When we’re cold we tend to shiver and shake, a response our body makes in an effort to warm us up, which also burns calories. Researchers have found the calorie-burn triggered by the cold can be controlled without the drop in temperatures, by manipulating the immune system instead of the brain, in a new hopeful approach to weight loss.

The team discovered two signaling molecules that are secreted by the immune system and flip the switch from fat-storing to fat-burning. The findings, which were published in the journal Cell, were built on previous work performed by the same research team at the Cardiovascular Research Institute at the University of California, San Francisco.

"Nutrient and energy metabolism has largely been thought to be under the control of the brain and endocrine system," said Ajay Chawla, MD, PhD, the study’s lead author and associate professor of medicine at the UCSF Cardiovascular Research Institute.

Humans and other similar mammals shiver to burn fat cells for fuel in order to keep the body warm and maintain a safe body temperature. If humans are kept inside at temperatures between 61 to 63 degrees Fahrenheit and have nothing to bundle up with, they will lose weight because their body adapts to switching from fat-storing to fat-burning cells.

The signaling molecules, interleukin 4 and interleukin 13 activate the macrophages, which is what triggers your body from storing to burning fat; an optimal weight loss function. Macrophages also regulate the body’s immune response. In healthy, non-obese people, microphages tend to function as wound healers that maintain insulin and promote inflammation.

Previously, researchers only knew that cold temperatures could activate interleukin 4, but when the team dug a little deeper they realized that interleukin 13 also caused the white, fat-storing cells to turn into beige fat-burning cells.

"If you could increase energy expenditure by even a few percent, over a period of a year or two year you would make a big difference," Chawla said.

When researchers turned interleukin 4 off in the white fat, the laboratory mice made less brown fat, burned less energy, and were unable to keep their body heat at normal temperatures. Chawla and his team believe that by exploiting beige fat, potential weight loss could be significant. Their next step is to figure out how to generate more fat-burning beige cells.

The new discovery is surprised the research team because it meant the control for fat burning bypasses the autonomic nervous system that regulate the body’s adaptions, Chawla said.

Although Chawla and many other researchers now believe that the potential to exploit brown fat for weight loss is significant, the amount of individual variation when it comes to brown fat reserves and the potential to generate more brown fat is unclear. "We don't know what the dynamic range is," Chawla said. "It appears that women have less, that we have less as we age, and that obesity is associated with having less brown fat."

Source: Chawla A, Qui Y, Nguyen K, et al. Eosinophils and Type 2 Cytokine Signaling in Macrophages Orchestrate Development of Functional Beige Fat. Cell. 2014.