Identification of carbohydrate gene clusters obtained from in vitro fermentations as predictive biomarkers of prebiotic responses.

BACKGROUND: Prebiotic fibers are non-digestible substrates that modulate the gut microbiome by promoting expansion of microbes having the genetic and physiological potential to utilize those molecules. Although several prebiotic substrates have been consistently shown to provide health benefits in human clinical trials, responder and non-responder phenotypes are often reported. These observations had led to interest in identifying, a priori, prebiotic responders and non-responders as a basis for personalized nutrition. In this study, we conducted in vitro fecal enrichments and applied shotgun metagenomics and machine learning tools to identify microbial gene signatures from adult subjects that could be used to predict prebiotic responders and non-responders. RESULTS: Using short chain fatty acids as a targeted response, we identified genetic features, consisting of carbohydrate active enzymes, transcription factors and sugar transporters, from metagenomic sequencing of in vitro fermentations for three prebiotic substrates: xylooligosacharides, fructooligosacharides, and inulin. A machine learning approach was then used to select substrate-specific gene signatures as predictive features. These features were found to be predictive for XOS responders with respect to SCFA production in an in vivo trial. CONCLUSIONS: Our results confirm the bifidogenic effect of commonly used prebiotic substrates along with inter-individual microbial responses towards these substrates. We successfully trained classifiers for the prediction of prebiotic responders towards XOS and inulin with robust accuracy (≥ AUC 0.9) and demonstrated its utility in a human feeding trial. Overall, the findings from this study highlight the practical implementation of pre-intervention targeted profiling of individual microbiomes to stratify responders and non-responders.

Comparing the impact of simple and educational point-of-decision messages on nutritional choice outcomes.

Emerging evidence suggests that point-of-decision messages may be an effective way to promote healthy food choices. Previous studies show improvements in overall nutritional quality, as well as increases in underconsumed food categories, such as fruits and vegetables, and underconsumed nutrients of public health concern, like dietary fiber. However, there have been multiple approaches used for delivering point-of-decision messages, including very brief messages that remind individuals to consider health during choice, as well as longer messages providing educational information about health benefits. While both approaches have demonstrated positive impacts on outcomes, there is no comparative evidence of the messages' effectiveness. In this study, we examine the impact of four messages on two nutritional attributes of cereals selected in a two-round pre- and post-message breakfast cereal choice exercise with numerous (n = 33) breakfast cereals available. Data were collected via an online survey of adult US residents recruited from the Prolific consumer panel. Three of the messages were simple reminder messages (taste, health, fiber), while there was additionally a longer fiber-focused messaging detailing the health benefits of fiber. Findings show that the simple messages outperformed the longer educational message, though there were some trade-offs between general health and fiber messages. The simple dietary fiber-focused message resulted in significantly higher dietary fiber content in cereals chosen than in any other messaging condition, while the general health message did not result in significantly higher measures of nutritional quality than the simple fiber message. The results of the study suggest that simpler messages may be more effective at increasing the nutritional quality of food choices. Additionally, messages focused on specific nutrients lead to significantly greater increases in the content of those nutrients.

Consideration of nutrients of public health concern highlighted in the Dietary Guidelines for Americans 2020-2025 among a large sample of US primary shoppers.

The objective of this research is to estimate the proportion of consumers who consider nutrients identified in the Dietary Guidelines for Americans 2020-2025 (DGA) as being of public health concern during food choice using a large, population-weighted sample of U.S. residents. A question was included in a bi-monthly survey of consumer scanner panel members, asking whether respondents considered each of eight nutrients in a check-all-that-apply format. Four of these nutrients are under-consumed nutrients, while three are nutrients to avoid. Calories was additionally included, as over-consumption of calories causes weight gain. Weighted mean proportions and 95% confidence intervals were estimated. The survey was administered to a population-weighted sample of 42,018 US consumers participating in a consumer scanner panel in May-June 2021 by an online survey firm that maintains the consumer panel. Over one-quarter of respondents considered none of the nutrients. Each under-consumed nutrient of public health concern was considered by less than 30% of respondents, ranging from a low of 14.5% for potassium (95%CI = 14.3-14.7%) to a high of 28.9% for dietary fiber (95%CI = 28.7-29.1%). Nutrients to be avoided were considered by higher percentages of the sample, ranging from 31.8% for saturated fats (95%CI = 31.6-32.0%) to 46.1% for added sugars (95%CI = 45.8-46.3%). Respondents considered an average of just over 2.4 total nutrients, with a greater focus on nutrients to avoid, including calories (weighted mean = 1.55), than under-consumed nutrients (weighted mean = 0.89). Over one-quarter of consumers considered no nutrients of public health concern. Consumers focused more on nutrients to avoid rather than under-consumed nutrients. Promoting increased awareness of important under-consumed nutrients may improve public health.

