Protein is a macronutrient, and it is essential that we get it through our diet. Protein's main roles are growth, repair of tissue, and cell renewal, all of which help to maintain our health. Protein is found within every cell of the body. It plays a role in the synthesis of hormones, enzymes, movement and structure, and in cases where we are not getting enough calories for energy, or not getting enough carbohydrates, protein can be used as an energy source. A large proportion of protein is found as muscle (around 43-50%), as well as the skin, bone, and blood. Protein provides us with around 10-15% of dietary energy. For every 1g of protein consumed, it provides us with 4kcal of energy.
Proteins are made up of chains of amino acids, and the role and function of a protein depends on the sequence of amino acids. Amino acids are known as the building blocks of proteins. There are 20 different amino acids, 11 of these can either be made in the body (non-essential amino acids), the other 9 we need to get through food (essential amino acids). Interestingly with the 11 non-essential, 6 are known to be conditionally essential, which become essential to get through our diet during times of illness, stress, or trauma.
The functions of amino acids include protein synthesis, regulating protein turnover, enzyme activity, neurotransmitter, gene expression and energy
Sources of protein
You can find protein (all the essential amino acids needed) in meats, fish, eggs and dairy. If you are vegetarian or vegan, you can get all the essential amino acids by combining different sources of plant proteins. There are a few plant proteins which contain all of the 9 essential amino acids, including:
With other plant proteins, these will not contain all 9 of the essential amino acids, or if they do contain all, they will not have enough of one of the amino acids to be counted with the plant proteins mentioned above. For example, hemp protein although it contains all of the amino acids, does not contain enough of the essential amino acid lysine, and for pea, it does contain all 9 of the amino acids, but not enough of the essential amino acid methionine. This is why it is important to include a variety of plant proteins mentioned in the list below, as this will ensure that you get all the essential amino acids. Plant proteins which do not contain all or an adequate amount of the essential amino acids include:
- nuts (including nut butters)
Usually, when we talk about these sources of protein it is discussed about making them complementary proteins by combining sources to ensure that you get all 9 of the amino acids, some examples include chilli (pulses), with rice (grain), nut butter on wholegrain bread, or oats with nuts. However, it is not essential that you have to eat these together, and instead can be consumed over the day. It is more important in the fact that it promotes variety of protein sources (and therefore an adequate amount of amino acids).
How much protein do I need?
In the UK the reference nutrient intake (RNI) is 0.75g of protein per kg of bodyweight for a sedentary adult. So, a female weighing 65kg would need 48.75g of protein a day, and a male weighing 75kg would need 56.25g per day. For women who are pregnant, to help during pregnancy you should include an additional 6g of protein per day on top of the reference nutrient intake. During the first 4 months of breastfeeding women require an additional 11g of protein per day, which reduces to 8g per day after 4 months of breastfeeding.
If you are regularly physically active you’ll most likely require more protein than the recommendation above and may want to increase protein intake to something between 1-1.2g per kg of body weight. Strength athletes have a higher protein requirement of 1.2-1.7g per kg of body weight, and endurance athletes have a requirement of 1.2-1.4g protein per kg of body weight. A post-workout snack which contains 15-25g of protein has been found to help boost glycogen stores, reduces muscle soreness, and help with muscular repair.
It is really important to include a wide range of sources of protein into your diet, and even if you aren’t vegetarian or vegan it is a good to also include plant-based sources. It is also ideal to try and have your protein intake evenly distributed throughout the day.
How much protein do certain foods contain?
I’ll only list a couple, but you can have a look at the labelling on the product to see how much protein it has per serving and also per 100g to give you an idea. These listed below are approximates. As mentioned before it is best to look at the product nutritional label.
Protein per 100g
- Chicken breast – 32g
- Beef steak – 31g
- Salmon – 24.2g
- Prawns – 22.6g
- Chicken eggs – 12.5
- Semi-skimmed milk - 3.4g
- Cheddar cheese 25.4g
- Chickpeas – 8.4g
- Black beans – 7.5g
- Kidney beans – 7.7g
- Lentils – 9g
- Tofu – 12.6g
- Oats – 11.2g
- Almonds – 21.1g
Do I need protein shakes or bars?
For most of us, we are able to get enough protein through our diet, and so we don’t need to be concerned about protein shakes or bars. If you are using shakes or bars, be aware of the sugar content (especially in protein bars). You may be surprised to see how much sugar is in some of them (remember that in ingredients labelling sugar can be labelled multiple ways). Go for high quality varieties if you are having them. In the UK the current average daily protein intake is 65g for women and 88g of protein per day for men, which for many is above the current RNI. Remember that with supplements they are not a replacement for meals as they do not always contain other vitamins and minerals and are there as an addition.
Protein has been found to be the most satiating macronutrient (in comparison to fats and carbohydrates), so including protein sources in meals can help people feel fuller for longer. It is not necessary to cut out any food groups from your diet, and you should still consume carbohydrates (read our blog on carbohydrates here), and healthy fats.
As always a healthy, balanced diet, getting your 5 a day of fruit and vegetables, getting 150 minutes of physical activity per week (at moderate intensity) or 75 minutes of vigorous activity a week, staying hydrated, managing stress, sleep, reducing alcohol consumption all play a role in weight and health.
Throughout our lifecycle it is important to make sure that you are consuming an adequate amount of protein. As we get older it is important for us to keep up with our protein requirements as it helps to maintain muscle mass (which as we get older starts to decrease naturally). Protein is an important part of our diet, you should try and get a variety, especially those who consume a plant-based diet. It is recommended that we spread our protein intake over the day, and not just in one meal alone. It’s best to try and get your protein through your diet first, and then if you need to increase it, looking at using a high-quality protein and just being aware if it contains any added sugar.
Daisy, MSc PGDip ANutr, is a Registered Associate Nutritionist with a Master's Degree in Public Health Nutrition, and a Post Graduate Diploma in Eating Disorders and Clinical Nutrition, both of which are Association for Nutrition (AFN) accredited. She, also, has a BSc degree in Psychology and Cognitive Neuroscience; and has completed an AFN accredited Diet Specialist Nutrition course.
Daisy has worked for an NHS funded project, the Diabetes Prevention Programme; and shadowed a nutritionist in Harley Street.
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