Can’t just be the food. There are people (I’m one of them) who just won’t get fat, no matter how much they eat.
Your genetics have a large influence on metabolic rates..... None the less obesity was NOT common in the last century. People were active. They did not spend hours in front of the tv or the computer. They ate food that was local and fresh (or they used the canned stuff that was unpalatable). They did not try and eat crap from Mexico or south america. Fast food joints weren’t the ‘go to’ place for your children’s food.
Take a look at the obese children. Their parents (IF they have two) are obese. They do not eat from all food groups. They eat crap. They sit around playing video games and computer games.
The truth is that if you eat less calories than you burn (unless you have a problem with your thyroid....and that isn’t all that common) you will lose weight. One cannot get around that.