In conclusion, the results of our study support the hypothesis that high intake of both RS and AX [wheat/rye fiber] is capable of changing the intestinal microbiota and SCFA production in subjects with MetS in contrast with a low-fibre diet (WSD). Most distinctly, Bifidobacterium was clearly enriched by the HCD [High-fiber diet], which was in strong agreement with the increased faecal acetate concentration. Also, dysbiotic changes observed during the WSD [low fiber] emphasise the need for balanced diets, including fiber from various sources.
In other words...We are sorely missing fiber. What kind and how much is the million dollar question. But these researchers seem to like Raw Potato Starch, Hi-Maize Corn Starch, and wheat fiber. Let's discuss.
Last week, "Another Becky" posted a great comment, and I just now had time to sit and read the paper. Her comment:
Published yesterday in PLOS ONE: Effects of Arabinoxylan and Resistant Starch on Intestinal Microbiota and Short-Chain Fatty Acids in Subjects with Metabolic Syndrome: A Randomised Crossover Study
Design summary: N=19 participants in a crossover design with two 4-week supplementation periods and a 4+ week washout in between. The RS used was RS2 from raw potato starch and high-amylose maize starch. It wasn't completely clear to me what the total RS daily intake was, though.
Results: microbiome modifications and increased SCFA, acetate, and butyrate. Maybe someone else can comment on the specific bacterial changes? I'm not familiar enough with the terminology to be qualified in that area.
Tim, do you think a 4-week washout period between the active "treatment" periods is sufficient to remove the effects of the first dietary intervention? The pre-intervention numbers in Table 4 are pretty similar, suggesting that the washout was effective, but the authors also didn't include a measure of variability for those single-timepoint estimates (so it's hard to establish the relative magnitude of the difference).
Thanks for the great comment, AB! This paper is right up my alley, and features my fave white powders!
What the study showed was that a diet enriched with RS and AX produced favorable changes in the gut. specifically increased short-chain fatty acids (SCFA) and increases in bacteria known to be beneficial.
There were some minor changes to bacteria we consider "good," ie. Akkermansia, Lactobacillus; but the biggest increase was in bifidobacteria. This seems to be the coveted strain, the gut-bug that makes babies bullet-proof, and the one that people spend billions of dollars annually by way of probiotic pills that rarley work.
The predominant change in the faecal microbiota with the introduction of [fiber] was the enrichment of members of Bifidobacterium, a genus regarded to be beneficial to human health. The capacity of fiber to promote Bifidobacterium has been found in many studies...Acetate production by Bifidobacterium confers protection against gastrointestinal pathogens and it may be consumed by butyrate-producing bacteria in the gut.
Even to the untrained eye, this is a dramatic display that Bifidobacteria was increased tremendously by the addition of RS and wheat fiber.
Was 4 weeks enough time to prepare the folks for the study? I think so. It looks to me to be well-designed, and I have always thought that 4 weeks is about the right amount of time to see beneficial changes. The study design was such that the participants kept a detailed food log for a month, then ate either the high-fiber or low fiber diet for 4 weeks, returned to their regular diet for 4 weeks, then switched to the other diet for 4 more weeks. This allowed the researchers to track the changes in each person regardless of which diet they started with.
A good friend taught me long ago, when reading these type studies, pay careful attention to "surprises." This paper had a few.
...the diet-induced differences in the SCFA concentrations observed in this study were mainly due to declining SCFA concentrations during the WSD.
The surprise here was not the dramatic increase in butyrate and other SCFA on a high fiber diet, but the dramatic decrease when shifting to a low fiber diet. Reasons for this surprise were given as:
- The normal diet of the participants was much higher in fiber than they estimated
- Participants ate much less fiber-rich foods during the study
- The researchers failed to take into account the increase in bowel movements on SCFA measurements
I think they may have overlooked the fact that fecal SCFA measurements are not a good indicator or SCFA production in the gut because it often gets absorbed in the colon and eaten by bacteria, especially in people with healthy guts...this same observation is in many fiber studies.
