# Olfactory Capacity and Obesity: A Narrative Review of the Literature
## 3 Results  
### Smell and Energy Regulation  
The hypothalamus is a master regulator of whole-body energy homeostasis [21]. It can detect an individual's nutritional state and integrate this information to regulate food intake, glucose levels, and energy balance [22]. In this context, food odors perceived by the olfactory system alter the activation state of hypothalamic AgRP and POMC neurons, thereby modulating appetite and satiety circuits [23; 24].  
Research shows a close relationship between the olfactory system and energy balance. Different odors are sensed by olfactory sensory neurons (OSNs) located within the olfactory epithelium (OE). Bidirectional connections have been observed between the olfactory circuit and hypothalamic nuclei, which maintain the body's homeostasis. The hypothalamus is organized into anatomically defined neuronal groups, known as nuclei, which form interconnected neural circuits through axonal projections and regulate functions such as energy balance. Among these nuclei is the arcuate nucleus (ARC), which contains two main cell populations: those that express orexigenic neuropeptides, such as agrp and neuropeptide Y (NPY), and those that express anorexia neuropeptide precursors, such as proopiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART). The sense of smell influences the metabolic state by participating in the cephalic phase of digestive physiology. Its function is also modulated by molecules related to food intake and by circulating levels of peptides that regulate energy metabolism. Specifically, orexigenic peptides like ghrelin enhance olfactory sensitivity, which is reduced by anorexia peptides such as leptin and insulin. In the case of individuals with obesity, peptides related to food intake would act as follows. Individuals with obesity are characterized by high circulating levels of leptin and insulin, which bind to their receptors,  
Figure 1: Flow diagram summarizing the article selection process.  
which are particularly abundant in olfactory structures. This exerts an inhibitory effect primarily on the mitral cells of the olfactory bulb, the first processing point of olfactory information. These cells play a key role in representing the identity and intensity of odors. In obesity, there is a reduction in circulating ghrelin levels, leading to a consequent decrease in olfactory function due to the diminished effect of this hormone. Previous studies have shown that olfactory dysfunction affects food intake, potentially leading individuals to adopt an unbalanced diet. These individuals report that food is less enjoyable and less flavorful. To compensate for the reduced gratification resulting from diminished olfactory stimulation, they tend to prefer more palatable foods, such as sweet and high-fat items, over fruits and vegetables, and they increase their use of condiments and spices (Figure 2).  
A reduced sense of smell is referred to as \"anosmia\", with a prevalence of 15%, while approximately 2% of individuals experience a total loss of smell, known as \"hyposmia\" [25]. It has been suggested that olfactory and gustatory perception can influence food choices and eating behavior, as changes in smell and taste at the individual level may play a crucial role in food preferences, selection, and consumption [26; 27].