Complementary proteins question

by Andrew
(Wilmington, Del. USA)

Andrew’s Question:


I am a reader of your website and I have a question. Does combining two different sources of protein from two different foods make a difference to the 40-30-30 plan? If I combine rice and beans I will have more protein than each individually, so would I have to adjust the ratio of carbohydrates, fats, and proteins from what I started with?

Suzy’s Answer:

Thank you for the great question, Andrew. Our complementary protein pages are some of the most popular pages on the site.

Plant-based proteins are generally not complete.

When you use plant sources of proteins, with a few exceptions, you are eating “incomplete proteins,” since some of the essential amino acids (building blocks of protein) are missing. As you know, when you eat certain plant proteins, such as beans and rice, together, they complete each other, since the one food “complements” the other by supplying the missing essential amino acids. This is where we get the term “complementary proteins.”

This is how vegetarians, particularly vegans, get all of their protein, and why it is important for these groups to eat a variety of plant foods in complementary combinations.

It’s all about balance.

With regard to the 40-30-30 concept of healthy eating--the idea that some health experts recommend, that you eat 40% carbohydrates, 30% protein and 30% fat--it is a bit more difficult to use this method if you are relying on plant proteins. The reason for this is that animal protein like meat, fish or eggs are mostly protein, while plant proteins are a combination of carbohydrates and protein.

For instance, those beans and rice you mentioned have a significant amount of carbohydrate to go with their protein, so they are not, strictly speaking, just a protein food. They are both great sources of plant protein, but must be counted as both protein and carbs in the 40-30-30 scheme.

How much protein is there?

In a nutritional analysis, cooked brown rice is 85% carbs, 8% protein and 7% fat, while cooked pinto beans are 74% carbs, 22% protein and 4% fat. As you can see, these plant foods, while great sources of plant-based protein, especially when eaten together for reasons listed above, they are still mostly carbohydrate. Also, the amount of complete protein you are getting is limited by how much of the missing amino acids are available to complete the proteins.

The 40-30-30 concept is about balancing the major nutrients, with a bit more carbohydrate (preferably in the form of vegetables, fruits and whole grains) to be healthy. Having too few of any of these is not conducive to good health and having too much of one nutrient is also not a good idea.

It is easier to visualize protein percentages when you get your protein from a mostly protein source like meat, fish or eggs, but plant proteins are a perfectly acceptable way to meet your protein requirement as long as you eat them from a variety of sources so that the need for complementary proteins is met.

In addition, plant foods like beans and whole grains have the added benefit of providing fiber, something that is often lacking in diets that rely heavily on animal-based proteins.

If I am concerned about the ratio of the three major nutrients, then whenever I assemble a meal or snack, I take a moment to see that each is represented, about equally, and that helps me to feel confident that I am getting a good balance.

In general...

The bottom line is that eating a variety of whole foods each day from all of the food groups, in the amounts appropriate for age, gender and activity level, with a special emphasis on vegetables and fruits, will provide the nutrients needed to feel well and be healthy.

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