...the decreased concentration of BCFAs in the faeces during the [high fiber diet]. This finding indicates reduced protein fermentation, which counteracts the accumulation of potentially harmful metabolites.
Here is an interesting surprise for sure, and one that may have far-reaching implications! BCFA's are branch-chain fatty acids, isobutyrate and isovalerate. This indicates that less animal protein is being fermented in the large intestine and could reduce a build-up of harmful chemicals. The effects of RS to counteract some dangers of red meat consumptions have been reported for many years in numerous studies, ie. Resistant starch prevents colonic DNA damage induced by high dietary cooked red meat or casein in rats.
The [high fiber] conferred a significant decrease in bacterial species richness in all individuals.
Normally we discuss the increase in bacterial diversity associated with a high fiber diet. Why the decrease? This could relate back to Another Becky's question, "Is 14 days long enough?" Another reason could be in the measuring tools they used...if there's one thing I've learned in the last couple years, it's that capturing bacterial diversity is tricky business. The loss in diversity in this study was not phenomenal (615 species vs 675 species), but it was statistically significant. Judging from the dramatic increase in Bifidobacteria, it's quite likely that this good species crowded out several bad species, so though the diversity was lower, the collection of bacteria was better.
...dysbiotic changes observed during the [low fiber diet] emphasize the need for balanced diets, including DF from various sources.
Around here, people complain of certain "TMI" aspects when starting a high fiber diet, but when switching between high and low fiber diets, more complaints were heard from people embarking on the lower fiber intakes...diarrhea and constipation were the main complaints on low-fiber. On the high-fiber diet, flatulence and stomach rumbling were reported, but not severe. Of interest: "Self-reported well-being was rated as moderately higher during the high fiber diet."
One person, however, did withdraw from the study during the high fiber portion due to "abdominal discomfort." Standard warnings apply! We are all unique when it comes to fiber.
The low fiber diet consisted of roughly 2200 calories worth of food: 300g carbs, 62g fat, 96g protein, and 21g of fiber. This looks to me to be similar to a "low fat" diet, but higher in fiber than we normally see in the western world where the average intake is about 15g/day of fiber.
The low fiber diet was high in corn flakes, wheat bread, pasta, and pancakes as the main carb sources.
The high fiber diet consisted of about 2000 calories divided into: 325g carbs, 63g fat, 83g protein, and 68g of fiber per day. This appears to be a typical high carb SAD diet augmented with fiber.
The big difference between the two diets, on the high fiber diet, the corn flakes, bread, and pasta were made with Hi-Maize corn starch (RS2), wheat bran (AX), and a smoothie containing 24g of Raw Potato Starch (RS2). This totalled 68g/day of total fiber intake versus 21g for the low fiber arm.
The low fiber diet was at the bottom of the recommended fiber intake range (25-38g/day) and the high fiber diet was considerably higher.
Wheat arabinoxylan (AX), was used in the study. There is no commercial source of a wheat AX supplement, so far as I can find. AX is found in many whole-grain flours (wheat, rye, spelt) in varying amounts, but removed from refined flours.
Take Home Message
The more fiber you consume, the healthier your guts will be. Keep in mind that most Americans and Europeans get much less fiber than even the low-fiber group in this study. I have long been an advocate for people eating at the high end of the near-universal guidelines for fiber consumption which are around 25-38g/day. Personally, I target 50g per day and sometimes get upwards of 100g/day through real foods like dandelion roots, onions, garlic, an cocoa nibs.
If you are looking for ways to increase fiber intake, please re-read my 5-part series, "In Search of the Perfect Fiber..." But as always, getting enough fiber is tough to do, even the most well-intentioned days can fall short on fiber intake. Here's where supplements fit in. A couple spoonfuls of Raw Potato Starch, easily found and cheap, or the harder-to-find, more expensive Hi-Maize cornstarch daily can go a long ways to meeting your fiber needs.