> Well, isn't it individual for every person?
Statistically speaking, no. Most people's physical response to food and exercise is almost exactly the same given the same inputs. There may be minor variations from person to person, but the variations aren't large enough to change the general advice. There are extreme exceptions, but those are natually extremely rare, and shouldn't be used to muddy the water.
> Secondly, if one wants to lose weight by doing sports, he should be reasonable about this and not eat a bar of chocolate after a 50 min run.
While that's exactly the point, the way you said it is too dismissive, IMO. This is exactly what happens to almost everyone. You don't need to exaggerate with chocolate bars. Unless you're counting your calories or consciously going hungrier, most people will naturally just eat a bit more at meal time because they're hungrier, because they worked harder. If that's not being reasonable, then you need to understand that millions and millions of people are not reasonable.
If one only wants to lose weight, he could reasonably skip his normal 2nd morning bagel, and just skip the run too. Save $5, save an hour, it costs less to eat less, in every way. One way to look at this is there's no such thing as losing weight by doing sports. There's only gaining weight by eating too much, and losing weight by eating less than you burn. Whether you exercise is perhaps irrelevant to your weight. (That's exaggerating, but is more true than the other way around.)
> I've found an interesting series of articles
These articles are from a sports magazine and are selling sports as the solution. In the (second) article, he admits that you have to keep diet under control, but he is dramatically over-emphasizing the importance of exercise on weight loss, and he's painting a picture of calorie counting being too difficult and too inaccurate to be effective. Speaking from personal experience, this is quite misleading bullshit. You don't need accuracy for it to work, and you don't have to account for secondary effects of exercise either, which the author claims at length. Compare these articles to the Vox article @scarface74 posted, you will see some striking differences.
I love going to the gym, I advocate exercise 100%. I think exercise keeps me happier and healthier. But the gym isn't a weight loss tool. If anything at all, I now use the gym so that I can eat more than I would be able to otherwise. I can burn 500 calories working out, and then feel okay adding an extra 400 calorie treat during my day.