The myth of being able to out exercise a bad diet is at odds with the “intake versus output” relationship of energy balance. At its most basic, weight control is a demonstration of energy balance, a simple equation representing the relationship between intake and output. It is true that the more you exercise,the greater the expenditure, which can positively affect the energy balance equation in favor of weight loss — but not if the input side remains higher than the output side.
Some clients, when they begin an exercise program, believe the effort to be so significant that they think they can ignore the input side and still achieve weight loss. Some may look at the calorie calculations on the cardio machines, calorie calculators, or their personal tracking devices and assume those 170 calories burnt (estimated for 150 pound person, 5% incline, 4 mph) on the treadmill over the last 20 minutes will far outweigh the calories of a post-workout smoothie.
On the positive side, understanding the energy intake versus output balance may also help sway someone's choice in snacking (e.g., looking at the calories contained in a few pieces of chocolate and deciding if it's really worth the 66 calories and an additional 8 minutes on the treadmill to burn them off).
Experts recommend a combination of prudent eating with manageable exercise to produce lasting weight loss success. This discussion might also present an excellent opportunity for nutrition experts to discuss nutrient density and the effect of nutrient choices on exercise performance.