19. You stock up on fresh veggies on Sunday for your week of healthy eating.

Result: Come Thursday or Friday, nutrients have done a vanishing act.

Some nutrients begin deteriorating in a fresh fruit or vegetable as soon as it’s harvested. In a week, green beans lose 77% of their vitamin C, spinach loses 50% of its folate, and prechopped cantaloupe, mango, and strawberry pieces lose 10% to 15% of their carotenoids. 

What to do: It’s less convenient, but buy fresh produce a few times a week. Also, shop smart: Ask the produce manager which veggies are freshest. And lean on locally grown, which has a shorter transit time, or frozen off-season vegetables, which are flash-frozen within hours of harvesting, sometimes right in the field.