Most people who are overweight or obese ~80% will have some form of metabolic dysregulation, eg T2 diabetes, insulin resistance, PCOS, NAFLD etc, as well as being at risk of other metabolic based conditions like certain cancers, heart disease, alzheimers etc.
40% of slim people aren't off the hook either, theyre what's known as TOFI... thin on outside, fat inside, and at the same sorts of risks as their higher bmi friends. They have high levels of visceral fat but tucked away wrapped around their internal organs so it doesn't show.
Humans aren't evolved or designed to eat any sugar, bar a few seasonal fruits and if caveman was v lucky, an occasional abandoned beehive. Likewise excess starchy carbs, though they breakdown to glucose rather than the supercharged fructose, still provokes a strong insulemic response in the body. Insulin is a storage hormone... tells the body to convert the sugars & starches in the diet to fat and lay them down. Too much and the insulin receptors on the cells become "deaf" to insulin, the pancreas has to produce more to overcompensate, and you get insulin resistance which is a precursor to T2 diabetes. Full blown diabetes comes along if you don't change course.
The neolithic diet with high amounts of grain, tubers, legumes and sugar has a whole slew of charges to answer for in terms of human health at the population level. Meat and greens/vegetables with modest amounts of high fibre/lower sugar fruits (like apples/pears/berries rather than mangos and bananas) with good fats like butter, dripping, EV olive oil and coconut is the ideal blueprint to aim for.
The industrial age diet of fondant fancies, snickers, sprite, bbq beef crisps, microwave chicken sweet & sour etc is knocking human health experiences & outcomes in to the rough.