Question: I’m concerned about my protein intake and retaining muscle tone as I age. I know animal foods have all nine essential amino acids but plant foods usually don’t, and the proportion of protein available from animal and plant foods differs. Do nutrition labels take account of the different levels of protein bioavailability in plant foods compared with animal-based foods?
Answer: Protein is a handy energy source and an essential building block for our body. We need protein throughout our lifespan: young children need it for growth, everyone needs it for maintenance and repair of the body, and older adults benefit from optimising their protein intake to slow the loss of muscle mass and strength that occurs with age. Muscle wastage affects physical function and increases the risk of frailty, falls and death, so protein intake is crucial to independent living in older adults.
The proteins in our body are made from 20 different amino acids, most of which our body can make itself. However, nine of these amino acids, called essential amino acids (EAAs), must be provided by our diet as our bodies cannot synthesise them appropriately.
All living cells contain protein, meaning protein is in all animal and plant foods. But although animal-derived proteins, such as meat, eggs and dairy, include a complete set of EAAs, most plant-derived proteins are deficient in one or more of them.
Importantly, food containing EAAs stimulates the body to build up more new muscle tissue; this process helps older adults maintain strength and stave off frailty.
The other difference between animal-derived and plant-derived protein is how available the protein in food is to being digested and absorbed by our body. In general, about 80% of the protein in plant-derived foods, such as legumes, grains and nuts, is available for absorption in the body. In animal-derived foods, about 93% of the protein is available for absorption. So overall, animal-derived foods are a better source of EAA-rich protein.
The nutrition information panel on food packages lists the amount of protein per 100g and in each serving. However, the quantity listed does not consider bioavailability, says New Zealand Food Safety deputy director general Vincent Arbuckle. “This aligns with international guidelines for food labelling from the Codex Alimentarius and key trading partners, including the European Union.
“Although bioavailability of nutrients can be an important consideration of a balanced diet, determining levels can be a complex process that would need to account for nutrient interactions within different foods. There is no standardised method to accurately measure bioavailability for all nutrients across different food products.”
Instead, scientists measure the nitrogen content of the food and then, using a food-specific multiplier, calculate the protein quantity of the food. Food manufacturers then print this calculated protein quantity on their food labels, says Carolyn Lister, science team leader, food and health information, at Plant & Food Research.
Rather than focusing on the bioavailability of protein, lift your intake of high-quality protein. Rich protein sources with a complete set of EAAs include meat, fish, poultry and eggs. Milk, cheese, yoghurt and other dairy products also have a complete set of EAAs and are good protein sources.
While vegetable-derived foods do not necessarily contain a full set of EAAs and the protein is less bioavailable, foods such as legumes, nuts and seeds are still rich protein sources with many other valuable nutrients. As well, wholegrains, vegetables and fruit do contain some protein and plenty of other beneficial nutrients.
A well-balanced diet containing protein-rich foods such as meat, poultry, fish and legumes typically provides enough protein for a healthy adult. If you eat only small portions of these protein-rich foods, you can easily add more with simple food swaps and additions (see chart).
