Researchers are increasingly interested in understanding the role of the olfactory bulb, which relays smell information from the nose to the brain, and contains one of the densest collections of insulin receptors outside the pancreas. The production of insulin, which is used to turn sugar into energy, is often impaired in obese people.
Debra Ann Fadool, a professor at Florida State University in the program in neuroscience and molecular biophysics, and Kristal Tucker, a research associate in pharmacology and chemical biology at the University of Pittsburgh School of Medicine, were studying the role of insulin in the olfactory system when they bred genetically modified "super-smeller" mice that could discriminate odors better than normal mice.
They observed that these modified mice were thinner than normal mice and appeared resistant to obesity, perhaps because the modified mice metabolized the fat differently. Even when they were fed a high-fat diet, they didn't put on extra fat. They also exhibited lower levels of insulin, glucose and leptin—chemicals that are usually elevated in obesity, said Dr. Fadool.
This observation led the scientists to remove the super-smeller mice's olfactory bulbs. When they did this, the mice ceased to remain resistant to obesity, Dr. Fadool said.
Further investigation found that the neurons in the bulbs of obese mice fired less frequently than in lean mice, suggesting that these mice didn't decipher odors as well, and they couldn't adapt well to different situations, such as an influx of insulin.
In another study, published last month in the Public Library of Medicine, they found that mice made obese on a high-fat diet also exhibited damped responses in their olfactory bulbs, suggesting obesity can disrupt the bulb's functioning.
It isn't clear how olfaction and body weight are linked. One theory: Excess fat and related hormonal changes could trigger changes in the olfactory system.
Another is that olfactory dysfunction comes first, and can cause or contribute to obesity, according to Dr. Tucker. In the future, targeting smell could be another approach to addressing obesity, she added.
"If you can modulate your olfactory function, it's possible it could be a future target for controlling food intake and metabolism," she said.
Obesity also influences sleepiness. Obese people often report feeling sleepier than their leaner counterparts. For a long time it was believed this was due to sleep apnea, a condition—common in the overweight—in which a person stops breathing repeatedly while sleeping.
But Alexandros Vgontzas, a sleep specialist at Penn State University, and others have found that the obese sleep worse and report being sleepy in the daytime—to the point of falling asleep at work or while driving—regardless of whether they have sleep apnea.
At the Associated Professional Sleep Society in Boston this summer, they presented data on 1,700 people they followed for 7½ years, studying the factors at work in those who reported significant sleepiness. Obesity, weight gain and depression were the biggest risk factors, they found. In addition, weight loss appeared to make people less sleepy.
"The weight gain and weight loss findings tell us it's indeed the obesity that makes you complain about sleepiness, not the other way around," said Dr. Vgontzas. This makes sense because fat produces certain molecules that are known to be sleep factors, he said.
These results could help clinicians treating patients with sleep problems, Dr. Vgontzas says. Rather than immediately treating an overweight person with what is known as a CPAP machine, a mask that forces air up the nose to improve breathing, the doctor should consider intervening to encourage weight loss instead, he said.
"It's a bad practice for sleep medicine physicians if someone comes with mild or moderate sleep apnea to stuff them with mask instead of [change] lifestyle," said Dr. Vgontzas.
Fertility is another area that obesity seems to disrupt. In a recent study of teenage boys, obese males had half the level of testosterone of lean ones, suggesting they could have problems with impotence and fertility later on, said Paresh Dandona, a professor and head of endocrinology, diabetes and metabolism at the University of Buffalo in New York state.
"It is still not fully appreciated that obesity could be a cause of sexual dysfunction and infertility," said Dr. Dandona. "It's a public health issue."
It isn't clear why there is a link, though it seems likely that the hormones produced by fat disrupt the typical balance of sex hormones, said Dr. Dandona.
Debra Ann Fadool, a professor at Florida State University in the program in neuroscience and molecular biophysics, and Kristal Tucker, a research associate in pharmacology and chemical biology at the University of Pittsburgh School of Medicine, were studying the role of insulin in the olfactory system when they bred genetically modified "super-smeller" mice that could discriminate odors better than normal mice.
They observed that these modified mice were thinner than normal mice and appeared resistant to obesity, perhaps because the modified mice metabolized the fat differently. Even when they were fed a high-fat diet, they didn't put on extra fat. They also exhibited lower levels of insulin, glucose and leptin—chemicals that are usually elevated in obesity, said Dr. Fadool.
This observation led the scientists to remove the super-smeller mice's olfactory bulbs. When they did this, the mice ceased to remain resistant to obesity, Dr. Fadool said.
Further investigation found that the neurons in the bulbs of obese mice fired less frequently than in lean mice, suggesting that these mice didn't decipher odors as well, and they couldn't adapt well to different situations, such as an influx of insulin.
In another study, published last month in the Public Library of Medicine, they found that mice made obese on a high-fat diet also exhibited damped responses in their olfactory bulbs, suggesting obesity can disrupt the bulb's functioning.
It isn't clear how olfaction and body weight are linked. One theory: Excess fat and related hormonal changes could trigger changes in the olfactory system.
Another is that olfactory dysfunction comes first, and can cause or contribute to obesity, according to Dr. Tucker. In the future, targeting smell could be another approach to addressing obesity, she added.
"If you can modulate your olfactory function, it's possible it could be a future target for controlling food intake and metabolism," she said.
Obesity also influences sleepiness. Obese people often report feeling sleepier than their leaner counterparts. For a long time it was believed this was due to sleep apnea, a condition—common in the overweight—in which a person stops breathing repeatedly while sleeping.
But Alexandros Vgontzas, a sleep specialist at Penn State University, and others have found that the obese sleep worse and report being sleepy in the daytime—to the point of falling asleep at work or while driving—regardless of whether they have sleep apnea.
At the Associated Professional Sleep Society in Boston this summer, they presented data on 1,700 people they followed for 7½ years, studying the factors at work in those who reported significant sleepiness. Obesity, weight gain and depression were the biggest risk factors, they found. In addition, weight loss appeared to make people less sleepy.
"The weight gain and weight loss findings tell us it's indeed the obesity that makes you complain about sleepiness, not the other way around," said Dr. Vgontzas. This makes sense because fat produces certain molecules that are known to be sleep factors, he said.
These results could help clinicians treating patients with sleep problems, Dr. Vgontzas says. Rather than immediately treating an overweight person with what is known as a CPAP machine, a mask that forces air up the nose to improve breathing, the doctor should consider intervening to encourage weight loss instead, he said.
"It's a bad practice for sleep medicine physicians if someone comes with mild or moderate sleep apnea to stuff them with mask instead of [change] lifestyle," said Dr. Vgontzas.
Fertility is another area that obesity seems to disrupt. In a recent study of teenage boys, obese males had half the level of testosterone of lean ones, suggesting they could have problems with impotence and fertility later on, said Paresh Dandona, a professor and head of endocrinology, diabetes and metabolism at the University of Buffalo in New York state.
"It is still not fully appreciated that obesity could be a cause of sexual dysfunction and infertility," said Dr. Dandona. "It's a public health issue."
It isn't clear why there is a link, though it seems likely that the hormones produced by fat disrupt the typical balance of sex hormones, said Dr. Dandona.
ArturoRodriguez, MD
md@thebariatric.comhttp://www.thebariatric.com
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