This article is an extract from my booklet “The Low Emissions Diet: Eating for a safe climate“. It updates and expands on previous articles.

One of the most common questions heard by any vegetarian or vegan is: “Where do you get your protein?”

The question arises because of a common misconception that protein is only available in meat or other animal products, such as chickens’ eggs or cows’ milk, or that plant-based protein is somehow inferior.

The fact that some of the largest, strongest animals are herbivores or near-herbivores should alert people to the fact that there is plenty of protein available without eating animals. The range of such animals includes elephants, rhinoceroses, giraffes, cattle, horses and great apes such as chimpanzees, gorillas, and orangutans.

The position is further highlighted by comments from Dr David Pimentel of Cornell University, who reported in 2003 that the grain fed each year to livestock in the United States could feed 840 million people on a plant-based diet.[i]

Referring to US Department of Agriculture statistics, Pimentel has also stated that the US livestock population consumes more than 7 times as much grain as is consumed directly by the entire American population.

He and Marcia Pimentel have also reported:

 “. . . each American consumes about twice the recommended daily allowance for protein”

Those comments partially reflect the gross and inherent inefficiency of animals as a food source.

Is it difficult to replace animal protein with plant protein?

The Physicians Committee for Responsible Medicine (PCRM) has stated:[ii]

“To consume a diet that contains enough, but not too much, protein, simply replace animal products with grains, vegetables, legumes (peas, beans, and lentils), and fruits. As long as one is eating a variety of plant foods in sufficient quantity to maintain one’s weight, the body gets plenty of protein.”


 “It was once thought that various plant foods had to be eaten together to get their full protein value, but current research suggests this is not the case. Many nutrition authorities, including the American Dietetic Association, believe protein needs can easily be met by consuming a variety of plant protein sources over an entire day. To get the best benefit from the protein you consume, it is important to eat enough calories to meet your energy needs.”

The US Department of Agriculture has reported the following protein content for a variety of food products:[iii]

Figure 1: Protein content of various foods (grams per kilogram)


The legume figures (soy beans, lupins, peanuts, mung beans, navy beans, chickpeas and lentils) are based on raw product. Due to increased water content, soaking or boiling reduces protein content per kilogram. (The emissions attributed to the product, per kilogram, are also reduced.)

Figure 11 shows that 81 per cent of protein produced in Australia in 2011/12 came from plants, and only 19 per cent from animals.

It includes products that are exported and/or used as livestock feed. The inclusion of the latter means there is some double counting of protein and other nutrients. However, given animal agriculture’s relatively low output level, the double counting is not significant in most cases.

 Figure 2: Nutrient Value of Australian Food Production 2011/12


The chart is based on: (a) production figures from the Department of Agriculture, Fisheries and Forestry’s “Australian food statistics 2011-12″;[iv] and (b) nutritional information for each product from the United States Department of Agriculture’s (USDA) National Nutrient Database for Standard Reference.[v]

 Adequacy of Alternative Diets

The American Dietetic Association (referred to earlier) has said:[vi]

“It is the position of the American Dietetic Association that appropriately planned vegetarian diets, including total vegetarian or vegan diets, are healthful, nutritionally adequate, and may provide health benefits in the prevention and treatment of certain diseases. Well-planned vegetarian diets are appropriate for individuals during all stages of the life cycle, including pregnancy, lactation, infancy, childhood, and adolescence, and for athletes. A vegetarian diet is defined as one that does not include meat (including fowl) or seafood, or products containing those foods.”

The extent of fortification of foods with nutrients such as vitamin B12 and vitamin D varies by country. As a result, it is important to review the adequacy of your diet based on local conditions, as partially reflected in this statement from Australia’s National Health and Medical Research Council (also supporting vegetarian and vegan diets):[vii]

“Appropriately planned vegetarian diets, including total vegetarian or vegan diets, are healthy and nutritionally adequate. Well-planned vegetarian diets are appropriate for individuals during all stages of the lifecycle. Those following a strict vegetarian or vegan diet can meet nutrient requirements as long as energy needs are met and an appropriate variety of plant foods are eaten throughout the day. Those following a vegan diet should choose foods to ensure adequate intake of iron and zinc and to optimise the absorption and bioavailability of iron, zinc and calcium. Supplementation of vitamin B12 may be required for people with strict vegan dietary patterns.”

