Sun & Seed Nutrition Science Library · Series 1: Protein
Introduction: an essential nutrient that has become a marketing obsession
Protein is everywhere. It appears on yoghurt pots, breakfast cereals, snack bars, drinks, breads and products that would once have been sold simply as food. Supermarket shelves increasingly distinguish between ordinary and “high-protein” versions of familiar products, while social media often presents protein intake as the key to building muscle, controlling appetite, ageing well and improving body composition.
Some of this attention reflects genuine nutritional science. Protein is essential for building and maintaining tissues, producing enzymes and hormones, supporting immune function and repairing the body. It supplies the amino acids needed to maintain muscle and other body proteins throughout life.
But the modern protein conversation can obscure some important questions. How much do people actually need? Is the recommended intake sufficient for everyone? Are plant proteins nutritionally equivalent to animal proteins? Does eating more protein improve health, or are the benefits dependent on a person's age, activity level and existing diet?
The evidence suggests a more nuanced picture than the packaging might imply. Adequate protein is essential, and some groups may benefit from particular attention to intake. However, the health effects of protein depend on more than the number of grams consumed. Protein quality, food source, the rest of the diet and physical activity all matter.
1. What does protein do in the body?
Protein is made from amino acids linked together in different sequences. The human body uses these amino acids to build and maintain a vast range of structures and molecules.
Muscle tissue is one important destination, but it is far from the only one. Proteins are involved in the structure of skin and connective tissue, the production of enzymes that drive biochemical reactions, transport of substances in the blood, immune responses and the production of many hormones and signalling molecules.
The body continually breaks down and rebuilds its proteins. Dietary protein supplies amino acids to support this process, although the body can also recycle amino acids from existing proteins. When intake is inadequate over time, maintaining body tissues becomes more difficult, particularly during growth, illness, recovery or ageing.
Nine amino acids are considered essential for adults because the body cannot synthesise them in sufficient quantities. They must be obtained from food. Other amino acids can be synthesised by the body under normal conditions, although requirements can change in particular physiological circumstances.
This is why protein quality matters. A food's protein content tells us how much protein it contains, but not by itself how well that protein supplies the essential amino acids the body needs or how readily they are digested and absorbed.
2. How much protein do we need?
For healthy adults in the UK, the Reference Nutrient Intake (RNI) for protein is approximately 0.75g per kilogram of body weight per day. This is a population reference intended to meet the needs of nearly all healthy people in the relevant group, rather than an optimum target for every individual.
For illustration, a person weighing 70kg would have a reference intake of approximately 52.5g per day. A person weighing 90kg would have a calculated figure of 67.5g per day.
These examples illustrate how the reference is calculated; they should not be treated as individual prescriptions. Body weight alone does not determine protein requirements, and applying a simple weight-based calculation to someone with obesity, a medical condition or unusual training demands may be inappropriate.
It is also important to understand what the RNI represents. It is designed to prevent inadequacy in almost all healthy adults. It is not a threshold below which the body suddenly stops functioning, nor is it proof that every person will achieve the same muscle mass, recovery or physical performance at that intake.
Requirements can differ according to life stage and circumstances. Infants, children and adolescents need protein to support growth. Pregnancy and breastfeeding create additional nutritional demands. People recovering from injury or illness may have different needs, while athletes may need more protein to support adaptation to training.
Ageing is another important consideration. Older adults can experience progressive loss of muscle mass and strength, particularly when physical activity declines or illness reduces appetite and food intake. Adequate protein is one part of preserving muscle and physical function, alongside appropriate exercise, sufficient energy intake and overall dietary quality.
The key distinction is between meeting basic requirements and pursuing a specific outcome. A person who is adequately nourished and physically active has different needs from someone recovering from illness, an athlete undertaking intensive training or an older person struggling to maintain muscle.
3. Are we eating enough protein?
Protein is often discussed as if the population is experiencing a widespread shortage. The UK evidence does not support that generalisation.
The National Diet and Nutrition Survey monitors the diets and nutritional status of people living in the UK. Its 2019–2023 report identifies several nutrients for which population intake or status raises public health concerns. Protein is not highlighted in the report's executive summary as a comparable widespread population shortfall.
That does not mean every individual consumes enough protein. Dietary surveys describe population patterns and can conceal differences between age groups, individuals and circumstances. Older people with poor appetite, people experiencing food insecurity, and those with restricted diets or illness may be at greater risk of inadequate intake.
