Does sugar cause constipation or bloating?

Bloating, sometimes, and from particular sugars. Constipation has not been shown. We found no randomized trial and no systematic review of sugar intake with constipation as the outcome. The link rests on survey data: among 7,979 US adults, those drinking the most sugar-sweetened beverages had 1.42 to 1.57 times the odds of constipation. When sugar does cause trouble in trials, it is poorly absorbed sugar, and its effect runs the other way. In 20 healthy adults, 3.5 oz (100 g) of honey gave 6 of them loose stools.

Unsettled. The constipation link comes from a cross-sectional survey and cannot show cause. People who drink a lot of sugary drinks may differ in many other ways, and the result is in odds, not risk. In 394 Brazilian schoolchildren, a diet heavy in ultra-processed food and sugary drinks went with slightly harder stools and was not linked to constipation itself.

What the trials found

Poorly absorbed sugars loosen stools

Some sugars are not fully absorbed, and the trials that measured this found looser stools. In a randomized crossover study in 20 healthy adults, 3.5 oz (100 g) of honey gave 6 of them loose stools and 50 g gave 3. A glucose and fructose mix gave none. In 17 healthy young women, 50 g of fructose produced malabsorption with gut symptoms in 53 percent. That second study was small and not randomized.

Children show the same pattern with juice. In a randomized trial in 104 healthy young children, pear juice was incompletely absorbed in 84 percent, against 41 percent for apple juice and 20 to 24 percent for grape juice.

Lactose: a meal-sized dose bloats little but loosens some stools

A meta-analysis of 21 blinded trials gave 7 to 25 g of lactose, roughly a meal-sized dose, to people who digest it poorly. Bloating rose by 5.9 more people per 100 than with placebo, which did not reach statistical significance. Loose stools rose by 15 more people per 100, with a confidence interval from 3 to 28.

Established. For people with irritable bowel syndrome, cutting fermentable sugars and fibers eases bloating. A 2022 network meta-analysis of 13 randomized trials in 944 IBS patients found a low FODMAP diet beat standard dietary advice for bloating or distension (RR 0.72, 95% CI 0.55 to 0.94).

Cutting sugar in IBS: better symptoms, no change in bowel habit

A 2025 network meta-analysis of 28 randomized trials in 2,338 IBS patients ranked a starch and sucrose reduced diet first for overall symptoms, with a relative risk of symptoms not improving of 0.41 against a habitual diet. That rank rests on two trials. The low FODMAP diet, tested in 24 trials, came fourth at 0.51. For bowel habit, across 23 trials, no diet beat any control diet. In a separate randomized trial of 155 IBS patients, the starch and sucrose reduced diet matched the low FODMAP diet, with 79.2 percent against 78.2 percent responding at 4 weeks.

Myth. Cutting sugar is often sold as a fix for constipation. In the 2025 review of IBS trials, no diet, including the one that reduced sucrose, improved bowel habit compared with a control diet. The gain was in overall symptoms and bloating.

Who should be careful

Not for everyone. Sugar alcohols and some sweeteners deserve as much suspicion as sugar itself. FDA requires foods with certain sugar alcohols to carry a label statement about their gastrointestinal effects. In a double-masked crossover trial in 37 healthy adults, 50 g of fructose taken with the sweetener erythritol caused more watery stools and worse tolerance than fructose alone or fructose with glucose.

People with irritable bowel syndrome are more often affected. Observational breath-test data pooled in a 2022 meta-analysis found lactose malabsorption in 54 percent and fructose malabsorption in 43 percent of IBS patients seen in secondary care. A positive breath test does not always mean symptoms.

What expert bodies say

FDA requires a label statement on foods containing certain sugar alcohols, because of their gastrointestinal effects. We found no expert body that names sugar as a cause of constipation, and the EU register of approved health claims has no gut claim for sugar.

How we searched

What would change this answer

• A randomized trial that varies added sugar in otherwise matched diets and measures stool frequency and consistency. Everything on constipation now is a survey snapshot.
• A prospective cohort that separates sugary drinks from the rest of the diet, especially fiber, before linking them to constipation.
• Larger, blinded trials of the starch and sucrose reduced diet outside one research group. Its first place ranking rests on two trials.

More on sugar itself is on the sugar page.

Sources

1. ev-sgcn-01 · Observational data · cross-sectional analysis with weighted logistic regression · n = 7979
   After adjusting for all relevant variables, SSBs quantified in grams (SSBs-grams) (ORQ3 vs. Q1 = 1.419, 95% CI: 1.064-1.893, p = 0.019; p for trend = 0.02) and SSBs quantified in kilocalories (SSBs-kcal) (ORQ4 vs. Q1 = 1.567, 95% CI: 1.100-2.234, p = 0.015; p for trend = 0.016) showed a significant positive association with constipation.
   
