February 10, 2020 7:02 am Leave your thoughts
In last week’s blog, we looked at how much protein we really need in our diet. Working it out, gram by gram, we examined how much protein particular foods contain – and how you can manage if you’re on a restricted diet.
Today, we’d like to know – what does protein actually do within our bodies?
The building blocks of protein
To answer that, we need to know a bit more about what protein is. It’s not one single element, but is made up of strings of amino acids. These are organic compounds made of carbon, hydrogen, nitrogen, oxygen: there are generally agreed to be 21 of them in total (with one additional amino acid not used by humans, so generally discounted). Proteins differ from one another depending on the sequence of the amino acids within these strings, and the length of the strings themselves.
You’ll have seen reference to ‘essential’ amino acids – these are amino acids that can’t be synthesized by the body itself from scratch at the necessary rate, and so must be obtained from food. Of the 21 amino acids, there are nine that humans can’t synthesize: phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine and histidine, and six others that humans can’t synthesize under certain conditions, referred to as ‘conditionally essential’: arginine, cysteine, glycine, glutamine, proline and tyrosine. (It should be noted that some experts consider there to be only eight in the first group, with the additional one only relevant to children.)
It’s important that we take in enough of all the essential amino acids. Meat, fish, milk, cheese and eggs contain all the essential amino acids in the right balance, making them ‘complete protein sources’. There’s some controversy as to whether any plant-based foods can be classed as complete proteins. Quinoa is generally considered to be a complete protein, but some argue that its levels of one particular type of amino acid (lysine) are not as high as is necessary. Soy is also thought by some to be complete – but others disagree – and other plant-based products are known to be incomplete. Incomplete amino acids have ‘limiting’ factors, which prevent the uptake of the required amount of protein.
Wherever you stand on the issue, none of this means that vegetarians or vegans can’t obtain enough protein from plant sources – they just can’t get everything from one source, so have to mix and match. Wikipedia lists some appealing combinations that would provide a complete amino acid profile:
This is, in any case, the best plan for meat-eaters too. A balanced diet lets everyone take in the right combination of elements, in the right balance, covering all the bases.
The building blocks of our bodies
Just as amino acids are the building blocks of protein, so protein itself is the building blocks of our bodies – particularly our muscle mass. Dietary protein is broken down, in the mouth, the stomach and the small intestine, into its individual amino acid elements. The amino acids travel to the liver, where they are reassembled into whatever our bodies need. These needs are significant: our bodies use protein to build and repair tissue and to make enzymes, hormones, bones, muscles, cartilage, skin and blood. We use protein within our bodies to transport nutrients, regulate the balance of acids and alkalis in our blood, balance fluids, provide energy, heal wounds and keep our immune systems healthy. The word ‘protein’ derives from the Greek for ‘first’ – ‘proteos’ – and it’s clear why: it really can be considered to be the primary element in our diets.
What if we don’t get enough protein?
If we’re not taking in enough protein from food, our bodies will, first of all, steal protein from our muscle tissue and use it to support our vital functions. We’ll experience muscle cramps, fatigue and weakness as a result – wounds will be slower to heal and infections more likely.
If protein deficiency continues, all of our body’s organs will suffer, including our brain and kidneys. Our muscles will weaken and our skin will become dull. In extreme cases, as you might find in famine areas, particular types of severe malnutrition (kwashiorkor or marasmus) will occur.
On a more prosaic level, protein is what makes us feel full when we eat a meal – so if we don’t get enough of it in our main course, we might find that we over-indulge in pudding afterwards (or just that we’re rather bad-tempered…).
Last week’s blog How much protein do we really need? gives some ideas for sources of protein for all diets. We’re going to look at those more closely next week, when we consider vegan and vegetarian sources of protein.
Tags: amino acids, beans, coconut, complete protein, corn, essential amino acids, protein, quinoa, Rice, soy, sweet corn, sweetcorn, tomatoes, vegan protein, vegetarian protein
This post was written by Yzanne