Determinants of gluten-free diet adoption among individuals without celiac disease or non-celiac gluten sensitivity.

OBJECTIVES: Gluten-free (GF) foods are typically less nutritious and more expensive than their gluten-containing variants, yet people without a diagnosed gluten sensitivity continue to adopt this diet. There is a lack of research about what factors drive people without Celiac disease or non-Celiac gluten sensitivity to follow the GF diet. METHODS: A nationally representative sample of 2982 US residents without a diagnosed gluten sensitivity were surveyed about their attitudes, perceptions, and experiences with the GF diet. Logistic regression was used to compare respondents who were currently avoiding or had avoided gluten previously (GF consumer) to respondents who had never tried a GF diet (non-GF consumer). RESULTS: Over one-fifth of respondents were GF consumers. Beliefs that a gluten-reduced diet is healthier (OR 1.69; 95% CI [1.30,2.18]), that GF products are more nutritious (OR 1.46, 95% CI [1.11,1.90), and that a GF diet can help clear acne (OR 1.46; 95% CI [1.13,1.88]) were all positively associated with trying a GF diet. Personal research was the most influential source of information associated with trying a GF diet (OR 2.92; 95% CI [1.91,4.52]). This was followed by "healthcare center or health professional" (OR 2.57; 95% CI [1.71,3.90]. Respondents who were never encouraged to try the GF diet were less likely to try the diet (OR 0.33, 95% CI [0.23,0.46]). CONCLUSIONS: Positive, but scientifically unsubstantiated, beliefs about the benefits of the GF diet were strongly associated with trying a GF diet, and the source of recommendation to try a GF diet was important.

Processing Has Differential Effects on Microbiota-Accessible Carbohydrates in Whole Grains during In Vitro Fermentation.

Whole grains are generally low in nondigestible carbohydrates that are available for fermentation by the gut microbiota, or microbiota-accessible carbohydrates (MAC). However, there is potential to increase MAC in whole grains through food processing. Five processing methods: boiling, extrusion, sourdough bread, unleavened bread, and yeast bread, were applied to whole wheat flour and then subjected to in vitro digestion followed by fermentation using fecal microbiomes from 10 subjects. The microbiomes separated into 2 groups: those that showed high carbohydrate utilization (CU) and those that exhibited low CU. The former exhibited not only enhanced CU but also increased butyrate production (MAC, 31.1 ± 1.1% versus 19.3 ± 1.2%, P < 0.001; butyrate, 5.26 ± 0.26 mM versus 3.17 ± 0.27 mM, P < 0.001). Only the microbiomes in the high-CU group showed significant differences among processing methods: extrusion and sourdough bread led to dichotomous results for MAC and short-chain fatty acid production, where extrusion resulted in high MAC but low butyrate production while sourdough bread resulted in low MAC but high butyrate production. Extrusion led to a noticeable decrease in α-diversity and some members of the families Ruminococcaceae and Lachnospiraceae, with increases in Acinetobacter, Enterococcus, and Staphylococcaceae This study demonstrated that only microbiomes that exhibited high CU responded to the effects of processing by showing significant differences among processing methods. In these microbiomes, extrusion was able to increase accessibility of the cell wall polysaccharides but did not increase butyrate production. In contrast, sourdough bread led to high butyrate production by supporting important butyrate-producers in the families Lachnospiraceae and RuminococcaceaeIMPORTANCE Dietary nondigestible carbohydrates, or dietary fiber, have long been recognized for their beneficial health effects. However, recent studies have revealed that fermentation of nondigestible carbohydrates by gut bacteria is critical in mediating many of the health-promoting properties of dietary fibers. Whole grains are excellent candidates to supply the microbiome with a plentiful source of nondigestible carbohydrates, although unfortunately a majority of these carbohydrates in whole grains are not available to gut bacteria for fermentation. Processing is known to alter the structural characteristics of nondigestible carbohydrates in whole grains, yet the relationship between these effects and gut microbial fermentation is unknown. This research aimed to address this important research gap by identifying interactions between whole-grain processing and gut bacteria, with the ultimate goal of increasing the availability of nondigestible carbohydrates for fermentation to enhance host health.

