Weight Loss and Hunger

Weight loss reduces all components of the energy budget, i.e. resting energy expenditure (EE), the thermic effect of feeding and the energy cost of physical activities. The corollary of this observation is that to achieve energy balance at a lowered body weight (if EE is not increased through purposeful physical activity), energy intake (EI) needs to be kept at this lowered level of EE. While the math of the equation is simple, the operationalization has proven to be quite different. In fact, a dominant feature of weight loss is that it produces increases in hunger that appear within the first days, persist into weight loss and for at least a year after the intervention. As such, identifying strategies that abate changes in hunger and facilitate post-weight loss appetite control should be viewed as a central tenant of obesity interventions. However, data points to the possibility that it may well be the reduction in EI needed to produce weight loss that actually increases hunger. If this were to be the case, then forcing lower EI after weight loss likely exacerbates the state of increased hunger, paving the way for weight rebound. If there is somewhat a set value of EI for each individual, then current dietary strategies aimed at tailoring a food landscape conducive of reduced hunger with reduced EI needed to sustain weight loss, are destined to fail.

Primary hypotheses- The increase of EI to pre-weight loss values will significantly attenuate weight loss induced increases in hunger.

Secondary hypothesis- The increase of EI to pre-weight loss values will significantly attenuate weight loss induced metabolic adaptations (Greater than Predicted decreased in EE).

The increase of EI to pre-weight loss will significantly improve post weight loss ghrelin, PYY and GLP-1 responses.

Research plan- Fifty individuals living with obesity (25 men and 25 women BMI ≥ 30 kg/m2) will undergo a 20-week weight-loss intervention. After weight loss they will be randomly assigned to a 1-month experimental condition comprising of either : 1) a weight maintenance diet; or to 2) an increase of EI to pre-weight loss levels combined with increased exercise to maintain energy balance. A detailed investigation of energy balance variables will be conducted at all three time points.

Relevance- Discovery drives paradigm changes, which hold the promise of catalyzing innovation in treatment. The clinical impact of a setpoint EI is that it would inform more tailored personalized dietary intervention based on one's individual pre-weight loss EI rather than post-weight loss outcomes, which is the current standard of care for maintenance of weight loss. In other words, it could inform the precise corrections in EE (from physical activity) needed to not exacerbate appetite control, and to likely favour healthier weights.

• Plasma concentrations of appetite-regulating hormones [Time frame: Blood samples will be collected at each experimental session: Baseline (1 week before the dietary intervention), end of week 20 (after the weight-loss intervention), and onset of week 25 (after the 1-month weight-maintenance period).]
• Resting Energy Expenditure [Time frame: Resting Energy Expenditure will be measured during the screening session (2 weeks before baseline), at baseline, end of week 20 (after the weight-loss intervention), onset of week 25 (after the 1-month weight-maintenance period).]
• Exercise Energy Expenditure [Time frame: Accelerometer: worn for 7 days at each sampling period (screening, week 20 (end of weight loss intervention), weeks 22 and 24 (middle and end of weight maintenance). Exercise energy expenditure will be measured once per week during weight maintenance.]
• Total Energy Expenditure [Time frame: The DLW dose will be consumed during the screening session, and participants will provide their first urine sample. A second sample will be collected on the following day, and a 3rd 7 days later.]
• Energy Intake [Time frame: In-lab energy intake: Baseline, end of week 20 (after the weight-loss intervention), and at the onset of week 25 (after one month of weight maintenance). Free-living energy intake will be measured for 3 days after the screening session.]
• Food Reward [Time frame: Baseline (1 week before the dietary intervention), end of week 20 (after the weight-loss intervention), onset of week 25 (after the 1-month weight-maintenance period). The test lasts approximately 10 minutes.]
• Olfactory and Taste Performance [Time frame: Olfactory and taste performance will be assessed during the in-laboratory at baseline (1 week before the dietary intervention), end of week 20 (after the weight-loss intervention), onset of week 25 (after the 1-month weight-maintenance period).]
• Body weight [Time frame: Baseline, weeks: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 21, 22, 23, 24, 25.]
• Height [Time frame: Baseline (1 week before the dietary intervention), end of week 20 (after the weight-loss intervention), onset of week 25 (after the 1-month weight-maintenance period).]
• Fat-mass [Time frame: Baseline (1 week before the dietary intervention), end of week 20 (after the weight-loss intervention), onset of week 25 (after the 1-month weight-maintenance period).]
• Fat-free mass [Time frame: Baseline (1 week before the dietary intervention), end of week 20 (after the weight-loss intervention), onset of week 25 (after the 1-month weight-maintenance period).]
• Bone mineral content [Time frame: Baseline (1 week before the dietary intervention), end of week 20 (after the weight-loss intervention), onset of week 25 (after the 1-month weight-maintenance period).]