# Olfactory Capacity and Obesity: A Narrative Review of the Literature
## 1 Introduction
#### Smell and Diet  
The etiology of obesity is multifactorial, involving both extrinsic and intrinsic factors. Among the extrinsic factors is the modern food environment, which promotes the excessive consumption of high-calorie foods, particularly ultra-processed products. These foods are rich in calories, sugar, saturated fats, trans fats, and sodium and are generally characterizedby intense aromas [7]. Among the chemosensory organs, it has been demonstrated that the sense of taste plays a significant role in nutrient selection and dietary intake [8].  
This dynamic balance between food consumption and energy expenditure requires a coordinated integration of inputs from the peripheral sensory system with internal response systems. In this context, the sensory system guides animals toward food, shapes food preferences, and contributes to the experience of satiety after consumption, thereby promoting dietary learning [9].  
The sense of smell plays a key role in our ability to enjoy food, as olfactory signals and odor perception significantly contribute to the experience of flavor, food preference, acceptability, and intake. Additionally, food odors released in the oral cavity travel to the olfactory receptors located in the nose, significantly stimulating salivation, insulin release, and gastric acid secretion in the stomach [10]. Furthermore, food odors act as triggers for food consumption in animals [11].  
Studies have shown that individuals with a reduced sense of smell are less attracted to new foods and derive less pleasure from eating [12]. Additionally, there is evidence of an association between poor diet quality and a lower variation in dietary habits among patients with olfactory dysfunction [13].  
The sense of smell is a sensory system present in animals, including humans. Odorant receptors expressed in olfactory sensory neurons can detect and distinguish a wide variety of olfactory signals [14]. The sensitive and precise detection of food can guide animals toward a nutrient source, stimulating appetite responses. Additionally, chemosensory perception is a key determinant of food palatability and is believed to play a fundamental role in food choices and energy intake [15; 16; 17].  
In this context, it has been observed that the smell of food can elicit either an attractive or aversive response mediated by odorant receptors [14].  
The sense of smell goes beyond mere sensory perception and is closely linked to hypothalamic function. This connection is evident in findings that show olfactory acuity decreases in a state of satiety but increases in a state of hunger [18; 19; 20]. In other words, hunger enhances olfactory sensitivity, while satiety reduces it, indicating a reciprocal relationship between food intake and olfactory sensitivity. The purpose of this narrative review is to answer the following research question: how does smell influence the perception, selection, and eating behavior of food? An overview of the role of smell in food perception and selection as well as its influences on eating behavior and obesity is presented in this narrative review.