Cucumber and watermelon: both mostly water, far apart in sugar

By a meta-analysis of 15 randomized trials in 415 middle-aged and older adults, L-citrulline supplements and watermelon lowered systolic blood pressure by 4.0 mmHg (95% confidence interval 1.5 to 6.5), with tablets and fruit pooled so that watermelon's own share cannot be read off. Diastolic pressure fell 2.5 mmHg. A newer trial outside our corpus, on 39 adults eating one to two cups of watermelon a day for four weeks, saw no significant change in blood pressure. Cucumber has no trial on this page, because we found no randomized trial or cohort on cucumber as a food. As foods the two are close in water and far apart in sugar. In USDA analysis of 8 samples each, cucumber with peel is 95.9 percent water and seedless watermelon flesh 90.9 percent. Watermelon carries 7.2 g of sugars per 3.5 oz (100 g), a figure that ranged from 5.1 to 8.4 g across samples. The UK table gives cucumber 1.2 g of sugars and 14 calories per 3.5 oz (100 g), against 7.1 g and 31 calories for watermelon.

How much is actually in it

• Raw cucumber with peel is about 96% water and gives 170 mg potassium per 3.5 oz (100 g), more than watermelon flesh. — USDA Foundation Foods, cucumber with peel, raw, 8 analyzed samples Evidence E source
  Water 95.87 g (range 95.38-96.38), potassium 169.6 mg (range 136-211) per 3.5 oz (100 g)
• Seedless watermelon flesh is about 91% water with 7.2 g sugars, 117 mg potassium and 6.5 mg vitamin C per 3.5 oz (100 g). — USDA Foundation Foods, watermelon, seedless, flesh only, raw, 8 analyzed samples Evidence E source
  Water 90.91 g (89.55-93.1), total sugars 7.197 g (5.11-8.44), potassium 117.3 mg (76.2-145), vitamin C 6.458 mg (5.02-8.67) per 3.5 oz (100 g)
• The UK tables give 14 calories and 1.2 g sugars per 3.5 oz (100 g) for cucumber against 31 calories and 7.1 g sugars for watermelon flesh. — CoFID 2021, cucumber raw flesh and skin (13-523) and watermelon flesh only (14-296) Evidence E source
  Cucumber 14 calories, 1.2 g total sugars, 96.5 g water; watermelon 31 calories, 7.1 g total sugars, 92.3 g water per 3.5 oz (100 g)

What a real portion looks like

• A US cup of sliced cucumber weighs 4.2 oz (120 g) and a cup of diced watermelon 155 g, while a medium watermelon wedge is 325 g. — US household measures, FNDDS food codes 75111000 (cucumber, raw) and 63149010 (watermelon, raw) (n = 16 measures) Evidence E source
  Cucumber: cup 120 g, regular 200 g, slice 10 g; watermelon: cup 155 g, small wedge 218 g, medium wedge 325 g, large wedge 432 g

What your body absorbs

• In a controlled feeding study on 23 adults, three weeks of watermelon juice raised plasma lycopene about fourfold, as much as tomato juice did. — 23 healthy nonsmoking adults aged 36-69, controlled diet, 3-week periods of fresh-frozen watermelon juice (20.1 or 40.2 mg/d lycopene) or tomato juice (n = 23) Evidence C source
  Plasma lycopene 1078 nmol/L after 20.1 mg/d from watermelon juice vs 272 nmol/L on the control diet, no further rise at 40.2 mg/d
• In a crossover trial on 16 postmenopausal women, two 12 fl oz (360 mL) servings of pasteurized watermelon juice a day for 4 weeks raised serum lycopene by 81% without changing cognition. — 16 postmenopausal women aged about 60, two 12 fl oz (360 mL) servings of pasteurized 100% watermelon juice daily for 4 weeks vs placebo (n = 16) Evidence B source
  Serum lycopene +81% (p = 0.002), no change in cognitive tests, oxidative stress or inflammation

What cooking and storage change

• Freezing fruit such as watermelon keeps about 70% of its vitamin C and 90% of its potassium by the USDA retention table. — USDA retention factors for the group Fruits and Fruit Juices, method FRUITS,FROZEN Evidence E source
  Vitamin C 70% retained, potassium 90%, folate 95% (Retn_Code 156)

