How much oat bran per day is too much?

One cup = 1 cup (3.3 oz, 94 g). USDA FoodData Central, Oat bran, raw. Limits count everything you eat and drink that day, so other foods and supplements use up part of each one.

• Level A In 18 randomized trials with 1024 people, whole oats and oat bran (20 to 136 g a day) lowered HbA1c, fasting glucose and fasting insulin, while beta-glucan extracts on their own did not. Food Funct, 2016
• Level B In a 6-week randomized dose trial of 156 adults with high LDL cholesterol, 2 oz (56 g) of oat bran a day lowered LDL by 15.9% against a farina control, more than the same weight of oatmeal. JAMA, 1991
• Level B In a blinded crossover trial of free-living adults with raised LDL on a step I diet, 0.99 oz (28 g) of oat bran twice a day lowered LDL by 3.9% while wheat cereal and diet alone saw LDL rise. J Fam Pract, 1991
• Level B Adding 3.6 oz (102 g) of oat bran a day (6 g soluble fiber) to a low-fiber diet for 2 weeks cut total cholesterol by 14% versus 4% on control in 24 young adults, and raised fecal energy loss by 37%. Eur J Clin Nutr, 2011
• Level B 1.1 oz (30 g) of oat bran a day (8.9 g fiber) for 3 months on top of dietary advice lowered office systolic and diastolic blood pressure and reduced antihypertensive drug use in 50 patients with essential hypertension. Nutr Metab Cardiovasc Dis, 2021

Only studies that give the amount eaten. Levels: A is a meta-analysis of trials, B a randomized trial, C an observational study. How we grade evidence.

• Level E NIH sets the adult upper limit for iron at 45 mg a day and notes high-dose supplements cause stomach upset, constipation, nausea and diarrhea. NIH Office of Dietary Supplements, Iron fact sheet for health professionals
• Level D A 1989 case report describes small-bowel obstruction caused by a bezoar, a solid mass, of oat bran. N Engl J Med, 1989

If you have kidney disease, take blood thinners or other medicines, or are pregnant, the right amount for you is a question for your clinician.

In 156 adults with high LDL, 2 oz (56 g) a day for 6 weeks lowered LDL by 15.9%, a significant difference from a farina control (Level B). In 50 people with high blood pressure, about 1 oz (30 g) a day for 3 months on top of diet advice lowered systolic and diastolic pressure more than diet advice alone (Level B).

Iron is the first nutrient limit, at about 8.5 cups a day, far past these doses. Calories come first in practice: two cups are 462 calories.

A 1989 case report describes a small-bowel obstruction caused by a solid mass of oat bran (Level D).

If you have celiac disease, a meta-analysis found that pure, uncontaminated oats eaten for 12 months did not affect symptoms, though the evidence quality was low (Level A). Across 40 gluten-testing studies, oats were the most contaminated food (Level C). Ask your clinician whether oat bran, and which kind, fits your diet.

Evidence behind this note

1. Level A In 18 randomized trials with 1024 people, whole oats and oat bran (20 to 136 g a day) lowered HbA1c, fasting glucose and fasting insulin, while beta-glucan extracts on their own did not. Food Funct, 2016
2. Level B In a 6-week randomized dose trial of 156 adults with high LDL cholesterol, 2 oz (56 g) of oat bran a day lowered LDL by 15.9% against a farina control, more than the same weight of oatmeal. JAMA, 1991
3. Level B 1.1 oz (30 g) of oat bran a day (8.9 g fiber) for 3 months on top of dietary advice lowered office systolic and diastolic blood pressure and reduced antihypertensive drug use in 50 patients with essential hypertension. Nutr Metab Cardiovasc Dis, 2021
4. Level D A 1989 case report describes small-bowel obstruction caused by a bezoar, a solid mass, of oat bran. N Engl J Med, 1989
5. Level A A meta-analysis of 28 studies in celiac disease found that pure, uncontaminated oats eaten for 12 months did not affect symptoms (SMD -0.22, 95% CI -0.56 to 0.13), with no difference between adults and children. Gastroenterology, 2017
6. Level C A meta-analysis of 40 food testing studies found gluten above 20 mg/kg in 15.12% of gluten-free foods, and oats were the most contaminated food. Br J Nutr, 2022

Written from the data and studies on this page, reviewed by the Bioma editorial system. How we verify.

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