How different oat processing methods affect blood sugar in people
What it found
Steel-cut, large-flake and muesli oats led to lower blood sugar rises after eating than quick-cooking or instant oats.
These results come from 72 tests in people.
What they found
Studies in people
Less processed, lower rise
Steel-cut oats had an average glycaemic index of 55, large-flake oats 53 and muesli or granola 56. These values represent a low to medium rise in blood sugar after eating.
Quick and instant oats
Quick-cooking oats had an average glycaemic index of 71 and instant oatmeal 75. Both caused a significantly higher blood sugar rise than large-flake oats or muesli.
Muesli stays lower
Muesli and granola are eaten without extra cooking. Skipping that heating step limits starch breakdown, keeping the average blood sugar response in the low to medium range.
Other findings
Why processing matters
Smaller oat pieces and more heat during production break down starch structures. This makes the starch easier for digestive enzymes to reach, which raises blood sugar faster.
What the authors conclude
- They conclude that milling and cooking practices significantly change how quickly starch in oat products is digested.
- The authors say steel-cut oats, large-flake oats, muesli and granola consistently produce lower blood sugar responses than quick or instant oatmeal.
- They suggest these less processed oat options are good choices for people who monitor their blood sugar after meals.
How it was done
Whole-grain oats are known to limit blood sugar spikes after meals, but milling and cooking change the grain's physical structure. The authors wanted to find out whether these changes alter how oats affect blood sugar in people.
They gathered 72 glycaemic index measurements from 20 published studies and three testing databases. The tests involved people, mostly healthy adults with six to nineteen subjects per test. They compared steel-cut, large-flake, quick-cooking, instant and muesli or granola oat products.
What it can’t tell you
- These tests measured short-term blood sugar responses after a single meal, so they cannot show long-term health effects.
- Most tests used healthy adults, so the results may not fully apply to everyone.
Who paid
- Authors work at
- 2Quaker Oats Center of Excellence, USA
The paper
- Title
- Systematic review of the effect of processing of whole-grain oat cereals on glycaemic response
- Type
- Systematic review
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Tosh SM, Chu Y (2015). Systematic review of the effect of processing of whole-grain oat cereals on glycaemic response. The British journal of nutrition. doi:10.1017/S0007114515002895Free full textPubMed 26330200DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error