Eating vegetables and whole foods helps with the second and third, and somewhat with the first. By not eating highly processed foods, your blood sugar doesn't spike and then crash. (I think of it as the difference between using coal and jet fuel to make a fire.)
Do they? What exactly does it mean? I had the impression that eating a lot of calories doesn’t mean keeping them – that it depends on what source they come from (fats/proteins/carbs).
Now, your body might try to compensate and change metabolism in response to this, so that you unwittingly burn fewer calories than you consume. And yes, the types of food you're eating can affect this. But ultimately, our bodies are not perpetual motion machines, and cannot expend more energy than they take in as fuel, over the long term.
Of course the arguments to physics are true. But they are largely irrelevant. Its not the truth that's going to help people.
People eat too much, not because they don't know better (and physics! will teach them), but because they have some behavioral issue that prevents them from doing the good actions repeatedly.
It always ends up here: "Just don't put the calories in your mouth. That's all you need to do." Which would be true, if food and eating were entirely volitional. But its an emotional need, a very fundamental one.
Imagine saying "Just put the gun to your head and pull the trigger. That's all you need to do." While its undeniably easy, most of us, because of emotional needs to survive and avoid pain, would find it very, very hard to accomplish. (Not saying a gun-to-the-head loses weight; just comparing an easy instruction with the accompanying difficulty in performing it).
I agree that no one should use thermodynamics as an excuse to be judgmental or dismissive toward people who are having trouble managing their weight.
But I also think that when people directly ask about calories (as the GP zoul did), it's worth being clear and unambiguous about the basic science.
No one is going to track of how much mass they breathe in and out, how much mass they lose through sweat, excretion, urination, how much mass they eat and drink or how much energy they gain or lose through radiation. You would have to track all of those things to model weight loss based on laws of thermodynamics.
If you are trying to predict weight loss based on the calorie count on the back of your food boxes and based on your level of activity, the laws of thermodynamics aren't going to be very helpful. The calorie count on the box of food is only a very rough approximation of how much usable energy your body is able to extract from the food. That amount will not be consistent for every person or even for a single person in differing scenario.
"All models are wrong, but some are useful", so why be pedantic about one model being more right when it is also much less useful in the scenario and still is not a completely accurate model of reality?
Simple physics says one thing, simple engineering says another which is anything controlled that finely is under hormonally driven feedback control.
Frankly I think in the 20th century, particularly in the US and Britain there was a strong cultural imperative to assign psychological causes for conditions medical 'science' wasn't able to explain. So fat people are gluttons, erectile dysfunction is physiological, ulcers are caused by physiological stress. Heart disease is caused by a 'type A personality'.
However, barring inaccuracies in these numbers, once a calorie has been consumed into your body, generally the only way to get rid of it is using it. Until such a time, it will be stored as sugar or fat.
Diets designed to "cut" (loose weight), yes. Some people want to gain weight, their regimens are also called diets.
But technicalities don't define words, usage and context do, and, for the vast majority of people, including people here, diet means a change in your habitual pattern of eating designed to induce weight loss. That's how it's universally understood in this context.
Being more technical does not mean being more correct.
Eating vegetables and whole foods without worrying about counting calories or limiting portion sizes doesn't feel like effort. You don't WANT to eat more. And your body becomes happier about burning fat rather than demanding that you eat.
Counting calories explicitly is a lot of work and a lot of self control. Few people can succeed at that.
Personally I follow the former strategy using http://www.weightgrapher.com/ to keep myself honest. About 15 years ago I decided to lose 20 pounds, and kept it off for close to a decade. Then I let my weight get away from me, because life got complicated. This time around I've decided to get back to that weight again, and I know it is sustainable. I'm not aiming for fast weight loss, I've been going at a comfortable pace for 3 months and expect to be dieting another 6 months to reach my target. But I know that I'll be able to get there and stay for years without a lot of willpower. Partly luck of genetics/gut biome. Partly because I'm doing it in a mentally easy way.