This idea comes from two false theories:
- Weight loss is a matter of burning more calories than taken in. Weight loss is actually a matter of hormone control, not energy imbalance. Your body reacts to the macronutrients you take in. If you consume non-fiber carbohydrates, then your blood sugar increases, the pancreas creates insulin, and insulin takes the excess sugar to fat tissue for storage. If you consume carbohydrates too frequently, you will basically fill up the other sugar storage spaces and consistently store the new sugar in adipose (fat) tissue (I discuss the two theories of weight gain/loss in depth here).
- It's possible to burn off a "bad" meal with aerobics (A.K.A. "cardio"). Even if creating a calorie deficit was the true way to lose weight, aerobics is such a poor way of going about it. "Cardio" generally does not use a significant amount of calories, and part of the calories used are due to metabolic rate (in other words, you would have burned those calories sitting on your couch). If you perform aerobics, it should be due to your enjoyment of that specific activity, not for calorie burning purposes.
The gentleman on the treadmill was running at 11 miles per hour, which is faster than many treadmills allow for. In addition, it's several miles per hour faster than the typical distance jogger on a treadmill. Being that the guy eating pizza consumed about 800 calories and the runner used 45 calories, it would take close to 20 hours at that fast pace to burn the whole pizza!
This brings up another problem: Excess "cardio" creates muscle wasting. Long, low to moderate intensity cardio actually decreases metabolism, so that 20 hour jogger will burn less calories on a day-to-day basis after all of that activity!