New Studies on the Gut, Microbiome and Dietary Fiber: 25% Reduced Glucose Response to White Bread, Fiber for the Health of Our Youngest & Oldest -- Nutrients September '16

When the average Westerner hears the word fiber, his marketing indoctrinated brain will associate "cereals"... thanks to the marketing campaigns of Kellog's and co. we have been brainwashed to forget that even the less processed cereals have a comparatively low fiber/kcal ratio compared to veggies, for example.

Initially, I wanted to add the word "all" into the headline of today's article, but that would have promised a bit more than today's article will deliver. It's not "all" as in "all the articles I haven't discussed, yet", but rather "all" as in all the articles from the albeit very recommendable peer-reviewed scientific journal Nutrients.

I promise, though: Even this version of "all" is going to have at least one "gem"that will awake SuppVersity reader's interest. You want examples? Here you go: (a) oat bran preload before high carbohydrate meal reduces post-prandial glucose excursions by ~25%; (b) Dietary fiber (DF) intake in infancy is good for cardiometabolic health - especially if the DA comes from potatoes; (c) fiber and metabolic / bacteria produced metabolites may help centenarians pass the 100-years-age-mark.

• Oat bran preload before high carbohydrate meal reduces post-prandial glucose excursions by ~25% (Steinert. 2016) -- It has been long-established that viscous dietary fibers, including oat β-glucan, are one of the most effective classes of functional food ingredients for reducing postprandial blood glucose. Intriguingly, however, the mechanism of action is not fully understood.
  
  Scientists believe, though, that the increase in viscosity of the stomach contents will delay gastric emptying and thus reduce the mixing of food with digestive enzymes, which, in turn, retards glucose absorption. As Steinert et al. point out, "[p]revious studies suggest that taking viscous fibers separate from a meal may not be effective in reducing postprandial glycemia" (Steinert. 2016).
  

  Table 1: Nutrient composition of the test meals (Steinert. 2016).

  It is thus only logical for them to to (re-)assess the effect of consuming a preload of a commercially available oat-bran (4.5, 13.6 or 27.3 g) containing 22% of high molecular weight oat β-glucan (O22 (OatWell®22)) mixed in water before a test meal consisting of white bread (GI = 100) on the glycemic responses of 10  healthy normal-weight, overweight and obese subjects (5 male/5 female, mean age (years): 48.0 ± 15.3 (range 22–65), BMI (kg/m2): 29.5 ± 4.4 (range 23.2–36.9)) subjects.
  

  Figure 1: Figure 1. Panel (A): Blood glucose concentrations after taking 0, 4.5, 13.6 and 27.3 g, respectively, of OatWell®22 (O22-0, O22-4.5, O22-13.6 and O22-27.3) at −5 min followed by 50 g available carbohydrate from white bread at 0 min. Values are means ± SEM for n = 10 subjects. a–c Means at the same time containing different letters within the superscripts differ significantly by Tukey’s test p < 0.05; (B,C): Percentage reduction from control in incremental areas under the curve (AUC); (B) and peak rise in blood glucose; (C) after taking 0, 4.5, 13.6 and 27.3 g of OatWell®22 (0, 0.9, 2.6 and 5.3 g oat β-glucan, respectively) at −5 min followed by 50 g available carbohydrate from white bread at 0 min | Steinert. 2016).

  As the data in Figure 1 goes to show you, the researchers found a significant effect of dose (meaning: more helps more) on blood glucose area under the curve (AUC) (p = 0.006) with AUC after 27.3 g of O22 being significantly lower than white bread only. Their linear regression analysis showed that each gram of oat β-glucan reduced glucose AUC by 4.35% ± 1.20% (r = 0.507, p = 0.0008, n = 40) and peak rise by 6.57% ± 1.49% (r = 0.582, p < 0.0001).
  
  What the scientists forget to mention in their conclusion, though, is that this effect, as good as it may be for the average sedentary slob, may hamper the strategic use of readily digestible carbohydrates to refuel your glycogen stores in athletes. Nevertheless, even athletes, who don't react like the one outlier the scientists removed before plotting the data in Figure 1, can benefit from "the use of oat bran as nutritional preload strategy in the management of postprandial glycemia" - not necessarily during or right after competitions, though.
• Dietary fiber (DF) intake in infancy is good for cardiometabolic health - especially if the DA comes from potatoes (van Gjissel. 2016) -- "Dietary fiber (DF) intake may be beneficial for cardiometabolic health. However, whether this already occurs in early childhood is unclear," that's the first sentence in van Gjissel et al.'s 2016 investigation of the associations between DF intake in infancy and cardiometabolic health in childhood among 2032 children participating in a population-based cohort in The Netherlands.

