Fibre gets talked about as a bathroom subject, which is probably why it is ignored. It is closer to a foundation: it feeds the bacteria in your gut, slows how quickly sugar arrives in the blood after a meal, and is one of the few dietary changes with decades of consistent evidence behind it.
How much is actually recommended
Common guidance lands somewhere around 25 to 30 grams a day for adults, and surveys repeatedly find most people eating roughly half that. The gap is not usually caused by one missing food; it is caused by a week of meals built mostly from refined grains, where fibre was never really present to begin with.
What it does beyond regularity
Soluble fibre forms a gel that slows digestion, which is part of why meals with fibre tend to keep people full longer than meals without it. Insoluble fibre mostly adds bulk and helps things move. Diets higher in fibre are associated with better cholesterol levels and steadier blood sugar — associations strong enough that they show up across very different populations.
Add it slowly, and add water
The most common reason people quit is going from very little fibre to a great deal in two days, which reliably produces bloating and cramps. Increasing gradually over a couple of weeks, and drinking more water as you do, avoids most of that. This is unglamorous advice and it is the part that decides whether the change survives.
Food first, supplements second
Beans, lentils, oats, fruit with the skin on, and vegetables do the job and bring other nutrients with them. Fibre supplements can help someone who genuinely cannot get there with food, but they are a patch on a diet rather than a replacement for one.
When it is not just fibre
Persistent bloating, pain, blood, unexplained weight loss, or a lasting change in your normal pattern are reasons to see a doctor rather than reasons to buy more supplements. Those symptoms have causes that fibre does not fix and can hide.
Most people do not need a new diet. They need one more fibre-containing thing at two meals a day, for long enough to notice.