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What a stupid statement. It is analogous to this: "Why is this building crowded?" Your answer: "It's due to too many people inside. Simple as that." Real answer: There is a popular band inside, which has caused more people to walk into the building in a given 3 hour period than leave it. The "too many calories" people (you are one of them)all think that the effect of a bad diet (which is often bad caloric partitionin…
What evidence do you have that too many calories dont result in weight gain? I bet you that if eat 5000 calories of "healthy" food and your daily requirement is 3000 you will gain weight, and if you eat 2000 calories of "bad" food you will lose weight.
You should read the parent again, more carefully. The point is not that that is not a true statement, the point is that is a vacuous statement, and therefore, the wrong question. It is not controversial that things that cause weight gain cause you to gain weight, but it's not a useful statement for either science or engineering, and we have collectively wasted an awful lot of time and research while laboring under the delusion that this was some sort of actual explanation, rather than a mere restatement of the problem.