Background:

• Dietary fiber consists of non-digestible forms of carbohydrate, usually as polysaccharides that originate from plant-based foods.
• Over recent decades, our diet within Westernized societies has changed radically from that of our hominid ancestors, with implications for our co-evolved gut microbiota. This includes increased ingestion of ultra-processed foods that are typically impoverished of dietary fiber, and associated reduction in the intake of fiber-replete plant-based foods.
• Over recent decades, there has been a transformation in our understanding of the health benefits of dietary fiber. Objective: To explore the current medical literature on the health benefits of dietary fiber, with a focus on overall metabolic health.
• Dietary fiber intake also correlates with mortality. The gut microflora functions as an important mediator of the beneficial effects of dietary fiber, including the regulation of appetite, metabolic processes and chronic inflammatory pathways.
• Multiple factors contribute to our fiber-impoverished modern diet.
• Given the plethora of scientific evidence that corroborate the multiple and varied health benefits of dietary fiber, and the risks associated with a diet that lacks fiber, the optimization of fiber within our diets represents an important public health strategy to improve both metabolic and overall health.
• If implemented successfully, this strategy would likely result in substantial future health benefits for the population.

     Introduction

• In our modern-day, 21st century world, chronic diseases predominate. Underlying much of this chronic disease burden are pathological pathways that implicate inflammation and metabolic dysfunction (including insulin resistance).
• In recent decades, much evidence supports an important role for our lifestyles in the development of such inflammatory and dysmetabolic processes, such as, for example, our sleep, physical activity and diet.
• Such lifestyle factors also contribute towards weight gain and obesity, which represent a particularly important contributor to chronic ill health, including >50 medical conditions (such as type 2 diabetes mellitus (T2D), dyslipidemia, hypertension, obstructive sleep apnea and cardiovascular disease). 
• See post https://healthinfo.site/preventing-obesity-new-approaches/
• Global obesity prevalence has tripled over the last half century, with current rates of obesity and overweight affecting 650 million and 1.9 billion people respectively.
• In addition to multi-morbidity, obesity also associates with premature mortality as evidenced by data from the Framingham Heart Study.
• Obesity has a substantial and diverse impact on psycho-social functioning, work productivity and global healthcare expenditure.
• Important advances have been made in recent years regarding our understanding of appetite and metabolic regulation, metabolic surgical and medical therapeutic approaches to obesity.
• However, regardless of therapeutic choice for obesity management, ultimately, weight loss stems from behavioral change at an individual level.
• At the heart of such behavioral change lies dietary modification. Despite this insight, however, it is remarkable how little we know about our diet.
• Nutritional studies are notoriously difficult to execute and interpret for a variety of reasons that include self-reporting of food intake, multiple confounding factors (such as variations in genetic, metabolic and gut microbial factors), impaired compliance with dietary changes and the difficulties associated with the study of macronutrient changes in isolation (with inevitable consequences for other ingested macronutrients).
• All of these factors conspire to create much uncertainty regarding the optimal dietary needs for the individual.
• To compound this uncertainty, the popular media is littered with an effusion of fad diets with phony promises of long-lasting weight loss and health, often based on little if any proper scientific evidence and rigor.
• It is little wonder that patients and many healthcare professionals are confused about the optimal diet to follow and advocate.
• In response, esteemed societies and governments around the world have tended to offer generic dietary advice on a population-based level.
• For decades, much focus has rested with advice to adopt a ‘low-fat’ diet that, more recently, has shifted towards a ‘low-carbohydrate’ diet (with associated examples of ‘sugar-tax’ and limitations on food advertising for children).
• In this narrative review, we focus on dietary fiber, a macronutrient that has perhaps not received as much attention as its more attractive counterparts, fat and carbohydrates.
• Our objective was to explore the current medical literature on the health benefits of dietary fiber, with a focus on overall metabolic health but also on gut motility, gut microbiota, chronic inflammation, mental health, cardiovascular disease, colorectal carcinoma and mortality.
• We also provide a suggested strategy for how we can optimize dietary fiber intake within the population in the context of our fiber-impoverished modern-day world.
• The laxative effects of fiber differ. Some fibers reduce constipation, but others increase constipation. This appears to depend on the individual and the type of fiber.

