is 0.4 g of protein / kg of body weight per meal, which equates to approximately 30g per meal 8. In the majority of cultures, the distribution of proteins across the day is not optimal, with breakfast often being low in protein.
Milk proteins: casein and whey protein are both rich in essential amino acids
Proteins are capable of stimulating muscle synthesis, but not all proteins have the same impact: proteins that are rich in essential amino acids such as leucine are known to be powerful activators of muscle synthesis. Milk proteins: casein and whey protein are both rich in essential amino acids, and can therefore have an effect on the balance between synthesis/degradation of muscle proteins. Each dairy protein has its own particularity, linked to its structure:
– Thanks to its particular structure, whey protein is digested quickly 9. The advantage of a rapidly digested protein is that it allows a large influx of leucine into the blood, which sends a signal to the muscles and stimulates muscle synthesis 10.
– Casein is digested more slowly in the stomach. Amino acids are therefore released into the blood more gradually and over a longer period of time than with whey proteins 9. Thanks to this slower release of amino acids, casein is able to reduce the degradation and increase the synthesis of muscle proteins 9,11.
Most elderly people consume too little protein at breakfast to induce muscle synthesis. Consuming whey protein or casein as a supplement to a meal could therefore help reach the threshold of 30g of protein per meal, which is the threshold necessary for muscle synthesis. The combination of whey protein with a physical activity is also a perfect way to stimulate muscle synthesis. Finally, a dose of casein at bedtime could also help reduce muscle degradation and increase muscle synthesis during the night-time fast12.
To conclude, ageing is an inevitable process but it is possible to age in good health. By doing a regular physical activity and having an adequate intake of dietary proteins, an elderly person can limit the loss of muscle mass and so maintain mobility.
 World Health Organization. Bien vieillir: une priorité mondiale.
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 Coelho-Junior, H. J. et al. Protein Intake and Frailty: A Matter of Quantity, Quality, and Timing. Nutrients 12, 2915 (2020).
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 Kouw, I. W. et al. Protein Ingestion before Sleep Increases Overnight Muscle Protein Synthesis Rates in Healthy Older Men: A Randomized Controlled Trial. J Nutr 147, 2252–2261 (2017).