Table 2.

Characteristics of included studies (early-onset colorectal adenomas).

Study	Setting and gender	Baseline participants	Study type	Dietary assessment	Study details	Results
Joh et al. (20)	United States of America Female	Nurse's Health Study II. 33,106 women included. Inclusion criteria: Women with completed High School FFQ and underwent at least 1 lower gastrointestinal endoscopy between 1999 and 2015. Exclusion Criteria: No lower bowel endoscopy during follow-up, history of cancer except non-melanoma skin cancer, colorectal polyps, Crohn's disease, ulcerative colitis before the return of the HS-FFQ, missing data, implausible energy intake.	Prospective Cohort Study	124 item HS-FFQ for participants diet from age 13–18. Questions asked how often on average a standard portion size of each item was consumed. 9 possible responses.	Primary study outcome: colorectal adenoma Total fructose = sum of free fructose and half sucrose intake. Total glucose = sum of free glucose and half sucrose intake. Added sugar = sugar added during processing/preparation. Western diet pattern = high intake of dessert, sweets, snacks, red and processed meat, refined grains. Prudent diet = high intake of vegetables, fruits, better quality grains, fish, poultry.	Per 1 serving/day higher SSB intake and risk of high risk adenomas: OR = OR = 1.34, CI = 1.01–1.79, p = 0.044. (Per 5% of calories) higher total fructose intake during adolescence and risk of high risk adenomas: OR = 1.30, CI = 1.06–1.60, p = 0.012. <1.3 fruit servings/day during adolescence and risk: OR = 1.51, CI = 1.26–1.82, p < 0.001 (for total fructose) OR = 1.34, CI = 1.12–1.60, p = 0.028 (for SSB).
Molmenti et al. (23)	Phoenix, Arizona Male and female	Men and Women recruited from 1990 to 1999 Wheat Bran Fiber and Ursodeoxycholic Acid Phase III chemoprevention trials 1,623 participants included Inclusion criteria: 40–80 years old with 1+ colorectal adenoma removed during colonoscopy evaluation within 6 month period prior to study registration. Exclusion: self-reported inherited syndromes.	Prospective Cohort Study	Dietary intake assessed using Arizona FFQ to evaluate dietary intake over the past few months in the previous year. Energy-adjusted dietary inflammatory index scores derived from FFQ.	Primary study outcome: metachronous colorectal adenoma (characterized as advanced or non-advanced)	Men and women < 50 YO with colorectal adenomas had a higher intake of protein (p = 0.03), total fat (p < 0.00) monounsaturated fat (p = 0.001), polyunsaturated fat (p = 0.049), red meat (p = 0.001) and more pro-inflammatory diet (p < 0.001) than those over 50. < 50 YO red meat consumption > 511 g/week and adenoma risk: OR = 0.84, CI = 0.233–3.021, p = 0.79.
Zheng et al. (22)	United States of America Female	Nurse's Health Study II 29,474 women included. Inclusion criteria: Undergone at least 1 lower endoscopy before 2011, younger than 50. Exclusion criteria: diagnosis of colorectal cancer, inflammatory bowel disease, previous history of colorectal polyps, missing data, implausible energy intake	Prospective Cohort Study	FFQ categorized into 40 groups and factor analysis derived scores for either Western or Prudent dietary pattern Derived DASH diet, Alternative Mediterranean diet, Alternative Healthy Eating Index-2010 scores (DASH 8–40; AMED 0–9; AHEI-2010 0–110).	Cases: confirmed newly diagnosed colorectal adenoma. Non-cases: Lower endoscopy with no adenomas. Primary analysis: associations between diet quality and risk of early-onset adenoma overall and according to high vs. low risk. Secondary analysis: association by location/size/histology; evaluated associations according to malignant potential in 2 logistic regressions using same reference group.	Highest quintile for the Western diet and risk of early-onset adenomas: OR = 1.67, CI = 1.18–2.37, p = 0.01. Risk and DASH diet score: OR = 0.65, CI = 0.45–0.93, p = 0.009, AMED score: OR = 0.55, CI = 0.38–0.79, p = 0.007, Prudent score: OR = 0.69, CI = 0.48–0.98, p = 0.03, and AHEI-2010: OR = 0.71, CI = 0.51–1.01, p = 0.01. Risk of adenomas in the distal colon and rectum for Western Diet: OR = 1.65, CI = 1.14–2.38, p = 0.01, Prudent: OR = 0.68, CI = 0.47–0.99, p = 0.04, DASH: OR = 0.63, CI = 0.42–0.94, p = 0.01, AHEI-2010: OR = 0.71, CI = 0.49–1.03, p = 0.02.
Nguyen et al. (21)	United States of America Female	Nurse's Health Study II 30,818 women included. Inclusion criteria: undergone at least 1 lower endoscopy before the end of follow-up and were younger than 50. Exclusion criteria: CRC or IBD before baseline and before each biennial follow-up, prior history of colorectal neoplasia/polyps, implausible energy intake, missing diet intake.	Prospective Cohort Study	FFQ every 4 years from 1991 (130 food items); 1998 gave HS-FFQ (124 food items) Previous study (Nguyen, Ma, Wang) identified 43 different sulfur-metabolizing bacterial species and foods were categorized as such: processed meats, liquor, low-calorie drinks positively associated with enrichment of bacteria; beer, fruit juice, legumes, vegetables, sweets are negatively associated with bacteria.	Primary endpoint was colorectal adenoma or serrated polyp diagnosed before age 50 Cases: had colorectal adenoma Non-cases: no adenoma Scored by summing the intake of putative foods weighed by their regression coefficients. Cumulative average of all sulfur microbial diet scores available from 1991- 2 year questionnaire cycle before most recent endoscopy calculated.	Highest quartile of sulfur microbial diets and risk of early-onset adenomas: OR = 1.13, CI = 1.10–1.56, p = 0.02. Association with high sulfur microbial diet and adenomas in the proximal colon: OR = 1.58, CI = 1.17–2.14, p = 0.01 and tubulovillous/villous histology: OR = 1.65, CI = 1.12–2.43, p = 0.04.