Location: Food Components and Health Laboratory
2025 Annual Report
Objectives
Objective 1: Elucidate the impact of differential bioavailability of dietary bioactive components, such as isothiocyanates and polyphenols, in predicting inter-individual response to dietary intake.
Sub-objective 1.A: Determine the role of differential bioavailability of berry flavonoids (proportion absorbed via the small intestine vs. proportion reaching the colon) in influencing glycemic response and gut microbiota metabolism.
Sub-objective 1.B: Determine the role of differential bioavailability (proportion absorbed via the small intestine vs. proportion reaching the colon) of phenolic compounds from a mix of polyphenol-rich foods in influencing glycemic response and gut microbiota metabolism.
Sub-objective 1.C: Determine the importance of isothiocyanate bioavailability on influencing xenobiotic metabolism via glutathione-S-transferase concentration and activity.
Objective 2: Elucidate the impact of differential digestibility of dietary macronutrients, such as fat and carbohydrate, in predicting inter-individual response to dietary intake.
Sub-objective 2.A: Determine the role of differential digestibility of fat from tree nuts in determining blood lipid response and gut microbiota metabolism.
Sub-objective 2.B: Determine the role of differential digestibility of carbohydrate from pulses (chickpeas and lentils) in determining blood lipid response and gut microbiota metabolism.
Approach
The nutrition community increasingly recognizes that a single set of dietary guidelines does not provide optimal health benefits to all individuals. Factors such as genotype, phenotype, efficiency in digestion and nutrient absorption, rates of metabolic pathways, gut microbiota, and other characteristics affect an individual’s response to diet. However, data to create predictive algorithms to prescribe targeted dietary recommendations are not yet sufficient. By combining data from our previous human feeding studies with new analyses utilizing novel analytical approaches, we will strengthen the evidence for predicting how certain individual characteristics may influence response to dietary interventions.
Progress Report
In support of Sub-objective 1A, two fully controlled diets were provided to 29 research volunteers in a two-period crossover study. The background diet was identical for both feeding periods and was free of anthocyanins (blue and purple plant pigments). This background diet was augmented with either 600 grams of blackberries daily or berry-flavored gelatin. Participants underwent a pharmacokinetic challenge of 300 grams of blackberries, followed by a collection of serial blood and urine at the end of each feeding period. Blood samples were analyzed for glucose and insulin, and fecal samples were analyzed for bacterial metagenomics. These data are being analyzed to determine if higher bioavailability of berry flavonoids (previously measured in these blackberries) is positively associated with improved control of blood glucose.
In support of Sub-objective 1B, a 10-week dietary intervention was completed with 28 volunteers of normal weight, overweight, and obese status to determine the effect of weight status on the bioavailability of polyphenols. These volunteers consumed a controlled diet that included berries, apples, and tea to provide a range of healthful compounds called polyphenols. There was a varied response across weight status for thirteen different polyphenol forms in blood and urine, and eight different phenolic metabolites in urine. To further investigate individual response, secondary bile acids were measured to determine if the higher bioavailability of phenolic compounds from polyphenol-rich foods is inversely associated with the formation of secondary bile acids. These secondary bile acids and weight status are putatively associated with the risk of certain cancers. Thus, secondary bile acid concentration may provide mechanistic insights into the association between cancer risk and weight status. The bile acid analyses were completed using a UPLC (ultra-high pressure liquid chromatography) tandem mass spectrometric method. The data have been analyzed to look for associations between weight status and secondary bile acid concentration.
Finally, in support of Sub-objective 1C, analyses of plasma and urine appearance of isothiocyanates are completed, and analyses are underway for xenobiotic (foreign compound) metabolism, specifically focusing on glutathione-S-transferase concentration and activity. This dataset is being developed to determine the importance of isothiocyanate bioavailability in influencing xenobiotic metabolism.
Accomplishments
1. Habitual oat and barley consumption reduces the risk of heart disease. Soluble fiber, found mostly in oats and barley, is particularly effective in improving blood cholesterol, a key risk factor for heart disease. ARS researchers in Beltsville, Maryland, conducted a dietary intervention study to compare the effects of diets containing whole grain oats, whole grain barley, and refined wheat (which is low in soluble fiber) on risk factors of heart disease. Oats were more effective for improving blood lipids, while barley was more effective for improving blood pressure. These results help food industry scientists develop more healthful whole-grain products and provide policymakers with science-based evidence to improve dietary recommendations for consumers.
2. Processed meat consumption does not increase the risk of heart disease. The extended shelf-life and ease of preparation of processed meats provide Americans with a convenient way to consume high-quality protein and important meat-associated nutrients. However, processed meats are thought to be less healthful than freshly cooked meats, despite the lack of clinical evidence. ARS researchers at Beltsville, Maryland, conducted a dietary intervention study in which research volunteers consumed four combinations of processed and unprocessed meats together with a typical American dietary pattern or a healthful dietary pattern that meets the Dietary Guidelines for Americans. The type of meat (processed or unprocessed) had little effect on the risk of heart disease. On the other hand, a healthful dietary pattern reduced heart disease risk factors compared to a typical American dietary pattern. The results of this study provide a scientific basis for making appropriate recommendations for what consumers can do to reduce their risk of heart disease.