Dietary fats have well-established impacts on blood lipids. For example, in short-term feeding trials, saturated fat tends to increase total cholesterol, increase LDL ("bad") cholesterol, and increase HDL ("good") cholesterol, while the omega-6 polyunsaturated fat linoleic acid decreases total cholesterol and decreases LDL cholesterol. For this reason, dietary advice to reduce cardiovascular risk tends to focus on dietary fat.
The hypothesis that refined dietary sugar is harmful to the cardiovascular system isn't new. In 1972, British physiologist and nutrition researcher John Yudkin published a classic book called Pure, White, and Deadly, which argued, among other things, that refined sugar is harmful to the cardiovascular system. Yet at the time, the supporting data were weak, and the hypothesis was never taken very seriously by the scientific community.
Peter Havel and his group at UC Davis have begun to breathe new life into this hypothesis with their rigorous work on the cardiovascular effects of dietary sugars.