These results in the studies point to a key connection between the olfactory or smell system of the body and regions of the brain that regulate metabolism, specifically hypothalamus, though the neural circuits are still unknown. Céline Riera, a former UC Berkeley postdoctoral fellow noted, "This paper is one of the first studies that really shows if we manipulate olfactory inputs we can actually alter how the brain perceives energy balance, and how the brain regulates energy balance."
The research was carried out on obese mice, it was noted that those mice that lost their sense of smell also lost weight. Interestingly, the newly slimmed-down and smell-deficient mice ate the same amount of food as mice that retained their sense of smell and, in fact, managed to gain more weight. Furthermore, mice with an enhanced sense of smell got fatter than the mice with normal smelling sense.
Humans who lose their sense of smell due to various factors like age, injury or diseases often tend to lose weight, the cause however has been unclear because loss of smelling sense may lead to depression, which itself can cause loss of appetite. The new study that was published in journal Cell Metabolism revealed that the loss of smell itself plays a role, suggesting possible interventions for those who have lost their smell and those having trouble shredding pounds.
Source - NDTV