If you lived in a lab and I controlled every morsel that passed your lips, this would be a no brainer. Being able to monitor you big brother style, like a nutrition overlord, would make life so simple.
I’d control your caloric intake (food quantity) ensuring you consume less then you burn and you’d lose weight. If the rate of loss slowed I’d restrict calories further. Admittedly being my dieting prisoner wouldn’t be much fun for you, but we’d burn some serious body fat together!
What food would I supply you with?
It doesn’t really matter to be honest.
Broccoli or biscuits, salmon or sheesh kebab, poached eggs or pedigree chum – as long as I controlled the calorie quantity – you’d drop the pounds.
This appears an open and shut case.
If you want to lose weight you MUST ensure a calorie deficit; ergo, food quantity is more important.