# Olfactory Capacity and Obesity: A Narrative Review of the Literature
## 3 Results
### Olfactory Dysfunction, BMI, and COVID-19  
Olfactory dysfunction is among the side effects of COVID-19 infection [70; 71]. This infection can cause quantitative olfactory dysfunction (hyposmia and anosmia) as well as parosmia, a qualitative dysfunction [72; 73]. The latter results in altered odor perception, where pleasant smells are perceived as unpleasant, impacting food choices, reducing appetite, and affecting nutritional status [74; 75]. An exploratory study in 9000 users in 2020 evaluated a thematic analysis of user-generated text from a Facebook support group on the loss of smell and taste due to COVID-19. Participants reported the following: difficulty explaining and managing an altered sense of taste and smell; lack of interpersonal and professional support; changes in eating habits; loss of appetite; changes in weight; loss of pleasure in eating foods, and social interaction; altered intimacy; altered relationship with self and others. The findings suggest that altered taste and smell due to COVID-19 can generate severe disruption of daily life, affecting psychological well-being, physical health, and relationships. Among the effects reported by participants were decreased desire and ability to eat and prepare food, weight gain, weight loss, and nutritional deficiency, and effects on emotional well-being, intimacy, social bonding, and altered sense of self and reality. Future research should take these findings into account and suggest areas for training, assessment, and treatment of healthcare professionals working with long-term COVID-19 [76]. However, associations with weight gain remain contradictory [77; 78; 79; 80; 81]. For example, a study evaluating behavioral changes in food intake and body weight during the COVID-19 pandemic showed that altered chemosensory perception (taste and smell) mainly induces a reduction in appetite, leading to a more rapid feeling of satiety during the consumption of a meal and, therefore, to a decrease in body weight [82]. In contrast to the above result, a study that included participants with COVID-19 conducted Sniffin' Sticks testing and BMI assessments one year apart and found that participants with persistent olfactory dysfunction and self-reported parosmia showed statistically significant increases in BMI after 1 year. Controls with transient olfactory dysfunction and participants without parosmia showed no statistically significant changes in BMI over the same time period [83]. The authors hypothesize that the etiology of weight gain in patients with secondary olfactory dysfunction likely arises from altered eating patterns in the context of chemosensory dysfunction. A qualitative study (telephonic exploratory analysis) in individuals with COVID-19 showed that increased food intake was a compensatory response to the lack of food flavor [76]. This behavior may lead to an increased preference for palatable foods, which are generally high in sugar and fats [84]. An example of the above is a study that examined behavioral changes in food intake and body weight during the COVID-19 pandemic. There was an alteration in chemosensoryperception (taste and smell), primarily resulting in a reduction in appetite, resulting in a faster feeling of satiety during meals and, therefore, a decrease in body weight [85]. It is important to note that the quality of evidence on this topic needs improvement. Future research should incorporate more precise measurements of body fat. First, many studies are based on small and non-representative samples, which makes it difficult to generalize the results, often lack control groups, and are not always randomized. In addition, most research is cross-sectional, which precludes establishing clear causal relationships between olfactory dysfunction and obesity. There is also a lack of standardization in the methods used to assess olfactory function, which may lead to inconsistent results.