Fitness recommendations can change as fast as Superman in a phone booth, so we can be forgiven for believing faulty information from time to time. But many of us hang on to our old beliefs (sometimes for decades), which hampers us from achieving our fitness goals—or sometimes from pursuing exercise at all. Exchange these three lies for fitness truth, and you may just find yourself in the best shape of your life.

Big Lie #1: Taking the stairs is enough.

We’ve all heard the recommendation to opt for the stairs over the elevator, or to park in the far corner of the grocery-store parking lot. These are great ideas, but they should be seen as bonus activity on top of a workout or regular sport—a side dish versus the main course. I learned this truth after the birth of my first child. For months, I tried to drop the baby weight with bonus activity: squatting to load or unload dishes in the dishwasher, doing curls with the grocery bags as I carried them into the house and so on. But it wasn’t until I resumed actual workouts that I made any progress.

Big Lie #2: Staying fit takes a lot of time.

I stay in good shape by working out three times a week, for 10 to 30 minutes each time. On top of that, I do bonus activity (see Big, Fat Lie #1), such as playing with my kids, walking with friends or taking the stairs. I exercise at home, which cuts out time killers like traveling to and from the gym, waiting for fellow gym-goers to get done with equipment and such. A few disclaimers: 1. Staying in shape this way requires intensity. When you work out for just a short time, you have to go hard to see results. 2. Notice I said “staying” in shape, not “getting.” If you’ve been sedentary for a long time, you’ll need to commit more time, primarily because intense workouts aren’t safe if you aren’t used to physical activity. But you’ll likely be able to ramp up the intensity sooner than you might think. 3. Elite athletes and those with big goals (think: half-marathon) will have to commit more time to achieve their targets.

Big Lie #3: I exercise, so I can eat whatever I want.

Even if you’re blessed with a supercharged metabolism that keeps you slim no matter what you eat, realize that the purpose of eating well goes way beyond weight management. Nutrition affects every aspect of your life—your cognitive abilities, energy levels, digestive health, moods, immune system and more—which means the quality of your diet choices matters as much as the quantity. Nutrition advice can be every bit as fluid as fitness recommendations, but if you follow the simple guideline of emphasizing whole foods over refined and processed ones, in reasonable quantities, you’ll likely come out OK.

Kellee Katagi is one of those strange souls who actually enjoys working out for the sake of working out. She’s spent most of her 20-plus-year writing and editing career covering fitness, nutrition and travel, as well as outdoor sports ranging from skiing to spelunking to street luge (yes, that’s a thing).