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Why Is Protein Important in Your Diet?

by Matt Durkin
MSc Nutrition Specialist

Protein, alongside carbohydrates and fat, make up the macronutrients – the food groups that provide the energy we need to live. Like most topics in nutrition, protein has received a massive amount of attention; both positive and negative. This has inevitably led to confusion on the topic. In this present article, we are going to learn all about protein, why it is so important in the diet and take an evidence-based look at whether the negative press is justified. 

What Is Protein?

Proteins are compounds that are made up of carbon, hydrogen and oxygen just like carbohydrates and fat. What makes protein unique however is its nitrogen content.  Similar to the way in which complex carbohydrates are made up of numerous sugar molecules, proteins are just numerous amino acids linked together. For this reason, amino acids are often referred to as ‘the building blocks of protein’. 

With regards to humans, there are 20 amino acids, with 9 of these classed as ‘essential’ as the body cannot create them. Conversely, 11 of these amino acids are classed as ‘non-essential’, as the body has the capacity to synthesise them. 

What Is Proteins Role in the Body?

Protein was named after the Greek word Proteios meaning ‘of prime importance’, so it should come as no surprise that protein has a plethora of crucial roles. Protein is widely thought to have 6 major roles in the human body. Here they are: 


As we found out earlier, protein can provide energy. Typically, a gram of protein proves 4 kcals worth of energy. The amino acids in protein can enter the mitochondria of our cells and be used for creating ATP which is the body’s energy currency. 

As well as being used for energy, the amino acids from protein can also be turned into glucose, a process that scientists call ‘gluconeogenesis’. This is important because certain areas of the body including the central nervous system and red blood cells need a good supply of glucose. 

Protein Balance 

In the body, we are constantly in the process of protein synthesis and protein breakdown. When protein breakdown exceeds protein synthesis, we lose muscle tissue and vice versa. When protein breakdown and synthesis are the same, we are said to be in protein balance. 

But why does protein breakdown occur? Well, the body is constantly removing damaged or abnormal protein to prevent their accumulation or removing enzymes that are no longer required. For this reason, it is important we obtain essential amino acids in the form of protein through the diet to ensure we meet our requirements. 

Our muscle tissue is very important as it works as part of the skeletal system to allow movement. The vast majority of the body’s protein is found in skeletal muscle. For example, protein makes up the contractile units known as actin and myosin, which ultimately allow muscle contraction. 


Enzymes are proteins that influence the rate of a chemical reaction in the body. There are an almost inexhaustible number of enzymatic reactions in the body, but some of the most important ones are the digestion and metabolism of carbohydrates, fats and proteins into ATP to provide the energy we need to carry out all bodily functions. 


Protein is primarily involved in the production of numerous hormones that also help to regulate bodily functions. One good example is insulin, a hormone created in the pancreas, that helps to ensure our blood sugar remains in a healthy range. 


Sufficient protein in the diet helps to ensure your immune system is working properly. This is important thanks to its role in creating the antibodies that fight off infection and illnesses. These antibodies work by identifying and destroying pathogens like bacteria and viruses, helping us to stay healthy.


Finally, protein is involved in the transportation of various molecules. One that could be regarded of high importance is haemoglobin – a protein that transports oxygen!

How Much Protein Should I Consume?


Now we have covered what proteins are, and their key functions in the body, it is important to ensure we are consuming the right amount. Like many aspects of nutrition, the amount that is needed depends on your goals and stage of life. 

For all adults, the current recommendation is 0.8g of protein for every kilogram of bodyweight. So, for a person who weighs 70kg, a protein intake of 56g per day would be sufficient to maintain protein balance, ensuring the body has all the amino acids needed for bodily functions. 

This recommendation is based off a meta-analysis study conducted in 2003. The analysis included 19 clinical investigations that assessed how much protein was needed to ensure nitrogen balance (a marker of protein balance) in adults.  Besides the methodological complications of measuring nitrogen balance, 18 out of the 19 studies analysed were conducted in young adults, meaning the 0.8g per day for all adults is not actually evidence-based.  

Rightfully, this recommendation has come under scrutiny. This is because research has shown that older adults (60+ years) consuming the recommended 0.8g per kg of bodyweight actually lost a significant amount of muscle in their legs over a 14 week period. More recent research has shown that older adults require substantially more protein to maximise protein synthesis than younger adults.

There are numerous factors that collectively work together to mean that older adults require more protein to maintain protein balance and thus muscle mass. Although muscle naturally declines as we age, rapid loss of muscle, also known as sarcopenia, can have serious health consequences. 

