Fiber — the most underrated nutrient

Fiber is the part of plant foods that the body doesn't digest: the husks of grains and the fibers of vegetables, fruit and legumes. It supplies almost no calories and sits in fine print on labels — and that's exactly why it's underrated.

What the series of meta-analyses in The Lancet found

In 2019, The Lancet published a major piece of work by Andrew Reynolds and colleagues — a series of systematic reviews and meta-analyses that pooled data from dozens of studies and nearly a hundred clinical trials on carbohydrate quality and health.

The conclusion: in people who consumed the most fiber, compared with those who ate the least, the risk of death from all causes and from cardiovascular disease was 15-30% lower. The greatest benefit was seen at an intake of around 25-29 grams of fiber a day, and the relationship was dose-dependent: more fiber, lower risk.

Why fiber works the way it does

There are several mechanisms. Fiber slows the absorption of sugars and smooths out glucose spikes, helps control cholesterol, provides satiety at a low calorie cost (which makes weight control easier) and feeds the gut microbiome. Bacteria ferment it into short-chain fatty acids that benefit metabolism and the intestinal wall.

How much that is in food

Most people eat noticeably less than the recommended amount. Reaching 25-30 grams is realistic without anything exotic: whole-grain bread and grains instead of refined ones, legumes (lentils, chickpeas, beans), vegetables and fruit with the skin on, nuts and seeds. Importantly, this is about fiber from whole foods, not from powdered supplements — in the research the benefit is consistently tied to foods. And you should increase your intake gradually, drinking plenty of water, so as not to overload the digestive tract.

Soluble and insoluble

Fiber comes in two main types, and both are beneficial in different ways. Soluble fiber (oats, legumes, apples, citrus) forms a gel in water, slows absorption and helps control cholesterol and blood sugar. Insoluble fiber (bran, vegetable skins, whole grains) adds bulk and improves bowel function. There's no need to chase the "right" type: a varied diet of whole plant foods naturally provides both. That's one more argument for foods rather than a single supplement — a powder usually contains just one kind of fiber.

Why fiber is "out of fashion"

Fiber has no marketing. It can't be sold as a shiny jar promising quick results, it produces no instant effect and it doesn't look impressive on social media. Protein is easy to turn into a bar or a shake, vitamins into pretty packaging, while "eat more vegetables and whole grains" sounds banal. Yet that very dull recommendation is backed by one of the strongest evidence bases in nutrition science. The paradox is that the most underrated nutrient is also one of the cheapest and most accessible.