Protein
Credit - Barbara Goldberg, CSN Health & Nutrition March 2020
Protein is essential for growth, repair and maintenance of good health. When we think of proteins, many of us think about muscles; building and repair, and maybe, if pushed, hair, teeth and nails, but proteins perform a wide range of functions on which we rely, for example:
Structure: the skeleton and it’s supporting tissues, such as cartilage, tendons and ligaments, growth and repair
Protection: skin and skin cells, and general cellular structure and function, blood and blood products, hormones and the immune system
Enzymatic functions – pretty much needed for all the systems which make our bodies work.
Proteins are made up of building blocks called amino acids, and the sequence of amino acids determines which function the protein is able to perform. Consequently, the proteins in the food we eat is broken down into amino acids by the digestive system and contribute to the pool of amino acids from which all proteins are then made, and used in the body.
There is no simple, or single way to determine the protein status of an individual - whether they are in a state of sufficiency or insufficiency – but the determination of lean body mass through a range of non-invasive procedures, including bioelectrical impedance and skin fold thickness assessment, can give a good estimation of total protein content.
How much Protein Your Body Requires:
So, how much protein do we need in our diet and, what function does it fulfil at different stages of our life course, as distinct from others? First of all, it is recommended that proteins represent 10-15% of our dietary content. The reference nutrient content, in other words, the amount needed by 97.5% of people, is 0.75g per kg of body weight for adults aged between 19-50 years, so, an average 60kg person in that age group will require 45g protein/day, and a 70 kg person 52.5g protein/day. But, the amount needed alters during the life course, for example in childhood, to take into account growth, development and maturation.
Childhood and adolescence is a period of rapid growth and development, indeed, adolescence is the period in which approximately half of bone mass is accumulated. The dietary needs of children change as they age, and the amount of protein required is set out in the table below.
In pregnancy, protein provides the material for laying down the tissues needed for the growing baby and, the formation of milk; on-going during lactation. It’s also important to note that vitamins and minerals, for example B vitamins and zinc, affect the way in which the proteins are used by the body.
In addition to growth and development, protein fulfils the demands of maintenance of the functioning body, response to physical activity, and recovery from physiological insults, such as illness or trauma, as well as the body’s immune response.
Protein: Requirements and functions during the life course
|
Stage of life |
Protein requirement (RNI)* g/day |
Functions specific to life- stage |
|
**Babies 7-9 months |
13.7 |
Growth, development and maturity Pivotal period of skeletal development |
|
10–12 months |
14.9 |
|
|
1-3 years |
14.5 |
|
|
4-6 years |
19.7 |
|
|
7-10 years |
28.3 |
|
|
11-14 years |
42.1 (m) 41.2 (f) |
|
|
15-18 years |
55.2 (m) 45.0 (f) |
|
|
19-64 years approx. values 0.75g /kg/body weight |
55.5 (m) 45.0 (f) |
Maintenance of healthy skeleton and avoidance of premature bone loss |
|
65-75+ 0.75g /kg/body weight |
53.3 (m) 46.5 (f) |
Prevention of osteoporosis |
|
70+ the daily requirement increases from 0.75 to 1.0-1.2g/kg/day*** |
Preservation of skin integrity, wound healing, immunity, recuperation from illness, reserve capacity |
|
|
For pregnant and lactating women, the values below should be added to pre-pregnancy values |
||
|
Pregnant women |
+ 6 |
Tissue deposition and milk production |
|
Lactating women |
+11 |
Milk production |
*Reference Nutrient Intake (RNI) is the amount which will meet the needs of almost everyone, although for some people this may be higher than necessary to meet requirements
**Please note no values have been provided for babies less than 6 months as in accordance with WHO recommendations, they should be fed exclusively on breast milk (or formula).
.*** In the acute or chronic disease state, this requirement may increase to as much as 2.0g/kg/day
Barbara Goldberg, CSN Health & Nutrition March 2020
References:
Department of Health Dietary Reference Values 1991, London
Mitchell, P.J., Cooper, C., Dawson-Hughes, B. et al. Life-course approach to nutrition. Osteoporos Int 26, 2723–2742 (2015). https://doi.org/10.1007/s00198-015-3288-6
Protein and amino acid requirements in human nutrition. World Health Organization technical report series. 2007.
Jackson AA. Protein, in The Essentials of Human Nutrition 3rd edition. Oxford University Press