This section describes how high sugar/carbohydrate diets can actually cause sickness, although it turns out some vegetable oils are nasty, too. In Sugar:Double Trouble I lay out the bad effects of sugar that are most studied and documented. Those effects lead to the condition labeled “metabolic syndrome” (defined on the Double Trouble page). Beyond that, it certainly appears that there are a cascade of physical and mental problems that are linked to toxic levels of sugars, particularly fructose, in your diet.
There’s some biological common sense at work here. If you expose your brain and body to substances that they aren’t “designed” by evolution to process, you should expect bad things to happen. Pure sugar, in enormous quantity, is the worst of those substances. That knocks you off balance. You get sick. The nature of your sickness depends on your genetic makeup and it’s weak points. When the entire population is eating a high sugar diet, that sets a toxic baseline, so the studies of genetic factors rest on that toxic foundation. Doctors, who are very good at treating the symptoms of pathology, tend treat those symptoms, not the cause, with drugs and surgery. You need to take control and change the underlying cause.