Onion and blood sugar in lactose-tolerant and lactose-intolerant adults
What it found
An onion drink lowered peak blood sugar more in people who cannot digest lactose than in those who can.
This was measured in 24 adults during a glucose test.
What they found
Studies in people
Peak blood sugar drop
The onion drink lowered peak blood sugar by 44.2% in lactose-intolerant adults. In lactose-tolerant adults, the drop was 19.3%. This difference was statistically significant.
Overall blood sugar levels
Total blood sugar over two hours fell by 54.5% in the lactose-intolerant group and 42.1% in the lactose-tolerant group. The authors say this difference was not statistically significant.
Timing of the effect
In lactose-tolerant adults, the onion drink slowed sugar uptake from 30 minutes up to 120 minutes. In lactose-intolerant adults, the effect lasted only until 60 minutes.
Other findings
Compounds in the onion drink
The filtered red onion drink contained 2.0 µg/ml free quercetin. It also held three types of quercetin glucosides, ranging from 3.5 µg/ml to 39.5 µg/ml.
What the authors conclude
- They suggest that foods rich in quercetin glucosides, like onions, may help control blood sugar more in lactose-intolerant people than in lactose-tolerant people.
- They note that lactose tolerance could confuse studies comparing diets across regions where tolerance rates differ, such as the Mediterranean basin and Northern Europe.
How it was done
Foods that slow down sugar absorption may lower the risk of type 2 diabetes and heart disease. Onions contain plant compounds called quercetin glucosides that might block sugar from entering the gut, but only if they stay intact.
The researchers tested 12 adults who digest lactose normally and 12 who do not. Each person fasted overnight, then drank a sugar solution on one day and the same sugar mixed with a filtered red onion drink on another day. Finger-prick blood samples were taken over two hours to measure blood sugar.
What it can’t tell you
- This was a small pilot study with only 24 people, so the results need checking in larger groups.
- The onion drink contained fibre and other plant compounds, so scientists cannot be sure which part caused the change in blood sugar.
Who paid
- Authors work at
- University of Hertfordshire, UK
The paper
- Title
- Inhibition of the glycaemic response by onion: a comparison between lactose-tolerant and lactose-intolerant adults
- Type
- Clinical trial
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Hoffman R, Ranjbar G, Madden AM (2016). Inhibition of the glycaemic response by onion: a comparison between lactose-tolerant and lactose-intolerant adults. European journal of clinical nutrition. doi:10.1038/ejcn.2016.44Free full textPubMed 27026422DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error