In vitro digestibility of proteins from historical and modern wheat cultivars.

BACKGROUND: Previous research has suggested that proteins and other quality parameters of wheats may have changed over a century of wheat breeding. These changes may affect protein digestibility. The in vitro protein digestibility of breads made with 21 cultivars of wheat introduced or released in the USA between 1870 and 2013 was therefore evaluated. RESULTS: Protein digestibility increased with release year, but was not normally distributed; three older cultivars had significantly lower digestibility than the other cultivars: 42.0 ± 0.3 mol% (primary amino N/total N) versus 34.7 ± 0.7 mol%; P < 0.001. High molecular weight (MW) protein fractions increased and low MW protein fractions decreased with release year, but these changes were not related to protein digestibility. Thus, other differences in protein composition or other flour components may contribute to diminished digestibility of the three older cultivars. CONCLUSIONS: This study identified differences in protein digestibility among wheat cultivars that may have important implications for human nutrition. Further investigation is required to determine the specific characteristics that differentiate high- and low-digestibility wheat cultivars. © 2020 Society of Chemical Industry.

Considerations for best practices in studies of fiber or other dietary components and the intestinal microbiome.

A 2-day workshop organized by the National Institutes of Health and U.S. Department of Agriculture included 16 presentations focused on the role of diet in alterations of the gastrointestinal microbiome, primarily that of the colon. Although thousands of research projects have been funded by U.S. federal agencies to study the intestinal microbiome of humans and a variety of animal models, only a minority addresses dietary effects, and a small subset is described in sufficient detail to allow reproduction of a study. Whereas there are standards being developed for many aspects of microbiome studies, such as sample collection, nucleic acid extraction, data handling, etc., none has been proposed for the dietary component; thus this workshop focused on the latter specific point. It is important to foster rigor in design and reproducibility of published studies to maintain high quality and enable designs that can be compared in systematic reviews. Speakers addressed the influence of the structure of the fermentable carbohydrate on the microbiota and the variables to consider in design of studies using animals, in vitro models, and human subjects. For all types of studies, strengths and weaknesses of various designs were highlighted, and for human studies, comparisons between controlled feeding and observational designs were discussed. Because of the lack of published, best-diet formulations for specific research questions, the main recommendation is to describe dietary ingredients and treatments in as much detail as possible to allow reproduction by other scientists.

Role of whole grains versus fruits and vegetables in reducing subclinical inflammation and promoting gastrointestinal health in individuals affected by overweight and obesity: a randomized controlled trial.

BACKGROUND: Whole grains (WG) and fruits and vegetables (FV) have been shown to reduce the risk of metabolic disease, possibly via modulation of the gut microbiota. The purpose of this study was to determine the impact of increasing intake of either WG or FV on inflammatory markers and gut microbiota composition. METHODS: A randomized parallel arm feeding trial was completed on forty-nine subjects with overweight or obesity and low intakes of FV and WG. Individuals were randomized into three groups (3 servings/d provided): WG, FV, and a control (refined grains). Stool and blood samples were collected at the beginning of the study and after 6 weeks. Inflammatory markers [tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), lipopolysaccharide binding protein (LBP), and high sensitivity C-reactive protein (hs-CRP)] were measured. Stool sample analysis included short/branched chain fatty acids (S/BCFA) and microbiota composition. RESULTS: There was a significant decrease in LBP for participants on the WG (- 0.2 µg/mL, p = 0.02) and FV (- 0.2 µg/mL, p = 0.005) diets, with no change in those on the control diet (0.1 µg/mL, p = 0.08). The FV diet induced a significant change in IL-6 (- 1.5 pg/mL, p = 0.006), but no significant change was observed for the other treatments (control, - 0.009 pg/mL, p = 0.99; WG, - 0.29, p = 0.68). The WG diet resulted in a significant decrease in TNF-α (- 3.7 pg/mL; p < 0.001), whereas no significant effects were found for those on the other diets (control, - 0.6 pg/mL, p = 0.6; FV, - 1.4 pg/mL, p = 0.2). The treatments induced individualized changes in microbiota composition such that treatment group differences were not identified, except for a significant increase in α-diversity in the FV group. The proportions of Clostridiales (Firmicutes phylum) at baseline were correlated with the magnitude of change in LBP during the study. CONCLUSIONS: These data demonstrate that WG and FV intake can have positive effects on metabolic health; however, different markers of inflammation were reduced on each diet suggesting that the anti-inflammatory effects were facilitated via different mechanisms. The anti-inflammatory effects were not related to changes in gut microbiota composition during the intervention, but were correlated with microbiota composition at baseline. TRIAL REGISTRATION: ClinicalTrials.gov , NCT02602496 , Nov 4, 2017.

