Investigation of the Relationship Between Live Dietary Microbe Intake and Health Outcomes, Using the Korean National Health and Nutrition Examination Survey (KNHANES)

Research has shown that the consumption of live microbes, including and beyond probiotics, is associated with health benefits. Fermented foods, such as yogurt and kimchi, are rich in live bacteria and may help to promote a healthy gut microbiome and support overall health. Consuming fermented foods may be associated with a range of health benefits, including improved digestive health, increased nutrient absorption, and a strengthened immune system. Some studies have also linked the consumption of fermented foods with a reduced risk of certain chronic diseases, such as type 2 diabetes, cardiovascular disease, and certain types of cancer. However, not all fermented foods contain the same types or amounts of live microbes, and further research is needed to delineate how the effects of live microbe intake can vary depending on individual factors such as age, gender, health status, and diet.

The study has four aims: (1) quantify live microbe intake in KNHANES); (2) identify foods that are top contributors to live microbe intake; (3) use KNHANES to investigate the potential association between live microbe intake from foods and systemic health indicators including BMI, blood lipids, HbA1c, and the Framingham 10-year risk score, and self-reported CVD diagnoses; (4) explore subgroup differences in live microbe intake from foods, such as gender, age group, and individual diet differences as represented by Korean Healthy Eating Index (KHEI) scores. The project aims are constructed around the following hypotheses:

• Live microbe intake from foods, including fermented food, is related to systemic health indicators in an age- and gender-dependent manner in the Korean population.

• Effects of live dietary microbe intake on systemic health in Korean adults vary depending on individual dietary factors such as the KHEI score.

Institution: Tufts University

Principal Investigator: Mei Chung, PhD

Year Awarded: 2023

This work is supported by the IAFNS Nutrition for Gut Health Committee

Health and Functional Effects of Dietary Protein Beyond Protein Turnover

As food systems and consumer food preferences evolve toward replacing animal protein with alternative protein sources, it is imperative to understand the long-term health consequences. This project aims to prioritize research approaches and ultimately food decisions that take into consideration evidence linking the impact of dietary protein and amino acid intakes on meaningful functional outcomes among the general adult population. Since growth is not the priority outcome among adults, it is imperative to prioritize health outcomes as well as the indicator measures that are meaningful to drive food formulation and consumer choices

Data generated from nearly three decades of highly-controlled laboratory studies evaluating the effects of dietary protein intake on isotopic measures of protein turnover serve as the basis for many contemporary dietary recommendations. For example, recommendations that advocate for equally distributing dietary protein intake across meals, how much to consume with each meal, post-exercise, and the amount necessary to overcome age-related anabolic resistance were all derived from acute tracer studies quantifying muscle protein synthesis in response to ingesting isolated intact proteins, free-form amino acids, or protein-containing foods or mixed-meals. However, studies leveraging the acute stimulatory effects of varying dietary protein manipulations on muscle protein synthesis to augment muscle mass and physical function over time have yielded mixed results (i.e., minimal to no benefit). The inability to extend findings from acute laboratory studies to long-term benefit can be attributed to costs, experimental limitations, inadequate controls, compliance, attrition, and the inherent variability in diet protein-related health outcomes such as body composition and physical function. The discrepancies between acute and long-term trials raise practical concerns that question the extent to which manipulating protein intake beyond current requirements provides tangible health benefits.

The project explores gaps related to alternative measures of how protein affects human health and what health outcomes, beyond tracer measures of protein turnover and body composition, should be the focus for new research to advance dietary protein research.


Institution: Eastern Michigan University together with additional experts from multiple institutions

Principal Investigator: John Carbone

Expert Writing Group:
John Carbone, Eastern Michigan University
Stefan Pasiakos, NIH
Connie Weaver, San Diego State University
Wayne Campbell, Purdue
Heather Leidy, Univ Texas Austin
Stu Phillips, McMaster University

Year: 2023

This work is supported by the IAFNS Protein Committee.

Understanding and Advancing Best Practices for Human Nutrition & Gut Microbiome Research


In 2017, the National Institutes of Health (NIH) collaborated with the US Department of Agriculture, Agricultural Research Service (USDA-ARS) to develop and document “Considerations for Best Practices in Studies of Fiber or Other Dietary Components and the Intestinal Microbiome” (Klurfeld et al. 2018). The primary recommendation resulting from this exchange was to “describe dietary ingredients and treatments in as much detail as possible to allow reproduction by other scientists.”

Since 2017, science around diet-gut microbiome-health relationships has continued to proliferate. While there have been several publications addressing methods for human research on diet-gut microbiome-and health, the extent to which “best practices” have been articulated in this field is not known. In addition, there are many publications focused on best practices in human nutrition research generally, but the degree to which these are applicable to gut microbiome studies versus needing additional or different guidance has not been explored.

