The study aims to investigate homeostatic and hedonic mechanisms regulating appetite, energy balance and metabolism in obesity and the effects of three distinct obesity treatments on these regulatory mechanisms.

Obesity is widely acknowledged health problem affecting millions of people globally. Enormous efforts have been made to solve the problem, but long-term results of the conventional weight loss and/or weight management strategies have been poor indicating still inadequate understanding of the problem. Surgical, rather than weight-centred lifestyle interventions, have proved to be the most effective tool available to treat obesity within individuals suitable for obesity surgery. Current surgical interventions are, however, suitable only for a small subset of obese individuals. In general, there is a need for development of new approaches and therapies that are safer and more individualized to each patient in the struggle against obesity and related disorders. To achieve these goals, research must focus to investigate and understand the complex homeostatic and hedonic regulation of eating behavior and energy balance in different physiological and pathological conditions.

This study aims to investigate homeostatic and hedonic mechanisms regulating energy balance and metabolism in obesity and the effects of three distinct obesity treatments on these regulatory mechanisms. The regulatory mechanisms are investigated at the level of metabolism, autonomic and central nervous systems as well as subjective, both implicit and explicit, experiences.

A total of 90 obese female volunteers (18-65 years, body mass index > 35 kg/m2), of which 30 females waiting for bariatric surgery (SURG), 30 females attending a dietary treatment program for obesity (DIET) and 30 females attending Health at Every Size (HAES) program, will participate in the study. The obesity treatment for SURG and DIET groups follows the principles of the Current Care Guidelines for Obesity (adults) and the treatment for the HAES group applies the strategies of the non-diet wellness-based HAES program. The treatment programs of the DIET and HAES groups include 8-10 weekly group sessions organized by authorised nutritionist.

The study includes also two four-hour visits at the research laboratory of the Institute of Public Health and Clinical Nutrition, University of Eastern Finland, the first visit organized before the participants attend any of the obesity treatments and the second visit 12 months later. During the laboratory visits psychophysiological signals (EEG, ANS, facial EMG and eye tracking) are monitored and blood samples taken throughout the experimental period. Participants will also perform two computer-based test sessions, the first one at baseline and the second before a snack meal. Two meals (breakfast and snack meal) are offered to the participants during the experiment in order to study the regulatory mechanisms of interest both at the homeostatic and hedonic states.

Inclusion Criteria:

• body mass index >34 kg/m2
• native finnish speaker
• right-handed

Exclusion Criteria:

• pregnancy or breast feeding
• severe visual impairments, severe scalp skin lesions or intracranial bleeding during previous six months
• severe neurological, psychiatric or cardiovascular disease
• type 1 or 2 diabetes mellitus
• use of weight loss medications or other treatments known to affect weight
• heavy alcohol use
• any other condition (medical or other) the principal investigator considers as an obstacle to participation