Idli: a high glycaemic index, and a fermentation nobody has tested

Idli is steamed, fermented and light, which has earned it a reputation as the gentle breakfast. The glucose curve is not gentle. In a randomised crossover in 19 healthy young men in Singapore, nine Chinese and ten Indian, rice idli scored a glycaemic index of 85, the highest of the ten breakfast foods tested. The five Western wholegrain breakfasts in that same study ran from 44 to 55. One commercial sample of each food was used, and a glycaemic index describes an isolated 50 g carbohydrate portion rather than the sambar and chutney plate idli arrives on. The fermentation is meant to earn its keep by breaking down phytate and freeing iron. A 2026 systematic review of 8 human intervention studies of bread fermentation found no study of adequate quality to answer that question, with five of the eight at high risk of bias. The same review reports one 12-week trial in which ferritin fell from 32 to 27 micrograms per litre on low-phytate sourdough rye bread. All of that is bread. What the batter fermentation of rice and black gram does to iron or zinc absorption in a person eating idli has not been measured.

What your body absorbs

• In 21 young women with low iron stores, adding sous vide cooked salmon to a phytate-rich bean meal significantly increased non-haem iron absorption at p < 0.001. — 21 young women with low iron stores, ferritin below 30 micrograms per litre, randomised crossover with iron stable isotopes (n = 21) Evidence B source
  Significant increase in non-haem iron absorption when fish was added to the bean meal, p < 0.001; the abstract gives no absolute percentage
• Across two national dietary surveys of 7017 and 9832 people, median daily phytate intake rose from 535.3 mg to 658.0 mg, and bread and cereals were the food group contributing most of it. — 7017 participants of the Turkey Nutrition and Health Survey 2010 and 9832 participants of the 2017 survey (n = 16849) Evidence C source
  Median phytate intake 535.3 mg/d in 2010 and 658.0 mg/d in 2017, p < 0.001

What cooking and storage change

• Fermentation lowers phytate and should free more iron, yet a 2026 systematic review of 8 human intervention studies found no trial of adequate quality to test it, and in one long trial ferritin fell from 32 to 27 micrograms per litre on low-phytate sourdough rye bread over 12 weeks. — healthy, iron-deficient or anaemic participants in 8 human intervention studies of sourdough and regular bread fermentation (n = 8 studies) Evidence B source
  Acute studies raised non-haem iron bioavailability, long-term trials did not raise ferritin, and one showed a fall from 32 to 27 micrograms per litre over 12 weeks

What it does to your health

• Rice idli measured a glycaemic index of 85 in 19 healthy young Asian men, the highest of the ten breakfast foods tested and far above the five Western wholegrain breakfasts in the same study, which ran from 44 to 55. — 19 healthy men, nine Chinese and ten Indians, mean age 24.7 years with BMI 21.7 kg/m2, randomised crossover (n = 19) Evidence B source
  GI 85 (sem 4) for rice idli, against rice dosa 76 (sem 5), upma 71 (sem 6) and 44 to 55 for the Western wholegrain foods

Safety, limits and interactions

• When the antibiotic cefuroxime axetil was taken 10 minutes after an idli and chutney breakfast, 8-hour urinary recovery of the drug was 16.59% against 28.44% after a poori and dal-fry breakfast in the same 8 volunteers. — 8 healthy male volunteers, crossover with a one-week washout, single 500 mg dose of cefuroxime axetil (n = 8) Evidence B source
  8 h urinary recovery 16.59% after idli and chutney against 28.44% after poori and dal-fry (P < 0.005); AUC and Cmax also lower with the idli breakfast

What people believe that the data does not support

• In pooled stable-isotope data from 236 children aged 8 to 50 months, a 500 mg daily rise in dietary phytate cut absorbed zinc by less than 0.04 mg a day, an effect too small to detect at P = 0.29. — 236 children between 8 and 50 months of age, data drawn from stable-isotope zinc absorption studies (n = 236) Evidence C source
  Absorbed zinc reduced by less than 0.04 mg/d per 500 mg/d of extra phytate, P = 0.29

Who this works differently for

• Across six South Indian cereal foods including idli, glycaemic index values ran from 67 to 90 in people with type 2 diabetes and from 44 to 69 in healthy volunteers, with the glucose peak after idli falling at 60 minutes in both groups. — patients with non-insulin-dependent diabetes mellitus and healthy volunteers, each food given as 50 g carbohydrate against a 50 g glucose load Evidence B source
  GI 67 to 90 in type 2 diabetes and 44 to 69 in healthy subjects; peak glucose response to idli at 60 min in both groups

