Purdue University Graduate School
The Effects of Dietary Protein on Postprandial Essential Amino Acids Bioavailability as a Substrate for Protein Anabolism in Young and Older Adults and on Cardiometabolic Health-Related Outcomes_Connolly.pdf (3.07 MB)


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posted on 2023-04-29, 09:20 authored by Gavin ConnollyGavin Connolly

Diet is the number one leading modifiable cause of poor health globally, with poor diets accounting for 10.9 million (22%) of all deaths among adults in 2017. In addition, one of our generation’s forthcoming challenges is the rapid expansion of the population aged 60 years and older. Although people are living longer, there is an associated increase in the prevalence of aged-related chronic diseases and functional impairment, such as cardiometabolic diseases and sarcopenia. As such, dietary components can play a role in positively or negatively influencing the prevention and treatment of chronic cardiometabolic diseases and sarcopenia. One such dietary component is dietary protein, which is essential throughout the life course, from gestation through old age. Evidence supports dietary protein playing an important role in reducing the risk of developing age-related chronic diseases such as sarcopenia and cardiometabolic diseases. 

     Study 1, Chapter 2: The Dietary Guidelines for Americans (DGA) recommends consuming a variety of “Protein Foods” based on “ounce equivalent” (oz-eq) portions. In addition, the 2020-2030 Strategic Plan for NIH Nutrition Research includes to “define the role of nutrition across the lifespan” with an objective to “assess the role of nutrition in older adults to promote healthy aging.” However, there is a paucity of primary research that directly compares EAAs bioavailability between young and older adults consuming the same oz-eq portions of varied Protein Foods. No study has assessed the same oz-eq portions of animal- versus plant-based Protein Foods on essential amino acids (EAAs) bioavailability for protein anabolism in young and older adults. Therefore, we conducted two sequential randomized, investigator-blinded, crossover, acute feeding trials with the same study design; first in a cohort of young adults and second in a cohort of older adults. The primary objective of this project was to assess the effect of consuming two oz-eq portions of animal-based (unprocessed lean pork or whole eggs) vs. plant-based (black beans or sliced almonds) Protein Foods as part of a mixed whole foods meal on plasma EAAs bioavailability for protein anabolism. Consistent with our hypotheses, participant age did not affect postprandial EAAs bioavailability, and consuming a meal with two oz-eq of unprocessed lean pork or whole eggs resulted in greater postprandial EAAs bioavailability compared to a meal with two oz-eq of black beans or raw sliced almonds in 1) young adults; 2) older adults; and 3) young and older adults combined. These findings show on the same oz-eq basis, consuming these animal- vs. plant-based Protein Foods more effectively provide bioavailable EAAs for protein anabolism. 

     Study 2, Chapter 3: Poultry meat is the most consumed type of meat worldwide and in the US. Poultry is generally considered to be a “healthy” meat as it is a high-quality protein source and provides other essential nutrients. However, research assessing poultry and its effects on and relations with chronic diseases in humans is sparse, and the forms of poultry typically consumed in the US, are not necessarily in line with recommendations provided by the DGA. Therefore, we conducted a scoping review to systematically search and chronicle scientific literature pertinent to poultry intake and human health. Main findings from this project were 1) historically, little research, especially randomized diet-controlled feeding trials, has been conducted to understand associations between and effects of consuming poultry products on human health; 2) the majority of research is from observational studies assessing relationships between poultry intake and risks of morbidity and mortality from various types of cancer; 3) a paucity of research exists to support chicken as a health-promoting food in children; and 4) research taking into account poultry product processing and cooking methods is needed. Science and health professionals, the poultry industry, and the public will benefit from new observational and experimental research to address cutting-edge scientific, public policy, and consumer topics pertinent to poultry intake and human health. 

     Study 3, Chapter 4: Emerging research on whey protein supplementation suggests it may be a potential modifier of type 2 diabetes mellitus (T2DM) risk factors, including glucose control. As systematic reviews and/or meta-analyses of randomized controlled trials are gaining importance in nutrition literature, we conducted an umbrella systematic review to search for and chronicle published systematic reviews and/or meta-analyses of randomized controlled trials pertinent to whey protein supplementation and T2DM modifiable risk factors (study 3, Chapter 4). Among the 13 systematic reviews, including 12 meta-analyses critically assessed for this umbrella review, no reviews reported any adverse effects of whey protein on any reported T2DM-related risk factor. Collectively, a preponderance of evidence indicates whey protein supplementation improves multiple clinical indicators of glucose control in apparently healthy adults and those at increased risk for type 2 diabetes mellitus. 


Degree Type

  • Doctor of Philosophy


  • Nutrition Science

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

Wayne W. Campbell, PhD

Additional Committee Member 2

Brendan Egan, PhD

Additional Committee Member 3

Chad C. Carroll, PhD

Additional Committee Member 4

Gregory C. Henderson, PhD

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