   Who: US adults in NHANES with two 24-hour dietary recalls; constipation by Bristol Stool Form Scale
   Effect: SSBs in grams OR Q3 vs Q1 1.419 (95% CI 1.064 to 1.893); SSBs in calories OR Q4 vs Q1 1.567 (1.100 to 2.234)
   Certainty: Cross-sectional; sweetened drinks may be a marker of a low-fiber diet. OR is odds, not risk.
   BMC Public Health, 2025 · checked 2026-10-07 · we read the abstract
2. ev-sgcn-02 · Observational data · cross-sectional analysis within a birth cohort · n = 394
   The Unhealthy Eating Score was negatively associated with stool consistency (β=-0.10; 95%CI -0.18 to -0.02), but not with constipation.
   
   Who: school-aged children, Botucatu Infant Cohort Study, mean age 7.9 years
   Effect: Unhealthy Eating Score vs stool consistency beta -0.10 (95% CI -0.18 to -0.02); no association with constipation (prevalence 10.2%)
   Certainty: The "unhealthy diet" score mixes sugary drinks with other ultra-processed foods.
   Rev Paul Pediatr, 2026 · checked 2026-10-07 · we read the abstract
3. ev-sgcn-03 · Meta-analysis or systematic review · systematic review and network meta-analysis of RCTs · n = 2338
   For global IBS symptoms, assessed in 28 randomised controlled trials and when considering only the dietary interventions studied in more than one trial, a starch-reduced and sucrose-reduced diet ranked first (RR of global IBS symptoms not improving 0·41 [95% CI 0·26-0·67]; P-score 0·84; two trials), a low FODMAP diet ranked fourth (0·51 [0·37-0·70]; P-score 0·71; 24 trials), and a BDA/NICE diet ranked tenth (0·62 [0·43-0·90]; P-score 0·44; eight trials), versus a habitual diet.
   
   Who: patients with irritable bowel syndrome in RCTs of dietary interventions
   Effect: starch- and sucrose-reduced diet RR of global symptoms not improving 0.41 (95% CI 0.26 to 0.67), 2 trials; low FODMAP 0.51 (0.37 to 0.70), 24 trials; vs habitual diet
   Certainty: Direct comparisons with the usual diet: moderate confidence; the rest of the network: low or very low.
   Lancet Gastroenterol Hepatol, 2025 · checked 2026-10-07 · we read the abstract
4. ev-sgcn-04 · Meta-analysis or systematic review · systematic review and network meta-analysis of RCTs · n = 23 trials
   For bowel habit, assessed in 23 randomised trials, none of the dietary interventions was superior to any of the control interventions, but a low FODMAP diet was superior to a BDA/NICE diet (RR of bowel habit not improving 0·79 [95% CI 0·63-0·99]).
   
   Who: patients with irritable bowel syndrome in RCTs of dietary interventions
   Effect: bowel habit: no dietary intervention superior to any control; low FODMAP vs BDA/NICE RR 0.79 (95% CI 0.63 to 0.99)
   Certainty: About constipation as stool rhythm, diets with reduced sugars gave no evidence.
   Lancet Gastroenterol Hepatol, 2025 · checked 2026-10-07 · we read the abstract
5. ev-sgcn-05 · Meta-analysis or systematic review · systematic review and network meta-analysis of RCTs · n = 944
   A low FODMAP diet was superior to British Dietetic Association (BDA)/National Institute for Health and Care Excellence (NICE) dietary advice for abdominal bloating or distension (RR=0.72; 95% CI 0.55 to 0.94).
   
   Who: patients with irritable bowel syndrome in RCTs of a low FODMAP diet
   Effect: abdominal bloating or distension vs BDA/NICE advice RR 0.72 (95% CI 0.55 to 0.94)
   Certainty: FODMAP includes fructose, lactose and polyols, and also fructans; the contribution of the sugars alone is not isolated.
   Gut, 2022 · checked 2026-10-07 · we read the abstract
6. ev-sgcn-06 · Meta-analysis or systematic review · meta-analysis of randomized, crossover, blinded trials · n = 21 studies
   For abdominal bloating, the ID was 5.9 more people per 100 with symptoms after lactose than placebo (CI -0.07 to +0.19). This same nonsignificant relationship was found for abdominal pain. The ID for diarrhea or loose stools was 0.15 (CI 0.03 to 0.28).
   
   Who: lactose maldigesters free of gastrointestinal problems, older than 4 years, given 7-25 g lactose vs placebo
   Effect: bloating incidence difference +5.9 per 100 (CI -0.07 to +0.19, NS); diarrhea or loose stools ID 0.15 (0.03 to 0.28)
   Certainty: Lactose is milk sugar; the result is about a usual serving (~1 cup of milk), not large doses.
   J Nutr, 2006 · checked 2026-10-07 · we read the abstract
7. ev-sgcn-07 · Randomized controlled trial(s) · randomized non-inferiority trial · n = 155
   The responder rate of SSRD was non-inferior compared with low FODMAPs at week 2 (79.2% vs. 73.1%; p = 0.661;95% confidence interval (CI) = -20-7.2) and week 4 (79.2% vs. 78.2%; p = 1.000;95%CI = -14-12).
   
