People often overestimate the number of calories they've burned by exercising, and underestimate how many calories are in the food they eat, experts say.

Exercise is important for many reasons such as cardiovascular fitness, but long-term studies have shown the amount of weight loss specifically from exercise programs is modest.

After burning off calories during exercise, the body tends to seek a balance by replacing the calories, driving up hunger, explains Steven Bray, a health psychologist at McMaster University in Hamilton.

"What's challenging for most people is that it takes quite a bit of time at a high intensity to burn a lot of calories," Bray said. "But we can consume a lot of calories very quickly. It's very easy to probably overconsume and overcompensate for what might be a hunger that's developed through the exercise that we've done."

If you think a hard, fast-paced workout on a treadmill has earned you the right to eat a burger and fries, think again. (Carlos Barria/Reuters)

McMaster kinesiology Prof. Martin Gibala set up a mini-experiment for CBC News to test how much men and women choose to eat after working out on stationary bicycles while researchers measured the intensity of exercise and estimated how many calories were burned.

"I kind of got hungry and started craving a big meal so I chose pizza," as well as fruits and vegetables, said Jeninel Sayes, one of the participants in the high-intensity group. "I think it is based on how much I sweat out."

But an average person burns off only 200 to 300 calories at a moderate pace, Gibala said.

Those 300 calories don't go far. For example, a commercially prepared apple fritter can contain 290 calories, and three-quarters of a blueberry muffin or less than a small-sized pumpkin spice latté both pack 330 calories.

"I tell my students that we control our body weight by what we put in our mouth and we control our fitness through exercise," Gibala said.