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Op-Ed: ‘Complete’ and ‘Incomplete’ Protein is BS

Why the macronutrient is more nuanced than these antiquated terms make it seem

As a registered dietitian, nearly every week I hear clients, colleagues, journalists, coaches, students, friends, bus drivers, and barbers use the terms ‘complete’ and ‘incomplete’ proteins. We’ve become obsessive in our quest to consume more and more of the former. And this has led to a diet that overemphasizes animal products at the expense of plants. The ripple effect of a diet focused on animal food extends far and wide, influencing not only our personal health, but environmental sustainability and humane livestock production (and whether we like it or not, these last two influence all of us).

The idea: ‘Complete’ proteins supply the necessary proportions of all of the essential amino acids (nitrogen-rich compounds that our body cannot produce). If someone only ate a single ‘complete’ protein food for the day, and nothing else, they would meet 100 percent of their daily protein needs. Chicken, beef, eggs, fish, and soy are often referred to as ‘complete’ proteins.

‘Incomplete’ protein food sources, on the other hand, are often plant foods. The terminology suggests that if someone was to subsist exclusively on an ‘incomplete’ protein food, they wouldn’t meet 100 percent of their daily protein needs; they’d likely fall short of least one amino acid. Foods like rice, carrots, and beans are referred to as ‘incomplete’ proteins.

For years, health professionals thought that if one food contained a smaller amount of one essential amino acid, we’d need to pair it up with another food at the same meal in order for it to be useful to the body. Rice falls a bit short in lysine, for example, but black beans have plenty of lysine, which gives us black beans and rice.

After all, we need each amino acid in different amounts to build a protein—kind of like how you need different supplies (bricks, nails, wood) to build a house. Without enough of one supply, the house suffers.

Today, though, our knowledge and perspective has evolved. And classifying a food as a ‘complete’ or ‘incomplete’ protein (for the well-fed person in a developed nation with protein in their nutritional bullseye each day) is flawed and antiquated.

There’s no doubt that certain foods have more amino acids than others. But in my opinion, with a little thought and effort, it’s nearly impossible to fall short on getting enough essential amino acids in your diet, even if it’s plant-based.

Furthermore, continuing to use terminology that steers people away from having foods like legumes as a protein source is irresponsible and misguided, especially when you account for added benefits of eating more plant foods, such as decreased likelihood of chronic disease, a smaller environmental footprint, and improved animal welfare.

Nutrition science is a recent science, and it’s very complex. Food is made up of countless compounds that we are continuing to learn more about. And beyond nutrients, we all have unique differences in how we digest and process foods. This can make attaining certain nutrients from certain foods more difficult or easy depending on our genetic makeup, health history, gut microbiome, and medication use—things that cannot be captured in the ‘complete’ or ‘incomplete’ label. 

So instead of focusing on whether your protein source is ‘complete’ or ‘incomplete,’ follow these three guidelines.

  1. Eat enough food to support a healthy body size. If we don’t meet our energy and calorie needs (if we crash diet, fast for extended periods of time, or don’t eat enough during high volume periods of training), both dietary protein and proteins stored in the body might be diverted to other functions that protein is not ideal for, like producing energy. Eating enough calories allows protein to do what it’s meant to do in the body: aid in growth, repair, development, and in the synthesis of hormones, enzymes, and neurotransmitters. 

  1. Build a diet around a variety of foods. When a diet is built around a single food group, there’s a much better chance that the person will run into a nutrient deficiency problem. If you were only eating steak, for example, you might meet your protein requirements but you’d fall short on fiber, vitamins A, C, E, K, D, some B vitamins, calcium, magnesium, potassium, copper, and manganese. For people who love numbers, an active adult should aim for between 1.2 to 1.7 grams of protein per kilogram of body weight, or 82 to 116 grams of protein each day for a 150-pound adult. This protein can come from a variety of vegetables, fruits, whole grains, legumes, nuts, seeds, and animal foods.

  1. Include at least one cup of cooked legumes each day. Or closer to one and a half cups if you’re over 160 pounds. Legumes are a rich source of the essential amino acid lysine. If someone eating a highly plant-based diet is going to fall short in one of the essential amino acids, lysine is probably the one. That’s because it’s found in lower amounts in most plant foods—other than legumes, quinoa, pumpkin seeds, pistachios, and amaranth, that is.

Ryan Andrews, RD, CSCS completed his education in exercise and nutrition at the University of Northern Colorado, Kent State University, and Johns Hopkins Medicine. He’s written hundreds of articles on nutrition, exercise, and health, authored Drop The Fat Act & Live Lean, A Guide to Plant-Based Eating, and coauthored The Essentials of Sport and Exercise Nutrition Certification Manual