Grits and oatmeal: the oats have the trials, the grits have none

In people with type 2 diabetes, a meta-analysis of 14 controlled trials and two observational studies found oats lowered HbA1c by 0.42 percentage points (95% CI 0.23 to 0.61) and LDL cholesterol by 11 mg/dL (0.29 mmol/L) against controls, from a search of PubMed alone up to 2015. Almost everything on this page is about oatmeal. We found no human study of corn grits and no trial comparing the two. What we have for grits is a WHO definition, dry milled maize with particles of 600 to 1400 micrometres, coarser than corn meal. How the oats are processed changes the blood sugar response. Across 72 glycemic index tests, instant oatmeal scored about 75 and quick oats 71, against 55 for steel-cut and 53 for large-flake oats, and most of those tests were small. The cholesterol effect is real and small. A 1999 meta-analysis of 67 trials put it at about 0.13 mmol/L lower total and LDL cholesterol for 3 g of oat soluble fiber, which is three 0.99 oz (28 g) servings of oatmeal.

How much is actually in it

• WHO defines grits as dry-milled maize with particles of 600 to 1400 micrometres, coarser than corn meal, and notes that in the eastern USA grits are made from white maize. — maize products, global guideline Evidence E source
  Grits 600-1400 um; corn meal 300-600 um; flour under 212 um

What a real portion looks like

• In the US dietary survey database, a cup of cooked grits and a cup of cooked oatmeal both weigh 8.5 oz (240 g), but a cup of dry grits yields 965 g cooked against 485 g for dry oatmeal. — FNDDS portion weights Evidence E source
  1 cup cooked 240 g (both); 1 cup dry yields 965 g grits vs 485 g oatmeal

What your body absorbs

• In a crossover trial in 40 people, each gram of oat beta-glucan added to instant oatmeal cut the blood glucose area by 7% and the glucose peak by 15%. — 40 subjects, single test meals, 2 h glucose (n = 40) Evidence B source
  Per g oat beta-glucan: iAUC -7%, peak-rise -15%

What cooking and storage change

• Across 72 glycemic index tests, instant oatmeal scored a GI of about 75 and quick oats 71, against 53 to 55 for large-flake and steel-cut oats. — 72 glycemic index measurements from 20 publications and 17 unpublished tests (n = 72 tests) Evidence B source
  GI instant 75 (SE 2.8), quick 71 (SE 2.7), large-flake 53 (SE 2.0), steel-cut 55 (SE 2.5)
• In a crossover RCT in 48 adults, instant oatmeal increased fullness and lowered energy intake at lunch 4 hours later compared with an equal-calorie ready-to-eat oat cereal. — 48 healthy adults 18 years or older, single test breakfasts (n = 48) Evidence B source
  Fullness p = 0.001; lunch energy intake lower (p = 0.012)
• In 8 volunteers, porridge made from oat flakes gave a lower blood glucose response than porridge made from oat flour with the same nutrients. — 8 volunteers, crossover, 3 h (n = 8) Evidence C source
  Lower glucose response for flake porridge; size not given in abstract
• By the USDA retention table for Breakfast Cereals, cooking regular or quick grits and oatmeal keeps the same share of nutrients: about 70% of folate, 80% of thiamin and 95% of iron. — food group Breakfast Cereals, codes 358 and 352 Evidence E source
  Folate 70%, thiamin 80%, riboflavin 90%, iron 95%, zinc 100% (identical for both codes)

What it does to your health

• In a 45-day RCT in 62 mildly hypercholesterolemic adults, an oatmeal diet lowered LDL cholesterol by about 13% and total cholesterol by about 9% versus control. — 62 mildly hypercholesterolemic individuals in China, 45 days (n = 62) Evidence B source
  LDL-c -12.97% (p = 0.004); TC -8.59% (p = 0.013)
• In 122,680 US health professionals, eating cooked oatmeal or oat bran at least twice a week was linked to a 22% lower risk of gout. — 122,680 individuals, Health Professionals Follow-up Study and Nurses' Health Study (n = 122680) Evidence C source
  HR 0.78 (95% CI 0.70-0.86) for 2 or more servings per week

Safety, limits and interactions

• In a pilot RCT of 43 breastfed infants, oatmeal cereal as a first food raised gut microbial richness compared with beef after 1 week. — 43 exclusively human milk fed infants with no prior complementary food (n = 43) Evidence B source
  Observed ASVs higher with oatmeal cereal vs beef (P = 0.024)
• A case report describes severe anaphylaxis in a 52-year-old man caused by booklice infesting stored oatmeal, not by the oats themselves. — one 52-year-old man in Japan (n = 1) Evidence D source
  Anaphylaxis; skin prick positive only to leftover oatmeal

