How much fiber do I need a day?

How it works

1. The 2020-2025 Dietary Guidelines for Americans set fiber goals at 14 g for every 1,000 calories eaten. We multiply that by the calories you enter.
2. The fixed-number comparison is the National Academies Adequate Intake: 25 g for women and 38 g for men up to age 50, and 21 g and 30 g after 50.
3. The two differ because one follows how much you eat and the other assumes a typical diet. When appetite has shrunk, the calorie-based number is the realistic one to aim for.

Before you use the number

• Add fiber a little at a time and drink plenty of fluids with it, as the NIH's digestive health institute advises. A sudden jump tends to mean bloating.
• The 2025 GLP-1 nutrition advisory notes that high-fiber foods slow the stomach further and can worsen constipation, and that avoiding fatty or high-fiber foods in the first few days of treatment can ease nausea. Side effects are also more likely after a dose increase, so that is a sensible time to go gently too.
• Severe stomach pain, vomiting, or blood in your stool is a call to your doctor, not a fiber question.

This is general information, not medical advice, and it does not replace your prescriber or a dietitian who knows you.

Questions people ask

Sources

• Dietary Guidelines for Americans 2020-2025, Appendix 1 (14 g per 1,000 calories)
• National Academies: fiber Adequate Intake (38 g / 25 g, 30 g / 21 g over 50)
• NIDDK: eating, diet and nutrition for constipation
• Mozaffarian et al., Nutritional priorities to support GLP-1 therapy for obesity: a joint advisory from ACLM, ASN, OMA and TOS (2025)

Figures checked against the sources above on 21 September 2026.