There is also a difference between inadequate protein intake and the more common marketing question of whether people would benefit from eating more than they currently do. Evidence that some people benefit from additional protein does not establish that everyone needs a high-protein diet.
For many healthy adults, the practical priority is to eat a varied diet that supplies enough energy, protein and other essential nutrients. Increasing protein without considering the overall diet may simply displace other valuable foods, including those that provide fibre, unsaturated fats, vitamins and minerals.
Source: UK National Diet and Nutrition Survey 2019–2023, Office for Health Improvement and Disparities.
4. Protein quality: why the source matters
Protein quality is influenced by the essential amino acid profile of a food and by how well the protein is digested and absorbed.
Animal-derived proteins such as eggs, dairy, fish and meat generally provide all nine essential amino acids in proportions that are readily usable by the body. Many plant foods also provide all nine essential amino acids, but their relative amounts and digestibility vary.
For example, legumes are often rich in lysine but relatively lower in the sulphur-containing amino acids methionine and cysteine. Many cereal proteins have a different amino acid pattern, with lysine often being the limiting amino acid. Eating a variety of protein sources can help ensure that the diet supplies the full range of essential amino acids.
This does not mean that plant proteins are inherently inadequate. The relevant question is whether the overall diet supplies enough total protein and essential amino acids in a form the body can use.
Protein quality can be assessed using methods such as the Protein Digestibility-Corrected Amino Acid Score (PDCAAS) and the Digestible Indispensable Amino Acid Score (DIAAS). These methods account for amino acid composition and aspects of digestibility, although they have limitations when applied to mixed diets and whole foods.
A score for an isolated ingredient does not tell us everything about the nutritional value of the food containing it. Processing, preparation, the food matrix and the combination of ingredients can all influence how protein is digested and used.
For plant-based diets, variety is useful. Beans, lentils, peas, soy foods, grains, nuts and seeds each contribute different combinations of protein and other nutrients. A diet built around a range of these foods can supply adequate protein without requiring every meal to contain a specially formulated protein product.
5. Plant protein and animal protein: what does the research show?
The question of whether plant protein is as good as animal protein is often framed as a competition between two categories. The evidence is more informative when we distinguish between different outcomes.
Muscle protein synthesis
Muscle protein synthesis is the process through which the body builds muscle proteins. It responds to dietary amino acids and to physical activity, particularly resistance exercise.
Some animal proteins, including dairy proteins, have characteristics that can stimulate muscle protein synthesis effectively in acute studies. These include digestibility and the quantity of essential amino acids, including leucine, supplied by a given serving.
However, findings from short-term studies of muscle protein synthesis do not automatically predict long-term differences in muscle mass, strength or health. Plant proteins vary widely, and evidence depends on the specific source, dose, population and training programme.
A 2026 systematic review and meta-analysis comparing plant- and animal-based proteins found small differences in some muscle protein synthesis outcomes, with considerable uncertainty and variation among the plant and animal proteins studied. The authors cautioned against generalising results across all sources.
In practical terms, people following plant-based diets can support muscle maintenance and training adaptation by consuming sufficient total protein and a varied selection of protein-rich foods. Particular attention to protein quantity and quality may be useful for older adults and people with demanding training programmes.
Long-term health outcomes
A 2020 systematic review and dose–response meta-analysis published in The BMJ examined 32 prospective cohort studies investigating total, animal and plant protein intake in relation to mortality.
Higher plant protein intake was associated with lower all-cause mortality and lower cardiovascular mortality in the pooled analysis. The researchers also found an association between higher total protein intake and lower all-cause mortality, while the results for animal protein were not clearly associated with lower mortality.
These results are relevant, but they do not prove that plant protein itself caused the differences. Prospective cohort studies observe people's diets and health over time. Even after statistical adjustment, people who consume more plant protein may differ in other important ways, including their intake of fibre, wholegrains, nuts and vegetables.
A 2023 systematic review and meta-analysis in BMC Medicine examined what happens when animal-based foods are replaced by plant-based foods. It found evidence that replacing processed meat with foods such as nuts, legumes and wholegrains was associated with lower cardiovascular risk. Some substitutions were also associated with lower type 2 diabetes incidence and all-cause mortality.
The distinction is important: replacing one food with another is different from simply adding protein. The overall nutritional effect depends on what is removed and what takes its place.
For example, replacing some processed meat with beans or nuts changes not only the protein source but also the intake of fibre, fatty acids, minerals and other food components. The resulting health effect cannot be attributed to protein alone.