So to avoid muscle loss with advancing age, numerous world-renowned research groups are in agreement that adults over the age of 60 should consume more protein: 1.2g of protein per kilogram of bodyweight specifically. This means that an older adult with a body weight of 70kg would have to consume almost 30g more protein per day (56g vs 84g). Unfortunately, many older adults struggle to consume this higher amount as appetite responses can naturally decline. This is compounded by the fact that protein is the most satiating nutrient (it fills us up quickly). Ways to get around this issue will be explored later in the article. 

Those Trying to Lose Weight

Individuals who are trying to shift some excess body fat are likely to enjoy greater success if they increase their protein intake. To lose weight, we need to burn more calories than we consume. To meet our energy needs, the body has to start using up its fat stores which is the goal of weight loss. However, the body also tends to use protein for fuel, which inevitably decreases muscle mass. 

This should be avoided at all costs, as muscle tissue is healthy and ensures we stay functional. Furthermore, muscle has a high-calorie demand. This means that losing muscle slows our metabolism, making weight-loss all the more difficult. So to preserve muscle, a higher protein intake is required.

Not only is a high protein intake good for muscle sparing, it also exerts benefits on appetite and metabolism. Protein has what nutritionists call a high thermic effect, meaning it requires a lot of energy to digest and utilise it, which increases metabolic rate – a good thing for weight-loss! 

Protein is digested slowly, which helps to make us feel full. It also suppresses ghrelin – the sole hormone that makes us feel hungry. Through this action, a high protein diet is thought to reduce overall calorie intake, leading to sustained weight-loss. To benefit from a high protein intake whilst trying to lose weight, 1.2-1.5g per kilogram of body weight will be sufficient. Try spacing the protein intake over the duration of the day for the best results. 

Athletes and Fitness Enthusiasts

Contrary to popular belief, our muscles do not grow during exercise. Instead, exercise actually causes damage to the muscle fibres, which needs repairing. With the right conditions such as good nutrition and rest, the muscle fibres grow back bigger and stronger than before. Due to this, it should come as no surprise that athletes and fitness enthusiasts require substantially more protein than their sedentary counterparts. 

The exact amount of protein needed by athletes depends on numerous factors such as their sporting discipline, stage of training, and body composition goals (muscle gain or fat loss). For example, endurance based sports will require a slightly lower protein intake than athletes who take part in events that demand high muscular strength and power. Providing exact figures, an endurance athlete may aim for 1.4g of protein per kilogram of bodyweight whereas a power athlete may aim for 1.6g per kilo.

If an athlete is in a particularly demanding training block or is performing new training sessions that their body is not used to, then elevating their protein intake slightly would be a wise idea. An increase by 0.2g per kilogram per day should be sufficient to ensure good recovery from their training. 

For athletes trying to lose weight, it is not uncommon to aim for a daily protein intake of 2.2-2.5g per kilogram of body weight. This is 154-175g of protein per day for a 70kg athlete. We will find in the next section how much food that actually equates to! 

Finally, injured athletes who will experience a sudden and dramatic drop in their training load are now recommended by nutritionists to have a high protein intake to try and avoid the loss of muscle which is often experienced. Again, an intake of around 2g per kilogram is frequently recommended. 

Protein sources

Now that we have looked at the importance of protein in the diet and why different populations often require substantially more than the recommended intake, it is time to discover what this actually looks like in food sources. 

Protein-containing foods can be categorised in two ways – “complete” or “non-complete” protein sources. Complete sources contain all the essential amino acids, whereas non-complete proteins are devoid in at least one of the 9 amino acids the body cannot create. 

Here are some examples of complete protein sources and how much they provide:

Chicken breast - 31g per 100g

Turkey breast – 30g per 100g

Minced beef – 21g per 100g (extra lean)

Eggs – 6g per medium-sized egg

Dairy – 8g in 250ml of milk; 10g in 100g of Greek yoghurt and 7.5g in 30g of cheddar cheese 

Tinned tuna – 28g per averagely sized tin

Quinoa – 14g in 100g uncooked

Below are some examples of non-complete sources and their protein content:

Nuts & Seeds – 6g in 30g of cashews 

Legumes – 19g in 100g of chickpeas 

Grains – 12g in 100g of uncooked pasta

Tubers – 6g in a large baked potato

Vegetables – 2.5g in a portion of broccoli, which is 80g 

Although complete protein sources such as those from meat, fish, dairy and eggs are superior in terms of their amino acid profile and sheer protein content, non-complete sources can also be very effective. For example, rice and beans are both non-complete protein sources. However, when combined in the same meal they will provide all the amino acids the body requires. 

