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  • Writer's pictureNick Allen

The truth behind "fat-burning"

While misinformation is present in the entire health and wellness universe, scammers and pseudoscientists seem to be especially fond of the weight loss and fat-burning segment of this space. Hardly a day goes by where I don’t see a juice cleanse or “belly-fat-burning” workout advertised on social media.

Without getting too deep into the woods here, it’s important to know that juice is one of the last things you should be having if you want to lose fat, and that no exercise can “target” fat in a specific area of your body. There’s really no shortcut on this front — even something like liposuction, which works aesthetically, can’t mimic the health benefits of losing fat through diet and exercise.

Rather than go on about things that don’t work for cutting fat, I’d like to take this opportunity to talk about how we can burn fat on a molecular level. It’s easiest to think of the fat stored in your body as one big pool which is constantly being added to (via calorie consumption) and subtracted from (via exercise and resting energy expenditure). I’ll save the diet component for another day, but a key takeaway there is that dietary fat is not the villain that it was once made out to be.

Focusing on the fat-burning side of the equation, stored fat in the cells needs to be transported to the mitochondria where it can be broken down and used for energy. In my opinion, the best way of doing this is Zone 2 training, a key component of our healthspan toolkit. This is such an important topic that it will be the subject of numerous future blog posts, but I wanted to introduce it here as a great method by which you can both burn fat and become more efficient at doing so.

Your body essentially uses carbohydrates and fat as energy sources. Which one you use is dependent on your exertion level. Zone 2 training is fairly low intensity, with most people finding their Zone 2 somewhere around 60-70% of their maximum heart rate. This is because oxidative phosphorylation, the process by which energy is most efficiently generated in the mitochondria, is not fast enough to keep up with the sudden energy demand brought on by high-intensity exercise.

When you surpass Zone 2, the quicker but less-efficient process of anaerobic glycolysis begins to ramp up. This process uses carbs rather than fat, and takes place in the cytosol instead of the mitochondria. It also leads to the byproduct lactate, which can be measured to clearly define a person’s Zone 2. A perfect Zone 2 workout will lead to blood lactate levels right around 2 mM. Anything above that is getting into the glycolytic arena, while anything below represents suboptimal energy consumption.

Now, there’s nothing wrong with high-intensity exercise. In fact, I think it is essential to incorporate some time in these higher zones into your exercise regimen. However, because Zone 2 is so great for fat-burning, mitochondrial efficiency, and even blood sugar control, it has become a core part of my training. If you want to try it for yourself, find something where you can generate a steady output for at least half an hour, and ideally closer to an hour. We’ve found that exercise bikes work well for Zone 2, and I’m interested in trying rowing machines in the near future. For some, brisk walking is enough to enter Zone 2, while others can stay in Zone 2 while jogging. The only requirement is that you keep the intensity low enough to stay in that aerobic zone but high enough to burn substantial fat and increase mitochondrial beta-oxidation (fat breakdown) capacity.

Since most people don’t have a lactate meter, I recommend using heart rate to get a ballpark estimate of your Zone 2 (60-70% of max. HR). From there, pay attention to your exertion. You should be able to maintain this pace for a long time, and you shouldn’t be struggling to catch your breath. It is commonly said that in Zone 2 you should be capable of holding a conversation, but it should be just enough strain so that you don’t want to have a conversation. With repetition you can almost feel your body going beyond aerobic capacity and can titrate your workload to remain right on that edge.


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