Fiber is an underrated aspect of nutrition, even among those who pride themselves on a healthy diet. It is a neglected afterthought behind the big three macros, themselves further outshined in society by the preeminence of the single calorie number. Worse yet, fiber is often mired in a comical reputation of being reserved for those with bowel issues, and as serious as that may be, it is just the tip of the iceberg lettuce. In fact, the neglect of indigestible fiber in the American diet is doing life-altering damage to people every day. In this article I will argue for its due respect.

On a nutrition label, dietary fiber falls under the carbohydrate section, as it is indeed made of chains of sugar molecules. However, this grouping is misleading given how differently dietary fiber is processed in the body from other sugar carbohydrates. Carbohydrates are classified as “simple” or “complex” depending on the length of their sugar molecule chain. Simple carbohydrates are one (monosaccharide) or two (disaccharide) sugar molecules, and complex carbohydrates (polysaccharides) are long chains of bonded sugar molecules.

The increased complexity of polysaccharides makes them more difficult to break down in the body, therefore reducing the bioavailability of the sugar. This is why digestible complex carbohydrates are generally healthier than simple carbohydrates, as they reduce the intensity of blood sugar spikes and therefore temper the insulin response in the body to a more manageable level.

But let’s stay focused on the indigestible complex carbohydrate: the fiber. These polysaccharides are bound in such a way that human digestive enzymes cannot break them apart. They can be further stratified into soluble and insoluble fiber.

Soluble Fiber

Soluble fiber means that the compound breaks down in water to form a gel like substance. It is often found in legumes, fruits, vegetables, oats, and barley. When in a gel form, it slows down digestion, which helps regulate the absorption of glucose and cholesterol, and also acts as a prebiotic to feed beneficial gut bacteria.

Insoluble Fiber

Insoluble fiber does not break down in water, and remains mostly intact through the digestive system. It may be found in whole grains, nuts and seeds, vegetables like celery and zucchini, or fruit skins. The bulk that it adds helps promote regular bowel movements, improve colon health, and increase the sensation of fullness or satiety.

Both insoluble and soluble fiber tend to be found in the similar types of foods, all of which are ultimately plant material. Together, the two types of fiber have tremendous health benefits that address the immediate health concerns of a significant portion of Americans. The recommended daily intake for fiber is around 25 grams a day for women, and 38 grams a day for men (about 14g of fiber is recommended per 1000kcal). Most American adults do not consume half of that, and only about 3-5% of Americans get to this level.

To explore the benefits, I will use the research of James W. Anderson et al. in the paper Health Benefits of Dietary Fiber (2009).

Cardiovascular Health

High fiber intake reduces the risk of coronary heart disease, stroke, and hypertension.

• In 7 cohort studies observing a total of 158,000 individuals it was found that coronary heart disease prevalence is 29% lower in individuals in the highest quintile (the top 20%) of dietary fiber intake compared to those in the lowest quintile.
• In four studies, totaling 134,000 people, a similar reduction in the prevalence of strokes was found; the top quintile of dietary fiber consumers had a 26% reduction in the prevalence of ischemic strokes.
• For hypertension, often dubbed the “silent killer”, increased fiber consumption is associated with a reduction in systolic and diastolic blood pressure. The soluble fiber, such as that found in oats, appears to be the form that is responsible for the improved blood pressure readings and is also effective at reducing harmful LDL cholesterol levels in the body. Interestingly, the soluble fiber can reduce LDL cholesterol values by 5.3% to 13% without significantly changing the healthier HDL cholesterol concentrations.

Diabetes Prevention and Management

It has only been about 100 years since a diabetes diagnosis was considered a death sentence. Since then, the discovery of insulin has saved millions of lives and allowed for a quality of life for diabetics that was previously inconceivable (read this short essay for a fascinating history of the discovery of insulin).

However, more Americans than ever have diabetes. About 1 in 10 Americans is diagnosed with diabetes, and an astounding 1 in 3 are considered prediabetic of which 80% are unaware of this diagnosis. These numbers are expected to increase significantly by 2030.

Higher societal intake of dietary fiber can help avoid this eventuality.

• Results from 5 epidemiological studies covering almost 240,000 subjects suggested that 19% experienced a protective effect from a high fiber diet.
• In 11 estimates covering 427,000 individuals with high levels of whole grain or cereal fiber consumption suggested there was a 29% reduction in the development of diabetes.
• In a Randomized Control Study, individuals with the highest level of fiber consumption had a 62% reduction in progression of prediabetes to diabetes in a 4.1 year period compared to the lowest fiber intake.

Obesity Prevalence and Management

More than 2 in 5 Americans are obese, about a quarter of whom are morbidly obese. Even with incredible medical developments like Ozempic I do not see this problem resolving itself in a sustainable way. The current cost and production constraints of GLP-1 agonists are just a couple of the dozens of roadblocks from a true societal level anti-obesity drug. I suspect there may be other costs to GLP-1 agonists other than price tag.

The fortunate news is that there exist dozens of alternatives for addressing obesity that do not involve drug prescription, one of which is increasing fiber consumption.

• Two cross-sectional studies (including more than 100,000 persons) and four prospective cohort studies (including more than 100,000 persons) indicated a strong negative association between fiber intake and obesity.
• The cross-sectional studies indicated that men and women with the highest level of fiber consumption have a relative risk for obesity of 0.77 (95% CI, 0.68–0.87) compared to those with the lowest fiber intake level.
• Prospective cohort studies reported that women and men with the highest level of fiber consumption had lower rates of weight gain and less obesity than those with the lowest level of fiber intake, with relative risks of 0.70 (95% CI, 0.62–0.78). Therefore, these studies suggest that high-level fiber consumption can reduce the risk of gaining weight or developing obesity by 30%.

Finally, though the research is not yet as conclusive as for its other benefits, there is a theoretical protective effect from dietary fiber against colon cancer. This is an area of ongoing research of immense importance. While cancer rates have been declining over the past few decades, colorectal cancer rates have been increasing in America particularly in younger demographics. While some of this increase may be due to increased screenings, it is likely that there are foods in the American diet that are carcinogenic. The US Preventive Services Task Force recommends that adults age 45 to 75 be screened for colorectal cancer. Due to the uptick in early-onset colorectal cancer, it is likely that this guidance will creep younger over time. It is currently accepted in the medical community that high fiber intake has a mildly protective effect against colon cancer, though the method by which it achieves this and its effectiveness is yet to be understood.

The benefits of fiber rich diets are scientifically clear and worthwhile, and yet there’s a mysterious lack of enthusiasm behind increasing consumption.

There is an aspect of American culinary culture that deems a proper meal incomplete without a protein. There is also an aspect that demonizes a high total carbohydrate value, without consideration for the nuanced effects of dietary fiber compared to simpler sugars. Further, based on our standard nutritional label, foods like oats or spinach appear to be devoid of useful macronutrients but they remain highly nutritious. These factors combine to steer consumers away from fiber, even those who are conscientious about their health. People, like myself, have to be educated specifically on the benefits of fiber in order to make an effort to integrate it into a diet. Instead of being avoided for being macronutritionally sparse, fiber can be consumed in significant quantities as a foundation for a more substantial macronutrient profile on top. Doing so offers an asymmetric risk/reward payoff that I see as too valuable to pass up, and too important to not share.

Below is a list of some useful fiber sources.

May they bring you good health.

Fruits