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What Are Proteins and What Is Their Function in the Body?

Last Updated : 16 December 2022

Proteins are made upward of many building blocks, known as amino acids. Our body needs dietary poly peptide to supply amino acids for the growth and maintenance of our cells and tissues. Our dietary poly peptide requirement changes throughout life. The European Food Prophylactic Dominance (EFSA) recommends adults eat at least 0.83 g of poly peptide per kg body weight per day (eastward.grand. 58 g/twenty-four hour period for a seventy kg adult). Plant and animal-based proteins vary in their quality and digestibility, only this is non ordinarily a business concern for almost people if their total protein meets their needs. Nosotros should aim to consume protein from a multifariousness of sources that benefits both our health and the planets.

What are proteins fabricated of?

Proteins are fabricated up of many unlike amino acids linked together. There are twenty different of these amino acid building blocks commonly found in plants and animals. A typical protein is made up of 300 or more than amino acids and the specific number and sequence of amino acids are unique to each poly peptide. Rather like the alphabet, the amino acid 'letters' can be arranged in millions of different ways to create 'words' and an entire poly peptide 'linguistic communication'. Depending on the number and sequence of amino acids, the resulting protein volition fold into a specific shape. This shape is very important equally it volition determine the protein'south office (e.grand. muscle or enzyme). Every species, including humans, has its own feature proteins.

Amino acids are classified every bit either essential or non-essential. As the name suggests, essential amino acids cannot be produced by the body and therefore must come from our diet. Whereas, non-essential amino acids can be produced by the body and therefore exercise not need to come from the diet.

Table ane. Essential vs non-essential amino acids.

Essential amino acids

Non-essential amino acids

Histidine

Isoleucine

Leucine

Lysine

Methionine

Phenylalanine

Threonine

Tryptophan

Valine

Alanine

Arginine*

Asparagine

Aspartate

Cysteine*

Glutamate

Glutamine*

Glycine*

Proline*

Serine

Taurine*

Tyrosine*

*these are conditionally essential amino acids, which ways they are only essential under certain conditions (e.g. for new-borns).¹

What do proteins exercise for the body?

Our bodies are made up of thousands of different proteins, each with a specific function. They make upwardly the structural components of our cells and tissues likewise equally many enzymes, hormones and the active proteins secreted from allowed cells (figure 1).

These body proteins are continually being repaired and replaced throughout our lives. This process (known equally 'protein synthesis') requires a continuous supply of amino acids. Although some amino acids tin can be recycled from the breakdown of old body proteins, this procedure is imperfect. This means we must eat dietary poly peptide to proceed up with our body'due south amino acid demand.

As protein is essential for cell and tissue growth, adequate intake of protein is especially important during periods of rapid growth or increased demand, such equally babyhood, adolescence, pregnancy, and breastfeeding.¹

Figure 1. Functions of proteins in the torso.

What foods are loftier in protein?

Protein can be found in both plant and animal-based foods. Figure 2 shows the protein content found in a typical serving of common beast and found-based foods. For more data on how to estimate healthy portion sizes, see measuring portion sizes with your hands.

Figure 2. Loftier poly peptide foods.²

Is there a difference between animal and plant-based proteins?

As we tin can see in Figure 2, both animal and plant-based foods can be rich sources of protein. Only practice they accept the aforementioned quality?

The quality of a protein tin can exist defined in many ways; however, all definitions relate to the distribution and proportion of essential and non-essential amino acids they contain. In general, animal-based proteins are of higher quality equally they contain higher proportions of essential amino acids compared to plant-based proteins.

At that place is a common misconception that plant-based proteins completely lack certain essential amino acids. In fact, almost plant-based proteins will contain all 20 amino acids but tend to take a limited amount of sure essential amino acids, known as their limiting amino acid(s). This means, if a small number of plant foods are consumed every bit the simply poly peptide sources, they are unlikely to supply enough essential amino acids to run across our requirements. For people who swallow little to no animal-based foods, such as vegans or vegetarians, it is important that they eat protein from sources with complementary limiting amino acids. For example, consuming rice (limited in lysine and thiamine but high in methionine) and beans (limited in methionine, but high in lysine and thiamine) will provide complementary amino acids that can help meet essential amino acid requirements.

