By Roberta H. Anding, MS, Baylor College of Medicine, and Texas Children's Hospital
Edited by Kate Findley and proofread by Angela Shoemaker, The Great Courses Daily
Even if you eat a high protein diet, you may not get the most out of your diet. Professor Anding explains what whole proteins are, why we need to combine proteins, and how to deal as a vegan.
Unlike fat and carbohydrates, our bodies cannot store protein, which is why a daily protein intake is essential in our diet. Photo by Oleksandra Naumenko / Shutterstock
Why we need complete proteins
Before learning how to combine proteins, it is first necessary to understand why it is necessary. Unfortunately, as humans, we have an infinite capacity to store fat. And we have little ability to store carbohydrates in our muscles and liver.
However, we cannot store protein. In order to produce new protein, the body needs a daily supply of amino acids.
If we cannot store protein, any loss of body protein means a loss of function. All of the protein's functions, including the benefits the protein provides for post-operative recovery, child growth, and immune system support, are also lost. Therefore, amino acids are needed to replenish our body's protein supply.
Some proteins contain all of the essential amino acids we need to make new proteins. They are often referred to as complete proteins. Usually they are of animal origin such as milk, cheese, chicken, fish, and red meat.
An exception to this rule is soybean, a vegetable protein found in tofu. Soybeans are just as nutritious as the other sources of whole protein, which contain all of the essential amino acids.
Other proteins may be lacking an essential amino acid or not in sufficient quantities. These are known as "incomplete proteins". You are missing one or more essential amino acids.
Most breads contain between two and three grams of protein per serving, but it's not a complete protein. Likewise, nuts, rice, beans, and vegetables are good sources of protein, but are incomplete on their own.
You will need something else to make up for the missing essential amino acid. This is called "combining proteins". They combine a protein that alternatively supplements the missing amino acid into a complete protein.
When you have a missing amino acid or that amino acid is running out, protein synthesis stops. It doesn't slow down. It stops because you lack the structures to complete this protein.
This is called the "limiting amino acid". This is why it is important that you maintain a balance between foods that contain protein.
Protein for vegans
"The only time I really see a problem with this in the US is with people choosing to go vegan," said Professor Anding.
Vegans eliminate all sources of animal protein and you can feel very healthy on a vegan diet. You just have to be wise in how you combine proteins.
For example, cereal grains are low in the essential amino acids lysine, and soybeans and other beans can be used in place of low-lysine foods to supplement this. Red beans and rice are good examples of complementary proteins. Peanut butter – a nut – and bread – a grain – are also complementary proteins.
We used to believe that you had to eat two incomplete proteins like rice and beans at the same time. Science no longer supports this belief. You should have them the same day, but you don't have to eat them within the same meal.
So, if you want to start your day with a spoonful of peanut butter and a banana, you have incomplete protein. However, if you have a granola bar later in the morning, you are now lacking that essential amino acid. It wasn't the same meal, but the same day. It's not difficult to balance amino acids if you eat frequently.
This article was edited by Kate Findley, author for The Great Courses Daily, and proofread by Angela Shoemaker, proofreader and editor for The Great Courses Daily.
Professor Roberta H. Anding is a registered nutritionist and director of sports nutrition and a clinical nutritionist at Baylor College of Medicine and Texas Children's Hospital. She also teaches and teaches in the Department of Pediatrics at Baylor College of Medicine, the Department of Adolescent and Sports Medicine, and the Department of Kinesiology at Rice University.