Genotype, environment, seeding rate, and top-dressed nitrogen effects on end-use quality of modern Nebraska winter wheat.

BACKGROUND: Fine-tuning production inputs such as seeding rate, nitrogen (N), and genotype may improve end-use quality of hard red winter wheat (Triticum aestivium L.) when growing conditions are unpredictable. Studies were conducted at the Agronomy Research Farm (ARF; Lincoln, NE, USA) and the High Plains Agricultural Laboratory (HPAL; Sidney, NE, USA) in 2014 and 2015 in Nebraska, USA, to determine the effects of genotype (6), environment (4), seeding rate (3), and flag leaf top-dressed N (0 and 34 kg N ha-1 ) on the end-use quality of winter wheat. RESULTS: End-use quality traits were influenced by environment, genotype, seeding rate, top-dressed N, and their interactions. Mixograph parameters had a strong correlation with grain volume weight and flour yield. Doubling the recommended seeding rate and N at the flag leaf stage increased grain protein content by 8.1% in 2014 and 1.5% in 2015 at ARF and 4.2% in 2014 and 8.4% in 2015 at HPAL. CONCLUSION: The key finding of this research is that increasing seeding rates up to double the current recommendations with N at the flag leaf stage improved most of the end-use quality traits. This will have a significant effect on the premium for protein a farmer could receive when marketing wheat. © 2017 Society of Chemical Industry.

Impact of whole grains on the gut microbiota: the next frontier for oats?

The gut microbiota plays important roles in proper gut function and can contribute to or help prevent disease. Whole grains, including oats, constitute important sources of nutrients for the gut microbiota and contribute to a healthy gut microbiome. In particular, whole grains provide NSP and resistant starch, unsaturated TAG and complex lipids, and phenolics. The composition of these constituents is unique in oats compared with other whole grains. Therefore, oats may contribute distinctive effects on gut health relative to other grains. Studies designed to determine these effects may uncover new human-health benefits of oat consumption.

Processing of oats and the impact of processing operations on nutrition and health benefits.

Oats are a uniquely nutritious food as they contain an excellent lipid profile and high amounts of soluble fibre. However, an oat kernel is largely non-digestible and thus must be utilised in milled form to reap its nutritional benefits. Milling is made up of numerous steps, the most important being dehulling to expose the digestible groat, heat processing to inactivate enzymes that cause rancidity, and cutting, rolling or grinding to convert the groat into a product that can be used directly in oatmeal or can be used as a food ingredient in products such as bread, ready-to-eat breakfast cereals and snack bars. Oats can also be processed into oat bran and fibre to obtain high-fibre-containing fractions that can be used in a variety of food products.

Use of whole grain and refined flour from tannin and non-tannin sorghum (Sorghum bicolor (L.) Moench) varieties in frybread.

Frybreads were prepared using wheat flour and wheat-sorghum composite flours (refined and whole grain; white, tannin-free and red, tannin-containing) at 0, 25, 50, and 75% sorghum flour. Hardness, volume, specific volume, color, and oil uptake were determined. Frybreads made with refined white, tannin-free sorghum were also evaluated in a sensory panel. Substitution of sorghum flour for wheat flour reduced the volume and increased the darkness of the fried dough pieces compared with wheat flour controls. Oil absorption was unaffected when using white, tannin-free sorghum. When using red, tannin-containing sorghum, oil absorption increased for refined flour and decreased for whole grain flour, suggesting that a component only present in the whole grain tannin-containing Sorghum--perhaps tannins themselves--may decrease oil uptake. Panelists rated frybreads containing up to 50% white, tannin-free sorghum flour as not significantly different from control frybreads made with refined wheat flour.

