Tuesday, July 15, 2008

The “Complete” Story on Protein

The following is part two of a series from nutritionist Dipa Shah-Patel, MPH:

In my last article, I included a list of different foods and the grams of protein they contain. I also mentioned that although certain items appear to have similar amounts of protein, they differ in the composition of those proteins.

You may think of protein as a single nutrient, but it actually consists of building blocks called amino acids, each with a somewhat different structure. The human body uses about twenty amino acids to make body proteins. Eight of these are called “essential” amino acids because they cannot be produced by the adult body. They must be found in the foods that you eat. These eight essential amino acids are: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. For children, histadine is also an essential amino acid, so they require a total of nine essential amino acids. Other amino acids are "nonessential", which means that your body makes them if you consume enough essential amino acids and enough calories during the day.

Some foods are considered to be “complete proteins.” A complete protein is a protein that contains all nine essential amino acids for the dietary needs of humans.1 In general, complete proteins can be found in animal foods, including meat, poultry, seafood, eggs and dairy. Some plant and microbial sources also contain complete proteins, including spirulina, quinoa, soy, buckwheat, hempseed, and amaranth.

Meals consisting of different foods can also provide essential amino acids. Wheat, rice, and corn have low amounts of lysine, while beans and lentils contain significant amounts, making beans and rice a complete protein. Other combinations include:

  • beans and tortillas
  • rotis (Indian bread) and lentils
  • a peanut butter sandwich
  • tofu with rice
  • hummus with pita bread
It is important to note that complete proteins are not superior in quality to incomplete proteins. Lysine from beans has the same chemical structure as lysine from eggs.

Also, you do not need to eat foods containing all of the essential amino acids together at every meal. The myth of protein combining was widely accepted in the seventies largely due to the book “Diet for a Small Planet” by Frances Moore Lappe, but this was revised in a later edition. A 1997 position paper of the American Dietetic Association emphasized that because amino acids obtained from food can combine with amino acids made in the body, it is not necessary to combine protein foods at each meal. Adequate amounts of amino acids will be obtained if a varied diet containing unrefined grains, legumes, seeds, nuts and vegetables is eaten on a daily basis.2

Stay tuned for the next article, “Super Foods for Vegetarians!”

Dipa is available to answer any nutrition questions you may have. Email them to administrator@goeggless.com.

1."Protein in diet". Medline Plus Medical Encyclopedia. (June 26th, 2008). U.S. National Library of Medicine and National Institute of Health, Retrieved on July 12th, 2008.
2. Meddina, VK, Burke, KI. Position of the American Dietetic Association: Vegetarian Diets (1997). J Am Diet Assoc. 1997;97:11.
Fürst P, Stehle P (2004). "What are the essential elements needed for the determination of amino acid requirements in humans?". J. Nutr. 134 (6 Suppl): 1558S–1565S.


Anonymous said...

Great article. Very informative

Rupa Mohan said...

Great article, Mrs. Shah-Patel!

Samir Khandhar said...

Very informative, and easy-to-grasp article! I'm looking forward to the next installment. =)

Anonymous said...

Wow. I didn't know I could fulfill my daily protein requirement without eating any meat! I have a question though, why does eating rice for lunch make me sleepy?

Dipa Shah-Patel, MPH said...

The answer to the question about feeling sleepy after eating rice can be explained by understanding the role of L-Tryptophan, an essential amino acid that has been shown to have a sleep inducing effect. Tryptophan also can be metabolized into serotonin, which is a neurotransmitter that has a calming effect.

Although most people associate L-Tryptophan with turkey, and post Thanksgiving meal sluggishness, it's a carbohydrate-rich meal that increases the level of this amino acid in the brain and leads to serotonin synthesis.

When you eat a meal that is high in carbohydrates, the pancreas is stimulated to secrete insulin. When this happens, some amino acids that compete with tryptophan leave the bloodstream and enter muscle cells. This causes an increase in the relative concentration of Tryptophan in the bloodstream.

Tryptohan can cross the blood brain barrier and enter the CNS, where it is converted into Serotonin, which then causes you to feel sleepy.