● Food Intelligence · Vegetable

Onion Glycemic Index and Calculate Your Own Glucose Response

Across 64,025 onion-containing meals — the most-logged vegetable in the atlas — members averaged +31.2 mg/dL (median +27). With a published GI of 15 and GL of 1, raw onion is mostly water and sugar-free fiber. The cohort signal traces to what onions ride with: onion rings push the form anchor to +48 mg/dL, a sandwich pairing adds +16 mg/dL, and a burger adds +8 mg/dL — while an onion omelette runs −2 mg/dL below the onion-alone baseline.

GS
Reviewed by Grace Shryack
Signos Proprietary Data·Updated May 20, 2026·10 min read

● Powered by Signos cohort dataHigh confidence · n=64,025
The swap calculator below draws on 64,025 matched-pair logs — a broader cohort than the page's single-item primary, used to give every ingredient swap statistical power. Welch's t-test on matched pairs, not third-party glycemic-index tables. Each swap shows its sample size and confidence tier inline.
● FREE SIGNOS TOOL

Build Your Own Low GI Recipe

Powered by 64,025
Signos food logs

Tap any ingredient below to swap it for a glucose-friendlier alternative. Your Signos Glucose Score, predicted curve, and nutrition update in real-time. Every swap is data-backed by real CGM response measurements.

Ingredients — Tap to Swap
Meal Context
Pre-meal sequence
Activity after meal
Time of day
41
of 100
Signos Glucose Score
Moderate Spike Risk
75% of members fall between +25 and +35 mg/dL
Predicted Curve · 3-hr window
1401001201401601800m30m60m90m120m150m180m+30
Peak
+30
mg/dL
Time in Range
100%
3hr window
Above 140
0m
danger zone
Swaps
0
applied
Want your real response?
Predictions are cohort averages. Wear a CGM to see your actual response.
Get a Signos CGM →
● Key Findings · Does onion spike blood sugar?

Barely — onion has a GI of 15 and GL of 1, and the +31.2 mg/dL cohort mean across 64,025 logs reflects the carbs onion rides with, not the onion itself. Onion is the most-logged vegetable in the atlas: 64,025 logged meals from 12,772 unique members, with a median peak of +27 mg/dL and 35.7% of responses landing in the low-spike range. The lever is what the onion travels with. On a burger the average runs +38.1 mg/dL (+8 mg/dL above the onion-alone baseline of +29.7 mg/dL across 3,507 logs); in a sandwich or sub, +45.8 mg/dL (+16 mg/dL across 2,058 logs); in a stir-fry, +36.8 mg/dL (+7 mg/dL across 5,228 logs). Onion in an omelette is the cleanest pairing in the cohort at +27.6 mg/dL (−2 mg/dL below baseline across 2,456 logs).

  • ▸The carb-load effect dominates: meals with ≥60g of carbs alongside onion ran 65.8% higher than the low-carb baseline (n=12,355 vs n=39,586, p<0.001).
  • ▸Onion rings are the form outlier: battered fried onion (onion rings, Funyuns) averaged +48 mg/dL across 1,780 logs — a +18.7 mg/dL jump over raw onion, driven entirely by the batter.
  • ▸Sandwich and sub pairings drive the biggest spike: onion in a sandwich, sub, or wrap averaged +45.8 mg/dL across 2,058 logs — a +16 mg/dL jump over the onion-alone baseline of +29.7 mg/dL.
  • ▸Morning timing meaningfully lowers the spike: onion-containing meals before 10 am averaged 22.7% lower peaks than later in the day (CI: −7.85 to −7.02 mg/dL, n=9,008, p<0.001).
● Signos Rules