Vitamin B12

The vitamin B12 found in certain animal-based food products is produced by soil microbes that live in symbiotic relationships with plant roots, and which find their way into the animals’ digestive tracts. Such bacteria are also found in humans’ digestive tracts, but too far along to be readily absorbed for nutritional purposes.[viii]

Vitamin B12 is not synthesised by plants, nor is it generally found with vegetables in our modern sanitised lifestyle. However, B12 supplements are readily produced from microbes, to be ingested directly or incorporated in various other food products. That is a far more natural approach than: (a) destroying rainforests and other natural environs; and (b) operating livestock production systems; purely for animal-based food products.



There are ample plant-based sources of calcium, including unhulled tahini (sesame seed paste), chia seeds, almonds, turnips, kale, and spinach.

Animal proteins and excess amounts of calcium have been found to adversely affect bone density.[ix] PCRM (referred to earlier) has reported that animal protein tends to leach calcium from the bones, encouraging its passage into the urine and from the body.

Amongst many studies on the subject, a 2000 study from the Department of Medicine at the University of California at San Francisco showed that American women aged fifty and older have one of the highest rates of hip fractures in the world. The only countries with higher rates were Australia, New Zealand and certain European countries, where milk consumption is even higher than in the United States.[x]

 Vitamin D

It may be best not to rely on animal-based foods to satisfy your vitamin D requirements. The Medical Journal of Australia has reported: [xi]

“Most adults are unlikely to obtain more than 5%-10% of their vitamin D requirement from dietary sources. The main source of vitamin D for people residing in Australia and New Zealand is exposure to sunlight.”

 Whether or not you eat animal products, you need sunshine if possible, or perhaps supplements.


There are two types of iron in food: haem and non-haem. Haem iron is absorbed by the body more readily than non-haem, and is only available in animal products. Is that a problem? Not according to authors writing in the Medical Journal of Australia, who said:[xii]

“Well planned vegetarian diets provide adequate amounts of non-haem iron if a wide variety of plant foods are regularly consumed. Research studies indicate that vegetarians are no more likely to have iron deficiency anaemia than non-vegetarians. Vegetarian diets are typically rich in vitamin C and other factors that facilitate non-haem iron absorption.”

PCRM has highlighted the role of excessive iron levels in the formation of cancer-causing free radicals. It has argued that iron from vegetarian food sources may be the better choice, as it is sufficient to promote adequate levels without encouraging iron stores above the recommended range.[xiii]


While noting that vegetarians have an overall lower risk of common chronic diseases than non-vegetarians, another article in the Medical Journal of Australia concluded that well planned vegetarian diets “can provide adequate zinc for all age groups, and vegetarians appear to be at no greater risk of zinc deficiency than non-vegetarians”.[xiv]

Although phytic acid in legumes, unrefined cereals, seeds and nuts can inhibit zinc absorption, the effect can be offset by the presence of sulphur-containing amino acids in a range of seeds, nuts, grains and vegetables and hydroxy acids in citrus fruits, apples and grapes, which bind to zinc and enhance its absorption.

Everyday practices such as soaking, heating, sprouting, fermenting and leavening food also assists. Soaking is the typical approach in relation to legumes, as is fermenting and leavening bread by including yeast as an ingredient.

In any event, our bodies generally adapt to a lower zinc intake by absorbing more of the zinc consumed and excreting less.

The authors also noted that “different types of protein influence zinc absorption in different ways”. For example, casein in milk inhibits zinc absorption but soy protein does not.


Hopefully the sample of nutrients referred to in this article has highlighted the need to investigate your nutritional options independently of the food industry’s slick and expensive PR and advertising campaigns.


Paul Mahony (also on Twitter, Scribd, Slideshare, New Matilda, Rabble and Viva la Vegan)


  1. No information in this article is intended to represent nutritional, dietary, medical, health or similar advice, and should not be relied upon as such.
  2. Comments on zinc added 21st February, 2016.


