Onion soup: the onion is studied, the bowl is mostly salt

The strongest onion evidence does not come from soup. A meta-analysis of 14 randomized trials found that onion supplements improved LDL and total cholesterol, HDL, systolic blood pressure and body fat percentage, and the abstract gives no sizes for any of these. Those were supplements and extracts, not a bowl of soup. The soup itself has been tested only in tiny single-meal studies. In a double-blind pilot, onion soup with 69 mg quercetin raised blood quercetin to a peak of 2.59 µmol/L, significantly higher than after a soup with 5 mg. The abstract does not say how many people took part. What a bowl reliably delivers is sodium. One cup (245 g) of French onion soup in the USDA survey database has about 265 calories and 926 mg sodium, about 40 percent of the 2,300 mg Daily Value, and a 19 oz (525 g) can nearly 2 g.

The numbers, per 3.5 oz (100 g)

How much is actually in it

• French onion soup in the USDA survey database carries 378 mg sodium per 3.5 oz (100 g), about 926 mg per cup and nearly 2 g per can. — Food composition record Evidence E source
  378 mg/100 g; 926 mg per cup (about 40% of the 2,300 mg Daily Value); 1,985 mg per can
• A UK homemade French onion soup has 41 calories and 231 mg sodium per 3.5 oz (100 g), well below the US survey figures of 108 calories and 378 mg. — Food composition record Evidence E source
  41 calories, 231 mg sodium, 2.2 g fat, 0.9 g protein per 3.5 oz (100 g) versus FNDDS 108 calories and 378 mg

What a real portion looks like

• One cup of French onion soup (245 g) provides about 265 calories, and a 19 oz (525 g) can about 567 calories, in the USDA survey database. — Food composition record Evidence E source
  108 calories per 3.5 oz (100 g); 264.6 calories per cup; 567 calories per can

What your body absorbs

• In a double-blind crossover pilot trial, onion soup with 69 mg quercetin raised plasma quercetin to a peak of 2.59 umol/L, significantly higher than after a 5 mg soup. — Healthy adults, single servings of high- or low-quercetin onion soup Evidence B source
  Plasma quercetin peak 2.59 (SEM 0.42) umol/L; significantly higher than after the 5 mg soup
• In 6 healthy men, one serving of soup from 100 g red onion (47 mg quercetin) gave urinary quercetin similar to a 544 mg quercetin tablet. — Healthy non-smoking adult males, single dose after fasting (n = 6) Evidence B source
  24 h urinary quercetin 1.69 umol (soup) vs 1.17 umol (tablet), P=0.065
• In 16 healthy adults, quercetin from onion powder reached a peak plasma level about four times higher than from apple peel (273 vs 64 ng/mL). — Healthy volunteers, 8 women and 8 men (n = 16) Evidence B source
  Cmax 273.2 vs 63.8 ng/mL; tmax 2.0 vs 2.9 h

What cooking and storage change

• In rats and a small human test, onion peel powder raised plasma quercetin more than peel extract or sauteed bulb, so processing changes uptake mainly for peel quercetin. — Rats fed onion products; small human ingestion study Evidence C source
  Peel powder meal > peel extract, bulb powder, bulb extract and bulb saute (direction only)

What it does to your health

• A meta-analysis of 14 RCTs found onion supplements improved LDL and total cholesterol, HDL, systolic pressure and body fat. — Adults in 14 randomized trials of onion supplementation (n = 14 RCTs) Evidence A source
  Significant improvements in LDL-c, TC, HDL-c, SBP, body fat percentage; pooled WMDs not given in abstract
• Observational data from 7 cross-sectional studies (45,292 people) link soup eating with 15% lower odds of obesity. — Adults in 7 cross-sectional studies (n = 45292) Evidence C source
  OR 0.85 (95% CI 0.79-0.91)

Who this works differently for

• In a pilot study, an onion meal cut peak blood glucose more in 12 lactose-intolerant adults than in 12 lactose-tolerant adults (44.2% vs 19.3%). — Lactose-tolerant (n=12) and lactose-intolerant (n=12) adults, glucose tolerance test (n = 24) Evidence C source
  Peak glucose reduction 44.2% vs 19.3% (P=0.04); iAUC 54.5% vs 42.1% (P=0.42)