Health Prompts Affect Consideration of Health but Not Intertemporal Preferences While Promoting Healthier Food Choices.

Diet-related diseases impact populations across the globe. While intertemporal preferences-a fundamental preference for the distribution of benefits across time-have been used to explain low-quality food choices, the recent literature proposes another cause: inattention to the future implications (or opportunity costs) of the options faced. Food choices tend to become habitual to conserve cognitive resources, rather than carefully modeling future health impacts. Both low discount rates for future benefits and attention to future health impacts predict healthier decisions. While intertemporal preferences are stable, attention may provide an opportunity to intervene in the decision process to promote healthier decisions. In this study, we test the impact of a simple message that highlights health during food choice on the healthiness of the foods chosen and on health consideration and intertemporal preferences. Our results show that actively considering health outcomes and lower discount rates lead to healthier food choices. We find that messaging increases the consideration of health outcomes during food choice but does not affect intertemporal preferences, suggesting that simple prompts may be an effective way to promote decisions balancing short- and long-term benefits by drawing attention to the overlooked opportunity costs of choices.

Influence of overcooking on in vitro digestion and fermentation of ground beef and whole wheat bread.

Areas of char or overcooking commonly appear in foods people consume. It has been reported that overcooked food is harmful to human health. However, little research exists on the effect of overcooking on digestible protein and starch content and gut microbial fermentation. This study aimed to reveal the connection between overcooking and the content of digestible protein and starch, as well as its impact on gut microbial fermentation. Digestible protein in the standard cooked ground beef patty was significantly higher than the overcooked samples (p = 0.009). Standard-cooked whole wheat bread also showed a significantly higher digestible protein content compared with overcooked (p = 0.009). A significant difference was also found in digestible starch content between standard cooked and overcooked bread samples (p = 0.02). Overcooking decreased acetate, propionate, iso-butyrate, iso-valerate and ammonia production by the gut microbiota during fermentation of the beef sample, and decreased propionate and ammonia production during fermentation of the bread sample (p < 0.05). Interestingly, overcooking enhanced butyrate production by the microbiota during fermentation of the bread sample (24 h of fermentation, p < 0.001; 48 h of fermentation, p = 0.02), while no significant difference was found between overcooked and standard cooked beef samples (24 h of fermentation, p = 0.15; 48 h of fermentation, p = 0.4). Overcooking resulted in reductions in many Pseudomonadota and favored several Bacillota, especially Ruminococcaceae and Oscillospiraceae, which contain butyrate producers. Overall, overcooking reduced digestible protein, digestible starch, and fermentation of proteins. Unexpectedly, overcooking induced several purportedly favorable effects on the gut microbiota due to the decreased protein fermentation, which, in future studies, should be weighed against the previous reports that overcooking is deleterious to human health.

In vitro characterization of the impact of selected dietary fibers on fecal microbiota composition and short chain fatty acid production.

The effects of six dietary fibers [pectin, guar gum, inulin, arabinoxylan, ß-glucan, and resistant starch] on the human fecal microbiota during in vitro fermentation were determined. Bifidobacterium increased almost 25% on pectin compared with the control; a significant increase in Bifidobacterium adolescentis type-2 was observed on resistant starch. Bacteroides exhibited a positive correlation with propionate/short chain fatty acid (SCFA) production (r = 0.59, p < 0.01), while Ruminococcaceae and Faecalibacterium displayed positive correlations with butyrate/SCFA production (r = 0.39, 0.54, p < 0.01). A negative correlation was detected between inulin utilization and Subdoligranulum (r = -0.73, p ≤ 0.01), while strong positive relationships were found between ß-glucan utilization and Firmicutes (r = 0.73, p ≤ 0.01) and resistant starch utilization and Blautia wexlerae (r = 0.82, p < 0.01). Dietary fibers have specific and unique impacts on intestinal microbiota composition and metabolism. These findings provide a rationale for the development of functional ingredients targeted towards a targeted modulation of the gut microbiota.

Toxicity of cadmium on dynamic human gut microbiome cultures and the protective effect of cadmium-tolerant bacteria autochthonous to the gut.

