Is Protein Combining Necessary After All?

Combining complementary plant proteins was fashionable back in the 70s, dismissed in the 90s, and may now be making a comeback thanks to new research. Protein researcher Doug Paddon Jones joins me to discuss his latest study.

Monica Reinagel, MS, LD/N, CNS
7-minute read
Episode #509

One of the biggest nutrition trends right now is a move toward more plant-based or plant-forward diets. Although the number of strict vegetarians or vegans has not changed all that much, a lot of people are trying consume fewer animal products. I’m sure you’ve seen the explosion of plant-based milk and meat substitutes in your local grocery stores and restaurants, and we’ve talked about many of them on the podcast.  

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At the same time, there’s been a lot of interest in how dietary protein affects things like satiety, weight loss, muscle building, aging, and recovery.  We’ve talked about a lot of that research on the podcast as well. In particular, protein’s role in building and preserving lean muscle may be particularly relevant for those who are older, recovering from illness or injury, or losing weight—because these circumstances carry an increased risk of muscle loss.

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The collision of these two nutrition trends—plants and protein—has resurrected an old question: Is it necessary to combine complementary plant proteins at the same meal in order to create a “complete” protein?  Is the traditional combination of rice and beans actually grounded in nutritional necessity?

Protein’s role in building and preserving lean muscle may be particularly relevant for those who are older, recovering from illness or injury, or losing weight.

Joining me to unpack what we do and don’t know about this issue is protein researcher Douglas Paddon Jones, who runs the Nutrition and Metabolism Laboratory at University of Texas Medical Branch in Galveston, Texas.

Following are highlights of our conversation. To hear the entire interview, please click on the audio player above.

Nutrition Diva: If you are a long time listener of the Nutrition Diva podcast, then you are already quite familiar with Doug’s research because it has been the subject of at least half a dozen previous episodes.  

It was Doug’s research, for example, that I discussed in episode #398, on how to slow age-related muscle loss and again in episode #448 on how to build more muscle with less protein. If you have been eating more protein at breakfast (and maybe a bit less at dinner), or you’ve been shooting for 25-30g of protein per meal, it’s probably because of Doug’s research.

A lot of this research was done using animal proteins, such as beef, or eggs, or whey—because animal protein tends to be a higher quality source of protein. This is not a value judgment against vegetarians, just a biochemical reality.

Doug Paddon-Jones: Very true! To turn on protein synthesis—which essentially means the “muscle growth and repair machinery”—you need ALL the essential amino acids to be available in sufficient quantity at the same time.

You can absolutely get all the essential amino acids you need from plants, but it’s hard to get them all in ONE plant—at least in the proportions that make them most efficient.

Legumes, for example, tend to be lacking in methionine. Grains, on the other hand, are a decent source of methionine but tend to be low in lysine.

That means that, if you eat either of these foods by themselves, you still may be lacking one or more of the key ingredients (amino acids) that are needed to kick start the muscle building machinery.


About the Author

Monica Reinagel, MS, LD/N, CNS

Monica Reinagel is a board-certified licensed nutritionist, author, and the creator of one of iTunes' most highly ranked health and fitness podcasts. Her advice is regularly featured on the TODAY show, Dr. Oz, NPR, and in the nation's leading newspapers, magazines, and websites. Do you have a nutrition question? Call the Nutrition Diva listener line at 443-961-6206. Your question could be featured on the show.