What it does in the body
- Stool bulk formation and regularity
- Accelerated intestinal transit time
- Constipation prevention
- Diverticular disease prevention
- Colorectal cancer risk reduction (mechanical and dilution effects)
How much you need (Daily Value)
| Group | Recommended | Source |
|---|---|---|
| Adult male | Part of 38g/day total fiber; most fiber should be insoluble (~60-70% of total) | IOM AI |
| Adult female | Part of 25g/day total fiber | IOM AI |
| Pregnancy | Part of 28g/day total fiber; helps prevent pregnancy-related constipation | IOM |
| Children | Part of age-appropriate total fiber recommendation | AAP |
| Older adults | 25-30g/day total fiber; ensure adequate fluid to prevent impaction | IOM |
Richest food sources
| Food | Amount | Where |
|---|---|---|
| Wheat bran | 42g per 100g | global |
| Cauliflower (cooked) | 2g per 100g | global |
| Green beans (cooked) | 2.5g per 100g | global |
| Whole wheat bread | 6g per 100g | global |
| Brown rice (cooked) | 1.5g per 100g | east-asia |
| Cabbage/sauerkraut | 2g per 100g | europe |
| Corn/maize (cooked) | 2g per 100g | mesoamerica |
| Cassava/yuca (cooked) | 1.8g per 100g | sub-saharan-africa |
If you don't get enough
Mild: Constipation, hard stools, straining
Moderate: Chronic constipation, hemorrhoid development, diverticular disease
Severe: Fecal impaction, significantly increased colorectal cancer risk with chronically low intake
Time to onset: Constipation within days of low intake; chronic disease risk develops over years
Too much
Upper limit: No UL. Very high intake (>50-70g/day total fiber) with inadequate water can cause bloating, gas, and rarely intestinal obstruction (bezoar formation)
Bloating, flatulence, abdominal discomfort. May worsen IBS symptoms. Can reduce mineral absorption if excessive
How well you absorb it
Not absorbed; passes through the GI tract largely intact. Minimal colonic fermentation (~5-10% of cellulose fermented)
Helped by: Adequate water intake (prevents compaction), Physical activity (enhances GI motility), Gradual dose increase
Hindered by: Dehydration (can cause fiber compaction), Sedentary lifestyle (reduced GI motility)
Cooking & storage
Cooking softens insoluble fiber (breaking down cellulose structure) but does not eliminate it. Raw vegetables have more rigid fiber; cooking makes them easier to chew and digest while retaining bulk-forming properties. Overcooking significantly reduces fiber's structural integrity.
Nutrisize Health totals every nutrient from what you actually eat, against targets set for your age and sex, and flags what's short — across 4,995 foods, on your device.
