Can you get sufficient protein from a vegan diet?

Question

This image claims that you can get protein from non-meat sources, citing Broccoli as an example.

Do you really need meat to get Protein?

Beef 6.4 grams of protein per 100 calories. Broccoli 11.1 grams of protein pe 100 calories

Plants have all the protein you need with none of the violence.

Source: Albury Times-Union

VeganStreet.com

My initial reaction is "NO WAY! That's not the same amino acids or structure or something..." but then I realized I have no actual evidence to back this up.

I think the statement is technically correct, however, I can't shake the feeling that I'm not seeing the whole picture.

Answer 1

An amino acid was first isolated in 1806, by French chemists Louis Nicolas Vauquelin and Pierre Jean Robiquet

The proteins present in food are all composed of a group of amino-acids. The amino-acids constitute the building blocks for many different chemicals made inside the body: in hormones, enzymes, DNA. encoding, RNA. encoding.... they play vital roles in the body's immune system, they constitute the neurotransmitters in the brain, the cortisol which is involved with stress response - in short we know a fair bit about their roles in the body, and the body and mind can't function at full capacity without them.

About 500 amino-acids are known. Ref(1)

Altogether there are twenty amino-acids which we need. Of those twenty there are ten which the human body can synthesize, the other ten are only able to be obtained through our diet, these ten are called "essential amino-acids".

Animal proteins contain the amino-acids we can't produce ourselves, these are called complete proteins.

A vegetarian diet would still contain eggs and dairy products which, together with the vegetable proteins would cover the full count of the required ten essential amino-acids.

The question boils down to: can a vegan diet provide all ten essential amino-acids, if not, what supliments are available? (Which are not of an animal source)

It appears to be the case that vegetable proteins are on the whole likely to contain these amino acids, but some of them may be present in only small quantities. It is therefore necessary to find a variety of vegetable sources in order to obtain a balanced diet of complete protein.

From: vrg.org/nutrition/protein.php

Soybeans, quinoa (a grain), and spinach also are considered high quality protein. Other protein sources of non-animal origin usually have all of the essential amino acids, but the amounts of one or two of these amino acids may be low. For example, grains are lower in lysine (an essential amino acid) and legumes are lower in methionine (another essential amino acid) than those protein sources designated as high quality protein. Frances Moore Lappe, in her book Diet for a Small Planet advocated the combining of a food low in one amino acid with another food containing large amounts of that amino acid. This got to be a very complicated process, with each meal having specific amounts of certain foods in order to be certain of getting a favorable amino acid mix. Many people got discouraged with the complexity of this approach.

It may not always be possible or convenient to eat healthily on a vegan diet, but there are plenty of food supplements containing the individual elements you may need for that hard to get complete diet. Using a search engine to seek: "vegan amino-acids" many websites offer individual amino acids and quite a few pharmacies/health and fitness stores in your local town or city probably do the same. They do in mine. It would then be advisable for the individual to ensure that they are buying not only the appropriate supplements, but ones not obtained from animals.

Anyone embarking on a vegan diet would be well advised to seek advice from a dietitian about their specific requirements, particularly regarding feeding expectant mothers, children, young adults, the old and the very active or ill.

Refs: 1: Wagner, Ingrid; Musso, Hans (November 1983). "New Naturally Occurring Amino Acids". Angew. Chem. Int. Ed. Engl. 22 (22): 816–828.

Edit (1) - to include broccoli and a useful resource: Although the specific statement in the question refers to the website: VeganStreet.com, this answerer is unable to find the specific page making the claim, however there are other sites which make similar claims. Broccoli is not considered a complete source of essential amino acids, see here. A serving of 91 grams of the raw product contains:

> Tryptophan      30.0 mg
> Threonine       80.1 mg
> Isoleucine      71.9 mg
> Leucine        117   mg 
> Lysine         123   mg
> Methionine      34.6 mg
> Cystine         25.5 mg
> Phenylalanine  106   mg 
> Tyrosine        45.5 mg
> Valine         114   mg
> Arginine       174   mg
> Histidine       53.7 mg 
> Alanine         94.6 mg
> Aspartic acid  296   mg
> Glutamic acid  493   mg
> Glycine         81.0 mg 
> Proline        100   mg
> Serine         110   mg
> 
> Attribution: 
> http://nutritiondata.self.com/facts/vegetables-and-vegetable-products/2356/2#ixzz30ZrrGvhy

The bio-availability of these amino acids is not stated in the raw product, nor the cooked, nor is the RDA of any of them listed here.

