The fat in our bodies has a direct influence on the energy levels in our brain, with fat tissue found to communicate directly with the hypothalamus as the brain responds to food scarcity. New research published in the journal Cell Metabolism from the Washington University School of Medicine suggests there is an optimal amount of body fat, helping to explain the survival benefit of having a slightly overweight body mass index (BMI).
People with a body mass index toward the low end of the overweight spectrum are known to have a lower mortality rate. A number of studies have shown clear links between moderate fat levels and increased mortality, a connection known as the "obesity paradox". A BMI of 18.5-25 is considered the normal range, with 25-30 being overweight and 30-35 considered obese. Dozens of studies, including one massive study involving 2.9 million people, have shown a similar pattern. People with a BMI around 27, meaning they are slightly in the overweight category, are less likely to die at any given age.
While the "obesity paradox" has been known for a long time now, the reasons behind it have been shrouded in mystery. New research shines light on the problem, with fat tissue in mice found to affect brain function through an enzyme called NAMPT. According to Shin-ichiro Imai, senior author of the study, “As we age, people who are slightly overweight tend to have fewer problems... No one knows why people categorised as being slightly overweight tend to have a lower mortality rate. But our study suggests that if you don’t have an optimal amount of fat, you are affecting a part of the brain that is particularly important for controlling metabolism and aging.”
The study demonstrates the importance of NAMPT, which is known to be important for making fuel inside cells. As it turns out though, fat tissue also produces a lot of NAMPT that ends up circulating in the bloodstream outside cells, which in turn ends up affecting the hypothalamus. "We were not surprised to see that energy levels in the fat tissue plummeted when fat tissue lacked this key enzyme," Imai said, adding "Other tissues such as the liver and muscles were unaffected. But there was one distant location that was affected, and that was the hypothalamus."
The hypothalamus is responsible for maintaining the body's physiology, including the regulation of body temperature, sleep cycles, heart rate, blood pressure, thirst, and appetite. The study suggests that fat tissue communicates specifically with the hypothalamus, with low levels of NAMPT in fat tissue leading to low fuel levels in the brain and lower measures of physical activity. "We showed that fat tissue controls brain function in a really interesting way." said Imai, adding "The results suggest that there is an optimal amount of fat tissue that maximizes the function of the control center of aging and longevity in the brain... we know that if they don't have enough of a key enzyme produced by fat, an important part of the brain can't maintain its energy levels."
