Effects of oats on gastrointestinal health as assessed by in vitro, animal, and human studies

Oats are uniquely nutritious, owing to their composition of bioactive compounds, lipids, and β-glucan. Scientific research has established that oats can improve diet quality, reduce cholesterol, regulate satiety, and protect against carcinogenesis in the colon; however, determining the effects of oats on gastrointestinal health and the gut microbiome is a newer, evolving area of research. To better understand the effects of oats on gastrointestinal health in humans, a literature review with predefined search criteria was conducted using the PubMed database and keywords for common gastrointestinal health outcomes. Moreover, to examine the gastrointestinal effects of oats across the scientific spectrum, a similar search strategy was executed to identify animal studies. In vitro studies were identified from the reference lists of human and animal studies. A total of 8 human studies, 19 animal studies, and 5 in vitro studies met the inclusion criteria for this review. The evidence in humans shows beneficial effects of oats on gastrointestinal health, with supportive evidence provided by in vitro and animal studies. The effective dose of oats varies by type, although an amount providing 2.5 to 2.9 g of β-glucan per day was shown to decrease fecal pH and alter fecal bacteria. For oat bran, 40 to 100 g/d was shown to increase fecal bacterial mass and short-chain fatty acids in humans. Differences in study design, methodology, and type of oats tested make valid comparisons difficult. The identification of best practices for the design of oat studies should be a priority in future research, as the findings will be useful for determining how oats influence specific indices of gastrointestinal health, including the composition of the human gut microbiome.

Cereal β-glucan alters nutrient digestibility and microbial activity in the intestinal tract of pigs, and lower manure ammonia emission: a meta-analysis

Cereal β-glucan may be detrimental in pig production because of negative effects on nutrient digestibility, but they may act as functional ingredients by stimulating the intestinal microbiota. This study primarily aimed to investigate relations between dietary β-glucan and nutrient digestibility, intestinal fermentation, and manure NH3 emission in weaned, growing, and finishing pigs. Effects of dietary xylose, NDF, and CP, and pig BW on animal responses were also evaluated. A meta-analytical approach, accounting for inter- and intraexperiment variations, was used to compute prediction models. Data from 26 studies including 107 different dietary treatments with appropriate dietary and physiological measurements were used to parameterize these models. Dietary β-glucan inclusion ranged from 0 to 6.7%. Increasing dietary β-glucan reduced apparent ileal (AID) and total tract digestibility (ATTD) of CP and energy (R(2) = 0.12 to 0.29; P < 0.05), whereas the ATTD of DM was reduced by 10% up to a threshold β-glucan of 3.5%, above which the response became asymptotic (R(2) = 0.34; P < 0.01). Increasing dietary NDF content decreased ATTD of DM and energy, and increasing xylose concentration reduced ATTD of energy and CP (R(2) = 0.24 to 0.85; P < 0.05). Broken-line model indicated that cecal total VFA and butyrate concentrations increased up to a threshold of 2.5 and 1.4% β-glucan in the diet, respectively, above which these responses became asymptotic (R(2) = 0.77 to 0.96; P < 0.05). Ileal butyrate was negatively and colonic iso-butyrate was positively linked to increasing β-glucan concentration (R(2) = 0.17 to 0.41; P < 0.05). Greater β-glucan concentration were negatively related (R(2) = 0.86; P < 0.01) to NH3 emission, indicating a reduction in NH3 emission by one-half with 6% β-glucan. Backward elimination analysis indicated that greater BW of pigs counteracted (P < 0.05) the negative effect of β-glucan on AID of CP and energy and ATTD of DM and CP. Pig BW also enhanced effects of β-glucan on cecal total VFA, colonic iso-butyrate, ileal butyrate, and NH3 emission (P < 0.05). Dietary CP potentiated (P < 0.01) the β-glucan effects on cecal total VFA, cecal butyrate, and colonic iso-butyrate. In conclusion, this study indicates that β-glucan can stimulate cecal butyrate and ameliorate manure NH3 emission, thereby decreasing nutrient digestibility. Because greater BW ameliorates β-glucan effects, finishing diets may be formulated to contain more β-glucan than weaner diets.