Changes in body compositions, muscle mass and water content will all slow down in normal ageing process. Muscle is one of the protein reserves of human being, and the loss of muscle mass is associated with decrease in protein production with age, increase in protein breakdown, or a combination of the above. A comparison of the rate of muscle protein breakdown between young adult and old adult, through complicated tests, reveals substantial elevation in the senior patient group. This loss of the muscle is viewed as an inevitable consequence of ageing, which is similar to bone mass loss during ageing, making it worthwhile to mention here once again.

Loss of muscle mass

The muscle mass reaches a peak in adult years, and it usually declines by 0.5% to 1.0% every year starting from about 40 years of age. The loss of muscle mass is usually masked by a concurrent increase in fat mass until the patient shows signs of fall and fracture or impairment in the ability to perform daily routines such as shopping, bathing, toileting, and self-hygiene. Muscle loss is more prominent when one continues their life journey to their sixth decade, as sarcopenia is estimated to affect 30% of the people aged 60, and it may even affect more than 50% of those over 80.

In healthy adults, muscle and protein regularly turn over in a balanced manner between protein synthesis and breakdown. The balance is typically disrupted in senior citizens, with up to 30% lower synthesis rate of the muscle protein. To combat the progression of sarcopenia, a target control of daily protein consumption is one of the ways to slow down or prevent muscle protein breakdown and therefore sarcopenia, since the muscle protein synthesis is stimulated by dietary intake of protein. Although the general suggestion of Recommended Dietary Allowance (RDA) of an adult is 0.8g/Kg (body weight)/day, it is estimated that 15% to 38% of adult men and 27% to 41% of adult women have dietary protein intake below the recommended level. In addition, recent data suggests that even the intake of the protein by the standards of RDA 0.8kg/Kg (body weight)/day is insufficient to maintain muscle mass in the elderly. The sacropenia can also occur in young adult, who consume protein at a rate of 0.6g/Kg (body weight)/day. Although the possibility of higher level of RDA has been raised, fierce debate over the new RDA for protein is yet to be conclusive. Nonetheless, the amount of protein intake in older individual should be lightly above the RDA suggested level.

Ingestion of protein

The truth is, it may be more difficult for senior citizen to obtain adequate protein because of the cost of nutritious food, perceived intolerance to certain food groups, difficultly in tearing or chewing food, or fear in over-consumption of fat or cholesterol. Basically, protein is an essential nutrient composed of small units – the amino acids, also called the building blocks of protein. There are about 20 different types of commonly known amino acids, but eight of the amino acids cannot be put together in the body and therefore must be supplied by the food we eat. These eight amino acids are called essential amino acids, the adequate amount of which governs the biological value of protein.

Most of the animal proteins are considered to be of high biological values. The plant protein, in general, does not have complete amino acid profiles and are considered to be of low biological value. The protein of cereals, most beans, and vegetable may contain all the essential amino acids, but the amount of essential amino acids in these plant foods is less ideal.

Apart from the quantity of protein ingested, the quality of protein ingested is worth considering too. One of the most important types of protein is the essential amino acid content of a protein leucine, which serves as the primary anabolic factor in terms of muscle protein production. Leucine-rich sources include legumes such as soybeans, cowpeas, beef and fish. Amino acid supplement without enough leucine had been reported to be lacking in protein synthesis stimulation. Adequate supplement accompanied by resistance training is vital to combat sarcopenia.

All in all, adequate and suitable nutritional intervention is vital to preventing or retarding the process of sarcopenia. While it is wise for senior citizens to pay more attention to their diet, the underlying chronic illnesses of older individuals should also be considered before adapting the strategy. And please remember to consult your dietician or doctor should you have any queries.

Dr Liu Kin-wah
Specialist in Geriatric Medicine