A study conducted by researchers has found that two ounce-equivalents (oz-eq) of protein from animal sources have greater essential amino acids (EAA) bioavailability compared to an identical quantity of plant-based protein. This research contradicts the existing Dietary Guidelines for Americans (DGAs), which propose that these protein sources are nutritionally similar.
When individuals consume equal ounce-equivalent portions of both animal and plant proteins as recommended by the DGAs, they experience differing levels of essential amino acid bioavailability, regardless of their age group.
According to scientists at Purdue University, two-ounce-equivalents of protein derived from animal foods provide higher bioavailability of EAAs than the same amount from plant sources.
The content of essential amino acids in a meal, known as protein quality, plays a crucial role in how the body utilizes amino acids for overall protein construction and muscle growth.
The DGAs stress the importance of consuming various protein foods, taking into consideration ounce-equivalent portions with seemingly comparable nutritional values. For instance, one oz-eq can equal one ounce of meat, a single egg, a quarter cup of beans, or half an ounce of nuts.
Dr. Wayne Campbell, the lead researcher of the study at Purdue University, questioned the DGAs’ claim that these protein foods are ‘equivalent’ and possess ‘similar nutritional content’, calling the basis of this assertion unclear.
He pointed out differences in energy, nutrient content, protein quantity, and quality among various protein foods. Additionally, he noted a lack of detailed information about how consuming different protein sources as part of mixed meals affects protein digestion and utilization.
The table below presents the energy, fat, carbohydrate, protein, and EAA content of the test meal and various protein sources:
| Energy (kcal) | Fat (g) | Carbohydrate (g) | Protein (g) | EAA (g) |
|---|---|---|---|---|
| Test meal | 218 | 11.5 | 25.8 | 6.2 |
| Lean pork loin (2 oz-eq) | 73 | 1 | 0 | 7.3 |
| Whole eggs (2 oz-eq) | 145 | 10 | 0 | 12.5 |
| Black beans (2 oz-eq) | 113 | 0.5 | 20 | 7.5 |
| Almonds (2 oz-eq) | 161 | 14 | 6 | 6 |
(Source: Connolly et al., 2023)
Younger adults, who might have limited protein variety, and older adults, who might not consume enough high-quality protein, could be particularly affected.
In response, the researchers conducted two randomized controlled cross-over trials on young and older adults to examine how two oz-eq portions of animal and plant proteins affected EAA bioavailability in a mixed meal.
The study included 30 young and 25 older adults, and blood samples were taken to analyze EAA bioavailability and other factors.
The results showed that animal-based protein foods, such as lean pork loin and eggs, led to a higher presence of EAAs in the bloodstream compared to plant-based sources like black beans and almonds, regardless of the participant’s age.
Dr. Gavin Connolly, project manager for the clinical trials, stressed the significance of these findings in relation to muscle and overall body health throughout an individual’s life.
Additional discoveries included higher EAA bioavailability from lean pork compared to eggs, no EAA bioavailability differences between black beans and almonds, and no age-related differences.
The study had limitations, including possibly unreflective portion sizes and the absence of direct measurement of muscle protein synthesis or whole-body protein balance.
More research is needed to further explore the impact of animal and plant proteins on overall health across various life stages.
Public health nutrition implications:
The authors believe the study’s findings could influence public health nutrition guidelines and urge future DGAs to reassess the practice of equating different protein sources on an oz-eq basis throughout the lifespan.
Dr. Campbell emphasized that, while increasing plant-based food intake has its benefits, the importance of nutrient-dense animal proteins as high-quality sources must also be considered in dietary recommendations.
This study was sponsored by the National Pork Board and the American Egg Board—Egg Nutrition Center.
References are available from publications including Nutrients, Clinical Nutrition, The Journal of Nutrition, and other cited works, dated from 2020 to 2023.
Table of Contents
Frequently Asked Questions (FAQs) about protein bioavailability
What did the study discover about the nutritional equivalence of animal and plant proteins?
The study found that two ounce-equivalents of animal-based protein foods provide greater essential amino acids (EAA) bioavailability than the same quantity of plant-based protein foods. This discovery challenges the existing Dietary Guidelines for Americans, which propose that these protein sources are nutritionally equivalent.
How does the protein quality affect the body’s utilization of amino acids?
The protein quality of a food, which refers to the essential amino acid content, is a significant factor in determining how the body can use amino acids for muscle and whole-body protein building. Higher quality proteins offer more effective utilization of amino acids.
Were there any differences in EAA bioavailability between different types of animal or plant-based proteins?
Yes, the study found that lean pork resulted in greater EAA bioavailability than eggs among animal proteins. However, there were no observed differences in EAA bioavailability between black beans and almonds among plant-based proteins.
What were the implications of this study on public health nutrition?
The findings of this study may have implications for public health nutrition guidance and could lead to a reevaluation of the appropriateness of equating different protein sources in the Dietary Guidelines for Americans. The results highlight the importance of considering nutrient-dense animal-based protein foods when providing dietary recommendations.
What were the limitations of the study?
The study’s limitations included the portion sizes of the protein foods possibly not reflecting actual consumption patterns and the lack of direct measures of changes in muscle protein synthesis or whole-body protein balance. More research is needed to understand the effects of animal versus plant-based protein foods on muscle and whole-body health across the lifespan.
Who funded the research?
The research was funded by the National Pork Board and the American Egg Board—Egg Nutrition Center.
More about protein bioavailability
- Effects of Consuming Ounce-Equivalent Portions of Animal- vs. Plant-Based Protein Foods
- Quality of meal protein determines anabolic response in older adults
- Metabolic Evaluation of the Dietary Guidelines’ Ounce Equivalents of Protein Food Sources in Young Adults
- Essential Amino Acids and Protein Synthesis: Insights into Maximizing the Muscle and Whole-Body Response to Feeding
6 comments
This study is quite the eye-opener! Finally, some hard data to back up what I’ve suspected all along. But the question is, how will this change the dietary guidelines?
The funding’s from the National Pork Board and the Egg Nutrition Center? Seems a bit biased maybe… But the results are interesting nonetheless!
Lean pork vs eggs, didn’t see that coming. Wonder if other meats were tested. Could really change the way I look at my protein sources.
i always knew animal proteins were better. It’s all about getting the right nutrients. This study just confirms it, right.
What about the environmental impacts? This might be good 4 human health, but what about our planet? Think we need to balance both.
So confusing! One day, they say one thing, the nxt they say another. How are we supposed to know what’s best for us?