Answering this question starts with an understanding of carbohydrates. There are simple carbs like table sugar, honey and fruits, there are less simple carbs in vegetables and then there are complex carbohydrates in found in grains, beans, bread, pasta and cereals. There are also some dangerous carbohydrates like alcohol and the “sugar free” sugars like sorbitol, as well as the all time evil sweetener called high fructose corn syrup.
There are two essential things to know about carbohydrates. First, they all digest or break down into single molecules like glucose and fructose. Second, how bad they are for us depends on how we digest them. My favorite example is starch. Starch is in almost everything we eat, it is in bread, pasta, popcorn, chips, grains and beans. One starch molecule is made of 160,000 glucose molecules, which means your digestive system has to work intensely hard for the energy you get from your food, and your digestive system may get damaged. Look up Leaky Gut Syndrome.
Some starches digest very quickly and affect your blood sugar and insulin metabolism in ways that predispose people to diabetes, heart disease, obesity and cancer. Other starches digest very slowly and may cause a Candida overgrowth, a naturally occurring yeast in the body, which weakens our immune system and predispose people to allergies and Auto-immune conditions.
Regardless of the kind of starches we eat they digest down to simple sugars, which are fuels, not nutrients, like vitamins, minerals, proteins and fats, and they mess with our metabolism creating the conditions for many of the diseases which plague modern society. When a person eats a diet containing a lot of sweeteners, a lot of starches and a lot of alcohol, it is almost impossible to avoid chronic illness, obesity, metabolic problems and immune system over-reactions.