INTRODUCTION

Obesity is one of the major public health issues with rates nearly tripling over the past three decades. In 2016, 39% of adults aged 18 years and over were overweight and 13% were obese [1]. The increasing emergence of obesity is associated with multiple morbidities, including an type 2 diabetes [2], hypertension [3], cardiovascular disease [4], and cancer [5]. When energy intake exceeds a person’s energy expenditure, excess energy contributes to weight gain [6]. Obesity results from changes in homeostasis and sybaritic food intake behavior resulting from changes in the plasticity of cortical and subcortical brain structures [7]. Therefore, unnatural eating habits are an important factor in defining obesity as a disease [8]. Food intake is modulated by various cognitive influences such as celebratory representation, environmental situations, and emotional and compensatory characteristics [9]. Studies have shown that structural differences in the brain may cause a more likelihood of obesity, but it is also likely that the condition of obesity itself can change the brain due to development of physiological control disorders [10]. A number of studies have reported that increased body mass index (BMI) is related to the increased cortical thickness and that there was a significant positive correlation between visceral fat ratio and cortical thickness throughout the brain [11,12]. In contrast, other studies showed that increasing BMI was associated with cortical thinning in the left inferior temporal and the inferior parietal cortex and increasing visceral adipose tissue was related to cortical thinning in the left fusiform gyrus, the right inferior temporal and mid-insular [13]. BMI showed a negative correlation with cortical thickness in the left lateral occipital cortex and right ventromedial prefrontal cortex area [10]. Studies that assessed gray matter volume (GMV) in obese subjects found that obese subjects showed enlarged left putamen which correlated with increasing BMI and enlarged amygdala and hippocampus [8,14]. Studies also showed that the higher waist-hip ratio and waist circumference, the lower the total brain volume (TBV) and GMV [15]. Previous studies that compared lean subjects and obese individuals showed that obese individuals had significant lower gray matter density in the postcentral gyrus, frontal operculum, putamen, middle frontal gyrus [16], left dorsolateral prefrontal cortex [17], ventral diencephalon, and brainstem than those of lean subjects [7].

A number of studies have suggested the relationships between obesity and morphology of the brain area. However, the results of previous research are diverse and consistent results on regional brain changes in obesity have not been established. The purpose of this study was to examine the structural differences of the cortical gray matter (e.g., cortical thickness, surface area, and volume) between obese patients and healthy controls. We hypothesized that obese patients would exhibit regional cortical structural alterations in brain areas which are involved in food intake behavior regulation.

MATERIALS AND METHODS

Subjects

Thirty-eight male subjects, 21 with obese (age=24.05 ± 3.41 years; body mass index [BMI]=29.81 ± 3.89 kg/m2 ) and 17 healthy controls with normal weight (age=25.65 ± 4.29 years; [BMI]=22.46 ± 1.43 kg/m2 ) were recruited from Chungbuk National University. BMI was calculated as body weight in kilograms divided by the square of height in meters. Obesity was designated as a BMI ≥ 25.0 kg/m2 using the adjusted Korean guideline. Subjects with neurological abnormalities, history of psychiatric illnesses, illicit drug dependence or alcohol abuse were excluded from this study. This study was approved by the Institutional Review Board (IRB) by College of Medicine Chungbuk National University in Cheongju, Korea. All subjects provided written informed consent after detailed instructions of the study.

MRI acquisition

Brain imaging data were acquired on a 3T MR scanner (Achieva 3.0T TX, Philips Medical Systems, Eindhoven, Netherlands). A 32-channel receive-only phased array head coil was used for receiving. Structural images were acquired using a high-resolution T1-weighted threedimensional (3D) magnetization prepared rapid gradient echo (MPRAGE) with the following parameters: repetition time (TR)=7 ms, echo time (TE)=3 ms, flip angle=9º, slice thickness=1.2 mm, field of view (FOV)=256 mmâ…¹ 256 mm, and matrix=243.