Protein: How Much You Actually Need

What protein does in the body

Protein is one of the three macronutrients (alongside carbohydrates and fat), but it plays a uniquely structural and functional role that the others do not.

Building and repairing tissue

Every cell in the body contains protein. Skin, muscle, bone, organ tissue, hair, and nails are all built from protein structures. After exercise, injury, illness, or normal daily cell turnover, the body uses dietary protein to repair and replace damaged protein structures. This is the reason protein requirements increase when tissue is being repaired rapidly, during illness recovery, after injury, in post-surgical patients, and during pregnancy and adolescence.

Enzymes and hormones

Most enzymes (the molecules that catalyse every biochemical reaction in the body) are proteins. Many hormones are also proteins or are derived from amino acids. Insulin, glucagon, growth hormone, thyroid hormones, adrenaline, and many others are made from amino acid building blocks. Without adequate dietary protein, these systems function less effectively.

Immune function

Antibodies (the molecules that identify and neutralise pathogens) are proteins. During illness, protein requirements increase because the immune system is producing antibodies and immune cells at an accelerated rate. Chronic low protein intake is associated with impaired immune function.

Transport and storage

Many molecules in the body are transported around in the bloodstream bound to protein carriers. Oxygen (haemoglobin), fats and fat-soluble vitamins (lipoproteins), and iron (ferritin) among them. Myoglobin in muscle cells stores oxygen for use during exercise.

Satiety and weight management

Protein is the most satiating macronutrient per calorie. It triggers a stronger release of satiety hormones (GLP-1, PYY, CCK) and suppresses the appetite-stimulating hormone ghrelin more effectively than carbohydrate or fat. Protein also has the highest thermic effect of food of the three macronutrients. The body uses roughly 20 to 30% of the energy in protein just to digest and metabolise it, compared to around 5 to 10% for carbohydrates and 0 to 3% for fat. A 2024 meta-analysis of 52 studies confirmed that higher protein intake significantly increases total daily energy expenditure. This is why higher-protein diets are often effective for weight management. They maintain satiety on fewer net calories.

Amino acids. What makes a protein "complete"?

Proteins are built from chains of amino acids. The body uses 20 different ones. Of these, 9 are "essential", meaning the body cannot synthesise them and must obtain them from food: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

The remaining 11 can be synthesised from other compounds; they are called "non-essential" (though some, like glutamine and arginine, become "conditionally essential" during illness).

What "complete" protein means

A protein source is described as "complete" if it contains all nine essential amino acids in proportions suitable for human needs. Most animal-derived proteins (meat, fish, eggs, dairy) are complete. Most plant proteins are "incomplete". They lack or have very low amounts of one or more essential amino acids.

The complementary protein principle, updated

It was once believed that plant protein sources needed to be combined in the same meal to form complete proteins. For example, rice and beans together. This is now understood to be unnecessary. The body maintains a pool of amino acids and can draw on it throughout the day. Eating a variety of plant protein sources across the day provides all nine essential amino acids without needing to plan each meal as a complementary pair. A diet with diverse legumes, whole grains, nuts, seeds, and vegetables supplies all essential amino acids when calorie needs are met.

Protein quality beyond completeness

Beyond which amino acids are present, protein quality is also determined by digestibility and bioavailability. How much of the protein is actually absorbed and used. Animal proteins generally have higher digestibility than most plant proteins, though cooking and processing affect this significantly. The most robust measure of protein quality is the Digestible Indispensable Amino Acid Score (DIAAS), which assesses amino acid availability after digestion. Egg whites, dairy, and whey protein score highest. Most legumes score lower, but not so low that they cannot support good health when eaten in adequate quantities.

Leucine and muscle protein synthesis

Among the nine essential amino acids, leucine has a particularly important role in triggering muscle protein synthesis (MPS). Animal proteins (whey, eggs, meat) tend to be higher in leucine than most plant proteins. This partly explains why, in controlled studies, animal protein produces a more rapid and pronounced MPS response per gram than most plant proteins. However, this can be compensated for by eating slightly larger quantities of plant protein, or by combining plant protein sources. This is a nuance relevant mainly to athletes optimising for muscle growth, not to the general population assessing overall protein adequacy.

UK recommendations. The RNI and its limits

The UK Reference Nutrient Intake: 0.75g/kg/day

The UK RNI for protein in adults is 0.75 grams per kilogram of body weight per day. This is set by SACN and reflects the amount sufficient to meet the nutritional needs of 97.5% of the healthy adult population.

In practical terms, for an adult with an average body weight:

• Women (based on a reference weight of ~60kg): approximately 45g of protein per day
• Men (based on a reference weight of ~75kg): approximately 56g of protein per day

These are minimums, not optimal targets

This is critical to understand. The RNI represents the minimum intake to prevent deficiency. It is not a target to optimise health. It is derived from nitrogen balance studies, which measure the point at which the body is in protein equilibrium. Newer methods, including the Indicator Amino Acid Oxidation (IAAO) technique, consistently produce higher estimates of protein requirements than nitrogen balance studies. Suggesting the 0.75g/kg figure may underestimate true needs, particularly for older adults.

