I've lost about 100lbs in 2.5 years... The only thing that I really changed was doing a Keto diet. I've learned a lot about nutrition along the way, and it's amazing how bad nutrition info was when I was growing up..
Common Misconceptions I hear/see ALL THE TIME:
1) Fruit Juice is healthy. It's not. It is sugar-water.
2) A calorie is a calorie... No. Your body does not process all foods the same. A thousand calories of broccoli will effect your body VERY differently than a thousand calories of soda. Yes the energy-intake might be the same, but the resulting effects are very different.
3) Fats are bad. They are not. Your body uses fats for all sorts of processes, and most importantly, your body understands and can use fats.
4) Sugar is part of a healthy diet. Nope, sugar is not necessary in our diets at all.
5) Salt is bad. In moderation, salt and other electrolytes are actually needed by our bodies (unlike sugar).
6) Lack of exercise is the reason people get fat. No... Most people would have to run 10 miles per day to burn off the garbage they would eat in the morning (think of a young adult having an innocent bowl of cereal and OJ for breakfast). "People aren't obese because they eat too much and are lazy. People are lazy and eat too much because they are fat." Sugar and insulin and the whole endocrine system play a huge roll in how people feel physically and mentally eating sugary foods.
So many more misconceptions out there... It's hard to find good info when you have Big Sugar, Big Food, and Big Beverage shoving bad information down the masses throats.