It's a question everyone asks when they start out on a new diet or exercise regime — where does the fat go when you lose it?

There are several persistent explanations floating around, said Jeff Woods, a long-time personal trainer and fitness lifestyle commentator on the Canadian Learning Channel.

Some believe the fat converts to muscle — a theory that is "blatantly wrong," Woods said.

Jeff Woods is a long-time personal trainer and Edmonton AM fitness columnist. (Custom Fit) Others think fat is turned into heat energy and literally burns off. "Well, that sort of happens," Wood acknowledged.

Before fat can be reduced, a person must elevate his or her body temperature and burn calories, he clarified.

As for the idea that fat cells metabolize — "Well, that's just not true," he said.

While a small amount of fat is excreted in urine and sweat as part of the metabolic process over time, most of it is actually exhaled, Woods said.

"As we exercise, we inhale large amounts of oxygen which is metabolized, and it mixes with our blood and it's exhaled as a respiratory gas," he said.

"In layman's terms, the fat mass is actually breathed out of your body as carbon dioxide."

This metabolic process can make fat cells smaller, but will not eliminate them completely, he added.

Woods also has some suggestions about the best ways to cash in on your breathing out:

First, get mobile; a fit person is better able to work out intensely.

High-intensity interval training where you get very little rest and there's a high demand for oxygen is best.

"You're going to end up expiring lots of that carbon dioxide which is more responsible for eating up or reducing that body fat," Woods said.

And while longer duration training like walking or running is still good, it does not require the same degree of oxygen — so less fat is exhaled. To up the ante, add some sprints to your longer workouts, Woods advised.

Much to the displeasure of many, Woods said it is not possible to choose where the fat comes off. With diet and exercise, fat will eventually reduce across the entire body via blood circulation and expired gases.

The change will be notable first in areas that had less to lose in the first place — like your face or neck.

Common problem areas like stomachs, where there are more fat cells, will see the change last, Woods said.

Regardless of whether your plan is to tighten your cheeks or slim everything down, Woods said the approach is the same: "It all starts in the kitchen. You cannot out-exercise a bad diet."

According to Woods, a good diet starts with plenty of vegetables and high-quality proteins.