When I read internet discussions, I notice how people will often go and search for a magic ingredient which is responsible for (presumably them) being fat and unhealthy.
Often it's "the government", "medical system", "seed oils", "corn syrup" and as I have found recently, apparently folic acid. (Those are just examples, by the way.)
One thing that is seldom named is personal responsibility. Your health is your own and if you don't trust medical advice, it's up to you to search for better info, what with the resources we have nowadays at our fingertips.
In my experience, it's not so much one certain ingredient or a type of food, but rather, your overall diet. People will often say they are fat because of the official "food pyramid" as it promotes eating too much carbs. However, I have yet to encounter where the official health advice promotes drinking liters of soda, and eating high GI sugary foods or even white bread. Vice versa, nowadays they are on a very vigourous anti-sugar crusade and will warn you against stuff like French fries or white rice.
I have no opinion about seed oils as I try to only use cold pressed virgin olive oil and butter, as for corn syrup, I have been forever eating jams containing it and it hardly ever influences my weight. May be because I restrict myself to 2 teaspoons a day?
Have been forever taking folic acid and it didn't make me fat, either. I have read about many diets through the years and one of the most researched and beneficial appears to be the Mediterranean diet. It's quite common sense and not very restrictive, allows for both meat and poultry but emphasises fish, allows you some high quality alcohol, too, and stresses minimally processed foods. Sweets and quick carbs are restricted. It's not low fat, either, since you are encouraged to use plenty of olive oil. It encourages you to cook your food instead of going for TV dinners.
It's quite difficult to change your eating patterns but I do believe it's worth it, and it will benefit you more than supplements though they have their place, too.