Balancing diets: study reveals plant protein's impact on nutrient levels in Americans

By Pooja Toshniwal PahariaReviewed by Susha Cheriyedath, M.Sc.Apr 15 2024

In a recent study published in the journal Nutrients, researchers explored the impact of increasing dietary plant protein quartiles on nutritional adequacy in the United States (U.S.).

Dietary proteins, particularly amino acids, are critical to human health and lifespan. Plant-based diets, including legumes, seeds, nuts, and cereal grains, have gained public interest for health and environmental reasons. Animal-based protein sources, such as meat and dairy, include vital elements. However, a recent study indicated that increasing plant protein intake may reduce dietary protein amount and quality, emphasizing the need for balanced diets.

Study: Impact of Plant Protein Intakes on Nutrient Adequacy in the US. Image Credit: nnattalli / Shutterstock

About the study

In the present cross-sectional study, researchers investigated the influence of increasing plant-based protein on nutritional adequacy among American children and adults.

To analyze nutrient intakes, the researchers collected food and nutrient dietary recall information from 19,493 individuals aged nine years through What We Eat in America (WWEIA), the dietary component of the National Health and Nutrition Examination Surveys (NHANES) conducted between 2013 and 2018. Study participants were aged 9 to 18 years (n=4,605, 51% male), 19 to 50 years (n=7,617, 52% male), and above 51 years (n=7,271, 47% male), except pregnant and lactating females and those with no calorie consumption.

The team determined nutritional adequacy by calculating the proportion of U.S. residents with nutrient intakes that were less than the estimated average requirement (EAR) or more than the adequate intake (A.I.) and then assessing quartile trends using regressions and specified level numbers. They used the United States Department of Agriculture's (USDA) Food and Nutrient Database for Dietary Studies (FNDDS), unique to the NHANES cycle, to calculate energy and nutrient intakes.

The researchers used the Food Patterns Equivalents Database (FPED) to calculate the composition of the food group for the meals and drinks consumed. They used the National Cancer Institute (NCI) technique to establish individual usual intakes (IUI) of plant-based protein and divided the participants into quartiles based on their IUI. The total protein consumption from non-animal FPED components (vegetables, fruit, soybeans, grains, seeds, nuts, peas, and beans) represented plant protein intake.

Results

As plant protein quartiles rose, adolescents' sufficiency for vitamin D, potassium, and calcium dropped, but magnesium and copper increased. With increasing quartiles of plant protein, adequacy declined for choline, protein, zinc, vitamin B12, and selenium while increasing for folate, copper, magnesium, thiamine, vitamin C, and iron in individuals aged 19 to 50. Calcium, zinc, and vitamin A adequacy dropped, but magnesium, folate, copper, vitamin C, and thiamine adequacy increased as plant protein quartiles climbed in individuals aged >51.0 years.

Teenagers consumed 72 g of protein daily, with 36% originating from plant sources. As plant protein consumption grew, the proportion of individuals living below the estimated average requirement Increased for vitamin D and calcium while dropping for magnesium and copper. The percentage of individuals above the adequate intake rose for sodium while decreasing for potassium. Niacin, zinc, selenium, vitamin B6, vitamin B12, and vitamin D had the lowest percentages. Nutrient adequacy was best when plant protein consumption was below 50% (DFL 1 and 2) or between 50% and ≥75% (DFL 3 to 4).

Adults aged below 50 years consumed an average of 86 grams of protein per day, with plant sources accounting for 35%. Certain nutrients increase with plant protein consumption, whereas others decrease. In the first quartile, choline is the most abundant protein source, whereas selenium, vitamin B12, vitamin B6, vitamin D, and zinc are in short supply. Choline has the highest proportion in the first quartile, followed by fiber, vitamin K, potassium, and sodium in the fourth quartile. The lowest percentages are reported in DFL 2, whereas plant protein consumption ranges from 25% to 36% in DFL 4.

The typical protein consumption for adults above 51.0 years was 79 grams daily, with 36% from plant-based sources. The proportion of individuals below the estimated average requirement grew considerably for calcium, vitamin A, and zinc while dropping for copper, folate, vitamin C, magnesium, and thiamine. Vitamin A, calcium, vitamin B6, vitamin B12, zinc, and vitamin D were found at the first quartile (<29% plant protein), selenium at the second quartile (29% to <33% plant protein), riboflavin, niacin, and thiamine at the third quartile (33% to <37% plant protein), and folate, magnesium, copper, vitamin C, vitamin E, and iron at the fourth quartile (>37%) of plant-based protein consumption. The team noted the highest choline, sodium, vitamin K, potassium, and fiber percentages in the fourth quartile.

The study found that diets rich in animal and plant sources, with plant protein at the 50th percentile of current consumption, are nutritionally optimal for Americans. The population's dietary adequacy altered with increased plant protein consumption. Calcium, choline, niacin, riboflavin, selenium, vitamin A, vitamin B12, vitamin B6, vitamin D, and zinc had the lowest percentages below the Early Age Ratio in the first and second quartiles, while fiber, copper, folate, iron, magnesium, thiamin, vitamin C, and vitamin E were in the third and fourth quartiles, respectively.