[Pseudoscience-is-malarkey (OP)]

Our bodies encourage us to eat unhealthy by making it pleasurable to eat foods we should not be eating. Our bodies then passively discourage us from eating unhealthy by giving us various body pains after enjoying them, and, of course, by shortening our of life.

[Kryptid]

It's because we are adapted for life in a very different world than the one we are currently in. Hunting and foraging are high-calorie endeavors, so we crave high calorie foods to compensate. In developed society, we have access to an abundance of high-calorie food while not having to burn nearly so many calories in order to obtain it.

[charles1948]

Our bodies encourage us to eat unhealthy by making it pleasurable to eat foods we should not be eating. Our bodies then passively discourage us from eating unhealthy by giving us various body pains after enjoying them, and, of course, by shortening our of life.

It's because we evolved as Pliocene apes.  In that era, we ate fruit, for a lot of the time.  The fruit was healthy for. us.

And as the healthy fruit tasted sweet, we came to associate "sweetness" with "healthiness".  We thought instinctively:
 "If it tastes sweet - it's good and healthy to eat!"

Unfortunately, this paradigm broke down disastrously when we became civilised and invented "sugar".  I think you'll find that's right.

[Petrochemicals]

Because our bodies are actually optimising the food it needs at the bottom. Liver kidneys lung tissue may be umpaletable to most these days, but they contain many vital nutrients that you may suddenly find delicious if you had a shortage. Some Arctic explorers often sit and eat blocks of butter, which seems revolting to me but they find delicious because they need the energy.

It's actually beneficial to be tubby, but this can mount up to obesity.