Animal and found-based proteins also differ in their bioavailability and digestibility. The digestible indispensable amino acid score (DIAAS) is the recommended method for determining dietary poly peptide digestibility and is expressed in values beneath or sometimes even above 100.³ A DIAAS of over 100 indicates that the poly peptide has very loftier digestibility and quality and is a practiced complement protein to those that have lower qualities. Animal-based proteins tend to have higher DIAAS scores compared to found-based proteins (Table 2). As nearly people consume protein from a variety of sources the quality and digestibility of protein is non unremarkably a business organization.

Table 2. DIAAS and quality of different protein types 100g of food.^{three, iv}

Protein Type	DIAAS	Quality
Wheat	xl	Low
Almond	40	Low
Rice	59	Low
Peas	64	Low
Chickpea	83	medium
Chicken breast	108	Loftier
Egg	113	High
Whole milk	114	Loftier

How much protein should we eat every day?

EFSA has adult dietary reference values (DRVs) for protein. The DRVs for protein at different life stages are summarised in table 3. For an boilerplate adult, the recommendation is to consume at least 0.83 thou of protein for every kilogram of trunk weight per 24-hour interval.¹ In other words, a 70 kg adult should aim to eat at least 58 g of protein everyday day. This is the equivalent to the protein establish in around 200 g of craven chest or 240 grams of mixed basics.

During periods of growth, such as childhood, pregnancy, and breastfeeding, protein requirements are relatively high. In addition, during quondam age, our protein to free energy ratio begins to increment. This ways nosotros require the same amount of protein but less energy (or calories) due to a decrease in metabolic rate and a more sedentary lifestyle.^one

Table iii. Dietary reference values for life stages.¹BW: body weight.

	Reference Value	thou/day 70 kg adult
Babyhood (12 months – 17 years)	one.14 – 0.83 1000/kg BW	-
Adults (18-65 years)	0.83 yard/kg BW	58g
Elderly (> 65 years)	1 chiliad/kg BW	70g
Pregnancy	0.83 g/kg BW	58g
one^st trimester	+ 1g per day	59g
2^nd trimester	+ 9 g per day	67g
3^rd trimester	+ 28 1000 per day	86g
Breastfeeding (0-6 months)	+ xix g per day	77g
Breastfeeding (> 6months)	+13 thou per solar day	71g

How much protein do we eat every mean solar day?

In full general, Europeans swallow enough poly peptide and deficiency is rare among most developed countries (figure iii). As the diet of Europeans already exceeds the required level, EFSA has not recommended an increase in current protein intakes.¹

Figure three. Protein intake across European countries.

What are the health benefits of protein?

Eating enough protein to encounter our bodies' requirements is of import for many torso functions. However, in that location is prove to suggest that in certain situations increasing protein intake above required levels could provide additional health benefits.

Protein and Weight Command

Eating protein-rich foods has been shown to increase our feeling of fullness (also known as satiety) more than foods loftier in fatty or carbohydrate. There is good evidence from brusk term studies that diets high in protein (i.east. 1.two – 1.6 g/kg per twenty-four hours; 84 – 112 k per day for a 70 kg adult) tin can help reduce overall calorie intake and prompt weight loss. ⁵ Withal, the evidence for long-term weight maintenance is less clear.⁵ Like all diets, a high protein diet is just effective if it is stuck to, which tin be difficult for some people and low adherence may partly explicate the limited benefit observed for long term weight maintenance.⁵

Protein and sarcopenia

Sarcopenia is a disorder characterised by the progressive loss of muscle mass and concrete role that is commonly associated with older adults. Sarcopenia is associated with increased frailty, adventure of falls, functional decline and even early on death.⁶ Equally protein is essential for the repair and maintenance of musculus mass, it is no surprise that depression intake of protein is associated with an increased risk of developing sarcopenia.^{half dozen} Similarly, increasing poly peptide intake, equally well as increasing physical activity can help maintain muscle mass and strength as nosotros age, decreasing our risk of sarcopenia and skeletal disorders.

Poly peptide and athletic functioning

Protein has long been associated with athletic performance. Protein plays a primal role in helping to repair and strengthen muscle tissue afterwards exercise. Although protein is critical for building muscle, to maximise the benefits it should be considered in the context of the whole diet, which includes the correct amount of carbohydrates, fats, vitamins and minerals. Optimum protein intake will depend on the type (east.g. endurance or resistance preparation), elapsing and intensity of exercise, with more not always existence ameliorate. A protein intake of i.4–two.0 thou per kg trunk weight a day (eastward.g. 98 – 140 g per day for a lxx kg adult) is thought to be sufficient to come across the needs for most exercising individuals.⁷ Athletes should aim to achieve protein intakes through consuming a balanced diet, with protein supplements being used for individuals who need to go along protein high but limit total calorie intake.

