Geschatte leestijd: 3 minutenOlfactory function could play a significant role in how the body handles food. This is evidenced by research in which the olfactory function of rats was either disabled or increased. A disabled sense of smell led to lower weight while consuming the same amount of food.
Olfactory Function as Part of Metabolism
The nose has the ability to identify food and stimulate appetite. So, you might expect that rats would eat less if you disable their sense of smell, or conversely, eat more if you increase their sense of smell. Researchers at Berkeley did both. The mice without a sense of smell lost weight, and the ‘super-smellers’ actually gained weight. However, in both cases, the amount of food consumed remained the same.
The results suggest that the sense of smell plays an important role in how the body processes food. A role that it would play through a collaboration between the olfactory system and the part of the brain that regulates metabolism, particularly the hypothalamus. However, the exact mechanism is unknown.
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.
Céline Riera, UC Berkeley & Cedars-Sinai Medical Center
People who lose their sense of smell due to diseases such as Parkinson’s sometimes develop anorexia. To date, however, this has often been attributed to the depression that could accompany the disease. This research now shows that there may be a direct role of the sense of smell and that influencing it could be a method of weight management. Especially if you understand the exact link and can use it without actually disabling the sense of smell.
The researchers point out that both mice and humans are more sensitive to smells when hungry. The lack of smell could possibly make the body think that it has already eaten (and that present food may be burned rather than stored as fat).
Reduced Sense of Smell: Less Fat and Increased Burning
The researchers used gene therapy to temporarily disable the sense of smell. They destroyed the olfactory neurons in the nose, but left the stem cells intact. The olfactory neurons began to recover after three weeks.
Mice with reduced sense of smell burned more fat by activating the sympathetic nervous system, the body’s ‘fight or flight’ response. They converted beige fat cells into brown fat, which burns more fatty acids to generate heat. The white fat cells (which we don’t like as much due to their storage of fatty acids) decreased in size.
Disabling also reversed certain damages caused by previous overweight. The mice that were already overweight before their sense of smell was disabled also had to deal with glucose intolerance, which can lead to diabetes. With loss of the sense of smell, they not only lost weight despite a high-fat diet, but also gained normal glucose tolerance. The overweight mice, with their sense of smell disabled, reached the same weight as mice on a normal diet while muscle mass and bone mass remained the same.
Reduced Sense of Smell, More Noradrenaline
A downside of the reduced sense of smell was another effect of an active sympathetic nervous system: an increase in the stress hormone noradrenaline. If elevated for a long time, this can cause heart attacks in humans.
For now, it could primarily be a valuable method for people with morbid obesity who would otherwise need surgical intervention. The risks due to severe obesity would far outweigh the risks of increased noradrenaline.
For that small group of people, you could wipe out their smell for maybe six months and then let the olfactory neurons grow back, after they’ve got their metabolic program rewired
More Sense of Smell = More Fat Storage
The Berkeley researchers then collaborated with German colleagues who had developed mice with an increased sense of smell. Those mice actually gained more weight on a normal diet than normal mice on the same diet.
It’s unfortunate about the increased noradrenaline. It would be nice if the findings could help more people than just those with morbid obesity. There may be less invasive methods that only reduce the sense of smell and do not completely disable it. Perhaps the effects, both positive and negative, would then be smaller, but still form a positive balance. If these mice without a sense of smell could lose weight on a high-fat diet, maybe they can then maintain their weight on such a diet or lose weight on a normal diet with a reduced sense of smell. There’s still plenty to investigate, it seems to me.
So, don’t be too surprised if your fitness coach or dietitian gives you a clothespin to put on your nose soon.
References
- Celine E. Riera, Eva Tsaousidou, Jonathan Halloran, Patricia Follett, Oliver Hahn, Mafalda M.a. Pereira, Linda Engström Ruud, Jens Alber, Kevin Tharp, Courtney M. Anderson, Hella Brönneke, Brigitte Hampel, Carlos Daniel De Magalhaes Filho, Andreas Stahl, Jens C. Brüning, Andrew Dillin. The Sense of Smell Impacts Metabolic Health and Obesity. Cell Metabolism, 2017 DOI:10.1016/j.cmet.2017.06.015
