To test the hypothesis that more frequent consumption of sugar-sweetened soft drinks would be associated with increased risk of obesity-related cancers. Associations for artificially sweetened soft drinks were assessed for comparison.

Prospective cohort study with cancers identified by linkage to cancer registries. At baseline, participants completed a 121-item FFQ including separate questions about the number of times in the past year they had consumed sugar-sweetened or artificially sweetened soft drinks. Anthropometric measurements, including waist circumference, were taken and questions about smoking, leisure-time physical activity and intake of alcoholic beverages were completed.

The Melbourne Collaborative Cohort Study (MCCS) is a prospective cohort study which recruited 41 514 men and women aged 40–69 years between 1990 and 1994. A second wave of data collection occurred in 2003–2007.

Data for 35 593 participants who developed 3283 incident obesity-related cancers were included in the main analysis.

Increasing frequency of consumption of both sugar-sweetened and artificially sweetened soft drinks was associated with greater waist circumference at baseline. For sugar-sweetened soft drinks, the hazard ratio (HR) for obesity-related cancers increased as frequency of consumption increased (HR for consumption >1/d v. <1/month=1·18; 95 % CI 0·97, 1·45; P-trend=0·007). For artificially sweetened soft drinks, the HR for obesity-related cancers was not associated with consumption (HR for consumption >1/d v. <1/month=1·00; 95 % CI 0·79, 1·27; P-trend=0·61).

Our results add to the justification to minimise intake of sugar-sweetened soft drinks.

To evaluate the reliability and validity of the FFQ administered to participants in the follow-up of the Melbourne Collaborative Cohort Study (MCCS), and to provide calibration coefficients.

A random sample stratified by country of birth, age, sex and BMI was selected from MCCS participants. Participants completed two FFQ and three 24 h recalls over 1 year. Reliability was evaluated by intraclass correlation coefficients (ICC). Validity coefficients (VC) were estimated from structural equation models and calibration coefficients obtained from regression calibration models.

Adults born in Australia, Greece or Italy.

Nine hundred and sixty-five participants consented to the study; of these, 459 participants were included in the reliability analyses and 615 in the validity and calibration analyses.

The FFQ showed good repeatability for twenty-three nutrients with ICC ranging from 0·66 to 0·80 for absolute nutrient intakes for Australian-born and from 0·51 to 0·74 for Greek/Italian-born. For Australian-born, VC ranged from 0·46 (monounsaturated fat) to 0·83 (Ca) for nutrient densities, comparing well with other studies. For Greek/Italian-born, VC were between 0·21 (Na) and 0·64 (riboflavin). Calibration coefficients for nutrient densities ranged from 0·39 (retinol) to 0·74 (Mg) for Australian-born and from 0·18 (Zn) to 0·54 (riboflavin) for Greek/Italian-born.

The FFQ used in the MCCS follow-up study is suitable for estimating energy-adjusted nutrients for Australian-born participants. However, its performance for estimating intakes is poorer for southern European migrants and alternative dietary assessment methods ought to be considered if dietary data are to be measured in similar demographic groups.