Dietary Protein Consumption

Originally Published: December 3, 2019
Last Updated: February 4, 2021

COMMON MYTHS REGARDING dietary protein were a key focus of the presentation, titled “New News About Protein: How Much is Too Much…and Not Enough,” provided by Steve Hertzler, Ph.D., RD, Sr. Scientist, Clinical Research, Abbott Nutrition.

“Can protein give you energy?” questioned Hertzler. “Yes, theoretically! But this is not preferred and occurs only to a limited extent, as amino acids are not the ideal source to burn for energy.” This is because excretion products of protein oxidation, such ammonia and urea, can potentially be toxic to the body.

Hertzler noted that the current Recommended Dietary Allowance for protein is 0.8g protein/kg of body weight per day. “The RDA is the amount sufficient to meet the nutrient requirements of nearly all healthy individuals in a particular life stage and gender group,” he noted. RDAs are based on nitrogen balance studies; however, these studies are difficult to perform and interpret correctly.

Indicator Amino Acid Oxidation (IAAO) is a “newer method in which humans are fed different amounts of IAA (typically an isotopically labeled amino acid such as 13C-phenylalanine). The 13C comes out of the body as 13CO2 when the amino acid is oxidized and can be quantified in expired breath samples,” stated Hertzler. The IAAO method removes some of the limitations that have been associated with older nitrogen balance studies.

The theoretical basis underpinning the IAAO method is that, at low protein intakes, essential amino acid (EAA) intake is insufficient to support protein synthesis, and IAAO will be high. As protein/EAA intake increases toward requirements, protein synthesis improves, and IAAO falls.

“At breakpoint,” Hertzler explained, “IAAO reaches its lowest point, and further increases in protein intake do not alter it. This breakpoint is referred to as the estimated average requirement (EAR). A margin of safety is added (typically 2 standard deviations above the EAR), and that protein intake number becomes the proposed RDA.”

Data from ten IAAO human studies indicate an EAR higher than the present RDA. (See chart “IAAO Studies to Estimate Human Protein Requirement.”) “This is important,” stressed Hertzler, “because, for non-exercising adults of all ages, the protein RDA (1.15-1.30g/kg/d) is around 50% higher than the present RDA.” For athletes, the present RDA is two-three times lower than the proposed RDAs derived from more recent IAAO studies, which range from 1.7-2.6g/kg/d.

Expert groups are recommending increases in protein intake. For example, this would include, for healthy older people or those who are (or at risk of) malnutrition, at least 1.0-1.2g and 1.2-1.5g protein/kg BW/d, respectively. (Deutz NEP et al. Clin Nutr 2014. Hertzler stressed that nearly all new evidence points to benefits of protein intakes higher than current RDA, yet no specific changes are being implemented to current RDAs. Data from “National Health and Nutrition Examination Survey” (NHANES) 2011-2014 showed that 31-50% of older populations consume below the protein RDA (which may already be too low), as expressed on an actual BW (not ideal BW) basis. (Krok-Schoen JL et al. J Nutr Health Aging 2019/

There appears to be a benefit for older people to consume higher protein intakes. Intakes of 1.5 vs. 0.8 g/kg/day protein resulted in muscle mass more than doubling in arms and legs in frail elderly subjects. Indices relating arm and leg muscle mass to BW, BMI and body fat all significantly improved, as did gait speed. (Oikawa SY et al. Am J Clin Nutr 2018/

Hertzler emphasized that it is very difficult to consume “too much protein.” High-protein diets within the U.S. Institute of Medicine’s Acceptable Macronutrient Distribution Range (AMDR) of 10-35% of energy (and up to two-three times the RDA) pose no direct safety concern. “However, the key proviso is that a person has healthy liver and kidney function to start.” (Antonio J et al. J Nutr Metab 2016/

High-protein diets are unlikely to have an adverse effect on bone health and may have positive effects. Indirect risks of high-protein diets have less to do with the protein and more to do with other dietary factors that may do harm, such as saturated fat or low fiber. “My main concern is with protein crowding out other healthy foods,” stated Hertzler. Many high-protein foods are low in carbohydrate and fiber, yet many healthy high-carbohydrate foods are low in protein.

He noted, “Plant-based proteins, as part of your overall protein mix, are a great way to get protein, as well as a lot of other beneficial nutrients.”

Hertzler concluded that current research suggests protein recommendations, such as the RDA, may be too low to promote optimal health and function, especially as people get older. Proper distribution of protein intake may be helpful as well.

“New News About Protein: How Much is Too Much…and Not Enough,” Steve Hertzler, Ph.D., RD, Senior Scientist, Clinical Research, Nutrition Science & Innovation, Global Scientific and Medical Affairs, Abbott Nutrition

This presentation was given at the 2019 Protein Trends & Technologies Seminar. To download presentations from this event, go to

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