Taken together, the evidence supports plant proteins as valuable components of a healthy diet. It does not establish that every plant protein is nutritionally identical to every animal protein, or that protein source alone determines long-term health.
6. Protein, exercise and muscle maintenance
Protein and exercise work together in maintaining and building muscle. Exercise provides the stimulus for adaptation, while dietary protein supplies amino acids required for tissue repair and growth.
A 2018 systematic review and meta-analysis by Morton and colleagues examined protein supplementation during resistance training in healthy adults. The analysis found that protein supplementation increased gains in muscle mass and strength when added to resistance training, although the benefits depended on the overall context.
The study estimated that the additional benefit to fat-free mass tended to level off at a total daily protein intake around 1.6g per kilogram of body weight, with uncertainty around the precise threshold. This is not a universal requirement. It is an estimate derived from studies of healthy adults undertaking resistance training, not a recommendation that everyone should consume that amount.
For someone who does little physical activity, increasing protein without addressing inactivity is unlikely to produce the same muscle-building outcome as a combination of adequate nutrition and appropriate training.
The same principle applies to older adults. Maintaining muscle requires more than protein alone. Physical activity, particularly resistance exercise where appropriate, energy intake and the ability to eat enough food all matter.
7. Protein and ageing
Ageing can bring changes in appetite, activity, muscle metabolism and the ability to recover from illness. Some older adults also experience difficulty shopping, preparing food or eating sufficiently to meet their nutritional needs.
The PROT-AGE Study Group, an international expert group, published recommendations suggesting that healthy adults over 65 may benefit from daily protein intakes in the range of 1.0–1.2g per kilogram of body weight. The group also suggested higher intakes for some older adults who are physically active or experiencing illness, while identifying severe kidney disease as an important exception requiring individual clinical guidance.
These recommendations are higher than the standard UK adult RNI. They reflect a different question: how much protein may help older adults maintain or regain lean body mass and physical function, rather than the minimum amount intended to meet basic requirements in the general population.
The evidence should be interpreted carefully. Older adults are not a uniform group, and health status, physical activity, appetite and kidney function can substantially affect nutritional needs.
The practical message is that protein deserves particular attention when ageing is accompanied by low food intake, muscle loss or reduced physical function. It should be considered alongside overall nutritional adequacy and appropriate activity, rather than as a standalone solution.
8. Does eating more protein damage the kidneys?
Concerns about high-protein diets and kidney health have been investigated in clinical research.
A systematic review and meta-analysis of studies in healthy adults found that higher-protein diets were associated with a small increase in measured glomerular filtration rate in some comparisons, but changes from baseline did not show a clear adverse effect on kidney function. The authors concluded that the available evidence did not demonstrate that higher protein intake adversely affected this measure in healthy adults, while noting limitations in the evidence.
This finding should not be extrapolated to people with chronic kidney disease. Kidney disease can change the way the body handles protein-related waste products, and some people with impaired kidney function need individualised dietary advice.
It is therefore inaccurate to claim that high protein diets inevitably damage healthy kidneys. It would be equally inaccurate to conclude that any level of protein intake is appropriate for everyone.
For healthy adults, the evidence is broadly reassuring about moderate increases in protein in the contexts studied. People with diagnosed kidney disease or other relevant medical conditions should follow advice from their healthcare professional.
9. How can we obtain protein from everyday foods?
Protein can be obtained from a wide range of foods. The best dietary pattern depends on individual needs, preferences, culture, budget and health circumstances.
Legumes such as beans, lentils, chickpeas and peas provide protein alongside fibre and minerals. Soy foods, including tofu and tempeh, can provide substantial amounts of protein. Wholegrains contribute smaller but useful amounts, while nuts and seeds supply protein alongside unsaturated fats and other nutrients.
Animal foods such as eggs, dairy, fish and meat can also provide protein. Their nutritional contributions differ, so a balanced dietary pattern should be evaluated as a whole rather than by protein content alone.
Nuts and seeds are particularly interesting because they combine several nutritional components in a single food. Pumpkin seeds, hemp seeds, chia and flaxseed contribute varying amounts of protein, fibre and fats, but their composition differs considerably. They should not be treated as interchangeable ingredients.
A food's protein content per 100g is also not the same as the amount people typically consume in one serving. A small sprinkle of seeds can add nutritional variety, but it should not be assumed to provide the same quantity of protein as a serving of legumes or a concentrated protein ingredient.