 

     

     Dietary Fiber—” New Protein”

 

Table 1.

• Research on the gut microbiome has triggered a ‘revolution’ in nutritional science, and in the last few years, dietary fiber has become the “new protein” – added to foods in abundance to feed our gut and boost our health.

 

• A recent study on mice, however, suggests not all fiber supplements are equally beneficial.
• A form that is readily found in oats and barley, called beta-glucan, can control blood sugar and assist in weight loss among mice fed a high-fat diet.
• Researchers at the University of Arizona (UA) and the University of Vienna say it is the only type of fiber supplement they tested that decreased a mouse’s fat content and body weight within 18 weeks.
• The other fibers considered, including wheat dextrin, pectin, resistant starch, and cellulose, had no such effect, despite shifting the makeup of the mouse microbiome significantly compared to mice fed no fiber supplements.
  “We know that fiber is important and beneficial; the problem is that there are so many different types of fiber,” explained biomedical scientist Frank Duca from UA in July.
• 
  “We wanted to know what kind of fiber would be most beneficial for weight loss and improvements in glucose homeostasis so that we can inform the community, the consumer, and then also inform the agricultural industry.”
• Dietary fibers are the main source of energy for bacteria living in our guts, and yet less than 5 percent of people in the US consume the recommended 20-30 gram (0.9-1 ounce) of fiber a day.
• To make up for this, fiber supplements and ‘invisible fiber’-infused foods’ are growing in popularity. But fibers are extremely diverse, so which do we choose?

 

 

• Beta-glucan is found in oats and barley.
  Some fibers, like oat beta-glucans and wheat dextrin, are water-soluble, meaning they are easily fermented by gut bacteria. Others, like cellulose and resistant starch, are less soluble or insoluble, meaning they stick to other
  materials to form stool.
• Until now, writes biomedical scientist Elizabeth Howard from UA and her colleagues, “there is no study that has investigated the role of various fibers in one cohort.”
• To make up for this, the current study tested several forms of fiber in one cohort of mice. Only beta-glucan was found to increase the number of lleibacterium found in the mouse intestine. Other studies on mice have linked this bacterium to weight loss.
• Sure enough, long before the 10-week marker, mice fed beta-glucan showed reduced body weight and body fat content compared to mice fed other forms of fiber.
• The findings align with another recent study by Duca, which fed barley flour, rich in beta-glucan, to rodents.
• Even though the rats continued eating just as much of their high-fat diet as before, their energy expenditure increased, and they lost weight anyway.
• A similar outcome was observed in mice fed beta-glucan in the new study. These animals also showed increased concentrations of Butyrate in their guts, which is a metabolite made when microbes break down fiber.
• Butyrate induces the release of glucagon-like peptide-1 (GLP-1), which is the natural protein that synthetic drugs like Ozempic mimic to stimulate insulin release.

 

 

     High-fiber foods

Fruits	Serving size (grams)	Total fiber (grams)*
Raspberries	1 cup (123)	8.0
Pear	1 medium (178)	5.5
Apple, with skin	1 medium (182)	4.5
Banana	1 medium (118)	3.0
Orange	1 medium (140)	3.0
Strawberries	1 cup (144)	3.0

Vegetables	Serving size (grams)	Total fiber (grams)*
Green peas, boiled	1 cup (160)	9.0
Broccoli, boiled	1 cup chopped (156)	5.0
Turnip greens, boiled	1 cup (144)	5.0
Brussels sprouts, boiled	1 cup (156)	4.5
Potato, with skin, baked	1 medium (173)	4.0
Sweet corn, boiled	1 cup (157)	4.0
Cauliflower, raw	1 cup chopped (107)	2.0
Carrot, raw	1 medium (61)	1.5

