Lemon: the kidney stone question, and how much juice the trials used

Lemon has one serious research question behind it, and it is kidney stones. About 85 ml of fresh juice a day for three months raised urinary citrate 2.5-fold in people with calcium stones and low urinary citrate. Potassium citrate, the drug those patients were compared against, raised it 3.5-fold. That trial had 30 people in it, 10 per group. Then in 2026 a systematic review went through 31 studies on stopping stones from coming back, and the things it says may help are water, a diet normal to high in calcium and low in protein and sodium, thiazides and alkali therapy. Lemon juice is not among them. What the review says about lemon juice is that it may cause more minor adverse events. Read the dose before you read the result. The findings this page rests on come from juice by the glass, 85 ml a day for three months or 250 ml at a single meal. The USDA survey records a whole lemon at 65 g and a wedge at 8 g, which is what a person actually uses.

The numbers, per 100 g

How much is actually in it

• The US and UK food tables differ by 36% on vitamin C in lemon flesh, 53 against 34 mg per 100 g, and neither number carries a sample range because the US record predates the sampled Foundation programme. — Lemons, raw, without peel (FDC 167746, SR Legacy) against Lemons, flesh only, raw (CoFID 14-130) (n = 1 USDA record, no Foundation samples, so no measured spread) Evidence E source
  Vitamin C 53 mg per 100 g in USDA against 34 mg in CoFID, a 36% gap; vitamin B6 0.08 against 0.05 mg, a 38% gap; dietary fibre 2.8 g per 100 g in USDA

What a real portion looks like

• One lemon is 65 g and a wedge is 8 g, so the 250 ml of juice that flattened the glucose peak in the trial is far more lemon than anyone squeezes over a dish. — household measures recorded for Lemon, raw in the USDA food and nutrient database for dietary studies (n = 4 household measures for FNDDS code 61113010) Evidence E source
  1 fruit 65 g; 1 slice or wedge 8 g; 1 cup 200 g; quantity not specified 15 g, which is the weight the survey assumes when a person just says lemon

What cooking and storage change

• USDA has no cooking retention factor that fits a lemon: the only rows its group maps to are ten alcoholic beverage methods, and dietary fibre is missing from Release 6 altogether. — USDA Table of Nutrient Retention Factors, Release 6 (2007), rows reachable for lemon (n = 10 method rows, all under the Beverages group; 26 nutrients in the whole release) Evidence E source
  The ten reachable methods are all alcoholic beverage preparations, from ALC BEV,FLAMED to ALC BEV,STIRRED,BKD/SIMMRD 2.5 HR; dietary fibre has no factor anywhere in Release 6

What it does to your health

• At one meal in healthy adults, 250 ml of lemon juice with bread cut the peak of blood glucose by 30% and pushed it from 41 to 78 minutes. Black tea with the same bread did nothing, and the abstract does not say how many people were tested. — healthy adults eating 100 g of bread with 250 ml of water, black tea or lemon juice in random order, capillary glucose followed for 180 minutes, sample size not stated in the abstract, nobody with diabetes (n = not stated in the abstract) Evidence B source
  Mean glucose peak 30% lower with lemon juice (p < 0.01) and delayed by more than 35 minutes, 78 against 41 minutes with water (p < 0.0001); tea had no effect; no drink changed how much people ate 3 hours later
• About 85 ml of fresh lemon juice a day for 3 months raised urinary citrate 2.5-fold in patients with calcium stones and low urinary citrate, against 3.5-fold for the drug potassium citrate and 0.8-fold for diet advice alone. — 30 patients with hypocitraturic urinary calcium stones, 10 per group, treated for 3 months (n = 30) Evidence B source
  Urinary citrate rose 2.5-fold on lemon juice, 3.5-fold on potassium citrate and 0.8-fold on dietary advice; urinary calcium fell only in the lemon juice and potassium citrate groups; urinary oxalate did not change in any group
• 10 g of lemon juice with perilla oil in a tomato juice preload lowered blood glucose 30 minutes after a rice meal from 127.8 to 103.1 mg/dL in 21 young women. — 21 healthy Japanese women aged about 21 years, each taking three different preloads 10 minutes before 200 g of boiled white rice (n = 21) Evidence B source
  Plasma glucose at 30 minutes 103.1 mg/dL against 127.8 mg/dL with water (p < 0.001) and 113.9 mg/dL with plain tomato juice (p = 0.078); serum insulin at 30 minutes also lower than with plain tomato juice (p < 0.01)

