Nutrition news tends to reward novelty. A new supplement, a fasting protocol, an exotic superfood. Fiber is the opposite. It has been recommended for decades, it costs almost nothing and it rarely trends. It also has one of the strongest evidence bases of anything you can eat.
The Lancet review
In 2019, researchers at the University of Otago in New Zealand published a large analysis in The Lancet1, commissioned by the World Health Organization to inform its dietary guidance. They pooled data from about 185 prospective studies and 58 clinical trials covering several decades of research.
The findings were consistent. People who ate the most fiber had 15 to 30 percent lower all-cause and cardiovascular mortality than people who ate the least. They also had lower rates of coronary heart disease, stroke, type 2 diabetes and colorectal cancer. Clinical trials in the same review showed that higher fiber intake was associated with lower body weight, blood pressure and cholesterol.
The benefits were greatest at 25 to 29 grams a day, and the data suggested that going higher could bring further benefit. Whole grains showed similar patterns. Refined carbohydrates did not.
Fiber has been recommended for decades, it costs almost nothing and it rarely trends.
The gap
The Dietary Guidelines for Americans2 have long recommended about 14 grams of fiber for every 1,000 calories, which works out to roughly 25 grams a day for many women and 30 or more for many men. The 2020 to 2025 edition reported that more than 90 percent of women and 97 percent of men did not meet that recommendation. Typical intake sits around 15 grams.
The reason is not mysterious. Fiber is found in plants that are minimally processed, which are beans, lentils, whole grains, vegetables, fruit, nuts and seeds. A diet built around refined grains, meat, cheese and packaged snacks will run short no matter how healthy it feels.
Why it works
Fiber is the part of plant food that human enzymes cannot digest. That turns out to be its strength.
Soluble fiber, found in oats, barley, beans and many fruits, forms a gel in the gut that slows the absorption of sugar and binds bile acids, which helps lower LDL cholesterol. Insoluble fiber, found in wheat bran, vegetables and the skins of fruit, adds bulk and keeps digestion moving.
Many fibers are fermented by bacteria in the colon, producing short-chain fatty acids such as butyrate. Those compounds feed the cells lining the colon and appear to influence inflammation and metabolism throughout the body. Researchers are still mapping the details, but a diet rich in varied fiber supports a more diverse gut microbial community.
Fiber also makes meals more filling for fewer calories, which helps explain its association with healthier weight, and why it matters even more for people on GLP-1 medications, who eat smaller portions and are prone to constipation.
Getting to 30 grams without thinking about it
Counting fiber is tedious. Building it into habits is easier.
Beans and lentils are the most efficient source, with roughly 6 to 8 grams per half cup cooked. Adding a can of rinsed beans to soups, salads, chili or pasta is the single biggest lever.
Oats and barley contribute soluble fiber at breakfast and in soups. Whole grain bread should list a whole grain as the first ingredient, not just say "multigrain."
Raspberries, pears, apples with the skin and berries in general are among the highest fiber fruits. Vegetables count, especially broccoli, Brussels sprouts, artichokes, carrots and leafy greens.
Nuts and seeds, including chia, flax and almonds, add fiber along with healthy fats. Popcorn is a whole grain snack.
A Mediterranean pattern, rich in vegetables, legumes, whole grains, nuts and olive oil, delivers fiber naturally. The PREDIMED trial3 found that this way of eating reduced major cardiovascular events in people at high risk, and we explore how to eat it with a New England accent.
Go slowly
A sudden jump from 15 to 35 grams can cause bloating, gas and cramping as gut bacteria adjust. Increase over two to three weeks, spread fiber across meals, and drink more water, since fiber works best when it has fluid to hold. People with inflammatory bowel disease, a history of bowel obstruction or certain digestive conditions should talk with their clinician before making big changes.
Fiber supplements such as psyllium can help with cholesterol and regularity, but they do not replicate the full package of nutrients and plant compounds that come with whole foods.
The long view
Most American adults eat roughly half the 25 to 38 grams a day that dietary guidelines suggest, which means the gap is large and the fix is cheap. A cup of cooked lentils carries about 15 grams. A pear with the skin has about 6. Adding fiber gradually over two or three weeks, with more water, keeps the bloating that discourages most people to a minimum.
