Oat processing and blood sugar response after meals
What it found
In people, porridge made from steel-cut or large-flake oats raised blood sugar less than quick-cooking oats or instant oatmeal.
Muesli and granola also tended to raise blood sugar less than quick or instant oats.
What they found
Studies in people
Steel-cut and large-flake oats
Porridge made from steel-cut oats had an average glycaemic index of 55, and large-flake oats averaged 53. These were low to medium responses.
Quick and instant oats
Quick-cooking oats averaged a glycaemic index of 71 and instant oatmeal averaged 75. Both were significantly higher than muesli, granola or large-flake porridge.
Muesli and granola
Muesli and granola averaged a glycaemic index of 56, with a wide range from 39 to 70. This was not significantly different from steel-cut or large-flake porridge.
Rolled oats, type unspecified
Fifteen tests used rolled oats where the flake size was not stated. These averaged a glycaemic index of 51, but the effect of processing could not be assessed for these tests.
Other findings
Why processing matters
Smaller particle size and more gelatinised starch appear to increase the glycaemic response. Steel-cut oats keep their groat structure, so starch is less accessible to digestive enzymes.
What the authors conclude
“Steel-cut and large-flake hot oatmeal porridges, muesli and granola consistently demonstrate medium to low glycaemic responses, making them good options for people who are concerned about blood glucose response to foods.”
Also in their conclusions
- They conclude that milling and cooking practices produce significant changes in the digestibility of starch in oatmeal products.
- They say steel-cut and large-flake hot oatmeal porridges, muesli and granola consistently show medium to low glycaemic responses, making them good options for people concerned about blood glucose response to foods.
How it was done
Whole-grain oats are known to blunt the rise in blood sugar after a meal, but processing changes the physical structure of the grain. The authors wanted to know whether different milling and cooking methods affect this property.
They pooled 72 measurements of glycaemic index from 20 published papers and 3 independent testing laboratories. Most tests used 8 to 12 healthy people, with some tests in people with type 1 or type 2 diabetes.
What it can’t tell you
- The review pools many small studies of single meals, so it cannot show what happens to blood sugar over the long term.
- Many tests did not report the type of oats or the cooking method, so the effect of those details could not be separated out.
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 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error