Yes Virginia, There's Even Enough Protein In Carrots
There are some myths that just never seem to die. One of them is the issue of plants, protein and amino acids. Do plants have all the amino acids in the right combinations to meet our protein requirements?
I have written several articles on the issue of plants and protein and specifically about the issue of amino acids twice.
- The Myth Of Complementing Proteins
- Completing The Limiting Essential Amino Acid Picture
In my writings and teachings, I have often made the following comment...
It is virtually impossible to construct a diet that is protein deficient if you meet the following 3 criteria..
1) it is calorically adequate
2) it is based on a variety of unrefined, unprocessed, whole plant foods (no refined processed
3) it is not based on fruit alone
This issue raised its ugly head once again when I was working with someone recently on the issue of Emergency Food Preparedness. It reminded me of an earlier email exchange I had with a professional colleague and Registered Dietitian, who challenged me on the concept by using a diet of only carrots. I have included our exchange below, which took place in 2008.
"I tried Jeff's exercise and input the amount of carrots that would be needed to meet energy demands and calculated how much of the amino acids would be provided. I used ~2000 kcal, which is 11 pounds. It turns out that it met all of the needs for the amino acids except methionine for which it provided about 88% of the RDA. There two things that I'm not sure about, though. First, can the average human who needs 2000 kcal physically eat 11 pounds of carrots? I doubt it, plus once a person enlarges their stomach capacity to hold that much food, the stomach emptying rate slows to a crawl. For example, it takes several days for the stomach of a competitive eater to empty after gorging, so much of the amino acids won't make it to the small intestine before it's time to eat more carrots the next day. Secondly, this doesn't take into consideration the digestabilty of the carrots, so we don't really know what percentage of each of the amino acids will make it into the body for utilization. Any comments?"
A few things.
1) While most any one food would also pass the test, I did not recommend you do it on any one food. I said "a variety of unrefined, unprocessed, whole plant foods," not just a "carrot diet." However, being you have done an extreme version of the test, I will address it, as the challenge holds true for virtually any single plant food too.
So, lets do the experiment with just a carrot but lets use actual real numbers based on actual calorie and amino acid requirements.
2) You did not say why you used 2000 calories as my comment today and in the past was adequate calories. Also, you did not say whose standards of the amino acid requirements you are using as there are several but either way, as you will see, the carrots are more than adequate.
According to the FAO/WHO/UNU (2007). "PROTEIN AND AMINO ACID REQUIREMENTS IN HUMAN NUTRITION". WHO Press., page 150, the need for Methionine (and Cysteine) is 15 mg/kg for Methionine and Cysteine . The reason it says Methionine and Cysteine is because to meet the AA requirement for Methionine we do not have to meet 100% of the need for Methionine alone because ~ 85% of the requirement for Methionine can be met by Cysteine (a non essential AA). BTW, the 15 mg/kg in the 2007 paper was increased as the 1985 WHO/FAO document says 13 mg/kg for Methionine and Cysteine so this is even a higher number than before.
So, for a 70 kg man, that would be 1.05 gm and for a 100 kg man would be 1.5 gm. They would also have different caloric needs, so lets break it down for each one.
Using the standard of a 70 kg 25 yr old male who is moderately active, their caloric need according to the Harris Benedict (HB) formula is 2500. The 2500 calories of carrots (USDA #11125 - Carrots, cooked, boiled, drained, without salt ) supplied 1.2 grams of Methionine surpassing the WHO/FAU recommendation of 1.05 on its own. It also supplied 4.9 mg of Cysteine for a total or 6.1 mg, which is way above the FAO/WHO recommended amount.
For the 100 kg 25 yr old male who is moderately active, their caloric need according to the HB formula is 3000 calories. The 3000 calories of carrots would provide 1.5 mg of Methionine on its own, which equals the WHO/FAO need of 1.5 mg of Methionine itself. It also supplies 5.8 gm of Cysteine for a total of 7.3 mg, way surpassing the FAO/WHO amount.
