But some types of fat may be more dangerous than other types. Harvard Medical School estimates that most fat — about 90 percent — is subcutaneous. This is the visible jiggly fat, sometimes called “love handles,” that lies just beneath the skin. It’s the other 10 percent, though, called visceral fat, that may lead to the most trouble. A new large study, published September 9 in the journal Nature Medicine, suggests that this “hidden” fat, which accumulates around the abdominal organs, can play a major role in the development of metabolic and cardiovascular disease, and it poses much more of a health risk to women than men. Scientists conducted a genome analysis of 325,000 individuals from the UK Biobank, a database of people’s health details and a common resource for scientific research. The study authors also used a new method for measuring visceral fat that they say is cheaper and more efficient than current measurement approaches. “We were able to show that there is a causal relationship between visceral fat and risk of disease,” says the study investigator Torgny Karlsson, PhD, a statistician in the department of immunology, genetics, and pathology at Uppsala University in Sweden. “We were surprised that this causal effect was, in some cases such as for type 2 diabetes, stronger than previously thought. Although our results confirm earlier findings, we show that the difference in effect between the sexes is indeed large." RELATED: Can Eating Too Much Sugar Cause Type 2 Diabetes?
2 Pounds of Deep Belly Fat Increases Type 2 Diabetes Risk by a Factor of 7 in Women
Using the genetic data, scientists observed that visceral fat was strongly associated with increased risk for high blood pressure, high cholesterol, type 2 diabetes, heart attack, or angina, which causes chest pain. These associations were stronger in women compared with men, but “the largest difference in odds ratio between the sexes was found for type 2 diabetes,” the study authors reported. Dr. Karlsson says that adding just over 2 pounds (lb) of deep belly fat could increase the risk of type 2 diabetes more than seven times in women, while the same amount of fat accumulation only increased the risk in men by a little more than double their original risk. He says the effect of visceral fat on high blood pressure had a statistically significant difference in women compared with men as well. Researchers observed that the change in odds for having high blood pressure was 40 percent higher in women compared to men. Karlsson suggests that the study may have been limited by measuring fat mass through estimations or prediction, but they took “several measures and performed a large number of tests to make sure that the estimated visceral fat mass from the model works properly.” The investigation was also limited by a lack of population diversity — study participants were predominantly white. RELATED: Excess Belly Fat Poses Higher Health Risks for Some Normal Weight Women
Why Deep Fat May Especially Pose Health Risks for Women
Scientists don’t know why this deep belly fat increases health risks, nor did they study why women faced a greater burden. But they speculate that visceral fat may be harmful in general because it releases more free fatty acids than subcutaneous fat. These fatty acids travel to the liver, where they may increase the production of blood fats (lipids), according to Harvard Health. A study published in April 2014 in the Journal of Molecular Science suggested that visceral fat secretes greater levels of adipokines — chemicals that trigger inflammation. Inflammation is linked to chronic diseases, including heart disease and type 2 diabetes.
You Don’t Have to Be ‘Obese’ to Face Health Risks From Belly Fat
The scientists note that the risk of disease climbed fastest among people with small or moderate amounts of deep belly fat, but that it did not rise nearly as much in those who already had large amounts of fat in the abdomen and put on additional fat. “If a person with large deposits of visceral fat increased their amounts of deep belly fat further, their odds [for disease] did not increase, in contrast to a person with low amounts of visceral fat,” says Karlsson. Obesity raises health risk factors, but people with unhealthy amounts of visceral fat may not be obese. “For example, we know that Asian populations tend to have more visceral fat at lower overall weights than we see typically in Caucasian populations,” says Mitchell Roslin, MD, the chief of obesity surgery at Lenox Hill Hospital in New York City, who was not involved in this investigation. For this reason, body mass index (BMI) is an inaccurate measure of body weight in certain groups, including Asian people, according to a study published in Nutrition & Diabetes. BMI categorizes people as normal, over- or underweight, or obese, and is calculated by taking a person’s weight and height into account, per the CDC. RELATED: Why BMI Is Flawed and the History of How the Scale Came to Define Obesity
A New Approach to Measuring Belly Fat in Men and Women
To measure visceral fat, study authors developed an approach that they say may be easier than advanced technologies like magnetic resonance imaging (MRI) or X-ray imaging (CT or DXA), which are normally used. “We developed a method to estimate a person’s amount of visceral fat from other, more easily measured variables, including hip and waist circumference, weight, height, age, and a number of bioelectrical impedance measures,” says Karlsson. “The parameters of our model are publicly available, and it would be easier and cheaper for a clinician to use our model than to take an MRI or DXA scan in order to measure visceral fat.” Through their research, the scientists also identified more than 200 different genes that may affect amounts of visceral fat. “We found that many of the genes associated with visceral fat are expressed in the brain and the central nervous system, and linked to our behavior,” says Karlsson. Dr. Roslin adds, “The susceptibility to obesity is rising, but energy regulation is centrally determined by the brain. We have to stop blaming the patients and better understand this process.” RELATED: What Really Causes Obesity? Understanding the Risk Factors for a High BMI
What You Can Do to Help Fight Belly Fat and Lower Your Diabetes Risk
Although genetic factors may be involved, Roslin says that people can still make lifestyle changes that can reduce their fat levels. These include getting regular physical exercise and following a hheart-healthy diet, similar to recommendations from the American Heart Association. “When we see people who are at high risk for metabolic disease with central obesity being a good marker for this, we should immediately begin to change their diet and work on lifestyle," he says. “If that’s not successful, consider going to the next round of treatments, including medications and possibly bariatric surgery.”
