Sugar and carbs are very calorie dense, so it’s a distinction without a difference on a practical level.

It's perhaps more accurate to say sugars and simple carbs are easy to absorb whereas fats and complex carbs are harder to absorb. A single gram fat is the most calorie dense substance by weight that we can consume I think. It's just in practice it's hard to become fat by consuming only excess fat.

A carbohydrate and protein have the same calorie content, around 4kcal per gram. Fat is 9kcal per gram.

Again, on a practical level - what’s easier to over consume? Carbs and sugars or fats?

Sugar calories are not equal to say, calories in nuts. The sugar calories are indeed worse. One reason for this is the caloric energy in nuts are not fully absorbed like with sugar. So even though nuts are energy dense, they won’t cause obesity like sugar.

calories in / calories out is a foolproof way to track weight gain/loss over extended periods of time. So people tend to oversimplify nutrition and diet to this one number.

But it is indisputable that your body processes carbs, protein, and fat in very different ways. If you only eat donuts and bacon and candy consistently, in normal caloric levels, then you will likely develop type 2 diabetes (or more precisely insulin resistance). Glucose in your blood is toxic. Are you really going to argue that this diet is perfectly safe?

> Are you really going to argue that this diet is perfectly safe?

I'm not sure that I ever claimed it was? All I'm saying is there's no point in vilifying those food types as they can be part of a perfectly healthy diet.

There is (and let’s not bey coy: arguing all calories are equal implies a sugar diet is perfectly healthy). People literally don’t understand how bad excessive sugar intake is because it’s not vilified enough. A mature adult understands that everyone has vices and all things are usually fine in moderation, and that’s how we should approach sugar. I strongly believe in 20 years sugar will be seen similar to tobacco. And that’s okay. You and I can still enjoy an occasional donut.

Calories are pretty much meaningless. The kind of food, proportions of carbohydrates, and other components is very critical. Nutrition =/= filling gas in a car.

> Calories are pretty much meaningless.

I think you'll have to expand on what you're trying to say here as taking it at face value is clearly untrue.

There are calorie dense foods that are nutrition poor foods, and vice versa. In living things, it's not about energy only, the contents that help keep the body processing and regulating matter by a lot. The quality of calories matters a lot too.

High blood glucose levels are literally toxic. This will damage every cell in your body. Your body can buffer sugar intake to an extent in order to maintain homeostasis but over time this tends to cause insulin resistance. A little sugar is fine but larger amounts are poisonous. The exact limit depends on a number of factors such as muscle mass and liver glucagon level.

And proportion of visceral fat stores, genetics, epigenetics, etc.