Safety, limits and interactions

• The 2026 systematic review of 31 studies on preventing recurrent kidney stones found that lemon juice may cause more minor adverse events, and it names no benefit strong enough to list beside water, diet, thiazides and alkali therapy. — nonpregnant adults and children with recurrent nephrolithiasis, in 26 randomised trials and 5 nonrandomised studies through December 2025 (n = 31 studies) Evidence A source
  Increased minor adverse events with lemon juice (low strength of evidence); water, a diet normal to high in calcium and low in protein and sodium, thiazides, alkali therapy and allopurinol may reduce recurrence (low strength of evidence)

What people believe that the data does not support

• The one thing everyone says about lemon, that it helps digestion, is the exact claim the European Union refused: both submissions naming Citrus limon carry the status Non-authorised. — EU Register on nutrition and health claims, snapshot of 2026-09-21 (n = 2 claims naming Citrus limon, 0 authorised, 2 non-authorised) Evidence E source
  POL-HC-6937 (digestion, intestinal tract, digestive juice flow) is Non-authorised; the US register does not mention lemon at all

What is still unknown

• Ten days of eating lemon changed 10 organic acids in the morning urine of 14 volunteers, citrate among them, which shows the body registers the fruit and says nothing yet about health. — 14 healthy volunteers, a 10-day baseline phase followed by a 10-day lemon intake phase, first-morning urine analysed by GC-MS (n = 14) Evidence C source
  10 organic acid metabolites changed significantly (p < 0.05); citric acid and palmitic acid rose, uracil and vanillylmandelic acid fell; pathways enriched were the citrate cycle, glyoxylate and dicarboxylate metabolism, pyrimidine and tyrosine metabolism

The bottom line

Start with the stones, because that is what the page is about. About 85 ml of fresh lemon juice a day for three months raised urinary citrate 2.5-fold in people with calcium stones and low urinary citrate, against 3.5-fold for the drug potassium citrate. That trial had 30 people in it, 10 per group, and it measured citrate in urine, not stones. The 2026 review that went through 31 studies on keeping stones from coming back lists water, a diet normal to high in calcium and low in protein and sodium, thiazides and alkali therapy as the things that may reduce recurrence. Lemon juice is not on that list. The blood sugar finding is real and narrow. Drinking 250 ml of lemon juice with 100 g of bread cut the peak of blood glucose by 30 percent and pushed the peak from 41 minutes to 78. Black tea with the same bread did nothing, and no drink changed how much people ate three hours later. Narrow means this: one meal, healthy adults, blood sugar followed for 180 minutes afterwards. Nobody was tracked for months, nobody in these trials had diabetes, and the abstract of the bread trial does not say how many people were in it, so read that 30 percent as a single-meal result of unknown size. In a separate trial, 21 young women took 10 g of lemon juice with perilla oil in a tomato juice preload before white rice, and their glucose 30 minutes later was 103.1 mg/dL against 127.8 with water. That second trial mixed lemon with two other things, so it cannot tell you what the lemon did on its own. The first one used a glassful, far more lemon than anyone squeezes over a dish. The claim most people would name first is the one that failed. The European Union register holds two claims naming Citrus limon, both about digestion and the flow of digestive juice, and both are recorded as non-authorised. The US register does not mention lemon at all. The vitamin C number depends on which table you open. USDA gives 53 mg per 100 g of lemon flesh and the UK table gives 34 mg, a gap of 36 percent, and neither figure carries a measured range, because the US record predates the sampled programme that would have produced one. Take either number as an approximation with an unknown spread around it. Two things we cannot tell you, and you should know which is which. USDA keeps a table of what cooking does to nutrients, and nothing in it fits a lemon. The only rows its food group reaches are ten alcoholic beverage methods, and dietary fibre has no factor anywhere in that release, so what heat does to a lemon is simply outside our data. The second gap is larger. We found no research on who should be more careful with lemon, so nothing here covers pregnancy, children, older people or anyone on medication. That is an empty search result on our side and it is not a clearance. The single safety signal we do hold is those minor adverse events in the stone review, and they turned up in people drinking juice daily, which is the same daily glass the dose numbers on this page describe. One study did look at what a lemon does inside people. Fourteen volunteers ate lemon for ten days, and ten organic acids in their first morning urine shifted, citrate among them. It shows the body registers the fruit. About health it says nothing yet.

