It may seem counterintuitive, but eating less fat can actually make your body fatter.

"Fat consumption does not cause weight gain," doctor Aaron Carroll wrote in his book "The Bad Food Bible." "To the contrary, it might actually help us shed a few pounds."

This is because people who skimp on fat (something our bodies need to function properly) are more likely to fill up on sugar and refined carbohydrates instead, and that can lead to measurable weight gain over time. Studies of people around the globe show this to be true time and again.

Fat molecules help our body's cells stay healthy, and they aid us in absorbing nutrients in the other foods we eat. So if you prefer whole milk to skim, there's no reason to feel guilty about that.