Answering the Protein Question When Prescribing Plant-based Diets

Cate Collings, MD


September 02, 2022

Cate Collings, MD

Science supports the use of a whole food, predominantly plant-based dietary pattern for optimal health, including reduced risk for chronic disease, and best practice in treatment of leading chronic disease. But clinicians who prescribe such eating patterns encounter a common concern from patients whose health may benefit.

"Where will I get my protein?"

We've all heard it, and it's understandable. Patients know that protein is essential for their health and strength, and animal foods have developed a reputation for being the premier protein sources that humans should prioritize through diet. But widespread misconceptions about human needs for protein have inaccurately equated animal food as the best and only sources of protein, augmented by fad diets and modern food marketing. All of this leads to confusion about how much protein people should actually consume and the quality of protein found in plant foods, making many patients reluctant to fully embrace a whole food, predominately plant-based diet.

To ensure that patients have all the facts when making dietary decisions, clinicians need to be prepared to respond to concerns about protein adequacy and quality with evidence-based information. A good starting point for these conversations is to assess how much protein patients are already consuming. A review of the 2015-2016 National Health and Nutrition Examination Survey found that women normally consume an average of 69 g and men an average of 97 g of protein daily.

As a general point of reference, the recommended dietary allowance for protein is about 0.8 g/kg of bodyweight (or 0.36 g/lb), which equates to about 52 g of protein per day for a 145-lb woman and 65 g for a 180-lb man. But for many patients, it may be best to get a more precise recommendation based upon age, gender and physical activity level by using a handy Department of Agriculture tool for healthcare professionals to calculate daily protein and other nutrient needs. Patients can also use one of countless apps to track their protein and other nutrient intake. By using the tool and a tracking app, both clinician and patients can be fully informed whether protein needs are being met.

The recommended daily allowances for protein are easily met by consuming a variety of whole plant foods, including a variety of minimally processed vegetables, fruits, whole grains, legumes, nuts, and seeds. One cup of cooked red lentils or black beans, for example, contains between 15 g and 18 g of protein. A quarter cup of almonds contains about 7 g of protein and one cup of cooked oats has 5 g.

What About Those Amino Acids?

An area of contention around plant food protein is "complete vs incomplete protein," terms used to describe whether a protein contains all nine essential amino acids that our bodies require from a single source. Animal food sources usually contain all the essential amino acids, whereas plant sources of protein may contain varying amounts of these amino acids or may even be missing some.

This leads to a misconception that someone adopting a diet of predominately plant food may have to stack or combine specific plant foods in a meal to ensure their protein intake includes an appropriate proportion of amino acids. But the process of protein breakdown turnover solves this problem. The body continuously breaks down protein and recombines it with amino acids stored in tissue for use when needed. Once absorbed by the small intestine, it doesn't matter whether the protein or amino acids came from the same meal. As long as a person is eating a variety of plant-based protein sources, they will consume adequate amounts of all essential amino acids.

This is true even for athletes, older adults and pregnant women. It is also the position of the Academy of Nutrition and Dietetics that a whole-food, predominately plant-based eating pattern is appropriate for athletes and "all stages of the life cycle, including pregnancy, lactation, infancy, childhood, adolescence, older adulthood."

The Plant-based Diet

For examples of healthy plant-based eating plans, The American College of Lifestyle Medicine (ACLM) offers a complimentary guide for a whole food, predominantly plant-based diet that demonstrates how easily the recommended dietary allowance of protein is satisfied. A breakfast of rolled oats, a lunch of bean burritos, and a dinner of mashed potatoes, with chickpeas with a couple snacks throughout the day, adds up to 71 g of protein. Other plant-based meal plans top 100 g or 90 g, with all meal plans meeting or surpassing recommended allowances.

Along with the protein, plant food delivers other beneficial nutrients and dietary components like fiber, antioxidants, anti-inflammatory properties, various vitamins and nutrients, and phytochemicals and vitamin D, without the saturated fats and sodium in meat. But US adults get approximately two thirds of their protein from animal sources, which lack fiber and have higher levels of saturated fats or sodium that can raise cholesterol and increase the risks for heart disease and stroke.

For clinicians, ACLM published a 10-part series of research white papers on the benefits of a whole food, plant-predominant dietary lifestyle and offers a catalogue of food as medicine continuing medical education and continuing education courses.

Patients hunger for knowledge about health-promoting nutrition but may have difficulty sorting myths from evidence-based facts. Each healthcare professional has an important and powerful opportunity to steer patients in a healthier direction through their diet.

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