The thermodynamics are straightforward. The amount of calories you eat is a known quantity, the amount you expend is a function of a number of variables.
Perhaps something along the lines of:
calories_in(food) => calories_out(activity_level, gender, age, weight, body_fat_percentage, protein, carbohydrates, fat, genetics)
I think the complicated part is altering your environment and/or yourself so that you, on average, don't eat more calories than you expend. That is, to fix the feedback loop to make calories_in equal to calories_out at your desired weight.
It's not the simplest of problems, for instance, two people can do the exact same activities and eat the same amount of food and gain different amounts of weight.
Ideally, people would simply stop being hungry when they had eaten enough food, but if that was true, there would be far less fat people. So what actually seems to be the problem is that the biological system that controls hunger is often miscalibrated. I believe that diets attempt to fix that, to make people feel the 'correct' amount of hunger.
For instance, if sugar caused people to become hungry, or to eat more calories than they otherwise would, or to burn less calories than they normally would, you could create a diet that contained no sugar. The average person, if they followed the diet, would hopefully have a more appropriate hunger level at any given time.
The thermodynamics are straightforward but the mechanisms for energy expenditure aren't.
The body is a dynamic system. It responds to the stresses placed on it and adapts. Remove calorie inputs from the system and it tries to compensate by reducing the calorie expenditure.
Low-carb diets work because they control insulin levels. If you can control/avoid the insulin spikes that regulate the absorption/storage of blood glucose, you can modulate your adipose tissue creation/consumption.
Weightlifters/bodybuilders have known this for a long time. If you're looking for answers and evidence, take a good look at the population that's been experimenting and learning how to effectively build muscle mass and avoid excessive body fat.
Perhaps something along the lines of: calories_in(food) => calories_out(activity_level, gender, age, weight, body_fat_percentage, protein, carbohydrates, fat, genetics)
I think the complicated part is altering your environment and/or yourself so that you, on average, don't eat more calories than you expend. That is, to fix the feedback loop to make calories_in equal to calories_out at your desired weight.
It's not the simplest of problems, for instance, two people can do the exact same activities and eat the same amount of food and gain different amounts of weight.
Ideally, people would simply stop being hungry when they had eaten enough food, but if that was true, there would be far less fat people. So what actually seems to be the problem is that the biological system that controls hunger is often miscalibrated. I believe that diets attempt to fix that, to make people feel the 'correct' amount of hunger.
For instance, if sugar caused people to become hungry, or to eat more calories than they otherwise would, or to burn less calories than they normally would, you could create a diet that contained no sugar. The average person, if they followed the diet, would hopefully have a more appropriate hunger level at any given time.