"In particular, fat in the liver interferes with its function and insulin sensitivity," Katz said. This starts a domino effect, he explained. "Insensitivity to insulin causes the pancreas to compensate by raising insulin output. Higher insulin levels affect other hormones in a cascade that causes inflammation. Fight-or-flight hormones are affected, raising blood pressure. Liver dysfunction also impairs blood cholesterol levels," Katz said.
In general the things people do to make themselves fitter and healthier tend to make them less fat, he added.
"Lifestyle practices conducive to weight control over the long term are generally conducive to better overall health as well. I favor a focus on finding health over a focus on losing weight," Katz noted.
For the study, Retnakaran's team reviewed eight studies that looked at differences between obese or overweight people and slimmer people in terms of their health and risk for heart attack, stroke and death. These studies included more than 61,000 people overall.
In studies with follow-ups of a decade or more, those who were overweight or obese but didn't have high blood pressure, heart disease or diabetes still had a 24 percent increased risk for heart attack, stroke and death over 10 years or more, compared with normal-weight people, the researchers found.
Greater risk for heart attack, stroke and death was seen among all those with metabolic disease (such as high cholesterol and high blood sugar) regardless of weight, the researchers noted.
As a result, doctors should consider both body mass and metabolic tests when evaluating someone's health risks, the researchers concluded.