This project aims to improve the conduct of, and alignment across, gut microbiome research. Capturing the latest knowledge regarding best practices and “suggested” practices based on researcher experience and encouraging implementation would support the harmonization of research and improve the ability to compare studies and conduct meta-analyses to address key questions. This project starts with an umbrella review of published guidance to identify gaps. These gaps will then be addressed by an appropriate mechanism to understand and convey the state of knowledge on optimal research designs and methods in this field.

Expert Group:

Chris Cifelli, PhD, National Dairy Council
Cindy Davis, PhD, USDA-ARS
Tatiana Diacova, MS RD, UC Davis
Hannah Holscher, PhD RD, University of Illinois at Urbana-Champaign
Mary Kable, PhD, UC Davis and USDA-ARS
Philip Karl, PhD, RD, USARIEM
Johanna Lampe, PhD RD, Fred Hutch Cancer Center
Kelly Swanson, PhD, University of Illinois at Urbana-Champaign

Year: 2023

View this project on the Center for Open Science’s Open Science Framework.

This work is supported by the IAFNS Gut Microbiome Committee.

Fat Intake Modifies the Association between Restricted Carbohydrate Diets and Prevalent Cardiometabolic Diseases among Adults in the United States: National Health and Nutrition Examination Survey, 1999–2018

Sample Collection, Preservation, and Data Analysis in Gut Microbiome Research: Current Methods and Potential Impact on Results

The development of dietary guidance relies upon the ability to synthesize a body of evidence and arrive at a reasonably well-supported conclusion. Although publications have purported to identify characteristics of a “healthy gut microbiome”, the one certainty at present is that gut microbiome is highly variable across individuals. In addition, the reality is that gut microbiome research still requires method advancement and refinement. Continuing to improve methods, and working toward alignment across laboratories will move all closer to understanding how diet can impact health at the point of the gut microbiome. In a virtual workshop held on October 13, 2022, the current state of knowledge related to sample collection, utility of standards, sequencing, and bioinformatic and biostatistical approaches was reviewed by experts working in the field. Speakers expanded on how selection among the various methodological options can impact study results. This project includes generating a summary of these discussions will be prepared for submission to a peer-reviewed journal.

Scientific Editor: Riley Hughes, PhD, Independent Scientist

Amount: $3,000

Year: 2022

This work was supported by the IAFNS Gut Microbiome.

Understanding the Opportunities and Challenges to Sodium Reduction in Food Service and Key Strategies to Foster Progress

The objective of this project is to document the outcomes of a dialogue with leaders from the food service sector, government, and academia to understand the challenges and opportunities related to sodium reduction in the food service sector. This work related to the dynamics, initiatives, and challenges in the food service sector will help identify and communicate opportunities to foster progress with sodium reduction, inform public health initiatives around sodium and to track progress over time.

Scientific Editor: Paula Trumbo PhD, Liberty University, Lynchburg VA

Year: 2022

Read more:

Food Service Sector Sodium Dialogue

Perspective: Challenges and Strategies to Reduce the Sodium Content of Foods by the Food Service Industry

This work was supported by the IAFNS Sodium Committee.

Quality of Popular Diet Patterns in the United States: Evaluating the Effect of Substitutions for Foods High in Added Sugar, Sodium, Saturated Fat and Refined Grains

Reconciliation of Differences between Observational Studies and Randomized Controlled Trials: A Case Study on Low Calorie Sweeteners

Scientific evidence is commonly categorized into levels based on quality of evidence, commonly referred to as the hierarchy of evidence. The complexity of evaluating study quality based on study design becomes problematic for dietary exposures and health outcomes with conflicting evidence observed in observational studies and RCTs. Such conflicting evidence is well documented for low calorie sweeteners (LCS), in which observational trials tend to identify adverse associations between LCS use and adiposity, type 2 diabetes (T2D), mortality, cardiovascular disease (CVD), and cancer while RCTs highlight benefits or no effect of LCS on body weight, energy intake, markers of T2D, and markers of CVD (6). One possible explanation for this is that observational trials and RCT are simply addressing different research questions, evaluating different exposures, comparators, and outcomes.

The objective of the proposed project is to educate stakeholders on how to interpret contrasting evidence from observational studies and RCTs based on methodological differences between study designs, using LCS as a case-study. A rapid review of systematic reviews and metaanalyses on LCS and various health outcomes will be conducted to highlight how different intervention/exposures, comparators, outcomes, and study designs produce varying conclusions regarding the efficacy and safety of LCS. The deliverables of this project will be a peer-reviewed publication and presentation of findings at a conference for nutrition and dietetics practitioners

Institution: USDA Agricultural Research Service

Principal Investigator: Kelly Higgins, MPH PhD; David Baer, PhD

Year: 2022

This work was supported by the IAFNS Low- and No-Calorie Sweeteners Committee.