Today I'm sharing some things I think we all need to know about protein:
Protein is composed of amino acids arranged in long chains
There are 20 different amino acids. Eleven of these can be made in the human body and nine, known as essential amino acids, can be obtained only through diet.
Animal-sourced protein foods like meat and dairy are often called "complete proteins" as they contain all nine essential amino acids. Plant-source protein foods on the other hand don't contain all 9 essential amino acids. So people following a vegan or plant-only diet do need to be a little more mindful of what kinds of protein foods they are eating, to make sure they are getting all 9 essential amino acids.
Different plant protein foods are limiting in either lysine or methionine. It used to be thought that you needed to combine different plant protein foods in the one meal to get the full complement of essential amino acids. The conventional "protein combining rule" was that if you were vegan you "needed" to combine legumes and grains in the one meal. These days it is recognised that you don't need to co-ingest these foods at the same time - but you do need to make sure you are eating a variety of plant-based protein sources over the course of your day or week!
It’s important that we eat enough protein every day.
We need to eat protein every day for the amino acids it is comprised of, for muscle and other body tissues, hormones, enzymes and antibodies.
If we don’t eat enough protein each day, our body will break down the proteins in our body (such as in our muscles) to get the amino acids it needs to perform essential functions. And that's not a good thing. We don't want our body to cannibalise itself to release the essential amino acids it needs for important physiological processes.
So how much protein should we eat?
The National Health and Medical Research Council recommends that women consume 0.75g of protein per kilo of body weight per day and men consume 0.84g/kg.
But older people, or people recovering from illness or seeking to build their lean body mass will need more - 1.07g per kilo of body weight for men and 0.94g per kilo for women.
And we all know that when you are losing weight you don't just lose fat, you also lose lean body mass (aka muscle). Studies have shown that if you are actively seeking to lose weight by either reducing your energy intake or increasing your energy expenditure (or both), an intake of 1.4 to 1.6g per kilo per day is a better amount to ingest to minimise loss of lean body mass.
We need to divide our protein intake throughout the day, and not ingest huge amounts at one sitting.
This is where I see many people go wrong. They eat huge slabs of meat or slurp down a big protein shake. But studies show that we can only utilise 20-30g of protein at a time.
Our bodies can't store any protein we consume that is excess to our needs.
The protein we consume has to either be used for protein synthesis in our body or it has to be burned for fuel. We just don't store it for later. So if we eat a lot more than 20-30g in one meal, our body has to burn it. And while our body is burning protein, it's not burning fat....
It's not healthy to over-consume protein
As noted above, if our body doesn't need the protein it will have to be burned for fuel. It will be burned in preference to fat. And worse, protein is not a particularly clean-burning fuel. Too much can increase ammonia which needs to be eliminated via the kidneys in urine.
Protein stimulates insulin release
Yes you read that right.
I'm not making this up.
And I get that this may be the first time you have ever read anything like this, so let me break things down for you a bit:
A whole diet philosophy has been built around the "carbohydrate-insulin hypothesis" which has encouraged high-protein-low-carb diets in order to "keep insulin levels low and stable". Insulin is a "storage hormone" so while insulin levels are high, fat will be stored rather than burned. So upping your protein intake while lowering your carb intake has been promoted as a great fat-burning diet.
But while everyone knows that carbohydrates are broken down into glucose, which stimulates insulin release, what a lot of people don't realise that protein intake stimulates insulin secretion too.
Most people are familiar with the concept of a Glycaemic Index, which summarises the Glycaemic impact of different foods; how much they raise blood glucose levels (and then insulin).
But did you know there is also an Insulinemic Index?
Seriously, check it out.
It shows that many protein-rich foods, and especially beef and dairy, stimulate insulin release. And also seem to slow clearance of insulin from our system by the liver. This may explain why high intake of animal protein is associated with increased risk of type 2 diabetes.
When we consume protein we stimulate the release of insulin in our bodies. Insulin is an anabolic (or building) hormone. Insulin is the "trigger" for our body to synthesise (or manufacture) proteins (like muscle cells), which is why weight lifters love whey protein and beef - it stimulates muscle cell growth!
So insulin release can definitely be triggered by carb intake. The speed and volume of release will depend in large part on how processed or refined the carb is. When insulin is released into our bloodstream it stimulates the intake of glucose out of the bloodstream and into the cell, as well as stimulating intake of fatty acids from the bloodstream into fat cells (ie, fat storage!).
But insulin release can also be triggered by protein intake. Insulin is not the devil - if it is released in the right amounts. The right amount of insulin will help us use our food to fuel and nourish us. But too much can lead to insulin resistance, metabolic dysfunction and even type 2 diabetes.
