It's a nice thought—and people definitely try. But, sadly, you can't exercise off a crappy diet. Science backs it up. In one study—literally entitled: "It is Time to Bust the Myth of Physical Inactivity and Obesity: You Cannot Outrun a Bad Diet"—published last year in the British Medical Journal, researchers confirmed this, and also argued the over-emphasis on physical exercise at the expense of dieting encourages manufacturers to create a “health halo legitimization of nutritionally deficient products.”
The burn-and-refuel mentality is dangerous. If you burn 600-800 calories boxing, in a HIIT session, or running then treat yourself to a double cheeseburger, then yeah, your fat loss has just become a herculean struggle.
You are what you eat
"The myth that you can out-run a bad diet partially stems from conventional calories-in-calories-out thinking," says JJ Virgin, certified nutrition specialist and author of the Sugar Impact Diet Cookbook. "People become overweight because they eat too much and exercise too little, the theory goes, so to lose weight they should reduce calories and increase exercise."
Unfortunately it's not that simple. Thinking of your body as a bank where you just cash in and check out calories neglects the fact your hormones matter most for lasting fat loss, Virgin says. "What you eat signals hormones to store or burn fat, boost or crash metabolism, and build or break down muscle."
Calories are not created equally. You’d never say the calories in spinach are the same as the ones in a pint of ice cream, right? The calories in spinach trigger different reactions in your body than whatever Rocky Road concotion you're shoveling in by the spoonful.
"Sugar is the key player driving up insulin levels," Virgin says. The result: It gets stored as fat. "Whereas the spinach would trigger other hormones like glucagon, insulin’s sister hormone that releases fat to burn for energy."
Start to think of food as information; different nutrients have different physiological effects and distinct roles within the body. So, if your diet consists of lots of sugary crap, the thinking goes, you can exercise all you want and still struggle to stay trim.
So, what to eat?
But, eating a little extra on workout days in the form of good calories (like that spinach, protein-packed grilled chicken, a protein shake, etc) could actually help you reach your fitness goals. Figure out how many calories your body needs depending on your fitness level here. Then, make sure you're getting them from good sources. Check out the Get Ripped Grocery List for some ideas.
And... keep exercising!
Aside from bulletproofing your body against injury, crafting a killer physique, and helping your overall quality of life, research proves exercise can make marked improvements in preventing, managing, and reducing the symptoms of cardiovascular disease, Type 2 diabetes, dementia, and some cancers.
"Exercise is critical for long-term weight management because it helps burn up your fat-storing enzymes, and it boosts your metabolism so you burn more calories from fat throughout the day," Virgin adds. "Plus, exercise makes you look better naked." Can't argue there...