It's difficult to sort the science of nutrition out from the marketing spin vendors put out there. The thing to remember is their job is to sell... acidic diet, basic diet, raw diet... fat good, sugar bad, /sugar bad, fat good... the producers of the consumables want to move product, saturated markets need novel products, and long term consumer health has nothing to do with this week or quarter's numbers.
Fast food was fruits, berries, mushrooms, nuts, roots, and bugs up until the mid 20th century--processed sugar and fat rich diets were not the condition the species got here by. Periods of starvation/fasting/leanness riddle history, so our bodies got good at packing up calories for later. We now have access to unlimited amounts of very easy-storing raw materials. I'd imagine if we had to do the actual work to harvest and process a pound of sugar, potato chips, or butter we'd be leaner--and likely reach for more apples and nuts.