Grains	Serving size (grams)	Total fiber (grams)*
Spaghetti, whole-wheat, cooked	1 cup (151)	6.0
Barley, pearled, cooked	1 cup (157)	6.0
Bran flakes	3/4 cup (30)	5.5
Quinoa, cooked	1 cup (185)	5.0
Oat bran muffin	1 medium (113)	5.0
Oatmeal, instant, cooked	1 cup (234)	4.0
Popcorn, air-popped	3 cups (24)	3.5
Brown rice, cooked	1 cup (195)	3.5
Bread, whole-wheat	1 slice (32)	2.0
Bread, rye	1 slice (32)	2.0

Legumes, nuts and seeds	Serving size (grams)	Total fiber (grams)*
Split peas, boiled	1 cup (196)	16.0
Lentils, boiled	1 cup (198)	15.5
Black beans, boiled	1 cup (172)	15.0
Cannellini, Navy, Great Northern beans, canned	1 cup (180)	13
Chia seeds	1 ounce (28.35)	10.0
Almonds	1 ounce, about 23 nuts (28.35)	3.5
Pistachios	1 ounce, about 49 nuts (28.35)	3.0
Sunflower kernels	1/4 cup (32)	3.0

*Rounded to nearest 0.5 gram.

• Source: USDA National Nutrient Database for Standard Reference, Legacy Release

      Some tips for increasing fiber intake:

1. Eat whole fruits instead of drinking fruit juices.

      2. Replace white rice, bread, and pasta with minimally processed brown rice and other whole grains like barley, millet, amaranth, farro, and

      3. Add high-fiber foods to current meals: 1-2 tablespoons of almonds, ground flaxseeds, or chia seeds to cereals; diced vegetables to casseroles, stir-fried dishes, and soups.

      4. For breakfast, choose cereals that have a whole grain as their first ingredient.

      5. Another tip is to look on the Nutrition Facts label and choose cereals with 20% or higher of the Daily Value (DV) for fiber.

      6. Snack on crunchy raw vegetables or a handful of almonds instead of chips and crackers. Substitute beans or legumes for meat two to three times a week in chili and soups.

      7. If it is difficult to eat enough fiber through food, a fiber supplement such as psyllium or methylcellulose powders or wafers can be used. They can help bulk and soften stool so it is easier to pass. However, fiber supplements are not intended to completely replace high-fiber foods.

 

     Conclusion

 

• “Part of the benefits of consuming dietary fiber is through the release of GLP-1 and other gut peptides that regulate appetite and body weight,” said Duca.
• “However, we don’t think that’s all of the effect. We think that there are other beneficial things that butyrate could be doing that are not gut peptide related, such as improving gut barrier health and targeting peripheral organs like the liver.”
• Far more research is needed before these results can be extended to humans, but the findings suggest that some fibers may be better suited to weight loss and insulin control than others.