What it does to your health

• By a meta-analysis of 15 RCTs in 415 middle-aged and older adults, L-citrulline or watermelon lowered systolic pressure by about 4 mmHg. — 15 randomized controlled trials, 24 datasets, 415 middle-aged and elderly participants (n = 415) Evidence A source
  Systolic BP -4.02 mmHg (95% CI -6.54 to -1.50), diastolic BP -2.54 mmHg (95% CI -4.27 to -0.81)
• By a meta-analysis of 21 RCTs, citrulline or watermelon supplementation had no overall effect on body weight, BMI or fat mass. — 21 randomized controlled trials of citrulline or watermelon supplementation published up to March 2025 Evidence A source
  No substantial effect on BMI, body weight, fat mass, waist circumference, body fat percentage or fat-free mass

Safety, limits and interactions

• In 2024 whole cucumbers from two Florida growers were the likely source of a US Salmonella outbreak with 551 illnesses in 34 states. — US multistate outbreak of Salmonella Africana and Salmonella Braenderup, 2024 (n = 551) Evidence E source
  551 illnesses in 34 states and the District of Columbia
• A 2020 UK outbreak of E. coli O157 with 36 cases was traced to a fast-food product whose only specific ingredient was imported cucumber. — 36 cases of STEC O157:H7 in the United Kingdom, August 2020, case-control and case-case studies (n = 36) Evidence C source
  AOR 9.19 (95% CI 1.0-82.8) in the case-control study for eating the product
• A systematic review of 12 studies found watermelons among the fresh produce linked to human Salmonella Javiana infections. — 12 studies of risk factors for human Salmonella Javiana infection, mostly southern United States Evidence C source
  Watermelons and tomatoes named as produce vehicles, size not given

What people believe that the data does not support

• In a crossover RCT on 15 resistance-trained men, a week of watermelon juice concentrate did not improve bench press or isometric strength. — 15 resistance-trained men aged about 22, watermelon juice concentrate with 2.2 g/day L-citrulline or placebo for 7 days (n = 15) Evidence B source
  No difference in force, bench press performance, vessel diameter or perception, muscle oxygenation +4.1% only
• The EU refused a watermelon extract the right to claim antioxidant benefits for the body. — EU Register on nutrition and health claims, claim POL-HC-6934, Citrullus lunatus (watermelon) extract Evidence E source
  Non-authorized
• The EU also refused the same watermelon extract any weight-loss or weight-control claim. — EU Register on nutrition and health claims, claim POL-HC-6935, Citrullus lunatus (watermelon) extract Evidence E source
  Non-authorized

Who this works differently for

• In an RCT on 128 women discharged after hyperemesis gravidarum, adding watermelon to diet advice turned a 1.1 lb (0.5 kg) weight loss into a 0.55 lb (0.25 kg) gain over two weeks. — 128 pregnant women under 16 weeks at discharge after hospitalization for hyperemesis gravidarum, Kuala Lumpur, 2 weeks (n = 128) Evidence B source
  Weight change at week 2: median +0.55 lb (0.25 kg) with watermelon vs -1.1 lb (-0.5 kg) with advice alone (P = 0.001)
• Among 25 Turkish children with pumpkin seed allergy, 83% were also sensitized to watermelon seed and six reacted after eating it. — 25 children with IgE-mediated pumpkin seed allergy at a tertiary clinic in Turkey, 2016-2024 (n = 25) Evidence D source
  Watermelon seed sensitization in 83%, clinical reactions in 6 children

The bottom line

Cucumber has more potassium, 170 mg per 3.5 oz (100 g) against 117 mg in watermelon, though both swung widely between samples, from 136 to 211 mg in cucumber and from 76 to 145 mg in watermelon. A US cup of sliced cucumber weighs 4.2 oz (120 g) and a cup of diced watermelon 155 g. A medium wedge is 325 g, by household measures rather than eaten portions. Freezing fruit keeps about 70 percent of its vitamin C and 90 percent of its potassium by USDA's retention table, a factor for frozen fruit as a group from a table dated 1975, with no measurement on watermelon itself. The red pigment in watermelon, lycopene, does reach the blood. In a controlled feeding study on 23 adults aged 36 to 69, three weeks of watermelon juice with 20.1 mg of lycopene a day took plasma lycopene to 1078 nmol/L from 272 on the control diet, close to what tomato juice did. That study did not report randomization and used juice. In a small randomized crossover trial on 16 postmenopausal women, two 12 fl oz (360 mL) servings of pasteurized watermelon juice a day for four weeks raised serum lycopene by 81 percent. Cognition, inflammation and oxidative stress did not change. Watermelon as a workout aid was tested and did not work. In 15 resistance-trained men, a week of watermelon juice concentrate with 2.2 g of L-citrulline a day did not improve bench press, isometric force or blood vessel diameter compared with placebo, in a short and small trial. On weight, a meta-analysis of 21 randomized trials, most of them testing citrulline supplements, found no substantial effect on body weight, BMI or fat mass. The EU refused a watermelon extract both antioxidant claims and weight-loss claims, which means the evidence fell short when it was assessed. In 128 women leaving hospital after severe pregnancy sickness (hyperemesis gravidarum), adding watermelon to diet advice turned a median 1.1 lb (0.5 kg) weight loss at two weeks into a 0.55 lb (0.25 kg) gain. That trial was unblinded and run in one hospital, and readmissions and anti-sickness drug use did not differ. Both foods are eaten raw, and both have carried food poisoning. In 2024 whole cucumbers from two Florida growers were the likely source of a US Salmonella outbreak with 551 illnesses in 34 states and the District of Columbia, and FDA investigated two more cucumber outbreaks in November 2024 and May 2025. A 2020 UK outbreak of E. coli O157 with 36 cases was tied to a fast-food product whose only specific ingredient was cucumber, with a very wide interval (adjusted odds ratio 9.19, 95% confidence interval 1.0 to 82.8). A review of 12 studies named watermelons among the produce linked to Salmonella Javiana, mostly in the southern United States, without giving their share. Watermelon seed is a separate matter. Among 25 Turkish children with pumpkin seed allergy, 83 percent were sensitized to watermelon seed and six reacted after eating it, in a case series from a region where seeds are widely eaten. The pregnancy trial above is the only pregnancy data we hold, and we have no carded data on medicines for either food.

