This is not short. Deep dive. Dr Robert Lustig. 

Keep in mind table sugar, sucrose, is half glucose and half fructose. High fructose corn syrup is slightly higher in fructose but for all practical purposes is the same. He goes into grains and fruits and glycemic response.

Bottom line, excessive fructose is not good.

He is big on fiber (natural fiber, not added fiber). Doesn't say you have to have it (as in a carnivore diet), but says it is beneficial.

He says keep insulin down. Body weight is not a good indicator of metabolic health (20% or fat people are metabolically healthy, 40% of skinny people are metabolically unhealthy). 45% of American population has fatty liver disease. 25% of kids have fatty liver disease. His research team reversed it in kids (isocaloric diet) in ten days.

https://www.youtube.com/watch?v=GTMzFE1FNR4&t=605s

My personal opinion is that a person that is metabolically healthy can eat a variety of foods and be healthy. Excessive amounts of certain foods can take a healthy person into an unhealthy situation. And people that are metabolically unhealthy (as myself, diabetics and some other people with metabolic related health problems) need to change their diet to something that is less inflammatory and more oriented to better healing if they want to better their health.