[i]      Pimentel, D., Cornell University “Livestock production and energy use”, Cleveland CJ, ed. Encyclopedia of energy (in press), cited in Pimentel, D. & Pimentel M. “Sustainability of meat-based and plantbased diets and the environment”, American Journal of Clinical Nutrition, Vol. 78, No. 3, 660S-663S, September 2003, http://ajcn.nutrition.org/content/78/3/660S.full

[ii]      Physicians Committee for Responsible Medicine “The Protein Myth”, http://www.pcrm.org/health/diets/vsk/vegetarian-starter-kit-protein

[iii]     USDA National Nutrient Database for Standard Reference at http://www.nal.usda.gov/fnic/foodcomp/search/http://www.nal.usda.gov/fnic/foodcomp/search/ via Nutrition Data at http://www.nutritiondata.com

[iv]     Dept of Agriculture, Fisheries and Forestry, “Australian Food Statistics 2011-12”, http://www.agriculture.gov.au/SiteCollectionDocuments/ag-food/publications/food-stats/daff-foodstats-2011-12.pdf

[v]      USDA National Nutrient Database for Standard Reference, op. cit.

[vi]     Craig, W.J., Mangels, A.R., American Dietetic Association, “Position of the American Dietetic Association: vegetarian diets.”, J Am Diet Assoc. 2009 Jul;109(7):1266-82, http://www.ncbi.nlm.nih.gov/pubmed/19562864

[vii]     National Health and Medical Research Council, Australian Dietary Guidelines (2013), p. 35, http://www.nhmrc.gov.au/guidelines-publications/n55

[viii]    Trafton, A., “MIT biologists solve vitamin puzzle”, MIT News, 21 March, 2007, http://newsoffice.mit.edu/2007/b12 and McDougall, J., “Vitamin B12 Deficiency—the Meat-eaters’ Last Stand”, McDougall Newsletter, Vol. 6, No. 11, Nov, 2007, https://www.drmcdougall.com/misc/2007nl/nov/b12.htm

[ix]     Mahony, P., “Climate change and diet: Calcium”, Terrastendo, 29th December, 2012, https://terrastendo.net/2012/12/29/climate-change-and-diet-calcium/

[x]      Frassetto, L.A., Todd, K.M., Morris, C, Jr., et al. “Worldwide incidence of hip fracture in elderly women: relation to consumption of animal and vegetable foods”, J. Gerontology 55 (2000): M585-M592, cited in Campbell, T.C. and Campbell, T.M. II , Campbell, T.C. and Campbell, T.M. II, “The China Study: Startling Implications for Diet, Weight Loss and Long-Term Health”, Wakefield Press, 2007, pp. 204-211

[xi]     Nowson, C.A., McGrath, J.J., Ebeling, P.R., Haikerwal, A., Daly, R.M., Sanders, K.M., Seibel, M.J. and Mason, R.S., “Vitamin D and health in adults in Australia and New Zealand: a position statement”, Med J Aust 2012; 196 (11): 686-687, doi: 10.5694/mja11.10301, https://www.mja.com.au/journal/2012/196/11/vitamin-d-and-health-adults-australia-and-new-zealand-position-statement

[xii]     Saunders, A.V., Craig, W.J., Baines, S.K. and Posen, J.S., “Iron and vegetarian diets”, MJA Open 2012; 1 Suppl 2: 11-16. doi:10.5694/mjao11.11494, 4th June, 2012, https://www.mja.com.au/open/2012/1/2/iron-and-vegetarian-diets; https://www.mja.com.au/system/files/issues/196_10_040612_supplement/sau11494_fm.pdf

[xiii]    Physicians Committee for Responsible Medicine (PCRM), “Iron: The Double-Edged Sword” (Food for Life Cancer Project), Undated (accessed 4th February 2016), https://www.pcrm.org/health/cancer-resources/diet-cancer/nutrition/iron-the-double-edged-sword

[xiv]    Saunders, A.V., Craig, W.J., Baines, S.K. and Posen, J.S., “Zinc and vegetarian diets”, MJA Open 2012; 1 Suppl 2: 17-21. doi:10.5694/mjao11.11493, 4th June, 2012, https://www.mja.com.au/open/2012/1/2/zinc-and-vegetarian-diets and https://www.mja.com.au/system/files/issues/196_10_040612_supplement/sau11493_fm.pdf


Chana | PDPics | Pixabay | CC0 Public Domain

Vegetable carrot potato beetroot | AnnaPersson | Pixabay | CC0 Public Domain