I've lost over 150lbs, and can easily say sugar intake is closely tied to metabolism and brain activity. The habits formed around sugar intake are the hardest to control. It can be a major tax on mental agility and sharpness if a person is in the habit of using sugar to supplement their diet constantly. They can really struggle to find a different balance with healthy foods. There are a range of other factors that come into play that make it difficult. Chiefly, American budget food is typically very low quality, and most people have several minor food allergies. This makes people rely on junk food, likely unaware of issues like lactose intolerance that makes them unable to access healthy calories. Dairy is in EVERYTHING in American food. Like stupid stuff too. There is milk in most chips now. Like who the F puts milk in chips. It took me nearly a decade to fix how I eat, and realize we were all pretty much raised to be stupid consumers of whatever garbage is placed in front of us as Americans. Fixing the sugar addiction usually means fixing a bunch of other problems too.