  "Information on DF intake at a median age of 12.9 months was collected using a food-frequency questionnaire. DF was adjusted for energy intake using the residual method. At age 6 years, body fat percentage, high-density lipoprotein (HDL)-cholesterol, insulin, triglycerides, and blood pressure were assessed and expressed in age- and sex-specific standard deviation scores (SDS). These five factors were combined into a cardiometabolic risk factor score. In models adjusted for several parental and child covariates, a higher DF intake was associated with a lower cardiometabolic risk factor score."

  When the Dutch scientists examined individual cardiometabolic factors, they observed that a 1 g/day higher energy-adjusted DF intake was associated with 0.026 SDS higher HDL-cholesterol (95% CI 0.009, 0.042), and 0.020 SDS lower triglycerides (95% CI −0.037, −0.003), but not with body fat, insulin, or blood pressure - most intriguingly with potatoes having by far the most significant effects of all individual fibers the scientists examined.
  

  Figure 2: Covariate- and energy-adjusted association of dietary fiber intake from cereals, from potatoes, from fruits and vegetables, and from legumes (per 1 g/day) and cardiometabolic outcomes.

  Now, obviously that is not earth-shatteringly much, but since the overall results were similar for DF with and without adjustment for energy intake, it does, as the scientists point out suggest that a "higher DF intake in infancy may be associated with better cardiometabolic health in later childhood" (van Gjissel. 2016).
• Fiber and metabolic / bacteria produced metabolites may help centenarians pass the 100-years-age-mark (Cai. 2016) -- Scientists often pay too much attention to sick and too little attention to healthy people. Studies in centenarians are one of the few exceptions to this rule, as they are designed to elucidate what it is that allows these individuals to live for 100 years and more and still be in better health than many of us who are 20-40 years younger.
  
  Our knowledge of the relationships between diet and metabolites as well as element profiles in healthy centenarians, as important as it probably is, remains inconclusive. Therefore, scientists from the Guangxi University conducted a new study to potential role of short-chain fatty acids (SCFAs), total bile acids and ammonia in feces, phenol, p-cresol, uric acid, urea, creatinine and ammonia in urine, and element profiles in fingernails on the health and life-expectancy in 90 elderly people, including centenarians from Bama county (China)—a famous longevous region—and elderly people aged 80–99 from the longevous region and a non-longevous region.
  To identify relevant patterns, the authors used a partial least squares-discriminant analysis that revealed a distinct metabolic pattern with seven characteristic components: acetic acid, total SCFA, Mn, Co, propionic acid, butyric acid and valeric acid.
  

  Figure 3: No, it's not all about the microbiome, but it appears as if substances your gut tenants are going to produce from fiber in your colon are on of the reason centenarians make it past the 100 year mark.

  The concentration of these metabolites and minerals were significantly higher in the centenarians group (p < 0.05). How does that relate to fiber? Well, the dietary fiber intake was positively associated with the butyric acid contents in the feces of the subjects (r = 0.896, p < 0.01), which suggests "that elevated dietary fiber intake[s] should be a path toward health and longevity" (Cai. 2016 | my emphasis) - and I deliberately underlined and italicized the word "a", here, because a high fiber intake, alone, affects only butyric acid, propionic acid and short-chain fatty acid levels. With manganese, copper and valeric acid, which has a similar structure as GHB or GABA, even the obviously incomplete list of longevity promoters from the study at hand contains elements that are not directly related to your fiber intake. 

• Cai, D.; Zhao, S.; Li, D.; Chang, F.; Tian, X.; Huang, G.; Zhu, Z.; Liu, D.; Dou, X.; Li, S.; Zhao, M.; Li, Q. Nutrient Intake Is Associated with Longevity Characterization by Metabolites and Element Profiles of Healthy Centenarians. Nutrients 2016, 8, 564.
• Collins, S.; Reid, G.Distant Site Effects of Ingested Prebiotics. Nutrients 2016, 8, 523.
• So, W.K.W.; Law, B.M.H.; Law, P.T.W.; Chan, C.W.H.; Chair, S.Y.Current Hypothesis for the Relationship between Dietary Rice Bran Intake, the Intestinal Microbiota and Colorectal Cancer Prevention. Nutrients 2016, 8, 569.
• Steinert, R.E.; Raederstorff, D.; Wolever, T.M.S.Effect of Consuming Oat Bran Mixed in Water before a Meal on Glycemic Responses in Healthy Humans—A Pilot Study. Nutrients 2016, 8, 524.
• van Gijssel, R.M.A.; Braun, K.V.E.; Kiefte-de Jong, J.C.; Jaddoe, V.W.V.; Franco, O.H.; Voortman, T. Associations between Dietary Fiber Intake in Infancy and Cardiometabolic Health at School Age: The Generation R Study. Nutrients 2016, 8, 531.