Vegetarians and vegans will find that it is absolutely possible, albeit more difficult, to achieve the recommended protein intake. However, the situation becomes tricky when an older adult, athlete, or someone trying to lose weight wants to meet their protein requirement through plant-based foods. Indeed, it will be hard for many to achieve their required intake eating even including animal protein.

Looking again at the example of a 70kg athlete trying to lose weight, they would need to eat the equivalent of 300g of chicken breast and 3 tins of tuna every day to meet their needs. This is both impractical and expensive. Fortunately, there are numerous supplements that provide high-quality protein in convenient and cost-effective doses to help people achieve their requirements. 

Protein Supplementation

Although protein supplements were once almost exclusively used by athletes and fitness enthusiasts they are now being utilised by people of all ages with differing goals. Indeed, older adults or those trying to lose weight are routinely using protein supplementation to their advantage.

As elucidated earlier, older adults require more protein to help maintain muscle mass and health in their advancing years. However, appetite and life situations can make achieving the higher protein needs increasingly difficult. Research has also shown that older adults tend to only obtain an adequate protein dose once per day. Experts believe this is a key reason for muscle loss and therefore recommend numerous protein-rich meals a day. Again, this is often difficult and impractical.

For this reason, protein supplementation has become increasingly popular. Impressively, research has shown that protein supplements in the form of a bar, gel or a drink can negate the appetite suppression associated with protein. This allows older adults to obtain a sufficient amount of calories and protein to maintain their muscle mass and subsequently their health and wellbeing. 

There are numerous types of protein supplements such as whey, casein, egg, pea and hemp, but the one that is the most widely used and is underpinned by scientific evidence is whey. Whey is naturally found in milk, making up around 30% of the protein content, with casein contributing the remainder. 

Whey protein for supplements is obtained through cheese production as specialist enzymes are added to separate the curds from the liquid whey. The liquid is then pasteurised and dried to make a powder, which can then be added to the beverage of your choice, or even pancake mixtures to create a high protein drink/food. 

Not only is whey protein convenient it is also arguably the best source of protein available. It contains all of the essential amino acids in high amounts, whilst being very low in fats and carbohydrates. Whey is famous for its high content of the branched-chain amino acids (BCAA’s), which are well-known to be the most powerful stimulators of muscle protein synthesis. As whey protein has a high bioavailability and is rapidly digested, it is the perfect choice for anyone who values their muscle mass. Although not a vegan protein source, certain high-quality whey protein supplements are low enough in lactose that they are still well-tolerated by many lactose intolerant individuals. 

Health Concerns of a High Protein Intake 

Like many aspects of nutrition, protein has received some negative attention in recent years, supposedly linking a high protein intake to certain health conditions. One of the most commonly levied accusations is that a high protein diet causes kidney issues, as supposedly they have to work harder to clear by-products of protein metabolism. 

Thankfully, the evidence is clear that even a very high protein intake (above 3g per kilogram of bodyweight) is safe for healthy individuals, leading to no signs of impaired kidney function. That being said, a high protein diet can exacerbate the situation if someone suffers from kidney disease, so caution and seeking medical advice is advised. 

Another concern with regards to protein intake is that it causes weak bones. The theory is that a high protein intake creates an acidic environment in the body, which causes the bones to release calcium to rectify the imbalance. Again, this is not supported by scientific evidence. In fact, a higher protein intake is actually good for bone health as it stimulates hormones that synthesise bone tissue and promotes muscle gain which again helps bone density. 

Finally, high protein diets (mainly through a high red meat intake) have been linked to cancer, which has rightfully caused serious concern. The theory is that high protein diets stimulate a hormone called IGF-1 that stimulates cell growth in the body. As cancer is caused by abnormal cell growth the link has been developed. In short, IGF-1 does not cause cancer and actually has certain health-protecting effects. However, IGF-1 may quicken the growth of already present cancer cells. This topic is highly complex as there are a plethora of genetic, environmental and lifestyle factors that can increase the risk or lead to cancer, and it is never caused by one independent variable. 

A comprehensive review of this topic is beyond the scope of this article, but in short, a high protein intake as part of an active lifestyle is going to do far more good than harm. Such a confident assertion can be made as the positives of protein are backed by strong scientific evidence, whereas any negatives have weak evidence at best. 


To conclude, protein makes up a third of the macronutrients – providing the body with not only energy but the amino acids that are essential to life. Hopefully, this article has covered the importance of protein and where more protein may be beneficial to our health. Let us sum up the key areas of this article in the take-home points: 












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