Sources

1. cuwm-daily-r6-01 · USDA FoodData Central Foundation Foods, dataset
   Cucumber, with peel, raw: Water 95.87 g, range 95.38-96.38, n=8 · Potassium, K 169.6 mg, range 136.0-211.0, n=8
   USDA FoodData Central Foundation Foods, release 2026-04-30 · checked 2026-09-29
2. cuwm-daily-r6-02 · USDA FoodData Central Foundation Foods, dataset
   Watermelon, seedless, flesh only, raw: Water 90.91 g, range 89.55-93.1, n=8 · Sugars, Total 7.197 g, range 5.11-8.44, n=8 · Potassium, K 117.3 mg, range 76.2-145.0, n=8 · Vitamin C 6.458 mg, range 5.02-8.67, n=8
   USDA FoodData Central Foundation Foods, release 2026-04-30 · checked 2026-09-29
3. cuwm-daily-r6-03 · CoFID 2021, dataset
   CoFID 13-523 Cucumber, raw, flesh and skin: Energy 14 kcal · Total sugars 1.2 g · Water 96.5 g · CoFID 14-296 Melon, watermelon, flesh only: Energy 31 kcal · Total sugars 7.1 g · Water 92.3 g
   CoFID 2021, Public Health England, codes 13-523 and 14-296 (OGL v3.0) · checked 2026-09-29
4. cuwm-daily-r6-04 · USDA FNDDS portion weights, dataset
   FNDDS 75111000 Cucumber, raw: 1 cup 120 g · 1 regular 200 g · 1 piece/slice 10 g · FNDDS 63149010 Watermelon, raw: 1 cup 155 g · 1 small wedge/slice 218 g · 1 medium wedge/slice 325 g · 1 large wedge/slice 432 g
   USDA FNDDS 2021-2023, food codes 75111000 and 63149010 (FDC 2709784, 2709270) · checked 2026-09-29
5. cuwm-daily-r6-06 · controlled crossover trial
   All 23 subjects consumed the W-20 (20.1 mg/d lycopene, 2.5 mg/d beta-carotene from watermelon juice) and C-0 treatments (controlled diet, no juice). ... After 3 wk of treatment, plasma lycopene concentrations for the W-20, W-40, T-20 and C-0 treatments were (least squares means +/- SEM) 1078 +/- 106, 1183 +/- 139, 960 +/- 117 and 272 +/- 27 nmol/L, respectively.
   J Nutr, 2003 · checked 2026-09-29
6. cuwm-daily-r6-07 · randomized controlled trial
   A placebo-controlled, randomized, double-blind, crossover trial was conducted with postmenopausal women (n = 16, 60 + 4.1 years). Participants consumed two 360 mL servings of pasteurized 100% watermelon juice or a placebo beverage for 4 weeks. ... Serum lycopene exhibited a significant treatment effect (p = 0.002) with a mean increase of 81%. However, this increase was not associated with changes in oxidative stress, inflammation, or cognitive function.
   J Nutr Gerontol Geriatr, 2021 · checked 2026-09-29
7. cuwm-daily-r6-05 · USDA Table of Nutrient Retention Factors, dataset
   USDA-RETN-R6:156 FRUITS,FROZEN (Fruits and Fruit Juices): vitamin_c_mg 70% · potassium_mg 90% · folate_total_ug 95%
   USDA Table of Nutrient Retention Factors, Release 6, 2007, Retn_Code 156 · checked 2026-09-29
8. cuwm-daily-r6-08 · systematic review and meta-analysis of RCTs
   A total of 15 randomized controlled trials (RCTs) investigating the effects of l-citrulline supplementation and watermelon intake on BP in middle-aged and elderly individuals were included, comprising 24 datasets involving 415 participants. The results indicate that l-citrulline supplementation and watermelon intake significantly reduced SBP (-4.02 mmHg [95 % CI: -6.54 to -1.50], P = 0.002) and DBP (-2.54 mmHg [95 % CI: -4.27 to -0.81], P = 0.004) in the elderly.
   Clin Nutr ESPEN, 2025 · checked 2026-09-29
9. cuwm-daily-r6-09 · systematic review and dose-response meta-analysis of RCTs
   RESULTS: Twenty-one RCTs were included. Overall, CIT supplementation had no substantial effects on body mass index (BMI), body weight, fat mass (FM), waist circumference (WC), body fat percentage (BFP), and fat-free mass (FFM).
