There is a big difference between what we call "food" and what the human gut was designed to digest, assimilate and utilize
Think of your gut as an engine. All engines when built are designed to burn a specific fuel to create energy to operate that engine. So a jet engine burns kerosine, a car burns either diesel or gasoline, right. So you wouldn't put a different fuel in the engine or it would clog the fuel lines, filters, pistons, injectors, etc. Essentially you would wreak havoc on all the parts and soon the engine would not put out the power it was designed to produce, then it would start to breakdown and eventually go into a state of non repair. So kind of like going from the good, to the bad, to the ugly.
If we consume "foods" that our bodies were not designed to burn then essentially we are doing the same thing as putting the wrong fuel in an engine. We go from gas, bloating, pain to ulcers and when things get completely out of control, to cancer. It's really that simple.
Think of the gut as a warehouse/distribution center delivering nutrition to every cell in the body. If we don't consume the proper fuel for the body to break down, assimilate and utilize we are robbing the body of the very nutrients it needs to function. This is what is called a Relative Nutritional Deficiency leading to dysfunction in key, core body systems.
The second major factor dealing with Insulin Resistance through the wrong nutritional intake
Do we really need them?
Actually we really don't need any carbs to survive. Our number one problem in nutrition is stressing the body with an enormous intake of carbs. Especially the amount of sugar that turns into glucose in our bodies. We have turned our bodies into a glucose burning machine, not what it was designed to do.
Think of pouring gasoline on a pile of leaves and lighting it. There is a sudden burst of flames sucking in a tremendous amount of oxygen creating a massive amount of energy but then it quickly dies out. Now think of an oil lamp, when it is lit the flame burns long and steady, giving constant equal, energy, utilizing a lot less oxygen. See the difference.
When we ingest sugar the body ramps up insulin to store the glucose into tissue. When there is too much it diverts it to the liver. The liver then converts the glucose into saturated fat in the blood plasma, it doesn't belong there. Hence we have fatty livers, CVD and adipose fat tissue all over our body.
What does it do?
Proteins are the building blocks of tissue, cells, hormones, neurotransmitters. Without it we would not survive. When protein is digested in the stomach it is broken down into amino acids. Think of amino acids as a pile of lumber ready to be used to build something. Without the raw materials what can we build, nothing.
We also can get our glucose supply from proteins through gluconeogenesis, the conversion of protein to glucose. No that's interesting because if we over consume protein like all those high protein shakes that are all the rage then we are converting the extra protein to glucose. Back to what is our major problem already, TOO much glucose.
Why is is the most important?
This has to be the most misunderstood food group. Everyone has been trained that fat is bad for us. Well yes certain fats are, like trans-fat, but the majority are exceptional for our state of health. In fact ideally we should be in a state of nutritional ketosis which means we are burning predominatly fat for fuel not glucose.
Every cell in the body is covered with a lipid (fat) layer. Our brains are made of fat. Yet we consume ridiculous amounts of sugar or glucose every day with little nutritional fat. It should be the other way around. When we burn fat we have a steady supply of energy that sustains us throughout the day without the ups and downs of sugar highs and sugar lows.