Relationship between Olfactory Function and BMI in Normal Weight Healthy Subjects and Patients with Overweight or Obesity

Abstract

Smell plays a critical role in food choice and intake by influencing energy balance and body weight. Malnutrition problems or modified eating behaviors have been associated with olfactory impairment or loss. The obesity epidemic is a serious health problem associated with an increased risk of mortality and major physical comorbidities. The etiopathogenesis of obesity is complex and multifactorial, and one of the main factors contributing to the rapid increase in its incidence is the environment in which we live, which encourages the overconsumption of foods rich in energy, such as saturated fats and sugars. By means of the “Sniffin’ Sticks” test, we measured the olfactory threshold, discrimination and identification score (TDI score) in patients of the Obesity Center of the University Hospital (OC; n = 70) and we compared them with that of healthy normal weight controls (HC; n = 65). OC patients demonstrated a significantly lower olfactory function than HC subjects both general and specific for the ability to discriminate and identify odors, even when they were considered separately as females and males. For OC patients, a negative correlation was found between body mass index (BMI) and olfactory scores obtained by each subject, both when they were divided according to gender and when they were considered all together. Besides, normosmic OC patients showed a significantly lower BMI than hyposmic ones. A reduced sense of smell may contribute to obesity involving the responses of the cephalic phase, with a delay in the achievement of satiety and an excessive intake of high-energy foods and drinks.

Smell Impairment in Stage I‐II Obesity: Correlation with Biochemical Regulators and Clinical Aspects

“…In conclusion, the present study for the first time found that olfactory processing – influencing physiological and neural systems involved with appetite and eating behaviors–is not only a critical component for the development and the maintenance of obesity 67,68 but–further–its performance tends to worsen with the increase of obesity stage. These findings enlarge those experiences evidencing that olfactory perception may progressively decrease with a linear relationship with measures of obesity, 40,69 its low‐grade chronic inflammation 60 and the pattern of hormones–such ghrelin and leptin–involved in the gut‐brain underpinning of olfactory processing 6,45,48,53 . However, future studies are needed to expand such notions to ameliorate clinical and research deepening of obesity‐related olfactory behavior with possible consequences on diagnosis, treatment and–especially–prevention of onset and development of obesity, thus opening possible future strategies involving multidisciplinary contributions.…”

“…Indeed, previous studies demonstrated that individuals with obesity have a higher hedonic response to palatable food odors when compared to people of normal weight 10 and have decreased olfactory function. 1,[11][12][13][14][15]40 Especially odor sensitivity, which reflects perceptual function, 41 is decreased in individuals with obesity when compared to people with normal weight. 12,14 The mechanisms underpinning these alterations remain to be completely understood, however, it has been suggested that a reduced olfactory function may be linked to those hormonal and metabolic changes that are associated with obesity.…”

“…This aspect is worth noting because it strengthens those notions positing changes in olfactory perception to be involved in unhealthy eating and potentially lead to weight gain. Indeed, previous studies demonstrated that individuals with obesity have a higher hedonic response to palatable food odors when compared to people of normal weight 10 and have decreased olfactory function 1,11–15,40 . Especially odor sensitivity, which reflects perceptual function, 41 is decreased in individuals with obesity when compared to people with normal weight 12,14 …”

“…However, in such a suboptimal solutionpreviously adopted also in other cross-sectional studies 39 olfactory, biochemical, and anthropometric parameters of obese patients were found to be in line with previous works where differences with healthy participants have been investigated. 13,15,40,70,71 Further, we restricted enrolment to stage I and II obesity, and the lack of extreme BMI values may have limited the ability to detect variations in olfaction components with fat…”

The Effects of Olfactory Loss and Parosmia on Food and Cooking Habits, Sensory Awareness, and Quality of Life—A Possible Avenue for Regaining Enjoyment of Food

“…Several studies have highlighted patterns of unbalanced diets in patients with olfactory dysfunction, although these findings may reflect changes in intake and preference for specific items and not general patterns [ 18 ]. Moreover, obesity is also associated with lower olfactory test scores indicating that the causality of underlying mechanisms may be more complex [ 19 ].…”