   Who: patients with irritable bowel syndrome (Rome IV), 4-week intervention
   Effect: responder rate week 4: 79.2% (SSRD) vs 78.2% (low FODMAP), 95% CI -14 to 12
   Certainty: A study from one Swedish group.
   Nutrients, 2024 · checked 2026-10-07 · we read the abstract
8. ev-sgcn-08 · Randomized controlled trial(s) · randomized crossover breath-hydrogen study · n = 20
   Within 10 h after the ingestion of 100 g honey, 50 g honey, and the glucose-fructose mixture, six, three and none of the volunteers, respectively, reported loose stools (chi 2 = 7.1, df = 2, P < 0.03).
   
   Who: healthy volunteers, mean age 35.9 years
   Effect: loose stools within 10 h in 6, 3 and 0 volunteers (100 g honey, 50 g honey, glucose-fructose mix), P < 0.03
   Certainty: Fructose in excess of glucose (honey) is poorly absorbed; the effect is laxative, not constipating.
   Am J Clin Nutr, 1995 · checked 2026-10-07 · we read the abstract
9. ev-sgcn-09 · Observational data · prospective challenge study with breath tests, non-randomized · n = 17
   On day 1, 53% of subjects exhibited a significant (≥20 ppm) increase in breath hydrogen and gastrointestinal symptoms upon challenge with 50 g of fructose.
   
   Who: healthy female volunteers aged 16-27 years
   Effect: 50 g fructose: breath hydrogen rise of 20 ppm or more with gastrointestinal symptoms in 53%
   Certainty: Small sample, not randomized.
   Digestion, 2011 · checked 2026-10-07 · we read the abstract
10. ev-sgcn-10 · Randomized controlled trial(s) · randomized trial with breath hydrogen · n = 104
    Incomplete carbohydrate absorption (BH2 peak above 20 ppm) occurred more frequently after pear juice consumption (84%) than after apple juice (41%) or grape juice (white 20%, purple 24%) [p < 0.05].
    
    Who: healthy children aged about 1, 3 and 5 years
    Effect: incomplete absorption: pear juice 84%, apple 41%, white grape 20%, purple grape 24% (p < 0.05)
    Certainty: Healthy children; incomplete absorption on a breath test is not the same as symptoms.
    J Am Coll Nutr, 1997 · checked 2026-10-07 · we read the abstract
11. ev-sgcn-11 · Randomized controlled trial(s) · randomized, double-masked, controlled crossover study · n = 37
    Compared with fructose and glucose beverage and fructose alone, frequency of watery stools increased (P < .05) and gastrointestinal tolerance worsened (P < .05) when participants consumed fructose and erythritol.
    
    Who: nondiabetic healthy adults
    Effect: more watery stools and worse gastrointestinal tolerance with fructose plus erythritol (P < .05)
    Certainty: Concerns "sugar + sweetener" in sugar-free sweet drinks; the fructose dose is high.
    Nutr Res, 2011 · checked 2026-10-07 · we read the abstract
12. ev-sgcn-12 · Observational data · systematic review and meta-analysis of prevalence studies · n = 26 studies (6700) lactose; 13 studies (3415) fructose
    Using breath testing, 26 studies (n = 6700) and 13 studies (n = 3415) estimated the prevalence of lactose and fructose malabsorption as 54% (95% CI 44-64%) and 43% (95% CI 23-62%); 36 studies (n = 4630) and 22 studies (n = 2149) estimated that of SIBO as 49% (95% CI 40-57%) with lactulose and 19% (95% CI 13-27%) with glucose.
    
    Who: consecutive patients meeting IBS criteria in secondary care
    Effect: lactose malabsorption 54% (95% CI 44 to 64); fructose malabsorption 43% (23 to 62); higher than healthy controls
    Certainty: Malabsorption on a breath test does not always mean symptoms.
    Sci Rep, 2022 · checked 2026-10-07 · we read the abstract
13. ev-sgcn-13 · Position of an expert body · federal rulemaking preamble · n = —
    FDA regulations require specific labeling statements to accompany the use of certain sugar alcohols to provide information to consumers about any gastrointestinal effects.
    
    Who: consumers of foods with sugar alcohols
    Effect: specific labeling statements required for certain sugar alcohols
    Certainty: Polyols are "sugar-free" sugar alcohols; often it is they, not sucrose, that cause bloating.
    FDA, Food Labeling: Revision of the Nutrition and Supplement Facts Labels, proposed rule, Federal Register 2014 (FR Doc. 2014-04387), section II.D.4 Sugar Alcohols · checked 2026-10-07 · we read the section