Why is protein important?

Protein is one of the three nutrients, along with fat and carbohydrate, that we need in larger amounts in our diet. Our hair, skin, bone and muscle are all made from the protein we eat, as are the enzymes, hormones and neurotransmitters that play such important messaging roles in the body.


It is made up of long chains of smaller units called amino acids, the building blocks that the body puts to use for muscle growth and repair. There are 20 amino acids in total, of which nine are essential – meaning the body cannot make them and they must be obtained from our diet. Animal foods, such as meat and fish and certain plant sources – soy, quinoa, buckwheat and Quorn – contain all of these essential amino acids, making them high-quality sources of protein.

Protein is central to the maintenance of muscle mass over the course of our life, which is important for metabolic health, physical strength, mobility and ultimately our independence. Muscle is also the largest contributor to our resting energy expenditure, burning calories even while we rest.

Discover our full range of health benefit guides including everything you need to know about protein and the 10 best sources of protein. Plus, check out our high-protein recipes as well as those for vegetarians and vegans.

Who needs protein more?

We all need protein in our diet, but those who take part in endurance sports or weight training may benefit from increasing their protein intake as well as factoring it into their training regime.

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Studies suggest that as we get older our protein needs may also increase; this is because protein in our diets helps to reduce the muscle loss associated with lower levels of activity combined with the effects of aging. Insufficient protein intake may lead to an increased loss of muscle, known as sarcopenia, which can lead to physical frailty and higher probability of falling over.

What happens when I eat protein?

After eating protein, digestion starts in the stomach and continues in the first part of the small intestine, called the duodenum.

Absorption of 40-50% of the available amino acids takes place in the small intestine; this will be used for energy (1g protein supplies 4 kcals) and for local protein synthesis.

The remainder of the amino acids are released into the hepatic portal vein and taken up by the liver. It’s believed that only 10-20% of ingested protein ends up as skeletal muscle.

Different types of protein on black background

How does protein influence muscle health?

Protein is essential for making muscle since it forms the building blocks of muscle tissue. Eating adequate amounts helps us maintain muscle and promotes muscle growth and repair, especially after resistance exercise. Muscle growth is optimised when repetitive bouts of resistance training are combined with adequate intakes of dietary protein.

Both the quantity and quality (composition of amino acids) of the protein you eat influences the muscle your body makes. Other factors, such as age, general health and potentially your gut bacteria, may also influence how you utilise the protein you eat.

Are some protein foods better at building muscle than others?

Lower quality proteins, such as wheat protein, lack one or more of the nine essential amino acids and so fail to stimulate muscle protein synthesis to the same degree as complete proteins like whey. High-quality protein sources, which supply all nine of the essential amino acids, aid muscle gain.

Leucine is considered the primary amino acid to initiate muscle synthesis and is found in meat, fish, dairy, eggs, soy and nuts. Other examples of high-quality proteins include plant-based protein powders described as ‘concentrates’ or ‘isolates’.

What happens when we have too little protein?

Not eating enough protein poses a number of health risks: the associated muscle loss may result in lower physical strength; poor balance and potential mobility issues, especially in older adults. You may also find your appetite is not well-managed resulting in weight gain and increased body fat.

The first signs that you might not be eating enough protein may be a worsening in the condition of your hair, nails and skin. Other signs include wounds and injuries that take longer to heal, more frequent colds and infections, experiencing anaemia and muscle weakness, and possible swelling of your legs, feet and hands. You may also experience fatigue and start to notice changes in your body composition and posture.

Drinking a protein shake after a workout

How much protein do I need to build muscle?

In the UK, the Reference Nutrient Intake (RNI) is 0.75g/kg of body weight – the minimum amount required to prevent the loss of lean body mass and is based on an average, sedentary adult. These guideline figures are often misrepresented as being recommended optimal intakes, so if you’re an adult looking to build muscle this is unlikely to be enough.

That said, defining an optimal intake is tricky since our protein needs are specific to each and every one of us. How much we need depends on our age, weight, height, gender, general state of health, how physically active we are, as well as the type and intensity of that activity. It also depends on our body composition and how much muscle mass we already have.

The best way to calculate your daily protein needs is using your weight. Based on averages from evidence-backed recommendations, a general rule of thumb is to eat about 1.2g protein per kg of body weight to maintain muscle. This may increase to 1.2-1.6g/kg of body weight when looking to add lean mass or if you’re a woman in midlife.

A weightlifter or strength athlete looking to add muscle mass and who will be using their muscles more than the average person will naturally require more protein – between 1.4-2g/kg of body weight per day. The recommended daily amounts of protein for endurance athletes is 1.2-2.0g/kg of body weight.

If you know your body fat percentage, you can tailor this figure more accurately by calculating your body fat percentage in kg and subtracting this amount from your overall weight to arrive at your lean body mass. If your protein objective is to build muscle, you may need to aim for 2g/kg of lean body mass weight.

How much protein should I eat after exercising?

A number of studies suggest that after exercise, a protein intake of 0.2-0.5g/kg of body weight will stimulate muscle synthesis. Depending on your weight as well as the intensity and duration of your exercise, this is likely to be equivalent to a meal or snack supplying 10-30g of protein.

The longer we exercise and the more intense the activity, the more protein we’ll need since muscle breakdown and rebuilding is unregulated for 24 hours following activity. Eating some protein within 30 minutes of exercise is helpful because our muscles are particularly receptive at this time.

What are the dangers of too much protein?

A prolonged intake of high amounts of protein has been associated with bone loss and kidney damage. However, in otherwise healthy individuals, there is little evidence to this effect – it’s now understood that a high-protein diet is only a problem for those with an existing disease or kidney dysfunction. In fact, in an otherwise healthy adult, including the elderly, a higher protein intake may help prevent the loss of muscle mass and strength, and support bone health.

For the majority of healthy adults, a high-protein diet followed for a limited period (such as a few months) shouldn’t cause a problem. However, the implications of following a high-protein diet and restricting carbohydrates long-term is still being researched and may vary, depending on age and genetics.

In conclusion, for the majority of healthy adults, consumption of protein at 2g/kg of total body weight per day is to be considered safe.

How can I maintain and build muscle mass?

If you’re looking to maintain and build muscle mass, incorporate these practical steps:

Please note, if you’re considering any significant change to your diet please consult your GP or a registered dietician to ensure you can do so without risk to health.

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Are you looking to maintain or build muscle mass? Share your experiences in the comments below…


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