   Nutrients, 2025 · checked 2026-09-29
10. cuwm-daily-r6-14 · FDA outbreak investigation page
    The FDA and CDC, in collaboration with state and local partners, investigated a multistate outbreak of Salmonella Africana and Salmonella Braenderup infections with 551 illnesses in 34 states and the District of Columbia.
    FDA, Outbreak Investigation of Salmonella: Cucumbers (June 2024) · checked 2026-09-29
11. cuwm-daily-r6-15 · case-control study
    Both the case-case study (adjusted odds ratio (aOR) 31.8, 95% confidence interval (CI) 1.6-624.9) and the case-control study (aOR 9.19, 95% CI 1.0-82.8) revealed statistically significant results, showing that the consumption of a specific fast-food product was independently associated with infection. ... The only ingredient specific to the product was cucumbers.
    Int J Infect Dis, 2021 · checked 2026-09-29
12. cuwm-daily-r6-16 · systematic review
    Consumption of fresh produce (tomatoes and watermelons), herbs (paprika-spice), dairy products (cheese), drinking contaminated well water and animal contact were associated with human S. Javiana infections.
    PLoS One, 2019 · checked 2026-09-29
13. cuwm-daily-r6-11 · randomized controlled trial
    CONCLUSION: Short-term watermelon supplementation does not appear to enhance isometric force production, bench press performance, blood vessel diameter, or muscle oxygenation parameters compared to PL in resistance-trained men.
    Eur J Appl Physiol, 2022 · checked 2026-09-29
14. cuwm-daily-r6-12 · EU health claim register entry
    POL-HC-6934 Citrullus lunatus (Watermelon) extract - ACTI-08 Good source of antioxidants Contains naturally occuring antioxidants Has antioxidant properties Acts as an antioxidants Contributes to the protection against oxidation Helps increase the antioxidative capacity of the body Helps preventing oxidation Antioxidants help protect you from free radicals Antioxidants help protect your cells and tissues from oxidation Antioxidants contribute to the total antioxidant capacity of the body Antioxidants help to protect your body by reinforcing the body's natural defence against the effects of free radicals Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-6934, snapshot 2026-09-21 · checked 2026-09-29
15. cuwm-daily-r6-13 · EU health claim register entry
    POL-HC-6935 Citrullus lunatus (Watermelon) extract - ACTI-08 Helps to improve carbohydrate and fat metabolism of the body Used to facilitate the weight loss Helps to loose weight Contributes to loose weight Used to facilitate the weight loss Helps in weight control Contributes to body weight management. Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-6935, snapshot 2026-09-21 · checked 2026-09-29
16. cuwm-daily-r6-10 · randomized controlled trial
    128 women at their discharge following hospitalization for HG were randomized: 64 to watermelon and 64 to control arm. ... Weight change (kg) at end of week 1, median[interquartile range] -0.05[-0.775 to + 0.50] vs. -0.5[-1.4 to + 0.1] P = 0.014 and to the end of week 2, + 0.25[-0.65 to + 0.975] vs. -0.5[-1.3 to + 0.2] P = 0.001 for watermelon and control arms respectively.
    BMC Pregnancy Childbirth, 2023 · checked 2026-09-29
17. cuwm-daily-r6-17 · retrospective case series
    Co-allergy was common (tree nuts, 76%; other seeds, 72%); watermelon seed sensitization occurred in 83%, with six patients experiencing clinical reactions after watermelon seed ingestion.
    Allergy Asthma Proc, 2026 · checked 2026-09-29