What people believe that the data does not support

• US rules let rolled oats carry the soluble fiber and heart disease health claim only if they provide at least 4% beta-glucan and 10% total fiber on a dry basis, and no such claim exists for corn grits. — foods labeled in the United States Evidence E source
  Eligibility thresholds: beta-glucan 4% dwb, total dietary fiber 10%

Who this works differently for

• In people with type 2 diabetes, a meta-analysis of 14 controlled trials found oats lowered HbA1c by 0.42 percentage points and LDL cholesterol by 11 mg/dL (0.29 mmol/L) versus controls. — patients with type 2 diabetes, 14 controlled trials and 2 observational studies (n = 16 studies) Evidence B source
  HbA1c MD -0.42% (95% CI -0.61 to -0.23); FBG -7 mg/dL (95% CI -10 to -3.4; metric: -0.39 mmol/L, -0.58 to -0.19); LDL-C -11 mg/dL (95% CI -19 to -3.5; metric: -0.29 mmol/L, -0.48 to -0.09)
• In a 45-day trial of 80 g a day of oatmeal in 56 hypercholesterolemic adults, people with the CYP7A1 rs3808607 TT genotype lowered LDL more than G allele carriers. — 62 medication-naive hypercholesterolemic patients, 56 completers, 45 days (n = 56) Evidence B source
  Genotype-diet interaction for LDL p = 0.04; TT vs GG/GT p = 0.02

What is still unknown

• A meta-analysis of 67 controlled trials found 3 g of oat soluble fiber, about three 0.99 oz (28 g) servings of oatmeal, lowers total and LDL cholesterol by only about 5 mg/dL (0.13 mmol/L). — 67 controlled trials of soluble fiber (n = 67 trials) Evidence B source
  LDL -2.2 mg/dL (-0.057 mmol/L) per g soluble fiber (95% CI -0.070 to -0.044); about -5 mg/dL (-0.13 mmol/L) for 3 g

The bottom line

Cooked, both porridges weigh 8.5 oz (240 g) a cup in the US dietary survey. Dry, they behave very differently, since a cup of dry grits yields 965 g cooked and a cup of dry oatmeal yields 485 g. By the USDA retention table, cooked regular or quick cereal and cooked oatmeal keep the same shares, about 70 percent of folate, 80 percent of thiamin and 95 percent of iron, as group factors set in 1975. The single trials agree in direction and are small. In 62 adults in China with mildly high cholesterol, an oatmeal diet for 45 days lowered LDL by about 13 percent against control, and the authors call their sample small. In 40 people eating single test meals, each gram of oat beta-glucan added to instant oatmeal cut the two-hour glucose area by 7 percent and the glucose peak by 15 percent. In 48 adults, instant oatmeal left people fuller and eating less at lunch than an equal-calorie ready-to-eat oat cereal (p = 0.012), and the abstract gives no calorie figure. In 8 volunteers, porridge from oat flakes raised blood sugar less than porridge from oat flour with the same nutrients. In 122,680 US health professionals, cooked oatmeal or oat bran at least twice a week went with a 22 percent lower risk of gout (HR 0.78, 95% CI 0.70 to 0.86), an observational link. US rules let rolled oats carry the soluble fiber and heart disease claim only when they provide at least 4 percent beta-glucan and 10 percent total fiber on a dry basis. Grits are not named in that rule. The only safety card is a single case. A 52-year-old man in Japan had severe anaphylaxis from booklice that had infested his stored oatmeal, and the oats themselves were not the cause. For infants, a pilot trial in 43 breastfed babies found oatmeal cereal as a first food raised gut microbial richness compared with beef after one week, a microbiome measure only. We have no card on celiac disease, gluten or cereal allergy for either food, so this page cannot say whether either is suitable for people who must avoid gluten.

