All Fat Is Not Created Equal

By Fran Cronin
WBUR Intern
Imagine if your doctor were able to biopsy a plug of tissue from your belly fat and determine whether or not your body had the potential to fend off the known panoply of obesity-related diseases.

Well, that’s exactly what researchers at Boston University School of Medicine and Boston Medical Center have done. In a four-year study funded by the National Institutes of Health, researchers found that all fat is not created equal.

The study involved comparing the amount of inflammation present in samples of belly fat from 109 obese men and women with 17 lean
men and women. Surprisingly, thirty percent of the severely obese people sampled were found to have a fat type and vascular function comparable with a lean person — despite their obesity.

Dr. Noyan Gokce, a cardiologist at Boston Medical Center who led the study, says the findings suggest “it’s not just the quantity of fat but the quality of fat” that determines risk to obesity-related diseases.

Fat, despite its bad rap, may actually be an important defining factor to overall body heath. What differentiates good fat from bad fat, says Gokce, is the presence of inflammation. The combination of inflammation within fatty tissue is what makes obese people – those with a BMI above 30 – so susceptible to so many other complications and diseases, notably cardiovascular disease, type 2 diabetes, sleep apnea, fatty liver disease, high cholesterol and cancer.

Dr. Gokhan Hotamisligil, chairman of the Department of Genetics and Complex Diseases at Harvard School of Public Health, says: “We have known for at least 20 years that inflamed adipose (fat) tissue poses a high metabolic risk,” a known catalyst to disease formation in obese people. What surprised Hotamisligil about the study findings, he says, is the high percentage of obese people that appear to be relatively healthy.

But both Gokce and Hotamisligil echo caution over the study’s implications and the temptation to settle into an easy chair with a guilty pleasure. There are inherent limitations to the study and its findings. “I don’t want to screen out people and tell them not to lose weight,” says Gokce. Even with the protection of non-inflamed adipose tissue, development of cancer remains a risk.

The study, which included people 12 to 55 years old enrolled in Boston Medical's weight loss management program, was predominantly female and white. Not an intentional design feature, but more women than men seek advice and therapy for weight loss, researchers said. In addition to the female bias, the study did not screen for dietary, genetic, environmental, or racial factors. Also unknown is whether the added protection from non-inflamed fatty tissue can be sustained after effective weight loss.

Hotamisligil, who refers to the study “as an appropriate starting point,” cautions that findings from subcutaneous belly fat close to the skin’s surface, while telling, may not be the biggest source of concern. Implications of the harder to detect visceral fat surrounding our internal organs, he says, remain less well understood.

More deeply embedded in the body’s tissues, visceral fat is harder to lose than subcutaneous fat, such as in the belly. It is also harder to measure accurately without the aid of an imaging machine. A person may be within a healthy weight range, but still have too much intra-abdominal fat around their internal organs. “Some people believe,” Hotamisligil wrote in an e-mail, “that visceral fat is more dangerous and more prone to inflammation and other problematic responses” than subcutaneous fat. This is not an established rule, he says, and more work is needed before all these issues can be settled.

Gokce says additional studies are already under way to help answer questions about the correlation between fat, inflammation, and disease development. Other studies are trying to identify a blood marker that would indicate tissue inflammation.

In the meantime, Hotamisligil says: “If a little piece of fat can tell you your future [health] risks, that’s a pretty good deal.”