A term that gets thrown around a lot is 'clean eating'. Does this mean someone cleans their food before they eat it? Well I hope so but that's not the primary meaning. Really what clean eating is all about is better stated as whole food eating.
Often I hear that when someone has made a big impact on their health and fitness through nutrition, it is because they said they started to eat more whole foods. I think there are a couple primary reasons for this.
First, when you eat more whole foods (less processed, usually not in a box, bag or can) the food has more volume. When a food is more voluminous, it helps keep us satiated as it not only takes up more space in the gut, but also is usually high in fiber, requires more digestion time and slightly increases the metabolism due to these factors.
Second, because of the above, an individual who switches to a more whole food intake will usually eat less calories due to the above factors. This can often alone help put them into a calorie deficit which in turn, will help them lose bodyfat.
Certainly there are likely other factors in motion here (like the body is performing better, has more activity due to the more nutrient dense foods), but this in turn goes back to the two previous reasons.
I'm all about flexible nutrition and focusing on macros, but eating for digestion is a common theme and certainly, if you want to 'clean' up your food choices, it's good to know the how and why.