The bottom line

Cefuroxime axetil is the one interaction anyone has actually measured here. In 8 healthy men given a single 500 mg dose 10 minutes after breakfast, 8-hour urinary recovery of the drug was 16.59 percent after idli and chutney against 28.44 percent after poori and dal-fry, P < 0.005. That was a crossover with a one-week washout, eight men and one antibiotic, and because the comparison is between two whole breakfasts it shows that which breakfast you eat changes drug exposure rather than that idli blocks the drug. If you take an antibiotic with food, ask the pharmacist about the timing instead of rearranging breakfast. No card here covers idli in pregnancy or breastfeeding, and the only data in young children is about phytate and zinc in general rather than about idli. If you have type 2 diabetes, the peak comes early. Across six South Indian cereal foods including idli, each given as 50 g carbohydrate against a glucose load, glycaemic index ran from 67 to 90 in people with non-insulin-dependent diabetes and from 44 to 69 in healthy volunteers. Glucose peaked 60 minutes after idli in both groups. The abstract gives the range for the six foods together rather than a value for idli alone, and it does not report how many people took part, so this puts idli in an order rather than on a number. The phytate worry is weaker than it sounds, at least in the group that was measured. In pooled stable-isotope data from 236 children aged 8 to 50 months, a 500 mg daily rise in dietary phytate cut absorbed zinc by less than 0.04 mg a day, an effect too small to detect at P = 0.29. Those were children between 8 and 50 months, and absorption models for adults do keep a phytate term, so the finding questions the phytate to zinc ratio as a predictor rather than denying that phytate binds zinc. For scale, two Turkish national surveys of 7017 and 9832 people put median phytate intake at 535.3 mg a day in 2010 and 658.0 mg in 2017, estimated from a composition database rather than measured, with bread and cereals contributing most of it. For iron, the lever that has been tested is what sits next to the meal. In 21 young women with ferritin below 30 micrograms per litre, adding sous vide cooked salmon to a phytate-rich bean meal raised non-haem iron absorption at p < 0.001, and the abstract reports the significance without the size of the increase. That was a bean meal, not a rice and black gram batter. We have no USDA entry for idli in this cohort, so there is no independent figure for what a plate of it holds.

Sources

1. idli-daily-r1-06 · randomised crossover trial
   The addition of fish to the bean meal significantly increased (p < 0.001) iron absorption.
   J Am Coll Nutr, 2008 · checked 2026-09-24
2. idli-daily-r1-07 · cross-sectional dietary survey analysis
   The median daily dietary phytate intakes were 535.3 mg in 2010 and 658.0 mg in 2017 (p < 0.001).
   Nutr Bull, 2026 · checked 2026-09-24
3. idli-daily-r1-04 · systematic review of human intervention trials
   Despite convincing mechanistic evidence that the sourdough-fermentation process in bread fabrication improves iron bioavailability, through reduction of phytate, no human studies address this research question with the appropriate control and study quality.
   Front Nutr, 2026 · checked 2026-09-24
4. idli-daily-r1-01 · randomised crossover trial
   Asian breakfast foods were of medium (white bun filled with red bean paste=58 (sem 4); Chinese steamed white bun=58 (sem 3)) to high GI (rice idli=85 (sem 4); rice dosa=76 (sem 5); upma=71 (sem 6))
   Br J Nutr, 2018 · checked 2026-09-24
5. idli-daily-r1-03 · randomised crossover pharmacokinetic trial
   The 8 h urinary recovery of cefuroxime was 16.59 and 28.44 per cent (P < 0.005) with Diet-A and Diet-B respectively.
   Indian J Med Res, 2000 · checked 2026-09-24
6. idli-daily-r1-05 · pooled modelling of absorption studies
   The effect of dietary phytate on zinc absorption when controlling for dietary zinc was very small and not statistically discernable (P = 0.29). A 500-mg/d increase in dietary phytate reduced absorbed zinc by <0.04 mg/d.
   J Nutr, 2015 · checked 2026-09-24
7. idli-daily-r1-02 · randomised controlled trial
   The peak glucose responses for three foods, i.e. chapatti, idli and poori, occurred 60 min postprandially in both groups...The glycaemic index (GI) values ranged from 67 to 90 in NIDDM and from 44 to 69 in healthy subjects with no significant differences within the groups.
   Br J Nutr, 2000 · checked 2026-09-24