What happens if yous eat as well much protein?

At that place is bereft evidence to plant a threshold for protein intake and EFSA have stated that a protein intake of twice the DRV (1.7 thousand/kg per 24-hour interval, or 119 one thousand per solar day for a 70 kg adult) is withal considered condom under normal weather condition.¹For individuals with kidney affliction excessive protein can exist an issue and these individuals should consult a registered dietitian or full general practitioner before increasing protein levels.

Weight Gain

There is a common misconception that you can't gain weight from eating protein. This is not true, but like carbohydrates and fats, when consumed during a calorie surplus, backlog protein can be converted to body fat, leading to weight gain. When it comes to weight maintenance, the most of import thing is to stay in energy residuum.

Red and Candy Meat and Cancer Gamble

Protein is essential for good health, but some high protein foods may be better for our health than others. In item, consuming high amounts of cerise and processed meat has been associated with an increased take chances of sure cancers.⁸Blood-red meat is a expert source of protein too as many other essential nutrients such as iron, vitamin B₁₂, and zinc, and does not necessarily need to be avoided altogether to reduce risk. The World Cancer Research Fund recommends nosotros effort to consume no more than iii portions (around 350-500g cooked weight) of red meat per week and very petty, if any, processed meat.⁸

Protein sustainability

The food choices we brand not only touch on our wellness they besides affect the environs. In general, animal-based proteins such equally beef, dairy, and lamb have a higher environmental impact (i.e. uses more resource and produces more than greenhouse gases) compared to plant-based sources such as soy, peas and lentils (effigy four).^ix While it is not necessary or recommended to completely avoid animal-based foods, shifting dietary patterns to include more plant-based protein sources, can benefit our health and the planet.¹⁰ Sustainable eating is more than only choosing sustainable protein-rich foods, for more than tips on how yous can alive a more than sustainable life see tips to eat a healthy and sustainable diet and tips to reduce food waste.

protein content of foods linked to greenhouse gas emissions produced

Effigy 4. Protein content & greenhouse gas emissions (GHGe) of different foods.^ix

Determination

Protein is essential for life; it supplies the essential amino acids needed for the growth and maintenance of our cells and tissues. Our requirement for protein depends on our stage of life and most Europeans eat enough to encounter their requirements. As almost people consume a varied diet, the quality and digestibility of the proteins they consume should not be a concern as long as the full amount of protein meets their daily needs. As we eat foods and not nutrients, we should cull protein-rich foods that not only provide essential amino acids but also support a healthy and sustainable nutrition.

References

EFSA (2012). European Food Rubber Authority, Scientific Opinion on Dietary Reference Values for poly peptide. EFSA Journal 2022; x(2):2557
UK food limerick database.
Consultation, F.E., 2022. Dietary protein quality evaluation in human nutrition. FAO Food Nutr. Pap, 92, pp.1-66.
Phillips, S.M., 2022. Current concepts and unresolved questions in dietary protein requirements and supplements in adults. Frontiers in nutrition, 4, p.13.
Leidy, H.J., Clifton, P.M., Astrup, A., Wycherley, T.P., Westerterp-Plantenga, K.Due south., Luscombe-Marsh, Northward.D., Woods, S.C. and Mattes, R.D., 2022. The function of poly peptide in weight loss and maintenance. The American journal of clinical nutrition, 101(6), pp.132
Cruz-Jentoft AJ, Sayer AA (2019). Sarcopenia. The Lancet. 393 (10191): 2636-2646.
Jäger R., Kerksick, C.M., Campbell, B.I., Cribb, P.J., Wells, S.D., Skwiat, T.One thousand., Purpura, G., Ziegenfuss, T.Northward., Ferrando, A.A., Arent, Southward.1000. and Smith-Ryan, A.E., 2022. International society of sports nutrition position stand: protein and exercise. Periodical
World Cancer Inquiry Fund/American Plant for Cancer Research. Continuous Update Project Expert Written report 2022. Meat, fish and dairy products and the take a chance of cancer.
Poore J, Nemecek T. (2018) Reducing food'south environmental impacts through producers and consumers. Science Vol. 360, Consequence 6392, pp. 987-992
FAO and WHO. 2022. Sustainable healthy diets – Guiding principles. Rome