Weight Loss and Hunger

Desire to eat, hunger, fullness, and prospective food consumption (PFC) will be rated immediately before (after a 12 h overnight fast) and every 30 min*3 h after the standardized breakfast on a 100-mm visual analog scale (VAS) adapted from Hill and Blundell. Scores range from 0 to 100 millimeters. For hunger, desire to eat, and prospective food consumption, higher scores indicate greater appetite. For fullness, higher scores indicate greater fullness (lower appetite).

The satiety quotient will be calculated for each subject.

Blood samples will be collected during experimental sessions while fasting and every 30 minutes for 3 hours following the standardized breakfast. EDTA and Aprotinin (anti-protease) and DPP-IV inhibitors will be added to whole-blood before it is centrifuged at 3000 rpm for 5 minutes at 4˚C. Plasma will be treated within an hour of sampling and then stored at -80˚C until assayed. Total Ghrelin (EZGRT-89K), Leptin (EZHL-80SK), GLP-1 (EZGLP1T-36K) and PYY (EZHPYYT66K) will be assayed with commercially available ELISA (Millipore). All samples from one subject will be assayed in duplicates in the same plate to avoid inter-assay variability.

The ventilated hood technique and the Vmax Encore 29 N metabolic cart (SensorMedics Corporation) will be used to perform indirect calorimetry. Carts are calibrated with reference gases each day. Measures will occur between 7:00 and 9:30 am after a 12-h fasting period, while also abstaining from exercise for at least 24 h, always performed in the same room, kept dark and at an ambient temperature of 21° C. Indirect calorimetry will be performed for 30 minutes.

Free-living exercise energy expenditure will be measured using accelerometry. An accelerometer (Actical-Mini Mitter Co. Inc.) will be worn on the lower back for 7 days at each sampling period.

Exercise energy expenditure will also be measured with a COSMED K4b2 portable indirect calorimeter during in-laboratory exercise sessions completed on the treadmill to confirm the accuracy of exercise energy expenditure.

Total EE will be determined from doubly-labelled water (DLW) over a 7-day period to estimate carbon dioxide production over time in free-living subjects. After deuterated water is administered, 2H is lost from the body water at an exponential rate. When 18O-water is administered, the 18O is also lost with body water turnover (as per the 2H isotope) and with each molecule of carbon dioxide produced because carbonic anhydrase in the body rapidly facilitates the equilibrium exchange of water and carbon dioxide/carbonic acid oxygen. The difference between the rates of disappearance of 2H and 18O corresponds to the total carbon dioxide production over that period. These rates are determined from urine samples taken at the start and at the end of the measurement period. DLW is the gold standard for assessing free-living EE.

EI will be measured in the laboratory and in the free-living state for 3 days with a food menu that we have developed and validated. In the laboratory, foods are served upon request, while outside the laboratory, foods are selected and packed away into coolers, somewhat like grocery shopping, and leftovers are brought back with wrappings to assess the weight of foods consumed. Food Processor SQL (ESHA Research Inc.) will be used.

The Leeds Food Preference Questionnaire, a forced-choice computer task, will be used to evaluate the implicit hedonic wanting (speed and frequency of choice) and the explicit hedonic liking (subjective visual analog scale rating) for different visual food cues, which vary in both fat and sugar content. The task assesses explicit liking and explicit wanting for food stimuli. Scores range from 0 to 100, with higher scores indicating greater liking or wanting for the presented foods. The Leeds Food Preference Questionnaire will be administered both before and after lunch.

Nasal chemosensory and taste performance will be measured with Sniffin' Sticks and taste strips (Burghart Instruments, Wedel, Germany).

Body weight (kg) will be measured with a digital scale (BWB-800AS Digital Scale from Tanita Corporation of America).

Height (centimeter) will be measured using a stadiometer (HR-100 Height Rod).

Total body fat mass and percentage of total body fat will be assessed using dual-energy X-ray absorptiometry (DXA) (Lunar Prodigy, GE Medical Systems). Total body fat mass is reported in kilograms (kg), and percentage of total body fat is reported as a percentage (%) of total body weight. Higher values for both measures indicate greater total body fat.

Total body fat-free mass will be assessed using dual-energy X-ray absorptiometry (DXA) (Lunar Prodigy, GE Medical Systems). Fat-free mass is reported in kilograms (kg) and represents the mass of all non-fat tissues, including muscle, organs, and bone. Higher values indicate greater fat-free mass.

Total body bone mineral content will be assessed using dual-energy X-ray absorptiometry (DXA) (Lunar Prodigy, GE Medical Systems). Bone mineral content is reported in grams (g). Higher values indicate greater total body bone mineral content.

A standardized breakfast consisting of 2 slices of whole wheat bread (80 g), peanut butter (20 g), strawberry jam (20 g), cheddar cheese 27% milk fat (20 g), and orange juice (250 mL). The total energy content is 575 kcal, and its food quotient will be 0.89 (57% carbohydrates, 13% protein, 30% lipids) for the 3 experimental sessions. Comparable alternatives will be offered in cases of food aversions, intolerances, or allergies. After breakfast, resting energy expenditure will be measured for 30 minutes every hour for a total of 3h. The same protocol described in the "resting energy expenditure section" will be used to assess the thermic effect of food (increase in energy expenditure above fasting values for the digestion, absorption, biosynthesis, and storage of nutrients).

Eating behaviour will be assessed using the Three-Factor Eating Questionnaire-51 (TFEQ-51). The questionnaire assesses three domains of eating behaviour: dietary restraint, disinhibition, and perceived hunger. Scores are calculated according to published scoring procedures. Dietary restraint scores range from 0 to 21, disinhibition scores range from 0 to 16, and hunger scores range from 0 to 14. Higher scores indicate greater cognitive restraint, greater disinhibition, and greater susceptibility to hunger, respectively.

Health-related quality of life will be assessed using the 36-Item Short Form Health Survey (SF-36). The SF-36 evaluates eight health domains: physical functioning, role limitations due to physical health, role limitations due to emotional problems, energy/fatigue, emotional well-being, social functioning, pain, general health, and health change. Each domain is scored from 0 to 100, with higher scores indicating better health-related quality of life.

Mood will be assessed using the Positive and Negative Affect Schedule (PANAS). The questionnaire includes two subscales assessing positive affect and negative affect. Each subscale consists of 10 items scored from 1 to 5, resulting in total scores ranging from 10 to 50 for each subscale. Higher positive affect scores indicate greater positive affect, whereas higher negative affect scores indicate greater negative affect.