Study participants—Individuals were participants in a randomised controlled trial of the effect of the dietary supplement, chitosan, on body weight.21 Study participants were recruited using newspaper advertisements and all participants provided written informed consent. Men and women aged over 18 years who wished to lose weight and had a BMI of between 28 and 50 kg/m2 were included. Exclusion criteria were current treatment with chitosan containing supplements; current or recent treatment with weight loss medications; current or recent attendance at a commercial weight loss clinic/programme; allergy to seafood; pregnancy or lactation; active gastrointestinal disease or obesity surgery; involvement in another clinical trial; and individuals judged to be unlikely to comply with study treatment and follow-up procedures.

The study was conducted at the University of Auckland, New Zealand, between November 2001 and December 2002. The study protocol and related documents were approved by the Auckland Ethics Committee.

HRQoL—HRQoL was measured using the Australasian standard version (version 1) of the SF-36 questionnaire,18 a generic measure of HRQoL that assesses eight domains of perceived health over the previous 4 weeks. These domains are: physical functioning (PF), role limitations related to physical problems (RP), bodily pain (BP), general health (GH), vitality (VT), social functioning (SF), role limitations related to emotional problems (RE), and mental health (MH). These dimensions are ordered from first to last according to the extent to which they measure physical or mental functioning.

Scores range from 0 (worst health state) to 100 (best health state) for all domains. For example, a score of 100 indicates the individual can perform all activities without limitations related to health. In three domains (GH, VT, MH), scores of 50 indicate an absence of problems. To obtain scores in excess of 50 in these three domains, health must be evaluated positively. Two summary component scores can be calculated from the SF-36: the physical component summary (PCS) score and the mental component summary (MCS) score. Both scores have a mean of 50 and a standard deviation of 10 and are standardised using means, standard deviations, and factor score coefficients from the general New Zealand population scores. Scores below 50 represent scores below the population mean.

HRQoL was measured at baseline and 6 months post-randomisation in this study. All questionnaires were checked for errors or missing data prior to data entry and standard guidelines for handling missing data were applied.18

Statistical analysis—Crude PCS and MCS scores were calculated using the New Zealand-specific factor weights.22 Participants were stratified by baseline BMI tertile (28-32 [n= 83], 32.1-37 [n=85], >37 kg/m2 [n=80]) to ensure equal numbers of participants across all groups, and scores were compared across these groups using analysis of variance (ANOVA).

Potential confounding factors such as age, gender, ethnicity (European/Non-European), socioeconomic status (SES) (using the New Zealand Socio-economic Index),23 comorbidities (sum of doctor-diagnosed conditions including diabetes, hypertension, hyperlipidaemia, coronary heart disease, stroke, hyperthyroidism, hypothyroidism, gallbladder disease, osteoarthritis, back pain, sleep apnoea, shortness of breath, asthma, cancer, depression, other), and any other confounding factors discovered during stratified analyses, were controlled for by including these factors as covariates in an analysis of covariance (ANCOVA) model. Due to the small size of our study sample, comorbidities were not weighted, and a crude classification was used for adjustment as has been used in other similar studies.24,25

We assessed whether percentage weight change from baseline to 6 months was associated with changes in summary scores using multiple regression analysis after adjustment for age and other confounders (see above). Analyses were based on an intention-to-treat (ITT) approach with the last recorded observation carried forward (LOCF) for any missing data. In the case of missing SF-36 domain scores, scores were assumed to have remained the same as baseline scores—i.e. no change. In the case of missing weight data, the last recorded weight was used, which may have been recorded at baseline or at any of the subsequent 6 follow-up visits. A ‘completers only’ analysis (limited to participants with complete data) was also conducted as a sensitivity analysis. All statistical analyses were conducted using SAS for Windows (version 8.0) or Microsoft Excel (version 9.0).