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Brown or white? How the colour of fat determines weight

Skinny or voluminous, all of us have some amount of fat tucked away inside us, with the type, amount and distribution depending on our genes and lifestyle. Body fat is classified brown, white, subcutaneous and visceral. Some of it is healthy, most is not.

columns Updated: Jun 20, 2015 21:30 IST
Sanchita Sharma
Body-fat-is-classified-brown-white-subcutaneous-and-visceral-Some-of-it-is-healthy-most-is-not-Illustration-Abhimanyu-Sinha
Body-fat-is-classified-brown-white-subcutaneous-and-visceral-Some-of-it-is-healthy-most-is-not-Illustration-Abhimanyu-Sinha

Watching live surgeries is not a pretty sight, but since it's an occupational hazard for health reporters, I found myself in scrubs earlier this week watching a man getting operated for hernia and a woman for obesity. More than the pulsating pink innards and the relentless scalpels and probes, the image that stuck was that of the surgeons wading through a sea of waxy white fat choking the vital organs.

Skinny or voluminous, all of us have some amount of fat tucked away inside us, with the type, amount and distribution depending on our genes and lifestyle. Body fat is classified brown, white, subcutaneous and visceral. Some of it is healthy, most is not.

White fat stores excess energy and accounts for more than 90% of the fat found inside the body. It is essential in small amounts as small white fat cells are essential as they produce a hormone called adiponectin, which makes the liver and muscles sensitive to the hormone insulin that converts glucose into energy. When people put on weight, fat cells grow bigger and adiponectin production drops, raising the risk of diabetes.

White to brown
New research is focusing on how bad "white" fat can be converted to good "brown" fat, which when activated, burns calories instead of storing them. Brown fat burns both fat and glucose to keep the body warm and gets its darker hue from relatively high levels of mitochondria, the cell's power stations.

It is found in higher amounts in children but declines as we age. In adults, it's found in around such vital areas as the heart, brain, neck and spinal cord. Higher levels are also found in people exposed to extreme cold, with outdoor workers in northern Finland who are exposed to cold temperature having significantly more brown fat when compared to same-aged indoor workers.

Last week, Washington State University scientists announced they had turned white fat into active energy-burning brown fat using an antioxidant extract from berries (http://bit.ly/1MV6ffb). Mice fed on the antioxidant resveratrol in amounts equivalent to 350 gm of fruit (2-3 servings) a day for humans gained about 40% less weight than control mice, they reported in The International Journal of Obesity on Friday.

Resveratrol is found in all fruits but is higher in blueberries, strawberries, raspberries, grapes and apples. Past studies billed the compound as a natural way to slow ageing and fight cancer, heart disease, Alzheimer's disease and obesity.

Cold edge
Exposure to cold, however, kickstarts brown fat's energy-burning activity in normal adults by raising levels of a protein that is critical for its formation, report researchers from UC Berkeley in the journal Molecular Cell (http://bit.ly/1GZvBIF).

The protein, called transcription factor Zfp516, also induces the more abundantly present white fat to burn energy and raise metabolism. The UC Berkeley study showed that mice with boosted levels of Zfp516 protein gained 30% less weight than control mice when fed on an identical high-fat diet. This means that boosting levels of the protein can increase brown fat and help people lose weight without changing their diet or exercising.

Leaner adults have more brown fat than overweight ones, even though the actual amount of the darker fat remains a tiny fraction of total body fat. A 60 kg person has between 15-20 kg of fat -- lower if he or she is physically active -- of which less than 100 gm is brown fat. But just 100 gm of brown fat, if activated, can burn 300 to 500 calories a day, which can lead up to a weight loss of up to 2 kg a month.

Belly trouble
Abdominal fat consists of both subcutaneous fat found directly under the skin, and visceral fat that forms a layer around inner organs and prevents them from functioning optimally. Abdominal fat is linked with a clutch of diseases, including diabetes, heart disease, stroke and dementia. Women with a waist circumference of more than 35 inches and men with a waist circumference more than 40 inches should consider losing weight immediately to lower disease risk.

When you lose weight without exercising, white fat is the first to go from across the body. To target stubborn visceral fat embedded deeper inside the body, you need to add aerobic exercise and weight training to a healthy high-fibre low-saturated fat diet. For those who view hectic activity with trepidation, there's always gentler yoga.