So it is definitely worthwhile making a little effort to get the right amount of protein your body can use (20-30g during any single meal), but not going overboard and over-consuming high amounts of protein.
Too much protein will just spike your insulin and strain your elimination systems as your body seeks to excrete the excess nitrogen in your urine, producing ammonia along the way. This fits in with the research on the importance of staying out of overnutrition.
It makes far more sense to ingest 20-30g of protein at each meal, and if you are tall, male or are undertaking a weights program, consider adding in one or more protein-containing snacks.
And don’t just get your protein from meat and dairy. There are lots of amazing plant sources of protein, all packaged up with fibre, vitamins, minerals and healthy phytonutrients!
BUT HERE'S THE REALLY IMPORTANT THING TO REMEMBER ABOUT PROTEIN:
We don't eat "protein", we eat FOODS that contain protein!
There are two reasons why this is important.
Firstly, different "protein foods" contain different amounts of protein.
I became aware of the importance of sharing this message when I reviewed the weekly food record of one of my favourite clients and saw that she was eating 25-30g of salmon, chicken or lamb at each meal thinking that she was getting 25-30g of protein. Oops! My bad. I should have been clearer...
Here is a rundown of the approximate protein content of some of our most well-known "protein foods":
100g beef ~27g
100g lamb ~28g
100g skinless chicken breast ~34g
170g white fish ~45g
180g salmon ~39g
1 egg ~6g
100mL cow's milk (full fat) ~3.5g
100mL cow's milk (skim) ~3.7g
100g plain yoghurt (full fat) ~6g
100g cheddar cheese ~25g
100g feta cheese ~17g
100g ricotta cheese ~10g
100g firm tofu ~12g
100g silken tofu ~8g
100g red kidney beans ~7g
100g lentils ~7g
100g chickpeas ~6g
100g split peas ~7g
100g quinoa ~4g
25g almonds ~6g
25g walnuts ~4g
25g cashews ~5g
25g brazil nuts ~4g
25g sunflower seeds ~7g
25g pumpkin seeds ~6g
1 Tablespoon peanut butter ~6g
Secondly, "protein foods" come bundled up with other macro- and micronutrients.
So red meat will comes bundled up with haem iron and saturated fat, whilst legumes are bundled up with carbohydrates, fibre and phytonutrients, and dairy foods come with saturated fat, lactose, calcium, phosphorous, magnesium and iodine.
Thinking about protein in isolation is what we call "reductionist thinking" and in nutrition science terms it is soooo 1980's dahlink! These days, medical and nutrition scientists are realising that it is the overall dietary patterns that influence health and longevity, not individual nutrients.
So don't just consider the protein content of foods. Think about what else comes with it! And what you are eating throughout the day, and over the course of your week.
Finally, no single protein food is "better" than the others.
Just because skinless chicken breast contains more protein per gram does NOT mean that it is better than red kidney beans or greek yoghurt. Just because a protein food like red kidney beans comes bundled with carbohydrate does not mean it's not a good source of protein. All it means is that you might need a larger serve to get your 25g serve of protein (or eat it as part of a mixed meal with some yoghurt).
Remember, different foods contain different amounts of protein but they also come bundled with different macro- and micronutrients, and in the absence of a medically diagnosed allergy or intolerance they all have a place in a vibrant, varied, balanced diet!
Mero AA, Huovinen H, Matintupa O, et al. Moderate energy restriction with high protein diet results in healthier outcome in women. J Int Soc Sports Nutr. 2010;7(1):4. doi:10.1186/1550-2783-7-4.
Holt SH, Miller JC, Petocz P. An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods. The American journal of clinical nutrition. 1997 Nov 1;66(5):1264-76.
Lan-Pidhainy X, Wolever TM. The hypoglycemic effect of fat and protein is not attenuated by insulin resistance. The American journal of clinical nutrition. 2010;91(1):98-105.
Micha R, Wallace SK, Mozaffarian D. Red and processed meat consumption and risk of incident coronary heart disease, stroke, and diabetes mellitus: a systematic review and meta-analysis. Circulation 2010;121:2271–2283
Aune D, Ursin G, Veierød MB. Meat consumption and the risk of type 2 diabetes: a systematic review and meta-analysis of cohort studies. Diabetologia 2009;52:2277–2287pmid:19662376
Sluijs I, Beulens JW, van der A DL, Spijkerman AM, Grobbee DE, van der Schouw YT. Dietary intake of total, animal, and vegetable protein and risk of type 2 diabetes in the European Prospective Investigation into Cancer and Nutrition (EPIC)-NL study. Diabetes Care 2010;33:43–48 pmid:19825820