Women aged 18-65 years with a body mass index (BMI) ≥ 27 kg/m2 wishing to lose weight were recruited via advertisement in a local newspaper. Potential participants were screened during a telephone interview to determine eligibility, commitment to a nutrition-focused weight-loss program and existence of exclusion criteria. Potential participants were excluded if heart disease, cancer or kidney disease had been diagnosed; if they were taking medications influencing appetite and weight control; if they had participated in a weight loss program or had lost more than 1 kg bodyweight in the previous two months; or if they were pregnant, planning a pregnancy or breastfeeding. On the basis of the telephone call eighty-seven participants were invited to attend a screening visit during which a questionnaire relating to personal, demographic and health details was completed. The study protocol, risks and benefits were explained to each subject and written consent was given. The study was approved by the University of Otago Human Ethics Committee.
Two women did not meet the inclusion criteria and two withdrew before being randomized, thus 83 women were randomly assigned to treatment. One participant withdrew early because of unrelated surgery, two moved away and six others (4 on HP and 2 on HFib) opted out of the intervention and were lost to follow-up. Seventy-four women (89% of those randomized) completed the entire study (Figure ).
Consort diagram showing flow of participants through the trial.
The study involved an 8-week randomised, controlled, partially blinded dietary intervention. Participants were randomly assigned to either a high protein (HP) or a high fiber, high carbohydrate (HFib) energy-restricted diet using sequentially numbered, sealed envelopes containing a computer-generated allocation using random length blocks and stratified by age and BMI. Laboratory staff and those conducting dual X-ray absorptiometry (DXA) scans were unaware of group allocation but participants and those involved in the dietary intervention or making clinical measurements could not be blinded regarding group allocation.
The HP diet was based on the CSIRO Total Wellbeing diet [8
] in which approximately 30% of total energy (TE) is derived from protein, and 40% TE from carbohydrate. The HFib diet was designed to achieve at least 50% TE from carbohydrate, 20% TE from protein, and 35 g or more dietary fiber daily with emphasis on wholegrains and legumes. Total and saturated fat intakes were intended to be below 30% and 10% TE respectively. Energy intakes were designed to achieve weight loss of 0.5 - 1.0 kg per week requiring an energy deficit on both diets of approximately 2000-4000 kJ per day but with total energy of more than 5500 kJ per day to ensure adequate nutrient intakes.
Dietary instruction was centered on advice regarding the number of standard servings of key food groups to be eaten each day utilising exchange lists. The basic diet plan for the HP group recommended three 100 g servings of lean protein foods and three servings of breads, cereals or grains per day. The basic diet plan for the HFib group recommended one 100 g serving of lean protein foods, six servings of wholegrain breads, cereals or grains per day and one serving of legumes. Both diet groups received the same recommendations with regard to fruit, vegetable, and fat/oils servings (Table ). The basic diet plans were individually tailored by adjusting the number of servings of major food groups to achieve the desired level of weight loss while maintaining the appropriate macronutrient composition, taking into account a participant's estimated basal metabolic rate and confidence to reduce energy intake. Participants were required to complete a daily food group checklist in order to maintain adherence to macronutrient and energy intake goals. The HFib group was also asked to estimate their daily fiber intakes using a simple fiber calculator and to aim for an intake of 40 g per day by selecting high-fiber breads, cereals, fruits, vegetables, nuts and legume choices. To encourage compliance to the dietary regime participants on the HFib diet were provided with six servings per day of key high carbohydrate foods including wholegrain bread, wholegrain cereal, bran cereal, rye crackers and canned legumes. The HP group was provided with grocery vouchers equivalent in value to the food items received by the HFib group. They were instructed to use the vouchers to purchase lean protein foods such as lean meat, fish and chicken and to keep their receipts as proof of purchase. Both groups were given material especially prepared for this study, including checklists, recipes and menu plans. Participants met with nutritionists at randomization and every 2 weeks throughout the study to encourage dietary adherence. At these sessions participants were weighed, daily food group checklists were reviewed and strategies for maintaining adherence to the dietary advice were discussed. Participants were asked to maintain their usual levels of exercise for the duration of the study.