Sources

1. lem-r1-07 · reference dataset
   Lemons, raw, without peel (FDC 167746, SR Legacy) - Vitamin C 53 MG - Vitamin B-6 0.08 MG - Fiber, total dietary 2.8 G | CoFID 14-130 Lemons, flesh only, raw - vitamin C 34 MG - vitamin B-6 0.05 MG
   USDA FoodData Central, SR Legacy record 167746, with UK CoFID 2021 (Public Health England, OGL v3.0) · checked 2026-09-23
2. lem-r1-09 · reference dataset
   Lemon, raw - FNDDS 61113010 - 1 fruit 65 g - 1 slice or wedge 8 g - 1 cup 200 g - Quantity not specified 15 g
   USDA FNDDS, Lemon raw, food code 61113010 · checked 2026-09-23
3. lem-r1-08 · reference dataset
   lemon - 10 methods, all group Beverages: 5003 ALC BEV,FLAMED - 5001 ALC BEV,NO HEAT,STORED OVERNIGHT - 5010 ALC BEV,NOT STIRRED IN,BKD 25 MIN - 5002 ALC BEV,STIRRED INTO HOT LIQ - 5006 ALC BEV,STIRRED,BKD/SIMMRD 1 HR - 5007 ALC BEV,STIRRED,BKD/SIMMRD 1.5 HR - 5004 ALC BEV,STIRRED,BKD/SIMMRD 15 MIN - 5008 ALC BEV,STIRRED,BKD/SIMMRD 2 HR - 5009 ALC BEV,STIRRED,BKD/SIMMRD 2.5 HR - 5005 ALC BEV,STIRRED,BKD/SIMMRD 30 MIN
   USDA Table of Nutrient Retention Factors, Release 6 (2007) · checked 2026-09-23
4. lem-r1-01 · randomised controlled trial
   Lemon juice significantly lowered the mean blood glucose concentration peak by 30% (p < 0.01) and delayed it more than 35 min (78 vs. 41 min with water, p < 0.0001)...None of the tested beverages had an effect on ad libitum energy intake.
   Eur J Nutr, 2021 · checked 2026-09-23
5. lem-r1-02 · randomised controlled trial
   There was 2.5-, 3.5- and 0.8-fold increase in urinary citrate level of lemon juice, potassium citrate and dietary recommendation groups, respectively...Urinary calcium level was decreased only in lemon juice and potassium citrate groups after treatment.
   Urol Res, 2008 · checked 2026-09-23
6. lem-r1-04 · randomised controlled trial
   The plasma glucose at 30 min in tomato juice with lemon/n-3 PUFA-rich oil was significantly lower than that of water (103.1±3.4 mg/dL vs. 127.8±4.0 mg/dL, p<0.001, mean±SE) and tended to be lower than that of tomato juice (113.9±4.9 mg/dL, p=0.078).
   J Nutr Sci Vitaminol (Tokyo), 2025 · checked 2026-09-23
7. lem-r1-03 · systematic review
   Among 31 studies (26 RCTs and 5 NRSIs), none evaluated imaging strategies. All but 3 included adults only...There may be increased minor adverse events with lemon juice but no increased harm due to serious adverse events with thiazides and allopurinol (low SOE).
   Ann Intern Med, 2026 · checked 2026-09-23
8. lem-r1-06 · regulatory register entry
   POL-HC-6937 Citrus limon (Common Name : Lemon) Helps to support the digestion contributes to the normal function of intestinal tract helps support the digestive juice flow. Non-authorised
   EU Register on nutrition and health claims, claim POL-HC-6937, snapshot 2026-09-21 · checked 2026-09-23
9. lem-r1-05 · prospective observational study
   Fourteen healthy volunteers were prospectively recruited and divided into two sequential phases: a 10-day baseline phase and a 10-day lemon intake phase...Ten organic acid metabolites exhibited significant changes (p < 0.05) after lemon intake.
   Mol Nutr Food Res, 2026 · checked 2026-09-23