Where do we get our protein from?
Short answer: from plants
Animals cannot synthesise amino acids from scratch; therefore, all animal protein originates in plants, fungi and microbes. Livestock are like sentient food processing machines – they eat plant protein, remove the fibre and phytonutrients, concentrate it, and add harmful things like saturated fats and cholesterol. We don’t need to eat animals, birds, fish or insects. We can go directly to the source and get our protein from plants. Humans have relatively low protein requirements, which are easily met by eating a variety of whole plant foods.
Dietary protein is essential but rarely a limiting factor in human nutrition. Our primary nutrition requirement is for energy which may come from carbohydrates, fat or protein. Measures of food production relative to environmental cost need to reflect this and stop using protein as a measure of production.
How much protein do we need?
Short answer: the recommended protein intake is 0.8g/kg of body weight
The recommended dietary allowance for protein is 0.8g/kg body weight. This is the recommended intake, not the minimum intake. The estimated average requirement is only 0.66g/kg. It should also be noted that a normal body weight range is used to calculate protein requirements, so there is no upward adjustment for obesity. (The literature on the subject does not provide a precise body weight reference point, such as lean body mass or a particular BMI, illustrating the inherent inaccuracy in recommended nutrient intakes). Protein requirements can be expressed in grams/kg body weight, daily requirement for an average size person or as a percentage of energy intake:
-
- EAR (estimated average requirement) = 0.66 g/kg
- RDA (recommended dietary allowance) = 0.80 g/kg
RDA for an average-sized adult:
-
- 60kg adult female = 48g
- 70kg adult male = 56g
A macronutrient ratio of 10% of calories from protein provides the protein RDA (assuming an energy intake of 2,000 kcal for females and 2,400 kcal for males). A typical whole foods, plant-based diet based on whole grains, legumes, vegetables, and fruit provides at least 12% protein.
Protein recommendations are based on population averages with two standard deviations added to cover 95% of individuals. Many factors influence individual requirements. For example, regular carbohydrate intake reduces protein requirements by reducing gluconeogenesis (the one-way conversion of amino acids into glucose).
The following chart lists the protein content of whole plant foods. Note that expressing protein content as a macronutrient ratio corrects for energy density, giving what we consider a fairer ranking of the protein content of nuts, grains, and other items. Under this metric, whole grains have a similar protein content to nuts.
Protein in food
How does oil reduce protein intake?
Short answer: oil displaces protein-containing plant foods.
The principle of displacement is that when you add in more calories from one type of food, you displace a similar number of calories from all other types of food to keep your daily energy intake in balance. The following example shows the math for the high olive oil diet recommended by some nutritionists. The remainder of the day’s food is assumed to be a typical whole foods, plant-based diet of 2000kcal with a macronutrient ratio of approximately 12% protein.
-
- Whole plant foods only:
2000kcal 60g protein - Whole plant foods plus three tablespoons (60ml) extra virgin olive oil (480kcal oil + 1520kcal food):
2000kcal 45.6g protein
- Whole plant foods only:
Minimising zero protein foods – olive oil, soft drinks and alcoholic beverages, for example – is an effective strategy to increase daily protein intake.
Do athletes require more protein?
Short answer: yes, but these needs are easily provided by whole plant foods
Energy requirements are increased by regular exercise, and while this does not amount to much for average levels of physical activity, it may amount to a substantial increase for those with high levels of physical activity. For example, running 10km daily would add 30% to daily energy requirements. Food (calorie) intake will increase to compensate. (In reality, the body will partially compensate to conserve daily energy expenditure). In this scenario, a 30% increase in food intake will result in a 30% increase in protein intake, pushing intake up from 1.2g/kg to 1.6g/kg.
Do older adults require more protein?
Short answer: Probably yes, by a small amount
Protein requirements may be increased in the elderly. However, much of the evidence for this has been tainted by meat and dairy industry funding. Numerous studies have investigated strength training, with and without extra protein, and have not shown a consistent benefit above that of strength training alone.
Suggested RDA 1.0g/kg
Many factors influence energy and protein requirements and intake in the elderly—for example, disease processes, sedentary lifestyles and inadequate food intake. Sarcopenia (muscle wasting) is common even in normal-weight individuals. We consider the inadequate intake of calories and whole plant foods more important than focusing on protein intake.
