Abstract
Smell perception plays an important role in eating behavior and might be involved in body weight gain. Since a body of literature implies that olfactory perception and function is hampered in obesity, we here investigate neuroanatomical correlates of this phenomenon. We assessed olfactory bulb (OB) volume with magnetic resonance imaging in 67 healthy participants with a body mass index (BMI) from 18.9 to 45.4 kg/m2 (mean = 28.58 ± 6.64). Moreover, we obtained psychophysiological data on olfactory ability (Sniffin’ Sticks, Food associated odor test) and self-report measurements on eating behavior. Additionally, we collected parameters associated with metabolic health in obesity (waist-hip ratio, waist-height ratio, leptin levels, body fat percentage, fat mass index, insulin resistance) to investigate recently proposed mechanistic explanatory models of why olfaction may be altered in obesity. We showed that OB volume was significantly lower in participants with obesity when compared to those of normal weight. Moreover, we found weak to moderate negative correlations between OB volume and BMI and related measures of metabolic health, especially leptin, body fat percentage, waist-height ratio and insulin resistance. However, neither OB volume nor BMI were related to olfactory function in our young and healthy sample. Nevertheless, our results provide first indications that obesity is associated with brain anatomical changes in the OBs.
Highlights
Obesity has become a worldwide epidemic with an increased risk for major individual health consequences and a severe burden to the healthcare system (Stevens et al, 2012)
Participants with normal weight had significantly lower HOMA-IR scores as well as lower levels of plasma insulin, glucose and leptin when compared to obese participants
We demonstrate for the first time that olfactory bulb (OB) volume is reduced in individuals with obesity when compared to those with normal weight
Summary
Obesity has become a worldwide epidemic with an increased risk for major individual health consequences and a severe burden to the healthcare system (Stevens et al, 2012). One major factor driving the rapid increase of obesity is our obesogenic environment that encourages overconsumption of energy-dense foods even without physiological needs (Berthoud, 2012; Lopez-Gonzalez et al, 2020). External cues, such as the smell of foods, can trigger appetite and intensify food cravings (Firmin et al, 2016). Changes in olfactory perception might be involved in unhealthy eating and potentially lead to weight gain On this notion, it has been shown that individuals with obesity show several alterations in the olfactory system. Odor sensitivity, which reflects perceptual function (Hedner et al, 2010), is decreased in individuals with obesity when compared to people with normal weight (Skrandies and Zschieschang, 2015; Fernandez-Garcia et al, 2017)
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