It isn't bunkum and it will be always be difficult for people to understand this unless they go through with it.
And yes most people do eat a lot more crap than they should.
Metabolism makes a huge difference in tailoring an approach towards weight loss, there is no one size fits all solution here if you want quick and sustainable results. It is about knowing your body and how it reacts to different food, exercise routines etc.
People with different metabolism will deposit fat in different areas, burn fat at a different rate etc...
It is not bunkum but I do say it is not to be used an excuse to continue piling on the crap food and binge eat.
Metabolism is an excuse used to make sweeping statements and excuses. Metabolism does not determine where you put on weight.
Your basal metabolic rate is influenced by you body’s composition. Muscle requires more energy to function than fat. That’s why men, who typically have a higher muscle mass than women, will generally have a higher BMR than women. Other factors include:
- height (the taller you are, the higher your BMR will be, due to a larger skin surface area for heat loss)
- fever and stress
- smoking and caffeine, and
- environmental temperature (heat and cold both raise BMR)
A "slow" metabolism is usually found in conjunction with a thyroid problem and requires medical treatment.
Where you put on weight is also not determined by your bmr (i.e. the rate at which you burn calories to survive), but seems (based on sketchy evidence) to be related to genetics and hormones, although there is little conclusive data on this.
Interestingly, fat people have a higher BMR than not so fat people, simply due to their size. The reality is that you shouldn't even talk about "metabolism" when looking to lose weight.
The real answer is burn more calories than you consume and move off a carb rich diet to a protein rich diet with low carbs, so that you move into a state where your body runs on fats rather than glucose. With the latter you'll be surprised as to how much more volume you need to eat if you take carbs out in order to consume the same amount of calories.