Monday January 26 2015
Brown fat protects newborns against the cold
"Fat can protect you against obesity and diabetes," the Mail Online reports. However, the small study it reports on was looking at brown fat, which is only found in small amounts in adults.
In humans, brown fat is mostly found in newborns, who are more prone to heat loss and are unable to shiver to help keep themselves warm. Brown fat compensates by burning calories to create heat. As we grow older, we have less need for brown fat and it is mostly replaced by white fat ("bad fat").
The current study involved just 12 men. It looked at whether men with detectable levels of brown fat differed from men who didn't in terms of how their bodies dealt with sugar, particularly in cold conditions.
The researchers wanted to see what happened when the men were exposed to cold over five to eight hours.
The researchers found that, when exposed to the cold over five to eight hours, only the men with brown fat showed an increase in the energy they were burning and how fast they used up the sugar circulating in their blood.
This has led to the idea the effect could in some way be harnessed to help protect against type 2 diabetes or obesity.
However, any such advances are a long way off. This study was very small, only in men and, crucially, we cannot currently control the amount of brown fat we have.
Eating fatty foods will result in more white fat if you consume more calories than you burn off, and being overweight or obese increases your type 2 diabetes risk.
Where did the story come from?
The study was carried out by researchers from the Shriners Hospital for Children in Texas and other research centres in the US, Greece, Sweden, and Canada.
It was funded by the University of Texas Medical Branch, the National Center for Advancing Translational Sciences, the National Institutes of Health, the American Diabetes Association, Shriners Hospital for Children, the John Sealy Memorial Endowment Fund, the Claude D Pepper Older Americans Independence Center, and the Sealy Center on Aging.
One study author is a shareholder and consultant to Ember Therapeutics, a company that seems to work on treatments for type 2 diabetes and obesity by targeting brown fat. This represents a potential conflict of interest.
The study was published in the peer-reviewed medical journal, Diabetes.
The Mail Online covers this study reasonably well, pointing out early on that brown fat is not the type of fat you get from eating too many calories. However, it did not mention the small number of men in the study.
The suggestion from the study authors that, "This is good news for overweight and obese people" or those with diabetes probably overestimates the practical implications of these findings.
What kind of research was this?
This was an experimental study carried out in men with and without detectable brown fat. It aimed to see whether brown fat might influence how the body deals with sugar.
Brown fat generates heat to help keep the body's temperature constant. In humans, it is mostly found in newborns, who are unable to shiver and keep themselves warm.
As we grow we have less of a need for brown fat, so most is replaced by white fat. White fat differs from brown in that it stores energy for the body when we consume more calories than we burn off.
What did the research involve?
The researchers enrolled 12 healthy men for their study: seven with detectable brown fat and five without.
They then tested them at normal room temperatures (about 19C or 66.2F) and after five to eight hours of exposure to cold.
They looked at how much energy the men's bodies were burning at rest, and how their bodies were dealing with sugar and fat.
Participants were cooled by wearing a temperature-controlled vest and blanket, which gradually dropped in temperature until the participant was shivering and then raised in temperature by one degree. The participant was then kept at this temperature for five to eight hours.
At the start of the study, to check whether the man had detectable brown fat, their bodies were cooled and injected with a radioactively labelled glucose (a type of sugar).
Their bodies were then scanned using a positron emission tomography (PET) scan, which could identify where in the body the glucose was located.
As brown fat generates heat to help keep the body temperature stable, the idea was that as the men were cold, if they had brown fat, it would take up more glucose to make more heat.
This meant the researchers could see where the brown fat was in the body. They looked for brown fat specifically in the area just between the collar bone (clavicle) and the base of neck. They also took samples of tissue from this area to look for brown fat.
Men with and without brown fat were similar in their characteristics. Men without brown fat were slightly older (average 49.8 years versus 41.2 years).
Once the researchers knew which men had detectable brown fat and which did not, they then carried out a range of tests at normal temperature and at cold temperatures.
This included testing how much energy the men were burning at rest and how their bodies dealt with sugar and fat (fatty acids) infused into their bloodstreams. The normal temperature and cold temperature experiments were carried out two weeks apart.
During the study, the volunteers followed a controlled diet and wore standardised clothing to make them as comparable as possible.
What were the basic results?
The researchers found exposure to cold increased the amount of energy the men with brown fat were burning at rest. This was not the case for men without brown fat.
The extra energy being used up by the brown fat was coming from glucose and fatty acids being taken up from the blood.
Cold exposure increased the total amount of glucose being taken up by the cells of the body in men with brown fat, but not those without brown fat.
The researchers estimated brown fat could take up a considerable amount of glucose from the circulation and therefore could help control blood glucose levels.
This was also the case if the men were given insulin to reproduce what would happen after a meal. Insulin increased glucose uptake in both groups, but uptake was still higher in men with brown fat.
How did the researchers interpret the results?
The researchers concluded they found brown fat has a significant impact on the ability of the whole body to dispose of glucose.
They say this supports a role for brown fat in controlling glucose levels and sensitivity to insulin in humans.
They suggest brown fat could be a target for combating obesity and diabetes if we can develop ways to activate brown fat in the body, or get white fat to behave more like brown fat.
This small experimental study has suggested that in healthy men, brown fat can increase the uptake of blood glucose by cells in response to cold, and increase the amount of energy being used up at rest.
Because of the small size of this study and the fact it only included healthy men, it is not possible to say whether the results are representative of the general population.
With such small numbers, there could have been other unmeasured differences between the groups (such as biological and lifestyle differences) that influenced the results, rather than just brown fat.
Other groups of people or other tests, rather than just this single experiment, could have given different results. Larger studies will be needed to confirm its findings.
The study also only looked for an indication of brown fat in one area of the body, and this may not be representative of the rest of the body.
These results do not have implications for the general public, as we currently cannot control the amount of brown fat we have. The excess calories we eat are stored as white fat rather than brown fat, and being overweight or obese increases the risk of diabetes rather than reducing it.
Even for those who happen to have brown fat, standing in the cold for prolonged periods is unlikely to be a practical long-term way to improve your glucose metabolism or energy consumption.
As the researchers say, investigations will undoubtedly continue into finding ways to capitalise on brown fat in the fight against obesity and diabetes, but we will need to wait to see whether this brings results.
Until then, the most effective method to reduce your diabetes risk is to try to achieve or maintain a healthy weight.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.