Sometimes I get questions that remind me to question what I think I know. In general vegetables can not be counted on to be a high quality source of protein – meaning nutritionally complete and digestib-ly present protein. They can however, compliment other protein sources to improve total diet protein quality.
A recent conversation about protein in Romaine lettuce when like this:
He said, “I eat romaine lettuce because it has protein. It does have protein, right?”
I asked, ” Where did you obtain this information about protein in romaine lettuce?”
He said, ” An article online, a website for vegetarians.”
I said, ” Well, I don’t think there is protein in lettuce but let’s check the facts.”
After being 100% certain that romaine lettuce had zero protein, I looked it up on Food Data Central only to discover that one bunch of romaine lettuce contains about 7 grams of protein.
Looks like I have to “eat crow” on this one but what about the quality of the protein and the fact that you have to eat an entire bunch to get the same amount of protein in one egg or handful of almonds.
Protein quality is measured by the amount of amino acids present. An egg for example contains all nine essential amino acids at the highest level. Because it contains all nine, it is also a complete protein.
Nine Essential Amino Acids are below and I have indicated which ones are in Romaine and the amount in an entire bunch:
Phenylalanine – .066 grams vs one egg .322 grams
Valine .055 grams vs one egg .369 grams
Threonine .044 grams vs one egg .299 grams
Tryptophan .011 grams vs one egg .083 grams
Methionine .014 grams vs one egg .21 grams
Leucine .076 grams vs one egg .528 grams
Isoleucine .045 grams vs one egg .31 grams
Lysine .064 grams vs one egg .418 grams
Histidine .021 grams vs one egg .142 grams
So yes, my nutrition stands corrected. However, I don’t know many people who will eat and entire bunch of Romaine lettuce. There are a few, and on any given salad day, I might be one of them. While Romaine lettuce can’t be counted on to meet all your protein needs, and can be part of the puzzle providing small deposits that compliment other protein sources and add up each day!