Here’s an interesting study for you:
6 men, all roughly 50 years old were admitted to hospital, where they were fed roughly 6,200 calories per day for seven days.
They ate 230 grams of protein, 775 grams of carbohydrates, and 240 grams of fat in 3 meals per day plus some snacks.
They maintained bed rest (no exercise at all) for the entire 7-day study.
…By the 7th day their metabolism had increased by 16%, increasing the amount of calories they burnt per day by 237 calories!
Of course they also gained 7.7 pounds of body weight, all of which was body fat.
They also quickly developed systemic insulin resistance and oxidative stress.
The bottom line?
Increasing metabolism isn’t the end all be all it’s sometimes made out to be. And, even though overeating does increase metabolic rate, it’s never enough to counter the additional caloric load, nor prevent the deleterious effect on your insulin resistance.
Also keep in mind that the process of building new body fat increases your metabolic rate. So a “high metabolism” isn’t alway desirable.
If I had to hazard a guess, I’d say the major mistake here was the inactivity, and I’d be very curious to see this exact study replicated in men and women who were exercising.
My guess it that the insulin resistance would be mitigated, as would the oxidative stress.
In short, increasing your metabolic rate by overeating is a fools game that will almost always end up with more negatives (fat gain, insulin resistance, oxidative stress, disrupted sex hormones) than positives, ESPECIALLY with the absence of exercise.