They can slow digestion and cause the food to spoil in the gut (apparently). Different strokes for different folks but the healthiest people I know (anecdotal i know) live by this methodology.

They also don’t use stainless steel anything, non stick anything, microwaves, plastic containers, definitely no man made food additives, colours or flavours and zero dairy products. No alcohol, no carbonated drinks no juices and no sugar (except fructose from fruit and a little carob).

And then you have carnivores and keto people who eat only ghee, meat and berries who have great health outcomes as well.

Both groups of people are not putting shit into their bodies!