Epigenetic modifications in genes involved in smelling seem to correlate with obesity indicators, like body mass index and waist circumference, by influencing a person’s eating habits, a new study has found.
The study, “Associations between olfactory pathway gene methylation marks, obesity features and dietary intakes,” was published in the journal Genes & Nutrition.
It’s no stretch of the imagination to suppose that sense of smell might affect what food a person eats. And, while genetics and other environmental factors certainly play a role in how fat accumulates, food choices directly affect obesity.
This led researchers to hypothesize that differences in genes related to smell might predispose some people, for example, to eat a diet with more fat because high-fat foods smell better to them.
The researchers were specifically interested in DNA methylation, which is a type of epigenetic modification. Broadly speaking, these modifications don’t change the actual sequence of a person’s DNA, but they do change how that DNA is “packaged” and “read,” which can have significant biological effects.
To test their hypothesis, the researchers used data from the Methyl Epigenome Network Association (MENA) project, in which the methylation patterns of 474 people’s DNA were determined by analyzing cells in blood samples. The majority of participants in this project were female (64%), and 82% had “excessive body weight” based on criteria from the World Health Organization.
The researchers then looked for patterns between methylation in genes known to be related to smelling, and measurements to detect obesity, namely body mass index (BMI) and waist circumference.
After controlling for factors like sex and age, the methylation status of 15 smell-related genes was significantly associated with both BMI and waist circumference. In total, methylation differences at these sites accounted for 22% of the variation detected in BMI and for 20% of the variation detected in waist circumference.
Information on diet was available, in the form of answers to a survey, for a subset of 247 participants. Researchers noted that the methylation status of two genes — OR4D2 and OR2Y1 — was significantly associated with daily intake of carbohydrates, proteins, fats, and total energy.
Together, these data support the researchers’ initial premise that epigenetic variations in smelling genes could affect how a person puts on weight, specifically by affecting the diet they consume.
“To the best of our knowledge,” the researchers wrote in their paper, “this is a pioneer study exploring the role of epigenetics of olfaction [smelling] in obesity.”
Of course, the study is not without its limitations. First and foremost, this type of study cannot, by design, establish a cause-and-effect relationship; it can only suggest that associations exist. Additionally, the methylation patterns detected in the patients were detected in blood cells, not the cells that actually do the smelling, and it’s possible for such patterns to be different in different tissues, even in the same person.
More research needs to be done to fully understand these relationships, and this knowledge may allow for “epigenome-based dietary strategies for prevention, prognosis, and treatment of obesity within the era of precision nutrition,” the researchers wrote.