Eating fewer calories—no matter if you eat more fat, protein, or carbs—helps lower bad cholesterol, insulin, and triglycerides, but diets with more protein lower insulin a bit more, and diets with fewer carbs raise good cholesterol a bit more.

If you're overweight and have type 2 diabetes, cutting carbs and eating more protein for 6 weeks can lower your blood fats (triglycerides) 18% more than the usual diabetes diet—even if you lose the same amount of weight—meaning your body handles fats better.

Eating too many sugary, processed carbs and not enough good fats might make your body less responsive to insulin and mess up your cholesterol levels, which could raise your chance of heart disease—especially if you're older, female, don't move much, or are overweight.

Eating lots of highly processed foods like chips, sodas, and frozen meals can make you gain weight and worsen your 'bad' cholesterol compared to 'good' cholesterol—even if you eat the same number of calories as someone eating whole foods.

Eating a lot of sugary and refined carbs for four weeks lowered both the bad and the good cholesterol in overweight men—which is surprising, because usually only the bad kind goes down. This might be because the diet also had more healthy fats in it.

Eating too much sugar over a long time can mess up how your body uses insulin, which then causes high blood pressure, bad cholesterol levels, and raises your chance of heart disease.