Three citable insights from this recipe's data

Rule 1
"The Bread-Underneath Penalty"
+16 mg/dL vs. alone
Onion in a sandwich, sub, or wrap averaged +45.8 mg/dL across 2,058 logs — a +16 mg/dL jump over the onion-alone baseline of +29.7 mg/dL (high confidence). The bun, sub roll, or tortilla supplies essentially all of that delta; onion itself adds almost no fast-digesting carbs. The same pattern repeats on a burger (+8 mg/dL across 3,507 logs) and in French onion soup (+7 mg/dL, where the bread float and crouton-style topping drive the spike, not the onion broth).
Rule 2
"The Onion-Ring Form Penalty"
+18.7 mg/dL vs. raw
Battered fried onion — onion rings and Funyuns-style snacks — averaged +47.8 mg/dL across 1,780 logs, compared to +29.1 mg/dL for raw onion across 38,398 logs (high confidence). The +18.7 mg/dL gap is the breading and frying batter, not the onion. By contrast, caramelized onion (slow-cooked, often described as "sugary") averaged +28.3 mg/dL — slightly cleaner than raw.
Rule 3
"The Omelette Edge"
−2 mg/dL vs. alone
Onion in an omelette or scramble averaged +27.6 mg/dL across 2,456 logs — 2 mg/dL below the onion-alone baseline of +29.7 mg/dL (high confidence). It's the only pairing in the cohort that runs negative. The mechanism is the protein+fat anchor of the eggs slowing gastric emptying enough to absorb the small carb contribution onion brings. The same egg-anchor pattern shows up across our protein-pairing analysis: meals with ≥15g of protein alongside onion ran 8.0% lower (n=54,384, p<0.001).
● Curious about your own?

Curious how your body responds to onion specifically?

Across 64,025 logged meals containing onion, the average glucose peak was +31.2 mg/dL — but the IQR spans 26 mg/dL (p25: +16, p75: +42), meaning individual responses vary enormously. Your own result depends on meal context, carb pairing, and metabolic state. A CGM tells you which side of that range you actually land on.

Learn how Signos works
Why this meal spikes

This meal stacks 3 independent spike drivers — together they account for +29 mg/dL.

Driver 1
Meal-level carbohydrates (≥60g when paired)
+17.1 mg/dL
The dominant lever: meals with ≥60g carbs ran 65.8% higher than low-carb logs (n=12,355 vs n=39,586, p<0.001). Onion itself is GI=15 with a glycemic load of 1, so this effect is entirely from the bread, rice, or tortilla onion is plated with.
Driver 2
High-sugar pairings (≥20g sugar)
+10.1 mg/dL
Meals containing ≥20g sugar alongside onion spiked 34.5% higher than the low-sugar baseline (n=7,534, CI: 9.54 to 10.58 mg/dL, p<0.001). Sweetened sauces and condiments — BBQ, teriyaki, ketchup — drive much of this effect on burger and stir-fry pairings.
Driver 3
Individual glucose variability (IQR 26 mg/dL)
+12.5 mg/dL
The interquartile range spans 26 mg/dL (p25: +16, p75: +42 mg/dL), meaning personal metabolic state — insulin sensitivity, microbiome, sleep, stress — accounts for a substantial portion of any single reading.
● Which bucket are you in?

Some members spike +26 mg/dL. Others spike +47. The only way to know how you'll spike is to measure with a Signos CGM.

See Signos Plans
S
● What surprised us
What surprised us about onion is that it's the most-logged vegetable in the atlas — 64,025 entries from 12,772 members — and the cohort number of +31.2 mg/dL says almost nothing about the onion. Onion alone runs +29.7 mg/dL. On a burger, +38.1. In a sandwich, +45.8. In an omelette, +27.6. The vegetable is doing the same near-zero work in every meal; the variance is the bun, the sub roll, the fajita tortilla, or the eggs holding it. The one form that breaks the rule is onion rings at +48 mg/dL — and that's the batter, not the onion either.
— Signos Data Science Team

Why this happens, physiologically

Onion has a published glycemic index of 15 and a glycemic load of 1 — a 30g slice contributes roughly 3g of carbs, most of which is fiber and sulfur-compound chemistry that doesn't move glucose much. The +31.2 mg/dL cohort mean across 64,025 logs is therefore not a measurement of the onion; it's a measurement of the dishes onion tends to live inside. The data confirms this directly: meals with ≥60g of carbs alongside onion ran 65.8% higher than the low-carb baseline (n=12,355, p<0.001), and the carb-bucket analysis shows a near-linear escalation from +26.0 mg/dL in light (0–40g) meals all the way to +47.0 mg/dL in very-heavy (110g+) meals — an 80.8% jump. Two secondary levers pull in the opposite direction: protein pairings (≥15g) trimmed the response by 8.0% (n=54,384, p<0.001), and morning timing cut peaks 22.7% (n=9,008, p<0.001). The mechanism is observational, not yet causal, but consistent with protein slowing gastric emptying and morning insulin sensitivity damping the response.

