Obese women were recruited from the Chicago area by means of advertisements placed on and around the University of Illinois campus. Seventy-seven individuals responded to the advertisements, and 60 were deemed eligible to participate after the preliminary questionnaire, body mass index (BMI) and waist circumference assessment. Key inclusion criteria were as follows: female, age 35–65 y, BMI between 30 and 39.9 kg/m2, waist circumference >88 cm, weight stable for 3 months prior to the beginning of the study, i.e. <5 kg weight loss or gain, non-diabetic, no history of cardiovascular disease, no history of cancer, sedentary or lightly active for 3 months prior to the beginning of the study, i.e. <3 h/week of light-intensity exercise at 2.5–4.0 metabolic equivalents (METS), non-smoker, and not taking weight loss, lipid-lowering, or glucose-lowering medications. Perimenopausal women were excluded from the study, and postmenopausal women (defined as absence of menses for 2 y) were required to maintain their current hormone replacement therapy regimen for the duration of the study. The experimental protocol was approved by the Office for the Protection of Research Subjects at the University of Illinois, Chicago, and all volunteers gave written informed consent to participate in the trial.
Subjects were randomized by way of a stratified random sample, based on BMI and age, into either the IFCR-liquid diet (IFCR-L) group (n = 30) or IFCR-food based diet (IFCR-F) group (n = 30). A random number table was used to randomize the subjects from each strata into the intervention groups. The 10-week trial consisted of two dietary phases: 1) a 2-week baseline weight maintenance period, and 2) an 8-week weight loss period.
Baseline weight maintenance diet (Week 1–2)
Each subject participated in a 2-week baseline weight maintenance period before commencing the 8-week weight loss intervention (Figure1). During this period, subjects were requested to continue eating their usual diet and to maintain a stable body weight.
Weight loss diets (Week 3–10)
After the baseline period, subjects partook in either the IFCR-L or IFCR-F intervention for 8 weeks (Figure1). The Mifflin equation was used to measure energy requirements. IFCR-L subjects (n = 30) consumed a calorie-restricted liquid diet for the first 6 days of the week, and then underwent a fast on the last day of the week (water consumption + 120 kcal of juice powder only, for 24 h). The liquid diet consisted of a liquid meal replacement for breakfast (240 kcal) and a liquid meal replacement for lunch (240 kcal). All liquid meal replacements were provided to the subjects in powder-form in premeasured envelopes (Isalean Shake, Isagenix LLC, Chandler, AZ). For the dinnertime meal, IFCR-L subjects consumed a 400–600 kcal meal. Food was not provided to the subjects for the dinner meal. Instead, subjects met with a Registered Dietician weekly to learn how to make healthy eating choices that are in compliance with the National Cholesterol Education Program Therapeutic Lifestyle Changes (TLC) diet (i.e. <35% of kcal as fat; 50-60% of kcal as carbohydrates; <200 mg/d of dietary cholesterol; and 20–30 g/d of fiber). In following this 7 d intervention, IFCR-L subjects were energy restricted by 30% of their baseline needs. IFCR-F subjects (n = 30) consumed a calorie-restricted food-based diet for the first 6 days of the week, and then underwent a fast on the last day of the week (water consumption + 120 kcal of juice powder only, for 24 h). IFCR-F subjects ate 3 meals per day in accordance with the TLC diet guidelines. Food was not provided to the subjects. Instead, subjects met with a Registered Dietician weekly to learn how to make healthy eating choices by implementing the TLC guidelines. Subjects were instructed to eat approximately 240 kcal for breakfast, 240 kcal for lunch, and 400–600 kcal for dinner. In following this 7 d intervention, IFCR-F subjects were energy restricted by 30% of their baseline needs.
Dietary intake and physical activity assessment
A multiple-pass, telephone-administered, 24-h recall was used to assess dietary intake. The recalls were performed at weeks 1, 3 and 10 by a trained Registered Dietician. Dietary intake data were analyzed using Nutrition Data System (NDS) software (version 2012; University of Minnesota, Minneapolis, MN). Furthermore, IFCR-L subjects were provided with a checklist each day to monitor: 1) adherence to the liquid meal protocol, and 2) adherence to the fast day regimen. IFCR-F subjects were also given a checklist to monitor their adherence to the fast day regimen. Alterations in energy expenditure associated with changes in physical activity were measured by the use of a pattern recognition monitor (Sense Wear Mini (SWM), Bodymedia, Pittsburgh, PA). Subjects wore the lightweight monitor on their upper arm for 7 d at week 3 and 10 of the trial. The data was analyzed using Bodymedia Software V.7.0, algorithm V.2.2.4 (Bodymedia, Pittsburgh, PA).
Hunger, satisfaction, and fullness assessment
Subjects completed a validated visual analog scale (VAS) on each fast day approximately 5 min before going to bed (reported bedtime ranged from 8.00 pm to 1.20 am). In brief, the VAS consisted of 100-mm lines, and subjects were asked to make a vertical mark across the line corresponding to their feelings from 0 (not at all) to 100 (extremely) for hunger, satisfaction with diet, or fullness. The VAS was collected at the weigh-in each week and reviewed for completeness. Quantification was performed by measuring the distance from the left end of the line to the vertical mark.
Body weight and body composition assessment
Body weight measurements were taken to the nearest 0.5 kg at the beginning of every week in light clothing and without shoes using a balance beam scale (HealthOMeter; Sunbeam Products, Boca Raton, FL). Height was assessed using a wall-mounted stadiometer to the nearest 0.1 cm. BMI was assessed as kg/m2. Fat mass and fat free mass were assessed by dual energy X-ray absorptiometry (DXA) at weeks 1, 3 and 10 (QDR 4500 W, Hologic Inc. Arlington, MA). Waist circumference was measured by a flexible tape to the nearest 0.1 cm, midway between the lower costal margin and super iliac crest during a period of expiration.
Plasma lipids and adipokine assessment
Fasting blood samples were collected between 6.00 am and 9.00 am at weeks 1, 3 and 10 after a 12-h fast. Blood was centrifuged for 10 min at 520 × g at 4°C to separate plasma from red blood cells and was stored at −80°C until analyzed. Plasma total cholesterol, direct LDL cholesterol, HDL cholesterol, and triglyceride concentrations were measured in duplicate by enzymatic kits (Biovision Inc, Mountainview, CA). LDL particle size was measured by linear polyacrylamide gel electrophoresis (Quantimetrix Lipoprint System, Redondo Beach, CA), as previously described. Leptin, IL-6, TNF-alpha, CRP, 8-isoprostane, and IGF-1 were assessed in duplicate at week 1, 3, and 10 by ELISA (R&D Systems, Minneapolis, MN).
Results are presented as mean ± SEM. Sample size was calculated as n = 30 subjects per group, assuming a 5% decrease in body weight in the IFCR-L group, with a power of 80% and an α risk of 5%. An independent samples t-test was used to test baseline differences between groups. Repeated-measures ANOVA was performed, taking time as the within-subject factor and diet as the between-subject factor, to assess differences between groups over the course of the study. Post-hoc analyses were performed using the Tukey test. Differences were considered significant at P < 0.05. All data was analyzed using SPSS software (version 20.0, SPSS Inc, Chicago, IL).