When we measure cholesterol in the blood we really measure different sized particles called lipoproteins.
Sugar should be avoided in the diet, especially added sugar. Sugar has 61 different names when listed as a food ingredient. For the complete list of names and a host of interesting facts about sugar visit Sugar Science: The Unsweetened Truth.
Alzheimer’s: Sugar increases insulin levels, which if chronically elevated leads to insulin resistance which is highly correlated with Alzheimer’s.
For a more in depth description of the effects on sugar on the brain see How Sugar and Insulin Damage the Brain.