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While nutritional needs and preferences vary, there are certain agreed upon dietary recommendations with clear evidence of universal health benefits. Fiber is one such food group – and its intake may even prolong life.

What is fiber?

The FDA defines fiber as “non-digestible soluble and insoluble carbohydrates… intrinsic and intact in plants.” Soluble fiber attracts and dissolves in water, creating a gel like consistency that slows digestion. Examples of foods or supplements with soluble fiber include oats, beans, apples, citrus, chia and flax seeds, psyllium (ie. Metamucil), wheat dextrin (ie. Benefiber), and methylcellulose (ie. Citrucel). Insoluble fiber is less digestible and remains relatively intact as it passes through the gastrointestinal tract. Whole wheat or whole grain products, cauliflower, and sweet potatoes are examples of foods that have insoluble fiber.

The Food and Drug Administration suggests that adults, on average, aim for at least 28g of fiber per day, acknowledging some variability depending on sex, age, and total caloric needs. However, according to the Dietary Guidelines for Americans (2020-2025), published by the United States Department of Agriculture, 90% of women and 97% of men do not meet these minimal fiber intake recommendations, noting this is a public health concern.

Why is fiber so important?

A significant amount of research has been done on the health benefits of fiber and studies have consistently shown positive results. Soluble fiber has been shown to play a role in lowering cholesterol, stabilizing blood sugar, and promoting satiety. Insoluble fiber helps to regulate and promote bowel movements by bulking stool.

A systematic review published in 2019 examined 185 prospective studies and 58 clinical trials to better evaluate for relationships between carbohydrate quality and non-communicable (not transferable) disease incidence, death rates, and risk factors. When comparing the highest to lowest dietary fiber consumers, observational data displayed a 15-30% decrease in all-cause and cardiovascular related mortality, incidence of coronary heart disease, stroke, type 2 diabetes, and colorectal cancer. Clinical trials showed higher fiber consumers had significantly lower bodyweight, systolic blood pressure, and total cholesterol. This risk reduction was greatest when daily fiber intake was between 25-29 grams.

An updated review from 2023 produced similar results and provided additional evidence of a protective association between fiber intake and mortality. It showed high consumption of fiber decreased risk of all cause mortality by 23%, cardiovascular-related mortality by 26%, and cancer-related mortality by 22%. Insoluble fiber seemed to be more effective than soluble fiber in reducing total mortality.

Mechanisms by which fiber intake impacts longevity

At the biological level, fiber seems to exert a positive effect on telomeres – regions of repetitive DNA sequencing at the ends of chromosomes that prevent them from becoming frayed or entangled with other chromosomes. Each time a cell divides, the telomeres shorten until it then becomes impossible for the cell to divide further, resulting in cell death. Shortening of telomeres is thus a key mechanism of aging. Factors such as physical activity, obesity, smoking, sleep quality/quantity have all been shown to impact telomere length. Research also shows that diet – including fiber intake – may play a key role.

One study of 5,674 adults evaluated fiber consumption via 24h recall and telomere length via polymerase chain reaction. Controlling for age, gender, race, housing status, and misreported energy intake, researchers found a linear relationship between fiber intake and telomere length. For every 10g increase in fiber intake per 1000 kcal, telomeres were found to be 83 base pairs longer. This corresponds to an average of 5.4 fewer years of biological aging, based on previous research indicating that each additional year of aging is linked to a telomere shortening of 15.5 base pairs.

Another major benefit of fiber intake that we have often discussed in this newsletter is the positive effect on the health of the gut microbiome, specifically on its diversity and richness. The complex carbohydrates making up fiber are the optimal food for our gut microbes, increasing the ratio of beneficial to harmful species, and increasing the gut microbial short chain fatty acid production. Short chain fatty acids, in particular butyrate, have widespread anti-inflammatory effects throughout the body, including the brain.

How to increase fiber intake

There are obviously significant benefits to increasing fiber intake, though it is recommended that this is done gradually to minimize side effects such as gas or bloating as your body adjusts. Some easy ways to start are having a morning bowl of oatmeal topped with fresh fruit or whole grain toast with avocado, topping yogurt with chia or hemp seeds, snacking on popcorn with nuts, and integrating kale, spinach, or tomatoes into your meals.
Regularly eating a variety of these foods may help you surpass the recommended amount and may actually increase your health span, the years you live without developing a chronic disease.