If you eat 3000 cals per day of fat and protein only, and burn only 2000 per day, you will gain 2lbs per week.
With certainty.
To believe otherwise is insane.
No, I’m sorry but you can believe that people of all different ethnic background, physiotypes, and sets of enzymes will burn food energy the same way. How do you go about deciding the calorie needs for an individual? Using those useless height weight male female tables?
That is not where the science is but people who just repeat the old saws, including many family doctors, diet counsellors etc., think it is.
It’s so tempting to blame people as having no self control and eating unhealthy diets. That is certainly true for some people but not for many who struggle to be a healthy weight. IOW it’s a cop out, a just world hypothesis that satisfies the need to believe that if bad things happen it’s the fault of the person they happen to. Interestingly up to a point the less you eat the lower your calorie requirements, the body becomes more efficient. Freegards.