Every year, the scientific community reveals exciting new information about what is and isn't good for our health. But some of the most prevalent, obvious "facts" about how to live a fit lifestyle are actually myths, spread via misinterpretation or marketing departments until they become part of the vernacular. Below, we've traced the origins of five major health fallacies.

1. THE MYTH: YOU NEED EIGHT GLASSES OF WATER PER DAY, EVERY DAY.

It's common knowledge that human beings require exactly eight 8-ounce glasses of water each day, lest they die of dehydration. But that knowledge is, in fact, a myth—one that nobody can determine the origins of, despite much research into the matter. How much water a person needs is actually a highly individual question, but it's also one you probably don't need to ask; in The New York Times, Indiana University professor of pediatrics Aaron E. Carroll did a deep dive into the "eight glasses" fallacy, and came up with some reassuring guidelines:

"You don’t have to consume all the water you need through drinks. You also don’t need to worry so much about never feeling thirsty. The human body is finely tuned to signal you to drink long before you are actually dehydrated."

2. THE MYTH: 10,000 STEPS PER DAY IS A MAGIC BENCHMARK FOR FITNESS.

Now that most of us carry smartphones with built-in step counters, walking 10,000 steps (about five miles) per day has become a de facto benchmark for living a fit lifestyle. But that's not because 10,000 steps is a scientific gold standard for health; actually, the "10,000 steps" rule was invented by a 1965 Japanese marketing campaign for an early pedometer. Not that there's anything wrong with 10,000 steps as a goal—in general, the more active you are, the better. But you'll reap just as many health benefits by simply aiming to spend more time on your feet each day [PDF].

3. THE MYTH: HEALTHY PEOPLE WEAR MILK MUSTACHES.

Thanks to concerted marketing efforts by the American dairy industry, you might have come to believe that milk is synonymous with healthy nutrition. The truth? A vast majority of the celebs sporting milk mustaches in that 20-year series of ads, along with just about everyone else past the age of infancy, can't digest the stuff. Unless you happen to carry the gene for lactose tolerance (most common in people from Northern Europe), the effects of milk on your body will likely be the opposite of good.

4. THE MYTH: SKIPPING BREAKFAST WILL RUIN YOUR METABOLISM.

Breakfast has long been touted as vital to a healthy lifestyle, especially for those trying to lose weight; until its 2015 updates, even the government's Dietary Guidelines for Americans recommended eating it every day. But the most important meal of the day it isn't, as it turns out. This myth was founded on guesswork, based on easily misinterpreted observational studies. More rigorous, controlled trials reveal that there's no relationship between breakfast—or the lack thereof—and weight gain. And the best time to have your first meal of the day? Whenever you're hungry.

5. THE MYTH: AN ALL-JUICE DIET WILL CLEANSE YOUR BODY OF TOXINS.

You can put down that kale smoothie. If you want to rid your body of toxins, everything you need is already inside of you—in the form of a functional liver and kidneys, which work perfectly well on their own, at all times, to process and excrete anything that doesn't belong. And if you're trying to turn over a healthy new leaf after a period of overindulgence, there's a good reason not to join the juice craze: Even fresh juices are usually loaded with sugar, which has a host of negative effects on the body. A whole fruit is much more nutritious (not to mention more satisfying to eat).