A new large-scale European study has found that carrying visceral fat, which is the fat stored around the organs in the belly and around the intestines, appears to be a major risk factor for developing diabetes and cardiovascular disease, especially among women.
Carried out by researchers from Uppsala University, the new study looked at over 325,000 participants taking part in UK Biobank, a large long-term study which includes genomic data on more than half a million UK residents.
The researchers found more than 200 different genes which affect the amount of visceral fat. They then used a method called Mendelian randomization, which involves studying genetic variants to see whether certain factors are associated with a higher or lower risk of disease, to see if this type of fat was associated with an increased risk of hypertension (high blood pressure), heart attack/angina, type 2 diabetes, and hyperlipidemia, which is when the blood has too many lipids (or fats), such as cholesterol and triglycerides.
As Mendelian randomization gives more reliable results, any associations found are more likely to suggest a direct causal relationship.
The findings, published in Nature Medicine, showed visceral fat to be a causal risk factor for all four of the diseases.
In addition, the researchers also found that visceral fat is a larger risk factor in women compared to men.
"We were surprised that visceral fat was more strongly linked to risk of disease in women compared to men," noted one of the co-authors, Dr. Åsa Johansson. "Adding an extra kilogram of visceral fat can increase the risk of type 2 diabetes more than seven times in women, while the same amount of fat accumulation only increases the risk a little more than two times in men."
Perhaps surprisingly, the researchers also found that the risk of these diseases increases most rapidly in people with small or moderate amounts of visceral fat, and does not increase nearly as much if a person who already has large amounts of fat in the abdomen puts on additional fat.
"Nonlinear effects like this are very interesting to study and may help us to understand the biology behind the link between visceral fat and disease," said Dr. Karlsson.
Among the genes found which affect the amount of visceral fat, there was a large proportion that are also linked to our behavior, which the researchers say suggests that the main contributor to abdominal obesity is behaviors such as eating too much and exercising too little. However, they add that there are still individual differences in how fat is distributed in the body, and even a person who does not appear to be overweight may still carry a harmful amount of visceral fat.