This study will examine a potential relationship between family history of obesity, that is whether people with at least one parent who had obesity in adulthood compared to people with two parents who did not have obesity in adulthood, and the ability of protein intake to curb further intake of food.

1) Abstract of the study A positive energy balance (greater intake than expenditure) can explain weight gain and, when protracted, leads to overweight and obesity. The major question addressed in this proposal is if the timing of activation of specific regions of the brain is predictive of excessive food intake. Functional near infra-red spectroscopy (fNIR), seldom used in human eating studies, provides data similar to functional magnetic resonance imaging (fMRI) but allows for measurement of brain activation during food consumption. The investigator's pilot fNIR data reveal that varying patterns of regional PFC activation are associated with "loss of control" over eating, and that only 60% of individuals respond to acute protein intake with a reduction in food intake. Using fNIR and an acute protein challenge, the investigator will assess the effect of family history of obesity in humans on the satiation response to protein and concomitant activation of the prefrontal cortex (PFC). It is hypothesized that activation of the human medial PFC before the lateral PFC will result in greater intake of palatable food in those subjects with a proneness to obesity, and that these subjects will be less sensitive to the satiety-inducing effects of a protein preload. These results should provide an innovative and useful method for assessing risk for developing obesity and usefulness of preventative interventions.

Inclusion Criteria

• BMI 20-40
• weight stable for at least 3 months
• no parents with history of obesity in adulthood, or at least one parent with history of obesity in adulthood

Exclusion Criteria

• no current diagnosis of psychiatric disorders
• no current diagnosis of neurological disorders
• no current diagnosis or history of anorexia nervosa
• no current diagnosis or history of bulimia nervosa
• no pregnancy within the last 9 months
• not currently breastfeeding
• no use of investigational medication in the past 6 months
• no use of prescription anti-seizure medications.
• no use of prescription antidepressant medications
• no use of prescription antipsychotic medications

Participants consume two preloads one at each visit, but are not informed which preload is being consumed on which test visit.