Food group recommendations for basic HP and HFib diet plans
Participants completed a weighed 3-day diet record including 2 non-consecutive weekdays and one weekend day prior to commencing the intervention and at week 8 [20
]. They were given instruction on keeping the diet record and were provided with electronic food scales. Dietary intakes of macronutrients and dietary fiber were calculated using the Diet Cruncher for Macintosh V1.2.0 program (Waydown South Software), which uses the New Zealand food composition database (Crop and Food New Zealand). At the end of each dietary data collection day, participants were asked to rate their hunger, fullness, thirst, pre-occupation with thoughts of food, desire to eat and how much they could have eaten over that day on a 10 cm visual analogue scale (VAS) [21
To assess whether there was any change in physical activity level during the intervention participants completed the short International Physical Activity Questionnaire (Craig et al., 2003) at baseline and at week 8. At the final week 8 clinic visit participants completed an exit questionnaire where they were asked to rate their responses to a number of questions relating to the diet they followed on a scale of 0 - 10 where 0 was the extreme negative response and 10 was the extreme positive response.
Measurements were made on two occasions (to minimize intrapersonal variation) 2-7 days apart at baseline and at week 8 after a 10-hr overnight fast. Each participant's height, weight, waist circumference and resting blood pressure were measured in duplicate. Height was measured to the nearest millimeter using a stadiometer. Weight was measured in light clothing on electronic scales (Wedderburn) to the nearest 0.05 kg. Waist circumference (WC) was measured to the nearest millimeter using a standard non-stretching tape measure at the midpoint between the lowest part of the rib and highest part of the hip underneath clothing. Resting blood pressure was measured using a manual sphygmomanometer with participants in a seated position after resting for 5 minutes and then repeated 5 minutes later. A fasting blood sample was then taken for the measurement of lipids, glucose, insulin and high-sensitivity C-reactive protein (Hs-CRP).
Total body fat mass, lean mass, body fat percentage, and truncal fat mass were assessed by DXA (DPX-L scanner, Lunar Corp, Cincinnati, OH) using software version 1.35 (Lunar, Cincinnati, OH) at the Dunedin Public Hospital DXA Scanning Unit at baseline and week 8. DXA scanning was limited to participants weighing less than 120 kg (n = 70).
Whole blood samples were centrifuged at 1650 g for 15 minutes, then samples were pipetted into polyethylene cryovials and stored at -80°C. Laboratory results at all time-points for all subjects were performed in batch within the same assay. Serum insulin and C-peptide were measured using a specific insulin electrochemiluminescence immunoassay (ECLIA) (Roche, Cat. No. 12017547) for the Elecsys®
analyzer (Roche Diagnostics, Mannheim, Germany), with a coefficient of variation of 1.5%. Serum total cholesterol and triglycerides (TAG) concentrations were measured enzymatically with Roche kits and calibrators on a Cobas Mira analyzer (Roche Diagnostics, Manheim, Germany), as was plasma glucose (Roche Hexokinase Cat. No. 11447513216). Coefficients of variation were 2.8% for total-cholesterol, 4.4% for TAG and 0.5% for plasma glucose. HDL-cholesterol (HDL C) was measured in the supernatant after precipitation of apolipoprotein B containing lipoproteins with phosphotungstate/magnesium chloride solution [22
] with a coefficient of variation of 3.6%. LDL-cholesterol was calculated using the Friedwald equation [23
]. High sensitivity C-reactive protein (HS-CRP) was measured by latex enhanced immunoturbidimetric method (Roche CRP(Latex) HS Cat. No. 11972855 216) with a coefficient of variation of 4.3%.
Basal metabolic rate was calculated using Harris-Benedict equations [24
]. Insulin sensitivity was estimated by the homeostatic model assessment (HOMA-IR 2) using the HOMA-IR 2 calculator [25
] and by the McAuley index [26
]. A McAuley index value ≤ 6.3 was chosen as a cut-off to define insulin resistance. Presence of the metabolic syndrome (MS) was assessed for each subject based on International Diabetes Federation (IDF) cutoffs [27
The sample size (n = 35 per group) was determined on the basis of the number of participants required to detect a 1.4 kg (1.8 kg SD) difference in weight loss with 90% power at a level of significance of 0.05. Statistical analysis was performed using the STATA statistical software package 9.0 (Stata, College Station, TX). Data were checked for normality and presented as mean (SD) if normally distributed. Fasting insulin and glucose concentrations were not normally distributed and were thus log-transformed and geometric means (min, max values) are presented. The effect of treatment was analyzed by analysis of covariance with baseline values as a covariate. As this was a proof-of-concept trial data were analyzed on a "per protocol" basis and end of study data were not sought from those who elected to drop out of the study. This is consistent with studies of similar design and duration [13
] with which this study is compared.