10. What should consumers take away from the research?
The scientific evidence supports several practical conclusions.
First, protein is essential throughout life, and consistently inadequate intake can compromise the body's ability to maintain and repair tissues.
Second, protein needs differ. The standard UK adult reference intake is designed to meet the needs of nearly all healthy adults, while particular circumstances—such as ageing, intensive training, growth, illness or recovery—can alter requirements.
Third, the source of protein matters because foods provide more than protein alone. Legumes, nuts, seeds and wholegrains contribute fibre and other nutrients, while different animal foods have their own nutritional characteristics. The effect of a dietary change depends on the food being replaced and the food being introduced.
Fourth, more protein is not automatically better. Protein supplements and high-protein products can be useful in particular circumstances, but they are not inherently necessary for everyone. Adequate total intake, a varied diet and appropriate physical activity remain central.
Finally, protein quality should be considered alongside overall dietary quality. A diet that provides adequate protein while also supplying sufficient fibre, essential fats, vitamins and minerals is more nutritionally complete than one focused on a single number on a label.
Conclusion
Protein is fundamental to human health, but the scientific picture is more complex than the current high-protein trend suggests. The evidence supports adequate protein intake, attention to individual needs and a varied selection of protein sources. It also indicates that the wider food pattern matters: replacing some foods with legumes, nuts and wholegrains can affect health through multiple nutritional pathways.
For plant-based nutrition, the important question is not whether one protein source can win a universal comparison. It is whether the overall diet supplies sufficient protein and essential amino acids, alongside the other nutrients required for health.
The most useful approach is therefore food-first and evidence-led. Protein-rich foods have an important place in a healthy diet, but their value should be judged by their full nutritional contribution, not by protein content alone.
Seed proteins in our range
Seeds are one of the plant foods that bring protein alongside fibre and unsaturated fats, which is why they feature in this article. Our organic hulled hemp seeds are a whole food that can be sprinkled over meals, while our hemp, pumpkin seed and chia seed protein powders are concentrated ingredients made from the seed after oil pressing. As the research above shows, a spoonful of seeds is a useful addition to a varied diet rather than a replacement for it, and the protein in each product depends on its own composition and the serving used.
References and further reading
- Department of Health and Social Care / Office for Health Improvement and Disparities. National Diet and Nutrition Survey 2019 to 2023. UK government report, published 11 June 2025. https://www.gov.uk/government/statistics/national-diet-and-nutrition-survey-2019-to-2023
- Morton, R.W. et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine, 2018; 52: 376–384. https://pubmed.ncbi.nlm.nih.gov/28698222/
- Neuenschwander, M. et al. Substitution of animal-based with plant-based foods on cardiometabolic health and all-cause mortality: a systematic review and meta-analysis of prospective studies. BMC Medicine, 2023; 21:404. https://doi.org/10.1186/s12916-023-03093-1
- Naghshi, S. et al. Dietary intake of total, animal, and plant proteins and risk of all cause, cardiovascular, and cancer mortality: systematic review and dose-response meta-analysis of prospective cohort studies. BMJ, 2020; 370:m2412. https://www.bmj.com/content/370/bmj.m2412
- PROT-AGE Study Group. Evidence-Based Recommendations for Optimal Dietary Protein Intake in Older People. Journal of the American Medical Directors Association, 2013; 14(8):542–559. https://pubmed.ncbi.nlm.nih.gov/23867520/
- Devries, M.C. et al. Changes in Kidney Function Do Not Differ between Healthy Adults Consuming Higher-Compared with Lower- or Normal-Protein Diets: A Systematic Review and Meta-Analysis. The Journal of Nutrition. https://jn.nutrition.org/article/S0022-3166%2822%2910945-4/fulltext
- Akesson, A. et al. Animal versus plant-based protein and risk of cardiovascular disease and type 2 diabetes: a systematic review of randomized controlled trials and prospective cohort studies. Food & Nutrition Research, 2023. https://doi.org/10.29219/fnr.v67.9003
- UK nutrition and health claims legislation. Conditions for the use of “source of protein” and “high protein” claims. https://www.legislation.gov.uk/eur/2006/1924/annexes/2020-12-31
Editorial note: This is a narrative research article, not a registered systematic review. The studies cited examine different populations and outcomes, and their findings should not be interpreted as individual medical advice. Protein claims on food packaging must meet the applicable UK legal conditions.
