Subjects
As described previously [2], independently living subjects were recruited from the University of Illinois at Chicago campus by means of flyers. Of the 146 interested individuals, 83 were deemed eligible to participate according to a preliminary questionnaire and body mass index (BMI) assessment. Key inclusion criteria were as follows: age 25 to 65 years; BMI between 30 and 39.9 kg/m2; weight stable for 3 months prior to the beginning of the study (i.e. less than 5 kg weight loss or weight gain); non-diabetic; no history of cardiovascular disease; lightly active (i.e. <3 h/week of light intensity exercise at 2.5 to 4.0 metabolic equivalents (METs) for 3 months prior to the study); non-smoker; no history of bariatric surgery; and not taking weight loss, lipid or glucose lowering medications. The experimental protocol was approved by the Office for the Protection of Research Subjects at the University of Illinois, Chicago. All volunteers gave informed consent to participate in the trial.
Experimental design and randomization
A 12-week, randomized, controlled, parallel-arm feeding trial was implemented to test the effects of ADF, exercise, and ADF combined with exercise (combination group) on eating behaviors and weight loss. Eligible subjects were stratified on the basis of BMI, age, and sex, and then randomized into 1 of 4 groups: 1) combination group; 2) ADF group; 3) exercise group; 4) control group.
Diet protocol
As previously described [2], only the combination and ADF groups participated in the dietary intervention, which consisted of two periods: 1) a 4-week controlled feeding period, and 2) an 8-week self-selected feeding period. During the controlled feeding period (week 1–4) participants consumed 25% of their baseline energy needs on the fast day (24 h) and consumed food ad libitum on each feed day (24 h). Baseline energy requirements were assessed by the Mifflin equation [7]. The diet consisted of a 3-day rotating menu plan, and all fast day meals were prepared in the metabolic kitchen of the Human Nutrition Research Unit (HNRU). Fast day meals were consumed between 12.00 pm and 2.00 pm to ensure that each subject was undergoing the same duration of fasting. Meals were formulated on the basis of the American Heart Association guidelines (30% kcal from fat, 15% kcal from protein, and 55% kcal from carbohydrate). All meals were consumed outside of the research center. Participants were requested to eat only the foods provided on the fast days and to bring back any leftover foods to be weighed and recorded. Calorie-free foods, such as black coffee, tea, and diet sodas were permitted as desired. Subjects were also encouraged to drink plenty of water. During the self-selected feeding period (week 8–12) subjects continued with the ADF regimen but no fast day food was provided to them. Instead, each subject met with a dietician at the beginning of each week to learn how to maintain the ADF regimen at home. Subjects were also taught how to monitor energy intake by reading food labels, reducing portion sizes, and choosing low fat meat and dairy options. Control and exercise group subjects were asked to maintain their regular food habits, and were not provided with any food or dietary counseling.
Exercise protocol
Only the combination and exercise groups participated the exercise intervention. These subjects participated in a moderate intensity exercise program 3 times per week under supervised conditions, for 12 weeks. Exercise was performed using stationary bikes and elliptical machines at the HNRU. Training intensity was estimated for each individual using an age-predicted heart rate maximum (HRmax) equation [209 − (0.7 × age)] [8] and a Polar Heart Rate Monitor (Polar USA, Inc., NY). At the beginning of the study (weeks 1 to 4), each exercise session ran for 25 min duration and corresponded to 60% of the subject’s HRmax. Training duration and intensity increased incrementally at week 4, 7 and 10 by 5 min and 5% HRmax. As such, by week 10, each subject was exercising for a 40 min duration at an intensity of 75% HRmax. ADF and control subjects were asked to maintain their regular activity habits during the study.
Weight loss assessment
Body weight was measured weekly to the nearest 0.25 kg in the fasted state using a balance beam scale (HealthOMeter, Sunbeam Products, Boca Raton, FL). 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.
Adherence to the ADF diet and exercise protocol
During the controlled feeding phase (week 1–4), subjects were instructed to eat only the fast day food provided, and to report any extra food item consumed using an “Extra food log”. The log was collected and reviewed by study personnel each week. If the log indicated that the subject ate an extra food item on a fast day, that day was labeled as “not adherent”. Exercise compliance was assessed by recording attendance at each supervised exercise session. If an exercise session was missed, the subject was required to make up for the missed session that same week.
Physical activity maintenance assessment
Habitual, free-living physical activity was assessed by a pedometer (Digiwalker SW-200, Yamax Corporation, Tokyo, Japan SW). Subjects wore the pedometer for a 7-d period at week 1 and 12. The pedometer was worn attached to the participant’s waistband during waking hours (except while bathing or swimming), and reset to zero each morning. Number of daily steps were recorded in a pedometer log provided, and the log was collected by study personnel at the weigh-in each week. No subjects were enrolled in an exercise class, and all participants were asked to refrain from joining any exercise programs during the course of the study.
Eating behavior assessment
A validated visual analog scale (VAS) [9] was used to measure hunger, fullness, and satisfaction with the ADF diet. The scale was completed on each fast day (before bedtime). 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, or fullness. Quantification was performed by measuring the distance from the left end of the line to the vertical mark. The three-factor eating questionnaire (TFEQ-R18) [10] was used to assess restrained eating (conscious restriction of food intake in order to control body weight), uncontrolled eating (tendency to eat more than usual due to a loss of control over intake), and emotional eating (inability to resist emotional eating cues). The TFEQ consists of 18 items on a 4-point response scale (definitely true/mostly true/mostly false/definitely false). Responses to each of the 18 items are given a score between 1 and 4. The item scores are then summated into scale scores for restrained eating, uncontrolled eating, and emotional eating. The raw scale scores are transformed to a 0–100 scale [((raw score -- lowest possible raw score)/possible raw score range) -- 100]. Higher scores are indicative of greater restrained, uncontrolled, or emotional eating.
Energy and macronutrient intake
Each participant completed a 3-day food record on 2 feed days during the week, and on 1 feed day during the weekend, at each week of the 12-week trial. Thus, a total of 36 feed day food records were collected for each subject. At baseline, the dietician provided 15 min of instruction to each participant on how to complete the food records. These instructions included verbal information and detailed reference guides on how to estimate portion sizes and record food items in sufficient detail to obtain an accurate estimate of dietary intake. Subjects were instructed to record food items, in as much detail as possible, in the blank food diary provided. Any mixed foods were broken down to individual food items to be recorded one per line. Food records were collected at the weigh-in each week, and were reviewed by the dietician for accuracy and completeness. All dietary information from the food records was entered into the food analysis program, Nutritionist Pro (Axxya Systems). The program was used to calculate the total daily intake of energy, protein, carbohydrate, fat, cholesterol, and fiber.
Statistical analysis
Results are presented as mean ± SEM. Differences between intervention groups at baseline were analyzed by a one-way ANOVA. Within-group differences were analyzed using repeated-measures ANOVA. An intention-to-treat analysis was performed for all variables measured. A P value of < 0.05 was used as a criterion for statistical significance in all analyses. Data were analyzed using SPSS software (version 20.0 for Mac OSX; SPSS Inc, Chicago, IL, USA).
