Ethnic Influences on Stress, Energy Balance and Obesity in Adolescents

Obesity is one of the most serious public health problems in the US; its prevalence has
tripled in the last three decades and is associated with a range of short- and long-term
medical and psychosocial problems. Adolescence is a critical period for the development and
persistence of obesity, and is associated with changes in diet, physical activity and
fitness, fat distribution and insulin sensitivity. There are racial and sex-specific
disparities in the prevalence and burden of obesity. African-American (AA) females have the
highest rates of obesity, and the clustered risk factors for coronary heart disease and
metabolic syndrome are twice that of AA males. The reasons for racial and sex-specific
disparities in the prevalence and burden of obesity are not well understood. AA experience
higher stress levels than Non-Hispanic Whites (NHW) due to economic and social inequalities,
and the effect of stress on energy-dense diet and adiposity is more prominent in females. A
better understanding of the mechanisms that link stress to obesity, particularly during
adolescence when high rates of obesity, increased stressful experiences and stronger
behavioral and physiological responses to stress emerge, will contribute to new clinical
guidelines for reducing obesity and associated medical conditions in AA females.

The Physiological stress system affects obesity and mediates its adaptive functions via
hypothalamic-pituitary-adrenal (HPA) axis. Prolonged stress-induced glucocorticoid secretion
promotes the consumption of energy-dense diet (EI) and abdominal fat deposition both directly
and indirectly through its effects on metabolic hormones. Stress also reduces physical
activity and alters energy balance. The proposed study will examine the effects of stress and
HPA axis on EI and physical activity-related energy expenditure in 100 AA and 100 NHW
adolescent females. The effects on EI will be assessed in two contexts, the natural
environment and under controlled conditions incorporating a standardized psychosocial
stressor. Stress will be assessed in the natural environment as multiple domains (i.e.,
individual, family and social), and several indices of the HPA axis will be obtained to
represent diurnal variation, its status over 12-15 weeks and reactivity to stress.
Obesity-related parameters will be measured through anthropometry, fat distribution and
cardio-metabolic biomarkers.

Associations among stress, HPA activity/function, energy balance and obesity-related
parameters will be compared between and within AA and NHW samples. In combination they will
improve our understanding of the social factors and biobehavioral mechanisms of both racial
and individual differences in obesity and facilitate the development of effective treatments
within and across racial groups according to the principles of individualized medicine. To
our knowledge, racial differences in objectively-measured diet intake and energy expenditure
in response to stress, or their underlying physiological mechanisms, have not been assessed
in adolescents or adults. This is an important knowledge gap in our efforts to develop better
evidence-based translational obesity prevention and weight-control interventions as the
traditional interventions are not effective with minority youth.

Inclusion Criteria:

- African-American or Non-Hispanic White females from 13-17 years old and Tanner Stage
≥III.

- BMI values will be balanced (1/3rd normal, 1/3rd overweight and 1/3rd obese range
percentile BMI values) using CDC criteria

Exclusion Criteria:

- Participants with a BMI below the normal range, trying to lose weight, on medications
that affect appetite or hypothalamic-pituitary-adrenal axis, or with a history of
bariatric surgery, will be excluded.

- Restrained or binge eaters, individuals who score below 50 on a 100 mm Visual Analog
Scale for foods provided in the study, or those allergic to these foods will be
excluded.

- Participants with major psychiatric disorders (e.g., anxiety, eating, mood, substance
use disorders) or medical problems (e.g., endocrine disorders or unstable cardiac,
pulmonary or renal conditions) will be excluded.

- Pregnant females, or those suspected of being pregnant, will be excluded.