Do most UK adults already meet the RNI?

Yes, typically. On average, protein provides around 17% of dietary energy in UK adults. The British Nutrition Foundation notes that current protein recommendations are 56g/day for men and 45g/day for women, and most adults comfortably exceed these on a typical mixed diet. Protein deficiency is rare in the UK except in specific circumstances: severe food restriction, eating disorders, advanced age with poor appetite, and certain medical conditions.

This means that for most healthy UK adults, the primary protein questions are about food sources and quality, not about quantity.

How needs differ. Age, activity, and life stage

The 0.75g/kg/day RNI is a population average for healthy adults. Several groups have meaningfully different needs.

Older adults: the most under-recognised gap

Muscle mass declines progressively from around age 30 to 40. A process that accelerates after 60. This age-related muscle loss is called sarcopenia, and it is associated with frailty, loss of independence, falls, and increased mortality. In the UK, a study found that fewer than 50% of older adults met the current RNI, and fewer than 15% met the higher ESPEN recommendation.

Why older adults need more: anabolic resistance (older muscle responds less efficiently to protein), reduced appetite and food intake, and higher tissue-repair and immune-function demands.

Beyond total daily intake, protein distribution across meals matters more in older adults. Research suggests that at least 25 to 30g of high-quality protein per meal, eaten across three meals, optimally stimulates muscle protein synthesis. A diet where most protein is consumed in a single evening meal is less effective than one where protein is spread throughout the day.

Active people: post-exercise nutrition

Consuming 20 to 40g of high-quality protein within 0 to 2 hours after exercise stimulates a significant muscle protein synthesis response. However, overall daily protein intake matters more than precise timing for most non-elite athletes. The "anabolic window" is real but wider than once believed.

Healthy adults and kidney health

For healthy adults, higher protein intake (up to 2g/kg/day) does not damage the kidneys. The concern about protein and kidney health applies specifically to people who already have chronic kidney disease (CKD), where the kidneys are less able to filter protein breakdown products (urea, creatinine), so restricting protein may slow disease progression. People with CKD should not follow high-protein dietary advice without guidance from their healthcare team.

Personalised protein calculator

A rough working estimate based on your weight and the group that fits you best. The output uses the midpoint of each recommended range. Not medical advice. People with kidney disease, pregnancy, or other clinical conditions should follow tailored advice from their healthcare team rather than a calculator.

Protein myths. What the evidence actually says

Signs that protein intake may be inadequate

Protein deficiency in its true clinical form (kwashiorkor, marasmus) is extremely rare in UK adults. Subclinical low intake (not enough to support optimal health) is more common in specific groups.

Signs that may suggest protein intake is insufficient:

• Loss of muscle mass or strength that is progressing faster than expected with age
• Slow wound healing. Protein is required for tissue repair
• Frequent illness or slow recovery from infection. Immune function depends on protein
• Hair loss and brittle nails. Structural proteins (keratin) are affected by low intake
• Persistent fatigue. When protein is insufficient, the body breaks down muscle for energy
• Oedema. Very low protein intake reduces blood albumin levels, leading to fluid accumulation in tissues

These signs are non-specific. They have many possible causes, and should prompt a GP visit rather than immediate dietary self-diagnosis.

Who is most at risk of inadequate protein in the UK

• Older adults with poor appetite or reduced food intake
• People with eating disorders or severe food restriction
• People recovering from serious illness or surgery
• Some vegans and vegetarians who have not planned their diet to include adequate varied protein sources
• People living with food poverty who have limited access to protein-rich foods

Practical ways to increase protein. For those who need more

For older adults, active people, or those managing weight, here are practical ways to increase protein without dramatically changing eating patterns.

1. Start with breakfast. Breakfast is typically the lowest-protein meal for most UK adults. Swapping toast with jam for eggs (scrambled, boiled, or poached), plain Greek yogurt with fruit, or porridge with a spoonful of nut butter adds 10 to 20g of protein to the morning. Particularly important for older adults aiming to distribute protein across meals.
2. Add pulses to main meals. A 200g serving of lentils, chickpeas, or kidney beans adds 14 to 18g of protein to any soup, curry, stew, or salad. Tinned pulses require no preparation beyond draining and rinsing. This simultaneously adds fibre, iron, and folate.
3. Choose higher-protein dairy. Plain Greek yogurt contains roughly double the protein of regular plain yogurt. Cottage cheese, skyr (Icelandic-style yogurt), and kefir are similarly high in protein.
4. Eat fish twice a week. Two portions of fish per week, as recommended by the NHS, provides meaningful protein alongside omega-3, iodine, and vitamin D. Tinned fish (tuna, sardines, mackerel) is among the cheapest and most convenient protein sources available.
5. Snack on nuts and seeds. A 30g handful of almonds, walnuts, or pumpkin seeds adds 5 to 7g of protein alongside healthy fats and fibre. More nutritious than most packaged snacks.
6. Do not overlook eggs. Two eggs contain around 12 to 15g of protein and are among the most bioavailable and nutritionally complete protein foods available. Inexpensive, quick, versatile.

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