Sources

1. groa3-13 · guideline
   The commonly accepted terms used, according to ranges of particle size, include grits (600–1400 μm), corn meal (300–600 μm), fine meal (212–300 μm) and flour (less than 212 μm).
   WHO, Fortification of maize flour and corn meal with vitamins and minerals, 2016 · checked 2026-10-02
2. groa3-14 · dataset
   FNDDS 56201051 Grits, regular or quick, made with water, no added fat: 1 cup, cooked = 240 g; 1 cup, dry, yields = 965 g. FNDDS 56202960 Oatmeal, NFS: 1 cup, cooked = 240 g; 1 cup, dry, yields = 485 g
   USDA FNDDS (56201051 Grits, regular or quick, made with water, no added fat; 56202960 Oatmeal, NFS) · checked 2026-10-02
3. groa3-04 · RCT
   measured over 2 h in n = 40 subjects using a randomized, cross-over design. ... Each gram of OBG reduced iAUC by 7% and peak-rise by 15%.
   Food Funct, 2018 · checked 2026-10-02
4. groa3-03 · systematic review
   Steel-cut oats (GI=55 (se 2·5)), large-flake oats (GI=53 (se 2·0)) and muesli and granola (GI=56 (se 1·7)) elicited low to medium glycaemic response. Quick-cooking oats and instant oatmeal produced significantly higher glycaemic response (GI=71 (se 2·7) and 75 (se 2·8), respectively)
   Br J Nutr, 2015 · checked 2026-10-02
5. groa3-07 · RCT
   Forty-eight healthy individuals, 18 years of age or older, were enrolled in a randomized, crossover trial. ... Energy intake at lunch was lower after eating oatmeal compared to the RTEC (p = 0.012).
   J Am Coll Nutr, 2016 · checked 2026-10-02
6. groa3-08 · clinical trial
   These were fed to eight volunteers on separate days in a crossover study ... The flake porridge gave a lower glucose response than the flour porridge
   Am J Physiol Gastrointest Liver Physiol, 2017 · checked 2026-10-02
7. groa3-15 · dataset
   USDA-RETN-R6:358 CEREAL,REG/QUICK,COOKED and USDA-RETN-R6:352 OATMEAL,REG/QUICK,COOKED, Breakfast Cereals: folate_total_ug 70%; thiamin_mg 80%; riboflavin_mg 90%; iron_mg 95%; zinc_mg 100%
   USDA Table of Nutrient Retention Factors, Release 6 (2007), Retn_Code 358 and 352 · checked 2026-10-02
8. groa3-05 · RCT
   A total of 62 qualified participants were randomly divided into control group and oatmeal group with a 45-day follow-up. ... The results suggested that oatmeal could significantly decrease serum total cholesterol (TC) (-8.59 %, p = 0.013), low density lipoprotein cholesterol (LDL-c) (-12.97 %, p = 0.004)
   Food Res Int, 2022 · checked 2026-10-02
9. groa3-09 · prospective cohort
   We analyzed data from 122,680 individuals in the Health Professionals Follow-up Study and Nurses' Health Study. ... cooked oatmeal/oat bran (HR for those consuming ≥2 servings per week, 0.78; 95% CI, 0.70-0.86)
   Arthritis Care Res (Hoboken), 2026 · checked 2026-10-02
10. groa3-10 · RCT
    infants (n = 43) with no prior CF exposure were randomized to 1 of 4 groups (oatmeal cereal, beef, carrot, or prune) ... In phase 1, oatmeal cereal increased observed amplicon sequence variants compared with beef (P = 0.024).
    J Nutr, 2026 · checked 2026-10-02
11. groa3-11 · case report
    we identified the disease as anaphylaxis caused by accidental ingestion of L. bostrychophila that infested the oatmeal stored in the container.
    J Dermatol, 2025 · checked 2026-10-02
12. groa3-12 · regulation
    Rolled oats. Rolled oats, also known as oatmeal, produced from 100 percent dehulled, clean oat groats by steaming, cutting, rolling, and flaking, and provides at least 4 percent (dwb) of β-glucan soluble fiber and a total dietary fiber content of at least 10 percent.
    21 CFR 101.81, Health claims: soluble fiber from certain foods and risk of coronary heart disease · checked 2026-10-02
13. groa3-01 · meta-analysis
    Fourteen controlled trials and two uncontrolled observational studies were included. Compared with the controls, oats intake significantly reduced the concentrations of glycosylated hemoglobin A1c (HbA1c) (MD, -0.42%; 95% CI, -0.61% to -0.23%)
    Nutrients, 2015 · checked 2026-10-02
14. groa3-06 · RCT
    62 medication-naive hypercholesterolemic patients provided with staple food substitute of either 80 g/d oatmeal (n=31) or 80 g/d refined white rice (n=31) for 45 days. ... rs3808607-TT homozygotes exhibited significantly higher responsiveness to oatmeal (reduction in LDL cholesterol) than G allele carriers (GG/GT) (p=0.02).
    Asia Pac J Clin Nutr, 2020 · checked 2026-10-02
15. groa3-02 · meta-analysis
    The effect is small within the practical range of intake. For example, 3 g soluble fiber from oats (3 servings of oatmeal, 28 g each) can decrease total and LDL cholesterol by approximately 0.13 mmol/L.
    Am J Clin Nutr, 1999 · checked 2026-10-02