How smells contribute to obesity

Written by Natasha Fiera

The sense of smell enables us to experience our favorite scents and tastes, but new research shows that it also plays a role in obesity and metabolic health.

Humans and animals rely on the sense of smell for many purposes, from detecting food and places to recalling memories and emotions. Now, a new study published in Cell Metabolism reveals that the sense of smell also affects metabolic health and obesity.

When fasting, people tend to notice even the slightest smell of food wafting through the air, but after eating, smells aren’t as noticeable. For Andrew Dillin and his research team at the University of California, Berkeley, this connection raised the question of whether olfactory sensory neurons (OSN), which transmit the sense of smell, influence metabolism and energy balance.

To find out, Dillin and his team ablated the sense of smell in mice by genetically disrupting OSNs and then reared a “lean” group of mice on a normal diet and an “obese” group on a high-fat diet. They found that when fed the high-fat diet, mice that could not smell consumed less food and had a lower body weight and less fat than mice with their olfactory systems intact. Further studies showed that the reduced sense of smell prolonged the sympathetic nervous system responses to reduced energy and actually promoted an increase in fat breakdown though heat production.

The researchers next ablated the IGF1 receptor in OSNs to enhance sensitivity to smell in the resulting mice. When fed the high-fat diet, these mice developed increased fat mass, hyperinsulinemia, and insulin resistance, indicating that IGF1 receptors in the OSN play a role in regulating insulin sensitivity. The researchers concluded that even a short-term loss of smell improves metabolic health and weight loss when mice consume a high-fat diet.

“This study was carried out on mice, nevertheless there will be speculation that such a two-way functional system in the sense of smell will apply to humans and can be used to combat obesity,” said Tim Jacobs from Cardiff University who was not associated with this study.