The aim is to profile and elucidate the hormonal and neurological system interaction to food related behavior. The stimulus used will include visual and taste (gustatory) stimuli. The study will profile induced correlations of metabolic parameters, gut hormones and brain region (ROI - regions of interest) activation and interaction. In this study we will use fMRI (functional MRI) to compare brain responses in obese, normal-weight and reduced weight subjects. The food stimuli will be blocked into specific categories to allow for investigation of different responses to alternating energy density foods. The response will be tested prior to and following a brief low carbohydrate dietary regimen.

The study will be a longitudinal study where the participants will come back twice on the same phase of the period- both visits in the luteal phase with a month between each visit. In this part of the study there will be 40 participants with a wider range of BMI. This phase of the study will include a nutritional intervention - the participants will be asked to have a carbohydrate restricted diet (60 grams of carbohydrate)- for a period of a month with no caloric restriction. Food records will be kept and followed and a ketone test (blood test) will be done on the morning of the study visits.

Inclusion Criteria:

• Age 18- 45 years
• No contraindication to enter the MRI
• No significant visual problems that may hamper visualization of visual stimuli within the magnet
• No contraceptive hormonal replacement
• relatively regular menstrual cycle

Exclusion Criteria:

• contraceptive hormonal replacement
• under the age of 18
• over the age of 45
• pharmacological treatment that can effect brain response
• Irregular menstrual cycle

Only females without contraceptive treatment and with regular menstrual cycle