• To conclude, much evidence supports an important role for dietary fiber intake as a contributor to overall metabolic health, through key pathways that include insulin sensitivity.
• Furthermore, there are clear associations between dietary fiber intake and multiple pathologies that include cardiovascular disease, colonic health, gut motility and risk for CRC.
• Dietary fiber intake also correlates with mortality. The gut microflora functions as an important mediator of the beneficial effects of dietary fiber, including the regulation of appetite and metabolic processes and chronic inflammatory pathways.
• Many factors contribute towards the impoverishment of dietary fiber intake in the typical Western diet. Unfortunately, there is habituation of many of us to our modern-day environs, lifestyles, diets and eating-related behaviors.
• The problem is that what most of us consider normal is actually highly abnormal and about as far away from what our hominid hunter-gatherer ancestors experienced and enjoyed as it is possible to imagine.
• The fact is that over decades, a blink of an eye in hominid history, we have gradually migrated into our current environments, lifestyles and culture, and it is very hard for most of us to imagine an alternate scenario.
• Stepwise changes are required. By adopting some of the suggested strategies here, it is our belief that real change in dietary fiber intake can occur.
• Despite all the technological breakthroughs and progress of our species during much of the 20th century and the resultant radical changes in our lifestyles, environments and eating habits, we may spend much of the 21st century searching for ways in which to re-establish some healthier lifestyle choices.
• Some of these will, doubtless, include lifestyle choices that our ancestors enjoyed in the pre-industrialized era, including, fundamentally, the adoption of a non-processed diet that is full of fiber.
• Consumption of ultra-processed foods is not natural. We did not evolve to adopt this dietary maladaptive behavior and neither did our gut flora. Our hominid ancestors and all of their ancient ancestors never ate ultra-processed foods.
• Our current dietary habits in the Western world are extremely unusual and will even be considered as an anomaly by food historians from a future era.
• Whilst global poverty and ill health remains a major problem and concern, most Western societies have developed shelter, clean water, sanitation and advanced healthcare systems to improve our comfort, quality of life and overall longevity.
• Our modern Western diets, however, remain a problem. Unlike the other examples of human advanced development provided here, the clear benefits of which are incontrovertible, our diets seem to have deteriorated.
• This is unfortunate given the central role of our diet, including the multiple benefits mediated by our gut microbiota, as an important determinant of overall health and wellbeing.
• Although many aspects of our diet are concerning (including our excessive consumption of sugars and fat), the clear lack of dietary fiber in our modern-day diet is of particular concern.
• Despite a wealth of evidence generated over many decades to corroborate the multiple health benefits of dietary fiber, the health risks of a diet that lacks fiber and the corresponding efforts to provide public health messages to educate the populace, sadly, within the Western world, our diets remain lacking in fiber.
• It would be easy to apportion blame solely on the food companies that process fiber-impoverished food products.
• This would be wrong: we all have a choice regarding our diet, although it is unfortunate that a healthy diet generally costs around 25–30% more than an unhealthy diet based on highly processed foods.
• However, the wide availability, convenience and even relatively low cost of highly processed foods in our supermarkets should not compel us to make those relatively unhealthy choices.

     The Bottom Line

• As food consumers, our choice of high-fiber foods in preference to fiber-impoverished ultra-processed foods likely has a major positive impact on our future health and wellbeing and will ultimately influence the strategic commercial plans of food companies, with likely future improvements in the fiber content of processed food production.
• In our capitalist culture of modern Westernized societies with ‘consumer as king’,
• we all need to vote with our mouths, and in the process, re-discover the joy of cooking with fresh and fiber-replete ingredients.

 

      References:

       1.Oat beta-glucan – Wikipedia

      2.Increasing Fiber Intake | Patient Education | UCSF Health

     3.Scientists Create ‘Invisible Fiber’ That Can Make Cakes And Pizzas Better For You : ScienceAlert

     4.What Is Inulin And Why Is It Being Added to So Many Foods? A Nutritionist Explains : ScienceAlert

     5.Difference Between Soluble & Insoluble Fiber

     6.Impact of Plant-Based Dietary Fibers on Metabolic Homeostasis in High-Fat Diet Mice via Alterations in the Gut Microbiota and Metabolites – ScienceDirect

     7.Ileibacterium – Wikipedia

     8.Obese Mice Losing Weight Due to trans-10,cis-12 Conjugated Linoleic Acid 8.Supplementation or Food Restriction Harbor Distinct Gut Microbiota – ScienceDirect

    9.Differential effects of plant-based flours on metabolic homeostasis and the gut microbiota in high-fat fed rats | Nutrition & Metabolism | Full Text

    10.What Is Ozempic? : ScienceAlert

    11.How your morning oats could help you manage your weight | University of Arizona News

    12. https://nutritionsource.hsph.harvard.edu/carbohydrates/fiber/