● Three mechanisms explain onion's glucose range

Meal carb load, time of day, and protein co-ingestion each drive measurable shifts in onion's glucose response

  1. Mechanism 1
    +65.8%
    High carb co-load
    Meals logged with ≥60g total carbs showed peaks 65.8% above the low-carb baseline (n=12,355, p<0.001). Onion itself contributes ~3g of carbs per slice — every point of that 65.8% comes from the bun, tortilla, or stir-fry rice it's served with.
  2. Mechanism 2
    −22.7%
    Morning timing
    Onion-containing meals before 10 am ran 22.7% lower than later-in-day logs (n=9,008, CI: −7.85 to −7.02 mg/dL, p<0.001). Breakfast onion logs averaged +25.7 mg/dL — the lowest meal-time slot — compared to +33.2 mg/dL at dinner.
  3. Mechanism 3
    −8.0%
    Protein co-ingestion
    Protein pairings ≥15g cut the response by 8.0% (n=54,384 vs 5,221, p<0.001). The mechanism is delayed gastric emptying — an onion omelette runs −2 mg/dL below the onion-alone baseline, the only pairing in the cohort that's net-negative.
● Fit Check
Onion is the most-logged vegetable in the atlas — and on its own, one of the lowest-glycemic foods we measure. Almost every point of the +31.2 mg/dL cohort mean traces to the dish onion is hiding in.
✓ This is for you if
  • ▸You add onion to an omelette or scramble. That pairing averaged +27.6 mg/dL — 2 mg/dL below the onion-alone baseline across 2,456 logs, the only net-negative pairing in the cohort.
  • ▸You use raw or caramelized onion as an aromatic. Raw averaged +29.1 mg/dL and caramelized +28.3 mg/dL — both essentially flat across 38,398 and 453 logs.
  • ▸You reach for green onion or scallion as a garnish. Scallion averaged +26.8 mg/dL — the lowest form anchor in the cohort, across 2,792 logs.
  • ▸You keep total meal carbs under 40g. Light-carb onion meals averaged just +26.0 mg/dL — the lowest carb bucket in the cohort (n=39,586).
✗ Not for you if
  • ▸You eat onion rings or Funyuns. The battered-fried form averaged +47.8 mg/dL across 1,780 logs — +18.7 mg/dL above the raw-onion anchor, almost entirely from the batter.
  • ▸You build onion into a sandwich, sub, or wrap. That pairing added +16 mg/dL over the onion-alone baseline across 2,058 logs (treatment mean +45.8 mg/dL).
  • ▸You order a burger with onion as the lunch default. Onion-on-burger averaged +38.1 mg/dL — a +8 mg/dL delta over the onion-alone baseline across 3,507 logs.
  • ▸You stack onion into a high-carb meal (110g+ carbs). Very-heavy-carb meals with onion averaged +47.0 mg/dL — 80.8% above the light-carb baseline.
● How it fits your day

Calorie band and pairings (member-measured)

