system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do our bodies tend to crave unhealthy foods with lots of sugar and unhealthy fats more than healthy foods such as vegetables? Shouldn't it be the other way around?
gpt
So, back in caveman days, sugar and fat and salt were really rare. Sugar and fat were full of energy that would help us survive famines. Salt helps regulate our body's fluids. So we evolved to find them delicious, to encourage people to work hard to find those rare treats. 

It's only been relatively recently that getting too much fat, salt and sugar has been possible, where we can eat so much of them that we negatively impact our health. But, our bodies are still in caveman mode going "We need to store as much fat as we can to survive an ice age!" Evolution takes thousands of years, and so our bodies still act they way they did when we were cavemen hunting mammoths to survive.