Cadmium (Cd) is a heavy metal toxic to the gut microbiome. In this study, we cultivated two human gut microbiomes (A and B) in bioreactors with Cd at 0 and 20 ppm for 7 days to investigate effects of Cd on the gut microbiome and to isolate Cd-tolerant bacteria autochthonous to the gut. Cd showed profound toxicity, abolishing butyrate production, depleting microbes in microbiome B, and simplifying microbiome A to a small Cd-tolerant community after 2 d of incubation. When spiked into the Cd-sensitive microbiome B, the Cd-tolerant community from microbiome A and isolates from that community worked synergistically with microbiome B to enhance butyrate production and maintained this synergism at Cd concentrations up to 5 ppm. Bacteria isolated from this Cd-tolerant community included Enterococcus faecium, Enterobacter cloacae, Lactococcus lactis, and Lactobacillus taiwanensis species. This work demonstrates a straightforward method for identifying Cd-tolerant bacteria autochthonous to the human gut that synergize with the microbiome to protect against Cd-related loss of butyrate production.

US Consumer Identification of the Health Benefits of Dietary Fiber and Consideration of Fiber When Making Food Choices.

The purposes of this study were to (1) determine beliefs in the health benefits of dietary fiber, an under-consumed nutrient of public health concern, and (2) determine the relationship between beliefs about dietary fiber and consideration of fiber when making food choices. We conducted a nationally representative within-subject randomized online survey of 42,018 US primary shoppers in May-June 2021. Participants selected health benefits they believed were associated with consumption of fiber from a list of six benefits recognized by the Food and Drug Administration (FDA), one indirect benefit, and one unrelated benefit. Respondents then indicated which nutrients, if any, they considered when making food choices. Respondents selected 1.77 (95% CI = 1.76-1.77) FDA-recognized benefits out of a total six; half (50.6%) of respondents identified zero or one FDA-recognized benefit. The most-cited benefit was "improving bowel movements" (64.4%). Older participants perceived significantly more FDA-recognized fiber benefits. Identification of FDA-recognized benefits increased odds ratios for consideration of fiber during food choice (relative to zero benefits) from 3.0 for one benefit (95% CI = 2.8-3.3) to 14.3 for six benefits (95% CI = 12.4-16.6). Consumers are largely unaware of the many health benefits of dietary fiber, which dramatically decreases the likelihood that they consider this important, under-consumed nutrient during food choice.

End-Use Quality of Historical and Modern Winter Wheats Adapted to the Great Plains of the United States.

Improving milling and baking properties is important during wheat breeding. To determine changes in milling and baking quality of hard winter wheat, 23 adapted cultivars released in the Great Plains between 1870 and 2013 were grown in triplicate in a single location (Mead, NE, USA) over two crop years (2018 and 2019). Grain yield and kernel hardness index increased by release year (p < 0.05). The observed increase in hardness index was accompanied by a decrease in percent soft kernels (p < 0.05). Diameter and weight decreased with release year in 2019 (p < 0.05), and their standard deviation increased with the release year (p < 0.05). Flour protein content decreased with release year (p < 0.05) and dough mixing quality increased (p < 0.05). No significant relationship was found for baking property variables, but bran water retention capacity (BWRC), which is correlated with whole wheat bread quality, increased with release year (p < 0.05). In conclusion, wheat kernels have become harder but more variable in shape over a century of breeding. Mixing quality showed significant improvements, and loaf volume and firmness remained constant, even in the presence of a decrease in protein concentration. Bran quality decreased across release year, which may have implications for whole grain baking quality and milling productivity.

Genetic analysis of seed traits in Sorghum bicolor that affect the human gut microbiome.

Prebiotic fibers, polyphenols and other molecular components of food crops significantly affect the composition and function of the human gut microbiome and human health. The abundance of these, frequently uncharacterized, microbiome-active components vary within individual crop species. Here, we employ high throughput in vitro fermentations of pre-digested grain using a human microbiome to identify segregating genetic loci in a food crop, sorghum, that alter the composition and function of human gut microbes. Evaluating grain produced by 294 sorghum recombinant inbreds identifies 10 loci in the sorghum genome associated with variation in the abundance of microbial taxa and/or microbial metabolites. Two loci co-localize with sorghum genes regulating the biosynthesis of condensed tannins. We validate that condensed tannins stimulate the growth of microbes associated with these two loci. Our work illustrates the potential for genetic analysis to systematically discover and characterize molecular components of food crops that influence the human gut microbiome.