People looking to lose weight often think that long sessions of cardiovascular exercise are the best way to spur weight loss and jumpstart their way to health. Treadmills and ellipticals adorned with charts that display the mythical ‘fat burning zone’ that dictate how hard the user should be exercising serve as a guideline for many gym-goers.

However, things are not always as they seem to be.
During exercise, your body has two primary sources of fuel: carbohydrates (in the form of glucose) and fat. Let’s take a look at the difference between the two.

Glucose is the preferred energy substrate for a few reasons. First, it is readily available. Glucose is stored in the muscle, liver and blood, meaning it can be accessed at a moments notice. Also, glucose can be used either aerobically (in the presence of oxygen), or anaerobically (without oxygen).
To use fat as a source of energy, several things must happen first. The person exercising must achieve a steady state of exercise where oxygen is readily available. Basically, you must be exercising at a pace that allows you produce a sustained effort over long period of time. Also, oxygen can only be used in an aerobic state. This is why many people mistakenly think that cardiovascular exercise is the best way to shed fat.
The truth is, whenever you’re exercising, you are not limited to one form of energy substrate. There is a constant mix of fat, glucose and phosphate being used as energy. You are never using just one source of energy to exercise; it will always be a combination of different sources.
However, these sources of energy can be directly influenced by two factors: Intensity and duration. The greater the intensity of the exercise, the more reliant you’ll be on glucose, while lesser intensities will provide a greater ratio of fat use.

Exercise intensity also directly relates to the second factor, duration. Working at a very high intensity means that your body is relying almost exclusively on carbohydrates for energy and working in anaerobic state. High intensity combined with lack of oxygen to the muscle cells results in fatigue very quickly. This is known as ‘hitting the wall,’ the point where you can no longer sustain the intensity you are at, when you must either drastically decrease your exercise intensity or stop completely to catch your breath. Training at high intensity levels requires an individual to walk a very fine line, and being able to push themselves to the bring without going over. This type of training is very effective for cardiovascular training.
Another thought to consider when trying to ‘burn fat’ is quality vs. quantity. You can walk at a slow, low intensity pace for 40 minutes and use fat as your primary energy source. Conversely, you can workout at a high intensity for 20 minutes at a high intensity and use a mix of fat and carbohydrates for energy. The high intensity workout will use more total calories than the low intensity stroll, with the added benefit of taxing both the aerobic and anaerobic pathways, therefore improving your aerobic capacity much more so than the low intensity walk.

Yet another oft-overlooked tool to enhance weight loss is weight training. The combination of aerobic exercise and weight training is better than aerobic exercise alone in the fight to lose weight. Plus, muscle is much more metabolically active than fat tissue. At rest, muscle burns roughly three times as many calories than fat tissue.
Last, but not least, don’t forget the role diet plays. There is a saying that is as true today as it was 50 years ago: ‘you can’t out train a crappy diet.’ If you’re doing all the right things in the gym and still aren’t getting the results you want, give your diet a hard look. Heavily processed and packaged foods, whole milk dairy products, sugary drinks, alcohol and foods loaded with refined flour are not doing you any favors. Eating fresh fruits, vegetables, beans (not the canned kind), nuts and seeds are much better for you. Basically, if you can grow it, you should eat it.
Finally, don’t let the graph on the treadmill dictate how hard your workout is or what your heart rate should be; find an activity you enjoy doing, and do it often. If you prefer a more moderate intensity workout, that’s fine, but don’t be afraid to kick it up a notch once in a while; the results may surprise you.