Dietary Fiber & Health Outcomes 🍓🥦
Hey y’all, and welcome to the actual Memorial Day weekend edition of the humanOS newsletter (in the last newsletter, I seem to have mistakenly identified that week as Memorial Day weekend 🙃).
Anyway! Today, I thought I would look at some of the observational data on dietary fiber intake. Research on fiber is, of course, overwhelmingly positive, yet most people don’t seem to get nearly enough of it in the diet. Recent estimates suggest that around 95% of Americans do not meet the Institute of Medicine’s relatively modest recommended daily intake of fiber, and the average intake is only about half of the recommended value.
This is probably due, in large part, to the ever-growing dominance of ultra-processed foods in the US food supply, now constituting 57% of caloric intake on average. Higher intake of ultra-processed food has been shown to be strongly associated with lower dietary fiber intake, in various countries and age groups, as well as poorer diet quality in general.
Finally, I realize that observational research tends to be downplayed due its obvious limitations, especially with respect to dietary data. However, clinical trials have revealed numerous ways through which fiber might be working its magic. For instance, certain types of fiber have been shown to reduce serum cholesterol levels through increased SCFAs and accelerated bile excretion, as well as slowing glucose absorption. Fiber also appears to lower blood pressure, improve weight regulation, and increase estrogen excretion, all of which would be reasonably expected to have long-term health benefits. So there are certainly plausible biological mechanisms at play here.
This Week's Research Highlights
Researchers performed a meta-analysis of seventeen prospective cohort studies, including a total of 982411 participants, which examined how fiber was associated with mortality. Compared to those in the lowest third of dietary fiber intake, individuals in the top third of fiber intake had a 16% lower relative risk of dying during the study period. More fiber also appeared to be better, as each 10-g/day increase in dietary fiber was linked to a 10% reduction in risk of mortality.
Researchers analyzed cross-sectional data from a diverse sample of 23168 NHANES participants. They found, unsurprisingly, that dietary fiber was well below recommended levels (a mean of 16.2 grams, which isn’t good at all). But those who did consume more fiber seemed to do much better, from the standpoint of cardiometabolic biomarkers. Compared to participants in the lowest quintile of dietary fiber intake, those in the highest quintile had a 22% lower risk of metabolic syndrome, 34% lower risk of systemic inflammation (measured through CRP), and 23% lower risk of obesity, after adjusting for potential confounding variables.
🩸 High fiber intake is linked to dramatically lower risk of type 2 diabetes - especially cereal fiber.
Researchers in Finland looked at a cohort of 4316 adults who did not have type 2 diabetes at the start of the study. They captured food consumption data through a dietary history interview, and followed subjects for ten years. They found that those in the highest quartile of fiber consumption had a 49% lower risk of going on to develop type 2 diabetes over the course of the study. When they zoomed in on cereal fiber specifically, they found an even bigger difference - those in the highest quartile of cereal fiber intake showed a 61% reduction in risk of type 2 diabetes.
Digging a little deeper here: Why did cereal fiber appear to be uniquely beneficial? Well, some previous research has suggested that cereal fiber may have special properties with respect to cardiometabolic health, and that’s certainly possible. But take a look at these quartiles of intake. In this study, these subjects, on average, were eating a ton of fiber from cereal but only a fraction as much from fruits and vegetables, which makes me wonder if this might be an issue of dose. For instance, a Japanese cohort in which cereal fiber constituted a much smaller portion of total fiber intake (compared to what we see in Western cohorts) found that fruit/vegetable fiber was linked to lower mortality, but cereal fiber was not.
Random Trivia & Weird News
During the civil war in Mozambique, more than 90% of the elephants in Gorongosa National Park were killed for ivory. As a result, about a third of the female elephants in Gorongosa who had been born after the end of the civil war never developed tusks.
Normally, tusklessness occurs randomly in about 2-4% of female African elephants, due to mutations in genes that promote tusk development, but the overwhelming selection pressure of poaching has caused this trait to become far more prevalent.
Interesting from an ecological standpoint, albeit quite sad.
Podcasts We Loved This Week
- Drs. Erica & Justin Sonnenburg: How the microbiome affects your health and ways to optimize it. Via The Proof Podcast.
- David Jenkins: Lipid-lowering diets. Via Sigma Nutrition Radio.
Products We Are Enjoying
I have to emphasize that most of the research showing benefits associated with dietary fiber have looked at naturally occurring fiber in whole foods, not added functional fiber, and it would be a mistake to assume that supplements can serve as a substitute for whole foods. That having been said, if you are looking for an efficient way to boost your fiber intake and feed your gut bugs, this is a good option. This fiber blends really easily into beverages, smoothies, sauces, baked goods, etc with no discernible flavor, and it appears to be keto-friendly for those of you who are doing that. But what really sets oat fiber apart is that it is one of the richest, if not the richest, sources of beta-glucan, a soluble fiber that has been shown to lower blood lipids as well as help regulate blood sugar. From a nutritional standpoint, it might be the best option out there.
humanOS Catalog Feature of the Week
An ergogenic aid is simply a supplement that enhances physical performance. Dietary intake of these substances can, in theory, affect training adaptations in a couple of different ways. They can achieve this by simply increasing the exercise stimulus from a single training bout - basically just enabling an athlete to train longer or harder, or reducing perceived exertion. But they may also be able to affect gains in endurance by altering cellular responses to exercise-induced stress.
Importantly, these changes in cell signaling may not be universally beneficial from the standpoint of adaptation. For example, it is theoretically possible that a supplement could simultaneously make it easier for an athlete to exercise hard, but also have effects on cellular signaling that actually have a long-term negative impact on the adaptive response to training.
In this guide, we review some of the most rigorously researched supplements (including LactiGo), discuss how best to use them, and talk about why some supplements that sound like a good idea may actually not be helpful at all. If you are looking for a quick reference sheet of the latest evidence-based guidance on supplements to maximize your performance and adaptations, check it out! 👀
Thanks for reading, enjoy the weekend, and we'll see y'all next week!