I have never used margarine, even when it was marketed as healthier than butter, agree on natural fats.
I'm old so have had some time to experiment. Fasting 36 hours each week dropped my bad cholesterol a staggering amount while moderately raising the one considered good, and I didn't lose weight, but it decreased my quality of life because fasting is a migraine trigger for me.
Gaining weight to closer to the middle of what's considered healthy for my height has overall made me feel better, which pisses me off because I like the way I look skinny, so I think adequate nutrition is also healthy. Like, while you shouldn't overeat, it's also not great to undereat.
I avoid ultra processed food except for an occasional diet coke, maybe once a month, and flour tortillas because I usually cannot be bothered to make them. Most of what we eat is homemade from ingredients.
The thing I understand about nutrition is that there is a difference between a Therapeutic diet and an everyday nourishing diet. People do extreme diets and it fixes something so they then extrapolate to everyone else and think it's a perfect diet, but when continued or used by someone who doesn't need it, can cause problems itself.
I try to eat a moderate, enjoyable everyday nourishing diet so I don't end up needing a therapeutic diet!
How do you know you have this? I got so much benefit from Nicotinamide Riboside, and after years of low vitamin D levels finally found one supplement that raised them, VeganD3+K2 - I'm not vegan but that is the one that has worked. Not sun (I get plenty of that) nor fish nor any other supplement ever got it out of the alleged critically low range.