There is much concern with the amount of highly or ultra-processed foods the typical American eats - over 50% of the calories eaten daily! A very good book about ultra-processed food is Ultra-Processed People, by Dr. Chris van Tulleken. This book discusses the history of ultra-processed foods (e.g., coal to make "synthetic butter" or margarine), the health harms, and why they are such a big part of our diet.
Ultra-processed foods are food products manufactured with all sorts of ingredients (additives) not normally found in our kitchens. Examples of such ingredients are: emulsifiers, carrageenan, mono- and diglycerides, soy lecithin, polysorbate, cellulose, colors, titanium dioxide, high fructose corn syrup, hydrogenated oils, dextrose, whey protein, nitrates, flavors (artificial and natural), colors, etc.
These ingredients have typically been added to extend shelf-life or manipulate the taste, flavor, or appearance. Ultra-processed foods are "formulations of ingredients" that result from a series of industrial processes (thus "ultra-processed"). Researchers say that "ultra-processed foods are not real food" due to all the modifications and alterations.
One large review of studies (none of which were affiliated with companies producing ultra-processed foods) found that eating ultra-processed foods are linked to over 30 health harms. Some of the health harms: early death, death from heart disease (cardiovascular disease), type 2 diabetes, adverse sleep outcomes, wheezing, cancer (e.g., colorectal cancer), and obesity. In general, the more ultra-processed foods one ate, the higher the risk for harms (a dose-dependent effect).
Chris van Tulleken - Ultra-Processed People. Published by Cornerstone Press in the UK, and W.W. Norton in the US in 2023. Lots of references to back up what he writes.