Tools

Fiber calculator

Adults need roughly 25 g of fiber a day for women and 38 g for men — and most people in Western countries get about half of that. This calculator gives your target and shows what it takes to reach it.

Sex

Age

Your daily fiber target

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Choose your details to see your target.

Where the numbers come from

The commonly used targets come from the Institute of Medicine's adequate intake of about 14 g of fiber per 1,000 kcal. For most adults that lands at 25 g a day for women and 38 g for men, dropping to roughly 21 g and 30 g after age 50 as energy needs fall.

Why it is worth the effort

This is one of the better-supported things in nutrition. Higher fiber intake is associated with lower rates of cardiovascular disease, type 2 diabetes and colorectal cancer, and in controlled trials an extra 14 g a day was linked with eating roughly 10% fewer calories — largely through satiety rather than willpower.

What 30 g actually looks like

Raspberries, 100 g — about 6.5 g
Lentils, cooked, 200 g — about 16 g
Rolled oats, 40 g dry — about 4 g
Wholegrain bread, 2 slices — about 5 g
Almonds, 30 g — about 3.5 g
Broccoli, 150 g cooked — about 5 g
Avocado, half — about 5 g

Go up slowly — this is the part people get wrong

Jumping from 12 g to 30 g overnight reliably produces bloating, gas and cramps, and that is usually why people conclude fiber "doesn't agree" with them. Add roughly 5 g a week, drink more water as you go, and spread it across meals. Most discomfort settles within a couple of weeks as the gut microbiota adjusts.

When to talk to a doctor first

If you have inflammatory bowel disease, a history of bowel obstruction or strictures, have had recent bowel surgery, or are in a flare, do not increase fiber on your own — the right approach can be the opposite. Persistent bloating with blood in the stool, weight loss or severe pain needs medical assessment rather than a dietary experiment.

Frequently asked questions

How much fiber should I eat a day?

About 25 g for adult women and 38 g for adult men, based on roughly 14 g per 1,000 kcal. After 50 the targets fall to about 21 g and 30 g as energy needs drop.

Why does fiber make me bloated?

Usually because the increase was too fast. Adding about 5 g a week with more fluid gives the gut microbiota time to adapt, and most discomfort settles within a couple of weeks.

Is a fiber supplement as good as food?

Supplements can help close a gap, but whole foods bring different fiber types plus the rest of the nutrients. Food first, supplements to fill in — and check with a doctor if you have a gut condition.