The claims on the above site regarding the relative protein contents of broccoli and beef (per amount measured arbitrarily in calorific content) are contradicted here with citations, notably of USDA’s Agricultural Research Service’s Nutrient Data Laboratory database. It gives a list of the essential amino acids and their RDA. taken from the WHO database.

For reasons of complex formatting I have not quoted this, you should view the list here: http://eathropology.com/2013/04/08/broccoli-has-more-protein-than-steak-and-other-crap/

It is clear that to ascertain the minimum daily requirements of for example histidine, approximately 20 cups of broccoli need to be consumed per day. The story is similar for other essential amino acids. To most people this would make broccoli an unfeasible source of all necessary dietary protein.

Answer 2

Adele Hite wrote about this claim on her blog "Eathropology":

Let’s see how similar caloric intakes of steak and broccoli stack up when comparing how these two foods provide for essential amino acid requirements. A 275-calorie portion of steak (4 ounces) has 30.5 grams of protein and comes very close to meeting all the daily essential amino acid requirements for a 70 kg adult. A 277-calorie portion of broccoli is not only way more food—you’ll be chewing for a long time as you try to make it through 9 ¼ cups of broccoli—exactly NONE of the daily essential amino acid requirements for an adult are met: In reality, it takes twice that much broccoli, or over 18 cups, containing nearly twice as many calories, in order to get anywhere near meeting all essential amino acid requirements. While I’m willing to concede that individual amino acid requirements may vary considerably, I am not willing to concede that similar caloric amounts of steak and broccoli provide a similar supply of those requirements.

Answer 3

Since most of the answers base their claims on numbers and are a bit shaky here's something from human physiology and bio-availability perspective.

First lets start with mass, a very nice figure comparing protein intakes of different diets (strict veg = vegan):

Nutrient Profiles of Vegetarian and Nonvegetarian Dietary Patterns [pdf]

Of course, this just implies that protein is consumed in right mass amounts, but is it sufficient for life?

Another figure outlining the myths that have accumulated in public health discussions:

Plant proteins in relation to human protein and amino acid nutrition [abstract] [pdf]

The paper above analyzes protein intake of many nations (figure is taken from it).

Here's a statement from AHA outlining the unecessary worry over protein:

Whole grains, legumes, vegetables, seeds and nuts all contain both essential and non-essential amino acids. You don't need to consciously combine these foods ("complementary proteins") within a given meal. Soy protein has been shown to be equal to proteins of animal origin. It can be your sole protein source if you choose. -- American Heart Association [statement]

AHA wasn't always so precise and this is a nice example of how "wrong" they were:

The American Heart Association (AHA) Science Advisory, “Dietary Protein and Weight Reduction: A Statement for Healthcare Professionals From the Nutrition Committee of the Council on Nutrition, Physical Activity, and Metabolism of the American Heart Association,” contains often quoted, but incorrect, information about the adequacy of amino acids found in plant foods. This report states, “Although plant proteins form a large part of the human diet, most are deficient in 1 or more essential amino acids and are therefore regarded as incomplete proteins.” -- Plant Foods Have a Complete Amino Acid Composition [pdf]

Our body contains free amino acid pools from which it can reuse and recombine non-essential and essential amino acids, intracellular pools of lysine in muscle tissue allow for muscle growth even if daily sources do not contain significant amounts of lysine (lysine and leucine are very often low in plant proteins). [google books]

To worry about protein in situation where there is no starvation is unnecessary.

Every day in the adult human, approximately as much protein as that ingested with food enters the digestive lumen directly from the body. These proteins are called the gut endogenous proteins. They are subjected to digestion in the digestive tract, with about 80% of the material being digested and reabsorbed. The endogenous component constitutes a consistent supply of protein to the gut lumen. Sources of endogenous materials entering the digestive lumen are saliva, gastric secretions, bile, pancreatic secretions, mucins, sloughed epithelial cells and plasma proteins (e.g. serum albumin, immunoglobulins). In addition, a significant microbial population inhabits parts of the human digestive tract, and as such bacterial cells die and are lysed, they also offer a supply of proteins to the gut lumen. -- Food-derived bioactive peptides – a new paradigm [pdf]

The amounts of that protein are more than sufficient for proper body functioning.

Estimates of the amounts of the various materials entering the human gut are highly variable, but it would appear that some 90 grams of endogenous protein per day flows through the digestive tract from the mouth to the terminal ileum in the adult human. -- Gut luminal endogenous protein [pdf]

The body can easily from that material do whatever it wants, it won't require consumption of complete protein every single day for every single meal, there's no need for faddy protein combining, or complementary protein consumption.

