Protein: Its Functions, Food Sources and Daily Requirements

Protein is one of the body’s essential macronutrients. This means it is needed in relatively large amounts to support health and normal body function.

Protein contributes to growth, repair and maintenance throughout the body. It is needed by people of every age, not only athletes or those trying to build muscle.

Why Does the Body Need Protein?

Protein performs many important functions within the body. It helps to:

• Build and repair body tissues
• Maintain muscles
• Support growth and development
• Maintain healthy skin, hair and nails
• Produce enzymes
• Produce certain hormones
• Support the immune system
• Maintain normal body functions

Protein is found in every cell of the body and is an essential component of muscles, bones, skin, blood and organs.

Protein for Growth and Tissue Repair

The body constantly breaks down and replaces cells and tissues. Protein supplies the materials needed to support this continuous process.

Protein is particularly important during periods of:

• Childhood and adolescence
• Pregnancy
• Recovery from illness
• Healing after an injury
• Recovery following surgery
• Regular physical training

Protein and Muscle Health

Protein helps the body maintain and repair muscle tissue. Physical activity stimulates changes within muscles, while dietary protein provides the amino acids needed for repair and adaptation.

Protein alone does not automatically build muscle. Muscle development also depends on:

• Suitable resistance exercise
• Adequate energy intake
• Rest and recovery
• A balanced diet
• Consistent training

Protein and the Immune System

The immune system depends on an adequate supply of protein. Amino acids are needed to produce antibodies and other substances involved in fighting infection and supporting recovery.

A prolonged inadequate intake of protein and energy may affect the body’s ability to maintain normal immune function.

Protein, Enzymes and Hormones

Protein is required to make enzymes that support chemical reactions throughout the body. These include enzymes involved in digestion and metabolism.

Some hormones are also made from amino acids. Hormones act as chemical messengers and help regulate many processes, including growth, metabolism and blood-glucose control.

What Are Amino Acids?

Proteins are made from smaller building blocks called amino acids.

When protein-containing food is eaten, the digestive system breaks the protein down into amino acids. These are absorbed into the bloodstream and transported to the parts of the body where they are needed.

The body uses amino acids to:

• Repair damaged tissues
• Build and maintain muscle
• Support growth
• Produce enzymes and hormones
• Make important immune-system components
• Maintain cells and organs

Essential and Non-Essential Amino Acids

Some amino acids can be produced by the body. These are commonly described as non-essential amino acids.

Other amino acids cannot be made by the body in sufficient amounts and must be obtained from food. These are known as essential amino acids.

Eating a varied and balanced diet normally provides the range of amino acids the body requires.

Animal Sources of Protein

Many animal-derived foods are rich sources of protein. Examples include:

• Lean meat
• Poultry
• Fish
• Shellfish
• Eggs
• Milk
• Yoghurt
• Cheese
• Offal

Animal foods can also provide nutrients such as iron, vitamin B12, calcium and omega-3 fatty acids, depending on the food selected.

Choose leaner meat where possible and limit frequent or excessive consumption of processed meat.

Plant-Based Sources of Protein

There are many nutritious plant-based protein sources, including:

• Beans
• Lentils
• Peas
• Chickpeas
• Soya beans
• Tofu
• Tempeh
• Nuts
• Seeds
• Nut and seed butters
• Mycoprotein products

Bread, rice, pasta, oats and other cereal foods also provide smaller amounts of protein that contribute to the daily total.

Combining Plant Proteins

Different plant foods contain different amounts and combinations of amino acids. Eating a varied diet containing pulses, grains, nuts, seeds and soya products can provide all the essential amino acids the body needs.

Plant proteins do not normally need to be carefully combined within the same meal. Eating a suitable variety over the course of the day is generally sufficient.

How Much Protein Do Adults Need?

The UK Reference Nutrient Intake for adults is approximately 0.75 grams of protein per kilogram of body weight each day.

For example:

• A person weighing 60kg would require approximately 45g of protein each day
• A person weighing 70kg would require approximately 52.5g each day
• A person weighing 75kg would require approximately 56g each day
• A person weighing 80kg would require approximately 60g each day

This is a general population reference rather than an individual prescription. Personal requirements can vary.

Who May Need More Protein?

Protein requirements may be higher for some people, including:

• Children and adolescents who are growing
• People who are pregnant or breastfeeding
• Older adults
• People undertaking demanding physical training
• People recovering from illness or injury
• People recovering from surgery
• People with certain medical conditions
• People who are underweight or at risk of malnutrition

A doctor or registered dietitian can provide individual advice when a person has increased requirements or a medical condition affecting their diet.

Protein Needs for Physically Active People

People undertaking regular endurance exercise, resistance training or physically demanding work may need more protein than the general adult recommendation.

The precise amount will depend on:

• The type of activity
• The intensity and duration of training
• The person’s body weight
• Their training goals
• Their overall energy intake
• Their health and recovery needs

Most people can obtain sufficient protein from ordinary food without relying on specialist protein powders or supplements.

Protein and Older Adults

Protein becomes especially important as people get older because ageing is often associated with a gradual loss of muscle mass and strength.

Older adults can support muscle health by:

• Including protein-rich foods regularly
• Spreading protein intake across the day
• Remaining physically active
• Including appropriate strength-based activity
• Eating enough food and energy overall

Anyone experiencing unexplained weight loss, reduced appetite or difficulty eating should seek advice from a healthcare professional.

Does the Body Store Protein?

The body does not maintain a dedicated store of protein in the same way that it stores carbohydrate as glycogen or energy as body fat.

Body proteins are constantly being broken down and rebuilt. This is why it is important to consume adequate protein regularly as part of a balanced diet.

Spreading Protein Throughout the Day

Rather than consuming nearly all dietary protein in one meal, it can be helpful to include a suitable source at different meals throughout the day.

Examples include:

• Eggs or yoghurt at breakfast
• Beans, lentils, fish, chicken or tofu at lunch
• Meat, fish, pulses, eggs or a plant-based alternative at dinner
• Nuts, seeds, yoghurt or hummus as snacks

Do Most People Need Protein Supplements?

Most people eating a varied and balanced diet can obtain enough protein from food.

Protein supplements may be convenient in some circumstances, but they are not automatically necessary. Some products may also contain:

• Added sugar
• Sweeteners
• High levels of calories
• Unnecessary additives
• Ingredients unsuitable for certain medical conditions

A protein supplement cannot replace the vitamins, minerals, fibre and other beneficial substances provided by a balanced diet.

Can You Eat Too Much Protein?

Consuming more protein than the body requires does not necessarily provide additional health or muscle-building benefits.

A very high-protein diet may displace other important foods, including fruit, vegetables, wholegrains and fibre-rich carbohydrates.

People with kidney disease, liver disease or another relevant medical condition should seek professional advice before substantially increasing their protein intake.

Choosing Healthy Protein Foods

A balanced diet should include a variety of protein sources. Healthier choices may include:

• Beans, peas and lentils
• Fish, including oily fish
• Lean meat and poultry
• Eggs
• Lower-fat dairy products where appropriate
• Unsalted nuts and seeds
• Tofu, tempeh and other soya foods

When selecting protein foods, consider their wider nutritional content, including saturated fat, salt, fibre, vitamins and minerals.

Protein as Part of a Balanced Diet

Protein should be consumed as part of a varied and balanced diet alongside carbohydrates, healthy fats, vitamins, minerals and fibre.

Including a range of animal or plant-based protein foods can support tissue repair, muscle health, immunity, growth and normal body function.