American Society For Nutrition

Protein Complementation

Protein Complementation

Excellence in Nutrition Research and Practice
Posted on 03/22/2011 at 06:38:39 PM by Suzanne Price
By: Laura S.

I am currently training for my second marathon in my adult life, and while the aches and pains feel the same as last year, and as the mileage starts to creep up it feels like deja vu- one minor detail has changed: this year I am running the marathon as a vegetarian.
Vegetarian endurance athletes have become quite a trend in the last couple of years. Some noteworthy endurance athletes include Brendon Brazier (vegan ironman), Rich Roll (vegan ultra ironman), Robert Cheeke (vegan body builder), and Michael Arnstein (fruitarian ultra runner); just to name a few.
Giving up meat during this marathon training means I will be missing out on complete proteins and key amino acids from my diet. These amino acids are also called limiting amino acids and they are: lysine, threonine, methionine, and tryptophan. Limiting amino acids are found in the shortest supply from incomplete proteins. Incomplete proteins are those found in plant food sources and geletin.
The most frequently asked question I get asked when becoming a vegetarian involved getting enough protein. While I do not eat meat, fish, or dairy (except for yogurt) I get plenty of protein in my diet by using protein complementation.
Protein complementation is the most efficient way to get all 9 amino acids into a vegetarian's diet. Protein complementation is when you combine two vegetable proteins (legumes and grains for an example) to get all 9 amino acids that are essential for your body. The breakdown of protein complementation goes like this:


Limited Amino Acid




Grains, nuts, seeds


Lysine, threonine







Grains, nuts, seeds


Tryptophan, lysine


By combining vegetarian protein sources you can ensure that you are getting all 9 amino acids. Protein complementation does not have to be done at the same meal. If you ate beans for lunch and then had some raw almonds for a snack later, you would be adding the methionine that you had missed out on during lunch.
A vegetarian diet, if planned correctly, can provide you with all of the vitamins, minerals, and amino acids the body needs. 

Posted Mar 24, 2011 3:30 PM by Kim Smith

Thank you for your information on this subject for I do believe this will help me in doing my biking for I want to achieve a 50 mile bike ride and need direction on how to make that work in a healthy way!

I'm curious about where you're getting omega-3s from! Many vegetarians turn to flaxseed oil, but as you as you may or may not know, flaxseed oil is not a good source of omega-3.

Great post, would you be willing to share some of the differences you have experienced from such a bold dietary change. More specifically are you noticing some performance benefit?