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:


Food Limited Amino Acid Complement
Beans Methionie Grains, nuts, seeds
Grains Lysine, threonine Legumes
Nuts/seeds Lysine Legumes
Vegetables Methionine Grains, nuts, seeds
Corn Tryptophan, lysine Legumes

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.

7 replies
  1. Dr Peter Kay
    Dr Peter Kay says:

    The need for “protein complementation” has been exposed as a myth.

    Not only do you not need to eat all essential amino acids at the same meal, the body’s own amino acid pool makes good shortfalls.

    If you eat a healthy varied diet, your body takes care of the rest.

    • Eva
      Eva says:

      Hi, I am currently studying to become a nutritional therapist and I found your response really interesting. Not only was I told about the “protein complementation” being necessary but also that it has to be eaten at the same time in correct ratio (for example 2 cups of rice for 1 cup of beans). Is this not correct, or perhaps has this recently changed? Thank you

        • Erik
          Erik says:

          Hi all!

          I’m studying nutrition too and i agree that there little to no risk of amino acid deficiency on a vegetarian diet as long as you get enough energy from it.

          However, optimizing muscle protein synthesis for people doing vigorous physical exercise, seeking to maximize performance, is a different issue. In that context protein complementation may be beneficial.

      • Steve
        Steve says:

        Usually if we’re going beyond a normal and varied diet for nutritional purposes, it’s because of efforts to build or heal muscle from exercise. A bodybuilder will find that with the minimal intake of essential amino acids, they will lose muscle because the reserves run out. It also seems to be true, though there are plenty of inexperienced scientists who will argue the point, that increased intake of quality protein generally leads to increased capacity to add lean muscle mass. Though all are agreed that there are potential dangers in going too far.

  2. ThomasWilson
    ThomasWilson says:

    A plant-based vegetarian diet is healthier and can prevent diseases. According to the American Dietetic Association, vegetarians have a reduced risk of heart disease, obesity, colon cancer, adult-onset diabetes, osteoporosis, gout, gallstones, kidney stones, lung cancer, and breast cancer. A low fat vegetarian diet, combined with regular exercise, helps reduce blood pressure and can control, or even eliminate, non-insulin dependent diabetes.


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