That's the kind of thinking that has gotten our society into this mess.
Fats have more calories than carbs but the body processes the two differently. Carbs are processed rapidly and lead to spikes in blood sugar, which causes weight gain in most people.
Eliminating healthy fats which our ancestors ate in abundance and replacing them with modified fats, unhealthy fats, or carbs has caused most of the health challenges in our society.
That's why many primitive societies (such as found in parts of Africa) are healthier than our modern progressive ones, simply because they are still eating the diet that their ancestors for thousands of years have been eating. Natural selection automatically culls out members of the population that can't survive, and sadly, that is what we are seeing today: lots of natural selection for people who can't survive on the western diet of fast food, low-fat and high-carb junk food, low-nutrition food, unhealthy fats, and no exercise. Those people are not destined to poor health because of their genetics, they are just eating the wrong diet.
Europeans are generally healthier than Americans because they eat a more traditional diet for their society (anyone who has been to France or Germany will recognize this), not a diet founded on the USDA Food Pyramid, heavily weighted toward grains and starches.
There's lots of research on the subject here: Weston A. Price Foundation
Natural selection automatically culls out members of the population that can’t survive, and sadly, that is what we are seeing today
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no we do not. Natural selection is only going to weed out those that can’t survive long enough to reproduce. The diseases that obesity causes occur way after people stop having children.
People on a western diet are certainly capable of having lots of kids and they live much longer (and lower youth mortality rates) than those who live in primitive societies. probably for other reasons besides diet. But those people do choose to have more kids than most of those in the west.