So, to be technically correct, we only have to meet 15% of the Methionine need (which is .22 for the 100 kg man). As you can see, the carrots not only meet this minimal need on their own, but when combined with the Cysteine (which the FAO/WHO counts in their requirements) far surpasses the recommended amount they set. But as I just showed, we did not even need the Cysteine.
These numbers set by the FAO/WHO in the above report are recommended amounts and not "minimum" amounts necessary to maintain nitrogen balance. Recommended amounts include buffers over minimum amounts, to help account for most everyone in the population, differing digestibilities of different foods, etc etc, so any single individual will probably do fine on even a little less. The minimal amount of Methionine set by the WHO and the Food and Nutrition Board (FNB) is .22 (which as you can see from above is the 15% of the current need for the 100 kg man). And, as you can see, the carrots far surpass the minimal amounts in addition to meeting the recommended amounts.
Lastly, in regard to being able to consume this amount of carrots. That is a good question but not the point as I did not recommend anyone to consume a carrot diet. The point is that if all individual plant foods meet the requirements at the needed caloric level than ANY combination of all these foods would also do so.
I'm not trying to argue. I granted that you were correct that carrots could theoretically meet the RDAs for amino acids, but I thought the person had raised the question about complete proteins, not vegetarian diets overall. Also, you didn't address the carrot digestibility issue or the issue of our ability to eat that the amount of food that would meet all the amino acid needs. Can you address that by any chance? I'm guessing your post was just from a perspective of theory rather than reality, which is fun, too.
1) The issue of a "complete" protein originally meant containing all the essential amino acids (EAA). As you showed with the carrots, and also by entering any plant food into the USDA Database SR 20 (online for free), you see that all plant foods contain all the EAA's.
(NOTE. THE USDA Database is now on Standard Release 28)
2) the recommended amount includes a buffer to cover the issues of the bell curve and the needs of most everyone in a population and the differing digestibilities of differing diets throughout the world, many of which are plant based. Remember, those numbers were from the FAO/WHO and not the USDA and were recommended amounts. The actual minimal amounts needed for Methionine was .22 and the recommended set at 1.05. Even at 75-85% digestibility (the estimate used sometimes for plant based diets), it is well covered by the recommended amount. We will see the same for every other amino acid as we do for Methionine.
3) In regard to the ability to eat that amount of food, remember, there are already populations (like the Okinawans, the Chinese Centenarians, the Tarahumara, the Pima, etc) that already do. These diets can be up to 90-95% plant foods and they have no problem consuming enough calories for their highly active lifestyles.
But, here is a more realistic diet to address your question and to make my response acceptable to all our RD colleagues
To make the experiment realistic without my theoretical experiment, I entered a 2500 calorie diet, which would meet the caloric needs of a moderately active 70 kg man. I based the diet on the current Vegetarian food guide pyramid using only plant foods. I used beans in the protein group and in the dairy/calcium group I used soy milk instead of the dairy milk. All recommended servings are per the USDA pyramid for 2500 calories.***
The diet included oatmeal and berries for breakfast and a glass of soymilk, Brown rice and veggies for lunch and a glass of soymilk and the sweet potato and veggies for dinner with some fruit snacks. At 2500 calories, it provided 86 grams of protein (which is 1.23 grams/kg) and also provided 1.5 gms of Methionine (by itself) which surpasses the 1.05 by 43% easily covering any digestibility issue. The 1.5 gms of methionine would also surpass the amount needed for the moderately active 100 kg man consuming 3000 calories. So, it is well covered.
This diet also surpassed the RDA/DRI for every other vitamin and mineral including essential fatty acids except for B12 and Vitamin D. It also has no cholesterol and the saturated fat is less than 5% of calories.
Not bad. :)
PS ***NOTE: I was unable to find the above mentioned analysis but have done a similar analysis many times in this forum. I am attaching links to 2 recent ones.