Chronic kidney disease is common in older Australians and often undiagnosed (AIHW 2024). High protein intakes, particularly from animal products, place additional stress on failing kidneys and accelerate the decline in kidney function. Those who advocate a much higher protein intake in the elderly often neglect this important point.
Is protein the key to muscle growth and preservation?
Short answer: Strength training is the key to building and maintaining muscle.
Muscles respond to regular strength training by getting bigger and stronger. Protein intake, beyond meeting daily requirements, has minimal additional benefits. A particular study may show that the funding entity’s product appears to have short-term effects, such as increasing muscle protein synthesis rate, but in the long term, it’s the strength training that builds the muscles. Similarly, the timing of protein intake is not critical to building muscle.
Is more protein required during weight loss?
Short answer: a higher proportion of protein may be required
Examples of protein intake during low-calorie diets for weight loss:
In these scenarios, the proportion or concentration of protein in the diet will need to be higher to meet the recommended intake due to reduced daily intake of food/ calories. Dietary tweaks may include choosing higher protein grains (eg. Wheat, oats, quinoa rather than rice), higher protein tubers e.g. potatoes rather than sweet potatoes, eating more legumes, and eliminating zero protein calories (all oils, added sugar).
Similar adjustments may be needed for elderly people with sarcopenia (muscle wasting) who may have very low daily energy expenditure.
Resistance training reduces the loss of lean body mass during weight loss.
Is protein quality important?
Short answer: Protein quality is not an issue for people eating a whole foods plant-based diet.
The term quality protein seems to have made a comeback in nutrition media, putting a positive spin on animal products, implying superiority to plant protein and taking the focus off saturated fat and other harmful components of meat, eggs and dairy.
Human proteins are built from twenty different amino acids. The body cannot make an amino acid from scratch, but it can interconvert some amino acids. There are nine essential amino acids which cannot be synthesised from others. Each of these must be available in at least the proportion our body needs for protein synthesis. For example, if the proportion of the essential amino acid lysine (in our dietary protein) comprised only half the required amount, then our bodies could only utilise half of that protein. That would not be a problem if our protein intake was at least twice our minimum requirement.
Protein scoring systems such as PDCAAS (protein digestibility corrected amino acid score) give a numerical value to how much of a particular protein source can be utilised, considering the proportion of essential amino acids and digestibility (absorption). This is useful in animal husbandry, where the aim is maximum growth with minimum feed. Animal proteins tend to have higher PDCAAS scores than plants. One notable exception is gelatine (collagen), which scores zero because it has none of the amino acid tryptophan.
Plants contain all essential amino acids, but some plants have a lower proportion of one or other of these. This led to protein complementarity, combining two or more plant protein sources at each meal to match our body’s essential amino acid requirements, for example, a grain combined with a legume. Fortunately, our bodies maintain a small store of amino acids that balances out the intake of essential amino acids across the day. Protein quality may be clinically relevant for people in developing countries when the only accessible food is a single low-protein grain or tuber.
What’s wrong with ‘quality’ protein?
Short answer: ‘Quality’ (animal) protein promotes chronic disease.
The quality protein in meat, poultry, fish, eggs, and dairy is a health hazard because it is a rich source of some essential amino acids. High levels of methionine and branched-chain amino acids are not a quality that is desirable from a health perspective and lead to:
-
- Whole body acid load
- Kidney stress
- Osteoporosis
- Increased cholesterol
- Insulin resistance and diabetes
- acne
- Accelerated cancer growth
- Accelerated ageing
Are protein supplements healthy?
Short answer: No – eat peas, not pea protein
Plant protein supplements are whole food extracts, akin to other macronutrient food extracts like sugar and vegetable oil.
Taking protein supplements can worsen nutritional status by displacing nutrient-rich whole plant foods. A 50g protein powder serving has 200 kcal but none of the fibre, iron, vitamins and phytonutrients that could have come from an equal calorie serving of whole plant food, for example, a 200g serving of legumes. In most situations, dietary protein is sufficient to meet our needs, and the extra protein from the supplement is converted to glucose and fats, contributing nothing but nutrient-poor calories.
Plant proteins, when taken in concentrated doses, may have some of the adverse effects of animal protein via pathways such as insulin, IGF-1 and mTOR, as well as the gut microbiome. Soy protein has an amino acid profile midway between animal and other plant proteins, and supplements have been shown to raise IGF-1. Traditional soy products are associated with less cancer and better health.
Which whole plant foods are proteins?
