Sugar in moderation is not bad. High fructose corn syrup is bad. Big corporations began substituting HFCS for sugar in the late 70s/early80s. This is when obesity rates in the US began climbing. I grew up with millions of others in the 1960s and 70s. We ate candy, cakes, cookies, etc. and did not get fat. These were made with cane sugar.There were maybe 5-10 overweight children in the whole school.

"Sucrose, or regular cane sugar, is made of one molecule of glucose and one molecule of fructose – each the same size (a 50-50 ratio) – and tightly joined by a chemical bond. In the digestive tract, it takes time for enzymes to break the bond between the two molecules. Gradually, the glucose and fructose molecules separate and enter the bloodstream to be used for energy.

Though HFCS is also made of a glucose and a fructose molecule, the structure is different. The fructose molecule is larger, making the fructose to glucose ratio 55-45, and the two molecules are not bound together.

Because there is no chemical bond in HFCS, when we consume it, no digestion is needed to separate the glucose from the fructose. The sugars are immediately absorbed into the bloodstream.

The fructose, which is sweeter than glucose, goes immediately to the liver and causes it to produce triglycerides (fats) and cholesterol. Over time, this can lead to a type of liver damage known as “fatty liver,” a condition already affecting about 70 million people.

The rapidly absorbed glucose from HFCS triggers unnatural spikes in the body’s production of insulin, a hormone involved in fat storage, and the body’s ability to use sugar for energy."

https://eatingdisorders.com/lifestyle/general-lifestyle/cane-sugar-vs-high-fructose-corn-syrup-how-they-differ