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Brown fat

PET-scans reveal data on the proportion of brown fat

The two scientists Tobias Fromme (left) and Carlos Gerngross revealed that some persons have an easier time activating their brown fat, or even have more of it. (Credit: TUM/ Astrid Eckert)
The analysis of the PET scans also revealed that some groups of persons have an easier time activating their brown fat than others, or even have more of it in the first place

The quantity of brown fat in humans is three times greater than previously known, according to a study published in the Journal of Nuclear Medicine. Previously, the proportion of brown fat in humans was thought to be quite small, but now a study conducted by researchers at the Technical University of Munich (TUM) has revealed the amount of brown fat is much great, new obesity and diabetes drugs that activate brown adipose tissue are expected to be more effective.

For the study, ‘Active brown fat duringFDG-PET/CT imaging defines a patient group with characteristic traits and an increased probability of brown fat redetection’, nearly 3,000 for positron emission tomography (PET) scans of 1,644 patients were analysed. PET scans enable the visualisation of metabolic activity in the body. Since a tumour often has a different energy metabolism to healthy tissue, PET scans can be used to demonstrate the presence of metastases.

"A by-product of PET scans is that they allow us to see active brown adipose tissue," said Dr Tobias Fromme from the Else-Kröner-Fresenius Center at the Technical University of Munich. “Brown adipose tissue absorbs lots of sugar, and we can observe this activity through the scans." For example, it is conceivable that a drug could reduce excessive blood sugar levels in diabetics by increasing the activity of the brown fat.

Similarly, it is conceivable that patients with obesity could use the high rate of energy combustion through brown fat to melt away their excess weight, at least to a certain extent.

"In any event, the outlook for the efficacy of drugs in brown adipose tissue can be adjusted upwards," said Fromme.

However, some people activate brown body fat more than others

The analysis of the PET scans also revealed that some groups of persons have an easier time activating their brown fat than others, or even have more of it in the first place. As several previous studies have already shown, women more frequently have active brown fat than men. Similarly, thinner and younger persons have larger proportions of brown fat. Furthermore, brown fat does not react with the same level of activity in overweight individuals or in the elderly.

"However, active brown fat occurs with far greater frequency in about five percent of patients than in the general population," he added. “In these patients, 50% of the scans showed these active fatty tissue proportions."

He suggested that this may point to a possible explanation for the phenomenon that some persons seem to gain weight after only one extra piece of cake, while others can gorge on sweets without gaining at all, different body weights despite having the same diet.

"Ultimately, with medication that activates brown adipose tissue, we must anticipate that some groups of people are likely to benefit from an additional activation of brown fat more than others. So far, we don't know the causes for a particular individual to have especially active brown fat."

A newly discovered factor may prove key to solving this riddle: The researchers showed for the first time that brown fat activity is affected by a variable known as creatinine clearance, which is related to renal function.

"Further basic research is still needed," said Fromme. “But one hypothesis is that there may be signalling substances that affect both brown fat and the kidneys."

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