Short answer: all plants provide protein
Plant-based whole foods cannot be neatly divided into carbohydrates and proteins to match the classic plate model of a quarter protein, a quarter carbohydrate, and half non-starchy vegetables. Legumes are classified as protein, but most (other than soy and peanut) contain more carbohydrates than protein. Whole grains are classified as carbohydrates but are moderately high in protein. Nuts have a similar protein content to whole grains (on a per-calorie basis) but are classified as proteins or fats. Even potatoes, a vegetable that is typically described as a ‘starch’, have a protein content of 10% (of total calories), which approximates the recommended protein intake.
Non-starchy vegetables like broccoli and leafy green vegetables have a relatively high protein content, but due to their high water content, they have only 2-3g of protein per 100g, providing a small but significant proportion of the protein in whole food plant-only diets.
Our take-home message is that the plant plate does not need a ‘protein’ group to meet protein requirements – adequate calories of whole plants provide adequate protein.
See also:
Resources
- Protein needs: a moving target (41 min. video) – Dr Malcolm Mackay with Jenny Cameron, live stream on 12/01/2025. We discuss the changes made to this ‘Protein Needs’ page.
- The Truth About Protein and Disease Reversal with David Goldman, MS – Mastering Diabetes podcast (44 mins.)
- Dietitian Jeff Novick has written several useful posts about protein and protein needs:
- Protein requirements
- How Much Protein Do We Really Need?
- The Myth of Complementary Protein
- Completing The Limiting Essential Amino Acid Picture – includes quotes from the author of Diet For a Small Planet explaining why she no longer considers protein combining to be necessary; also Another Look at The Myth of Complementary Proteins
- The Percentage of Calories From Protein in Plant Foods
- Protein bioavailability and IGF-1
- McDougall Mastermind – Part 1 Everything You Need to Know About Protein
– (2 hr video) Dr John McDougall (2021) plus Part 2 (2 hr 16 min video) - The Mystique of Protein and Its Implications – (article) T. Colin Campbell, PhD discusses the exaggeration of the importance of protein over the past 100+ years and his decades long research showing the adverse health consequences of consuming too much animal protein.
- Where Do You Get Your Protein? – Alan Goldhamer, DC
- When Friends Ask: Where Do You Get Your Protein? – Dr John McDougall gives a comprehensive answer to the “where do you get your protein from” question.
- The No-B.S. Guide to Vegan Protein – Courtney Davison (2019)
- The Protein-Combining Myth – (4 min. video) Dr Michael Greger
- Meeting Protein Needs Simply by Eating (Forks Over Knives blog post by Micaela Karlsen)
- Where do you get your protein? – Dr. Neal Barnard, PCRM
- Protein: Power Up with Plant-Based Protein – PCRM
- Do Vegetarians Get Enough Protein? – Dr Michael Greger presents the data to show that the most important question to be asked is “Where do you get your fiber from?”
- Where Do You Get Your Protein? (video) – Tired of your friends and family asking you “Where do you get your protein from?” You may enjoy this song.
- Protein Isolates: Do They Have a Place in a Whole Food, Plant-Based Diet?
– Theresa “Sam” Houghton (2021 – updated 2023)
Peer reviewed articles
- Levine, Morgan E., Suarez, Jorge A., Brandhorst, S., Balasubramanian, P., Cheng, C.-W., Madia, F., . . . Longo, Valter D. (2014). Low protein intake is associated with a major reduction in IGF-1, cancer, and overall mortality in the 65 and younger but not older population. Cell Metabolism, 19(3), 407-417.
- Solon-Biet, Samantha M., McMahon, Aisling C., Ballard, J. William O., Ruohonen, K., Wu, Lindsay E., Cogger, Victoria C., . . . Simpson, Stephen J. (2014). The ratio of macronutrients, not caloric intake, dictates cardiometabolic health, aging, and longevity in ad libitum-fed mice. Cell Metabolism, 19(3), 418-430.
- Wahl, D., Solon-Biet, S. M., Wang, Q.-P., Wali, J. A., Pulpitel, T., Clark, X., . . . Le Couteur, D. G. (2018). Comparing the Effects of Low-Protein and High-Carbohydrate Diets and Caloric Restriction on Brain Aging in Mice. Cell Reports, 25(8), 2234-2243.e2236.
Page created 24 June 2013
Page last updated 5 January 2025 (major update)