Per serving
10–1,350 kcal
Ranges from a 30g raw onion slice (~12 kcal) to a full onion-and-rice fajita plate (~1,350 kcal in the very-heavy carb bucket); single-item onion logs averaged 375 kcal.
● Pair before
  • ▸Pair onion with eggs or another high-protein anchor: protein ≥15g cut peaks 8.0% (n=54,384, p<0.001), and onion-in-omelette runs −2 mg/dL below baseline.
  • ▸Keep total meal carbs under 40g: light-carb onion meals averaged +26.0 mg/dL vs. +47.0 mg/dL in the 110g+ carb bucket — an 80.8% escalation.
● Pair after
  • ▸Time a 15–20 min walk after high-carb onion meals (e.g. onion-and-rice stir-fries or sandwich-based lunches), which averaged +36.8 to +45.8 mg/dL — the highest pairing spikes in the cohort.
  • ▸If lunch is a burger or sandwich with onion, note that morning onion meals averaged +25.7 mg/dL vs. dinner at +33.2 mg/dL — favor morning timing when possible.
● Avoid pairing
  • ▸Avoid onion rings or Funyuns as the lunch default — the battered-fried form averaged +47.8 mg/dL across 1,780 logs, the highest form anchor in the cohort.
  • ▸Avoid stacking onion into a sub or wrap without a protein anchor — sandwich pairings added +16 mg/dL over the onion-alone baseline across 2,058 logs.
● Quick definitions (click to expand)
mg/dL — milligrams per deciliter. The unit blood glucose is measured in. A rise of "+30 mg/dL above baseline" means blood sugar went up 30 units after the meal.
Glycemic Index (GI) — a 0–100 score for how fast a food raises blood sugar in lab tests. Under 55 = low, 56–69 = medium, 70+ = high.
Glycemic Load (GL) — GI adjusted for portion size. Under 10 = low, 10–19 = medium, 20+ = high.
CGM — Continuous Glucose Monitor. A wearable sensor that tracks blood glucose every few minutes. Signos members wear CGMs while eating meals they log.
● Related Foods: How onion's glucose response compares to other low-GI aromatics and the dishes it lives in
Mushroom Glycemic Index & Glucose Score
Mushrooms ride with the same aromatic pattern — near-zero carbs of their own, amplifier of whatever the pizza dough, risotto rice, or stir-fry base brings.
Bell Pepper Glycemic Index & Glucose Score
Bell pepper is the other fajita-and-stir-fry staple — useful for understanding how aromatics behave alongside the same tortilla or rice base.
Tomato Glycemic Index & Glucose Score
Tomato runs in the same low-GI band and shares onion's compounding behavior — the sauce, the slice on a burger, the salsa underneath the chips.
White Bread Glycemic Index & Glucose Score
The sandwich bun under the onion is doing most of the work — see what white bread looks like on its own in the cohort.
Eggs Glycemic Index & Glucose Score
An onion omelette is the cleanest onion pairing in the atlas — see how eggs behave alone and why protein anchors lower the meal-level peak.
Track Your Onion Response with Signos →
See how your glucose reacts to onion on a burger vs. in an omelette vs. on a salad — CGM data, personalized to you.

Frequently Asked Questions

Methodology

This page draws on 64,025 onion-containing logs from 12,772 unique Signos members, collected through the Signos production CGM platform. Data were filtered to postprandial glucose responses (PPGR) between 0 and 100 mg/dL to exclude sensor artifacts and implausible readings. Modifier effects were estimated using Welch's t-test on matched pairs against a defined baseline; all reported effects carry p<0.001 unless noted. We report mean glucose peak across a right-skewed distribution — the median spike of +27 mg/dL is a few mg/dL lower than the mean of +31.2 mg/dL, which is typical for this type of data. The food was identified in member logs using a regex matching "onion" as a primary ingredient, excluding onion powder and dehydrated onion-soup mix where no fresh-onion mass is present. Any food-pair pairing slot requires at least 100 matched meals before it appears in the recipe builder.

Limitations

  • Self-reported portion sizes introduce measurement error — a logged "onion" may mean a thin garnish slice or a half-cup of caramelized onion, affecting per-serving estimates.
  • Cohort skews health-motivated; Signos members actively tracking glucose tend to eat more mindfully than the general population, so real-world average spikes may differ.
  • The pickled-onion sub-cohort is small (n=297) and carries medium confidence — its reported delta of 0.0 mg/dL versus raw should be treated as directional only.
  • The caramelized-onion sub-cohort (n=453) carries medium confidence; the −0.8 mg/dL delta vs. raw is directional pending a larger sample.
  • Modifier analyses reflect meal-level correlations, not controlled feeding trials — causality cannot be established from observational CGM data alone.
  • Because onion is rarely the meal's main carb, all food-pair deltas are functionally measurements of the paired carb (bun, sub roll, tortilla, rice) — not of the onion itself.
● Get your own data

See your own onion response

Across 64,025 logged meals containing onion, the average glucose peak was +31.2 mg/dL — but the IQR spans 26 mg/dL, meaning your personal response could land well above or below that. What you build onion into matters too: a sandwich adds +16 mg/dL, a burger +8 mg/dL, and an omelette runs −2 mg/dL below the onion-alone baseline. A CGM shows you exactly where you land and which builds work best for your biology.

Start with Signos
50,000+
Members Measuring