Abstract
An association between obesity and depression has been indicated in studies addressing common physical (metabolic) and psychological (anxiety, low self-esteem) outcomes. Of consideration in both obesity and depression are chronic mild stressors to which individuals are exposed to on a daily basis. However, the response to stress is remarkably variable depending on numerous factors, such as the physical health and the mental state at the time of exposure. Here a chronic mild stress (CMS) protocol was used to assess the effect of high-fat diet (HFD)-induced obesity on response to stress in a rat model. In addition to the development of metabolic complications, such as glucose intolerance, diet-induced obesity caused behavioral alterations. Specifically, animals fed on HFD displayed depressive- and anxious-like behaviors that were only present in the normal diet (ND) group upon exposure to CMS. Of notice, these mood impairments were not further aggravated when the HFD animals were exposed to CMS, which suggest a ceiling effect. Moreover, although there was a sudden drop of food consumption in the first 3 weeks of the CMS protocol in both ND and HFD groups, only the CMS-HFD displayed an overall noticeable decrease in total food intake during the 6 weeks of the CMS protocol. Altogether, the study suggests that HFD impacts on the response to CMS, which should be considered when addressing the consequences of obesity in behavior.
Highlights
Obesity is one of the main health concerns in today’s society.[1]
The diet-induced body weight increase was evident by the end of the experiment (5 months of age), with the CON-high-fat diet (HFD) animals weighting 30% more than the CON-normal diet (ND)
A delayed body weight gain of animals on ND is a well-known effect of the chronic mild stress (CMS) protocol.[13,22,23,24]
Summary
Obesity is one of the main health concerns in today’s society.[1]. It is mainly described as an excessive increase in body weight, with disproportionate accumulation of body fat mass, caused by excess energy intake over energy expenditure over a long period of time.[1,2] Besides the well-recognized set of metabolic alterations, obesity is suggested to be associated with psychiatric disorders, such as anxiety and depression[2] (albeit not all studies show such association).[3,4,5] Depression in itself is a serious chronic mental disorder characterized by health complications including, among others, anhedonia and changes in appetite and pattern of food intake.[6,7,8,9] Mild environmental stressors, to which individuals are exposed daily, can be both triggers of depression and alter feeding behaviors.[1,2] these may, directly or indirectly, contribute to the metabolic changes triggered by elevated glucocorticoids, as well as to the onset of obesity.[1,10,11] it is interesting to note that the individual’s response to stress depends on various factors, including the type of stressors, their intensity, frequency and duration.[12]. Studies in animal models of stress showed that while intense and painful stressors result in inhibition of food intake,[12] and exposure to chronic mild stressors leads to a reduction in food intake,[1,2,12,13] other mild stressors induce spontaneous feeding.[1] Still, most of the studies have focused on the acute effect of stress on animals’ feeding behavior and are mostly conducted using healthy animals displaying normal body weight and fed with regular rodent diet. Information is lacking on the effects of stress in animal models under other types of diets, namely high-fat diet (HFD). We used a model of HFD-induced obesity to evaluate the consequences of HFD on mood and cognition and on the animals’ ability to respond to chronic mild stress (CMS)
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