The conclusion is that, yes, one can get sufficient protein on a vegan diet, if one eats enough food in calories then the protein needs are most likely met.

Answer 4

You do not need meat (or even milk or eggs) to get all the protein (with all amino acids required) you need.

The Vegetarian Resource Group - Vrg.org:

It is easy for a vegan diet to meet recommendations for protein, as long as calorie intake is adequate. Strict protein combining is not necessary; it is more important to eat a varied diet throughout the day.

Academy of Nutrition and Dietetics - Eatright.com:

Myth #1: Vegetarians and Vegans Have a Hard Time Getting Enough Protein

Adequate protein needs easily are attained through a well-planned diet.

---

Broccoli is not really an appropriate food to be advertised as high in protein; one serving (1/2 cup, cooked, 78 g) contains only 2 g of protein. (NutritionData).

The meat/broccoli comparison in the image in the question is misleading because it's "per 100 Calories." You need only about 50 g meat but about 300 g of broccoli to get 100 calories, and they both contain about 6.5 g protein (not 11.1 g for broccoli, as the image states).

Answer 5

As pointed out in the answers by Looft and Jan, we don't need to eat animal products to get all the amino acids we need. Here we must also consider the fact that the recommendations by the IoM regarding the diet are not scientifically rigorous to such a degree that you can take their RDA as a scientifically established fact. Doing so would necessarily require putting people on potentially deficient diets for a long period of time and studying the health outcomes. Such experiments would be unethical, this is why a cautious approach is chosen where we give the traditional Western diet the benefit of the doubt and demand a lot of evidence for alternative ideas

This selective benefit of the doubt for the traditional Western diet makes the official RDA safe to use (relative to current eating habits), but it is not reliable when used in this question because it will biased against diets that will be lacking in some amino acids when there is no hard evidence that the RDA for such amino acids needs to be met for optimal health.

A plant based diet may be superior to a Western diet containing animal products, many studies on plant based societies report on an almost total absence of heart disease. E.g. here it is pointed out that:

Maybe the Africans were just dying early of other diseases and so never lived long enough to get heart disease? No. In the video One in a Thousand: Ending the Heart Disease Epidemic, you can see the age-matched heart attack rates in Uganda versus St. Louis. Out of 632 autopsies in Uganda, only one myocardial infarction. Out of 632 Missourians—with the same age and gender distribution—there were 136 myocardial infarctions. More than 100 times the rate of our number one killer. In fact, researchers were so blown away that they decided to do another 800 autopsies in Uganda. Still, just that one small healed infarct (meaning it wasn’t even the cause of death) out of 1,427 patients. Less than one in a thousand, whereas in the U.S., it’s an epidemic.

Similar studies have done in other such plant based populations with similar results. But here we have to note that people who live in such societies typically won't keep track of their amino acid intake, so they may actually get protein deficiencies from time to time. Nevertheless, they don't get heart disease. Autopsies on old people will not show any signs of atherosclerosis, while atherosclerosis already starts to affect our arteries at the age of ten.

But absence of certain diseases doesn't prove that such a diet is healthier overall. A good test for the vegan diet would be studies were the protein demand is increased by letting people do heavy strength exercises and then studying the impact of a vegan diet relative to other diets. It's all good and well to point out that you can get enough of all the essential amino acids in theory, what matters is if you can demonstrate that you are able to stick to a diet that gives you all the required amino-acids on the long term. Such studies have not been performed. But what we can do is look at whether there are vegan bodybuilders and how competitive they are. The absence of vegans in that professions or if they all perform poorly would be a red flag for the vegan diet.

It turns out that there are a number of vegan body builders, some like Frank Medrano supplement with protein powders while Patrik Baboumian manages to do with only vegetables, as he explains here. The most famous vegan bodybuilder is Jack Lalanne, but later in life he did start to eat egg whites and fish. So, we can say that there are no good reasons to believe that a vegan diet would lead to protein deficiencies in practice.

My personal opinion for which I cannot find independent sources, is that doing a lot of exercise is important for getting enough nutrients from a vegan diet. A lot of the foods you eat in this diet have a low density in nutrients (not just protein, also minerals like calcium), so you must eat large volumes. E.g. I regularly eat 1 kg of potatoes and 500 grams of broccoli for dinner, which isn't all that difficult if you run for an hour a day at a fast pace. This meal alone contains almost all the amino acids I need.