The bottom line

Recipes swing the numbers. A UK homemade French onion soup has 41 calories and 231 mg sodium per 3.5 oz (100 g), against 108 calories and 378 mg in the US survey entry. Two databases describing two recipes give a spread rather than an error, so read either figure as one version of the soup. Onion quercetin does get into the blood. In 6 healthy men, soup made from 100 g red onion (47 mg quercetin) gave 24 hour urinary quercetin of 1.69 µmol against 1.17 µmol from a 544 mg quercetin tablet, a difference that did not reach significance (P = 0.065). In 16 healthy adults, onion powder gave a peak blood quercetin about four times that from apple peel (273 against 64 ng/mL). Processing matters mostly for the skin. In rats and a small non-randomized human test, a meal with onion peel powder raised blood quercetin more than peel extract or sautéed bulb. Soup in general has one observational link. Across 7 cross-sectional studies of 45,292 people, soup eaters had 15 percent lower odds of obesity (OR 0.85, 95% CI 0.79 to 0.91), which shows association and not cause. In a non-randomized pilot, an onion meal cut peak blood glucose by 44.2 percent in 12 lactose-intolerant adults and by 19.3 percent in 12 lactose-tolerant ones. We have no evidence card on allergies, pregnancy or medicines for onion soup, so this page has no safety section. We also found no study where the food was French onion soup with its cheese and bread.

Sources

1. onsp-daily-r5-02 · Food composition dataset
   FNDDS 75608100 Soup, French onion (fdc 2710108): Sodium, Na 378 mg per 100 g; 1 cup 245 g 926.1 mg; 1 can 525 g 1984.5 mg; Protein 5.45 g; Total lipid (fat) 4.47 g; Carbohydrate, by difference 11.84 g per 100 g
   USDA FNDDS 2021-2023, food code 75608100 Soup, French onion (FDC 2710108) · checked 2026-10-01
2. onsp-daily-r5-03 · Food composition dataset
   CoFID 17-794 Soup, French onion, homemade: Energy (kcal) 41; Sodium (mg) 231; Fat (g) 2.2; Protein (g) 0.9; Carbohydrate (g) 5.0; Total sugars (g) 3.7; Potassium (mg) 90
   CoFID 2021, Public Health England (OGL v3.0), code 17-794 Soup, French onion, homemade · checked 2026-10-01
3. onsp-daily-r5-01 · Food composition dataset
   FNDDS 75608100 Soup, French onion (fdc 2710108): Energy 108 kcal per 100 g; 1 cup 245 g 264.6 kcal; 1 can 525 g 567.0 kcal; 1 individual container 440 g 475.2 kcal
   USDA FNDDS 2021-2023, food code 75608100 Soup, French onion (FDC 2710108) · checked 2026-10-01
4. onsp-daily-r5-04 · RCT
   The high-quercetin soup contained 69 mg total quercetin compared with the low-quercetin soup containing 5 mg total quercetin. Plasma quercetin concentrations were significantly higher after high-quercetin soup ingestion than after low-quercetin soup ingestion and peaked at 2.59 (sem 0.42) mumol/l.
   Br J Nutr, 2006 · checked 2026-10-01
5. onsp-daily-r5-05 · RCT
   The 24 h urinary excretion of quercetin (1.69 ± 0.79 μmol) from red onion in soup was not significantly different to that (1.17 ± 0.44 μmol) for the quercetin supplement tablet (P = 0.065, paired t-test).
   Food Funct, 2015 · checked 2026-10-01
6. onsp-daily-r5-06 · RCT
   Consumption of the OP resulted in C(max) = 273.2 ± 93.7 ng/mL, t(max) = 2.0 ± 1.7 h, and t(1/2) = 14.8 ± 4.8 h, whereas the AP resulted in C(max) = 63.8 ± 22.4 ng/mL
   J Agric Food Chem, 2012 · checked 2026-10-01
7. onsp-daily-r5-07 · Clinical trial
   The intake of a peel powder-containing meal provided a significantly higher increase of plasma quercetin concentration than the peel extract, bulb powder, bulb extract, and bulb sauté containing meals at each period tested.
   J Food Sci, 2015 · checked 2026-10-01
8. onsp-daily-r5-09 · Meta-analysis
   Among all the retrieved data, 14 RCTs were eligible to be included. The results of the crude analysis showed that onion supplementation significantly improved body fat percentage (BFP), low-density lipoprotein-cholesterol (LDL-c), total cholesterol (TC), high-density lipoprotein-cholesterol (HDL-c), systolic blood pressure, adiponectin, and aspartate aminotransferase (AST).
   Clin Nutr ESPEN, 2023 · checked 2026-10-01
9. onsp-daily-r5-10 · Meta-analysis of observational studies
   soup consumption is significantly related to lower odds ratio of obesity in combined data (n=45292, OR: 0.85, 95% CI: 0.79-0.91, p<0.0001)
   Physiol Behav, 2020 · checked 2026-10-01
10. onsp-daily-r5-08 · Clinical trial
    In a glucose tolerance test, reduction in peak glucose levels by an onion meal was higher in lactose-intolerant people than in lactose-tolerant people (44.2 versus 19.3%, P=0.04).
    Eur J Clin Nutr, 2016 · checked 2026-10-01