Mar 19, 2014 3:24 PM GMT
tl;dr: "Many of us have long been told that saturated fat, the type found in meat, butter and cheese, causes heart disease. But a large and exhaustive new analysis by a team of international scientists found no evidence that eating saturated fat increased heart attacks and other cardiac events."
In the new research, Dr. Chowdhury and his colleagues sought to evaluate the best evidence to date, drawing on nearly 80 studies involving more than a half million people. They looked not only at what people reportedly ate, but at more objective measures such as the composition of fatty acids in their bloodstreams and in their fat tissue. The scientists also reviewed evidence from 27 randomized controlled trials – the gold standard in scientific research – that assessed whether taking polyunsaturated fat supplements like fish oil promoted heart health.
The researchers did find a link between trans fats, the now widely maligned partially hydrogenated oils that had long been added to processed foods, and heart disease. But they found no evidence of dangers from saturated fat, or benefits from other kinds of fats.
The primary reason saturated fat has historically had a bad reputation is that it increases low-density lipoprotein cholesterol, or LDL, the kind that raises the risk for heart attacks. But the relationship between saturated fat and LDL is complex, said Dr. Chowdhury. In addition to raising LDL cholesterol, saturated fat also increases high-density lipoprotein, or HDL, the so-called good cholesterol. And the LDL that it raises is a subtype of big, fluffy particles that are generally benign. Doctors refer to a preponderance of these particles as LDL pattern A.
The smallest and densest form of LDL is more dangerous. These particles are easily oxidized and are more likely to set off inflammation and contribute to the buildup of artery-narrowing plaque. An LDL profile that consists mostly of these particles, known as pattern B, usually coincides with high triglycerides and low levels of HDL, both risk factors for heart attacks and stroke.
The smaller, more artery-clogging particles are increased not by saturated fat, but by sugary foods and an excess of carbohydrates, Dr. Chowdhury said. “It’s the high carbohydrate or sugary diet that should be the focus of dietary guidelines,” he said. “If anything is driving your low-density lipoproteins in a more adverse way, it’s carbohydrates.”
While the new research showed no relationship overall between saturated or polyunsaturated fat intake and cardiac events, there are numerous unique fatty acids within these two groups, and there was some indication that they are not all equal.