The purpose of this study is to better understand how female sex hormones influence the food intake in the gut system through the release of satiety hormones as well as through central regulative mechanisms in the brain that subsequently contribute to the control of eating in healthy women at different stages of the ovarian cycle.

Obesity and the associated severe consequences for health, i.e. cardiovascular diseases or Diabetes Type 2 reach the world-wide level of an epidemic with excessive eating as major cause of this development. Study results of veterinary physiology as well as in women let assume that steroid hormones, such as estrogen or progesterone are highly involved in the regulation of eating behavior and the female body weight. This connection is underpinned with the fact that prevalence of adiposity is increased in women in comparison to men in the United States, Switzerland and further countries. A better understanding of the underlying regulatory mechanisms, which in turn influence the food intake in the gut system through the release of satiety hormones as well as through central regulative mechanisms in the brain, provides important foundation in long-term development of new prophylactic and therapeutic options in reduction and prevention of obesity. This gets even more important, as current therapeutic options - beside bariatric surgery - could only show limited success.

Satiety is a process in the brain that leads to a meal being ended, whereby the ingested food causes a reflexive negative feedback mechanism. This mechanism is both fundamentally and specifically in the acute situation strongly influenced through subjective parameters, e.g. eating desires, socio-cultural factors, current social circumstances and individual relation towards eating. Furthermore, food intake is also influenced by genetic factors, whereas e.g. TaqIA1 allele is known to be associated with obesity. According to current knowledge, regulation takes place on peripheral as well as on central level, whereas not only steroid hormones but also satiety hormones - especially cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1) - are involved on both levels.

The current study aims to examine the connection of steroid hormones, gastrointestinal satiety hormones and neuronal activity in the brain through fMRI. Through the obtained data, the interaction between defined hormone constellations, gastrointestinal satiety hormones and the activation of specific brain areas in obese and normal-weight women should be evaluated. The study design involves the comparison of subjective, hedonic evaluation of different flavoured liquids with different caloric content each through a rating scale as well as objective peripheral (release of CCK and GLP-1) and central (activation of involved brain centres through fMRI) regulation processes in fasted and fed condition of each woman in the two study groups (obese and normal-weighted) in late follicular compared with the luteal phase of ovarian cycle.

Inclusion Criteria:

• Physically and psychiatrically healthy women
• Stable body weight (no changes ≥ 5 kg in past year)
• Age 18-35 years
• Regular menses (26-32 d cycles)
• Right-handed
• German language fluency
• Signed informed consent

Exclusion Criteria:

• Life history of eating disorders
• Aversion to the test foods
• Pacemaker or neurostimulator
• Hearing aid
• Surgery to head or heart
• Potential metal parts in body (pacemakers, metal splinters, gun wounds, shrapnel or surgical clips)
• Neurological or psychiatric problems or serious brain injury (such as alcohol or drug abuse, depression, schizophrenia, bipolar disorders, anxiety disorder, claustrophobia, Parkinson's disease, multiple sclerosis, epilepsy)
• High blood pressure, low blood pressure, history of heart disease, irregular heart rate
• Emphysema, chest or respiratory problems (including difficulty breathing through the nose)
• Pregnancy, nursing or pregnancy planned in next three months
• History of gall bladder disease or symptoms (right upper abdominal quadrant pain after meals)
• Polycystic ovary syndrome, as gauged by testosterone levels
• Allergy or sensitivity to lactose
• Allergy to quinine
• Current or previous malignancies
• History of difficult blood sampling

Normal-weight and obese women with regular menstrual cycles.