When does one actually burn fat?

headshot-3-for-kimQ: I heard that fat isn’t burned until 20 minutes into a cardio activity. A friend said fat is only burned when you exercise on an empty stomach. What’s the real deal?

 A: The answer to this question has eluded so many of us for so long because there are a lot theories circulating about fat and how it’s used as fuel. Adding to this is the fact that there have been hundreds, perhaps thousands, of studies that conclude slightly different things.
To begin, let’s make one point clear: Your body burns energy (or calories) just by existing. Even when you are sleeping, you’re burning calories. Some scientists report a 50/50 fat-to-carbohydrate ratio, meaning half of the calories you burn at rest come from fat that you’ve eaten recently, and the other half come from carbs; others claim it’s a 25/75 split. Both figures can be correct depending on the person, making the metabolizing of energy a very individual thing. So I can’t tell you what’s going on with your body, personally, but I can tell you that some of the fat you ate at lunch today will be burned tonight, even when you are not exercising.
The real question is: “When are we burning stored fat?” Stored fat is any extra girth that’s settled onto your hips, thighs and belly — the stuff you want to get rid of when you’re trying to lose weight. Fat is not entirely evil: It helps your body absorb nutrients and provides lubrication for your joints. But, as we all know, it can be undesirable, especially when it comes in the form of love handles, saddlebags and jiggly underarms. Cardiovascular exercise can burn stored fat, and there are two main ways.
The first method is to do some aerobic exercise when you haven’t eaten for eight to 12 hours — upon waking in the morning, for instance. A workout at this time burns more stored body fat than at any other time of day because, since you haven’t eaten in so long, your body does not have any glycogen (available carbohydrates) in the system to burn. Therefore, to get the energy it needs for your workout, your body taps more directly into the fat stores. (Warning: If you suffer from hypoglycemia or have diabetes, exercising on an empty stomach is not recommended.) A substantial downside to exercising without any fuel in your belly is that it can be uncomfortable due to hunger pains and lethargy. In saying that I am not encouraging you to exercise on an empty stomach. It makes working out no fun! I am just makikng a point.
The other, better way to burn stored fat is to do an aerobic activity for a substantial amount of time. Fat burning really kicks into gear approximately 30 minutes into a cardio workout — after your body has used up all of the sugar in the bloodstream that’s present after you eat — and turns to fat as a fuel source. This is why most fat-burning workout DVDs and classes are at least 45 minutes long. It’s also why doctors recommend power walking for those needing to lose weight — power walking provides a steady cardiovascular workout that’s easy to sustain.
Finally, if you want to burn more fat, you should also work on building more muscle. Research shows that the more muscle mass you have, the faster your metabolism gets; because muscle is a denser tissue than fat, it consumes more fuel during both activity and rest. So strength training can help you burn more fat, more easily, in the long run. Make sure to incorporate it into your workout regimen.

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