Not all types of exercises and metabolisms burn fat efficiently as science says, even if any physical activity burns calories. There is one single type of exercise and metabolism that relies directly on body fat and oxygen to provide energy when training, whereas other ways of exercising utilize entirely or majorly glucose.
Let’s see the differences between metabolisms in detail and which types of exercises target fat loss so you can become fit!
The Ways to Obtain Energy
Our body makes energy in two pathways:
- Oxidative phosphorylation, and
Oxidative phosphorylation process produces energy in the presence of oxygen and relies on body fat as fuel. Therefore, we need a significant oxygen supply to send the fuel in mitochondria that utilize oxygen to oxidize the fuel.
In the presence of oxygen, if we have enough of it, we’re going to make energy. This oxidation happens in the mitochondria. It’s the most preferred and efficient way for the body to produce energy and more so at rest for our basal metabolic rate or when we do low-moderate intensity training.
So every time you train at a low-moderate intensity, the energy will come from fat in a proportion of 85% and about 15% of it from glucose. Both sources channeled into the mitochondria for the use of oxygen.
The other alternative to making energy is called glycolysis. It’s when sugar breaks apart and happens when we don’t have oxygen around, or in insufficient quantities. The essential aspect to remember is that this process doesn’t occur in the mitochondria but the cytoplasm.
Differences Between Oxidative Phosphorylation Process and Glycolysis
The most significant difference between making energy with the use of oxygen and fat or glucose (sugar) is that we produce a hell lot more energy by using oxygen. In contrast, we have a limited amount of energy when we utilize glucose or glycogen.
As an example, we utilize glucose every time we exercise very intensively or when we engage in short bursts of power. In this situation, we can’t catch up with oxygen consumption. We fall behind. It’s when the metabolism makes the switch from fueling with fat to 100% sugars. And then, it doesn’t matter the abundance of oxygen in the air if you do a short burst of power, like a sprint at 100% capacity because you utilize sugar to fuel the body and only catch the breath after you stop and your heart reduces the beats below 120 bpm.
More practically said, aerobic exercise or cardio training uses the aerobic metabolism and oxidative phosphorylation process, whilst anaerobic training (HIIT, SIT -sprints intervals) uses glycolysis.
When You Burn The Most Fat?
You burn most of the fat available when you engage in aerobic activities because you do it with air, where you find the oxygen. Remember what I said at the beginning. When you do aerobic activity, slash cardio training, you are going to burn the vast majority of your fuel from stored body fat.
During cardio training at low-moderate intensity, you may utilize 85% from fats and 15% from glucose. Still, the ratios may change during your training session as you increase or decrease the intensity or speed.
Usually, you are using aerobic metabolism and oxidative phosphorylation when your heart rate is under 120 bpm. If you slowly increase the heartbeats up to 140, then depending on the fitness, you may still remain with oxidative phosphorylation but utilize a little less oxygen and a bit more glucose. It depends if the intensity you currently do still uses oxygen capacity and to what extent. Can you keep up with breathing, or are you falling behind? These are the signals!
From a point on (over 120-130 heartbeats), you gradually cross over into anaerobic metabolism. You start to rely on glycolysis by breaking down carbohydrates on top of oxidative phosphorylation. And you can switch back again or use a mixture depending a lot on the type of exercise, intensity, speed, fitness level and if you recatch air back.
What Type of Exercise Burns More Calories? Cardio or HIIT?
High-intensity interval training (full-body calisthenics circuits) or sprints intervals will burn more calories than cardio training, but getting fit and burning out body fat is not about how many calories you burn out. It is about from where you burn those calories, and you only burn body fat during the aerobic threshold.
The oxygen consumption is what draws the line. Don’t also forget that 86% of your burnt fat goes out as you exhale, into the mass of CO2 and the rest of 14% goes out as water. Does that make sense? Fat has mass, and that doesn’t just become nothing. That’s why once it is burnt off, it has to go out somehow. Find out more on the topic: Where Does the Fat Go When We Lose It? Mathematics of Weight Loss.
There are a lot more fat reserves than glucose or glycogen available. You have glycogen stored in the muscles for direct use by the muscles, and they will utilize them depending on the exercise you do. But glycogen cannot go out of the muscle, re-enter circulation or in the liver to become blood sugar.
As you engage more and more into anaerobic activity and rely on the glycolysis pathway, it’s not just the muscles that start using glucose, but the whole body creates a state of emergency and begins to utilize sugar from everywhere possible. So other than the muscles, it will utilize the reserves available in the liver. The liver can only store about 400 calories of glycogen, and that’s about 100 grams of sugar you can utilize if you do high-intensity training or sprint intervals at full capacity.
However, the body doesn’t want to blow that carbohydrate resource entirely. It will start finding ways to turn what it can into available sugar. Then, cortisol (the stress hormone) will tell the liver to turn everything it can into glucose, and that means it will convert amino acids into sugar. At this point, the body starts to bring glucose into the bloodstream, and insulin will begin to rise and get glucose back from the blood into the cells where it’s needed. Don’t forget that every time you have sugar in the blood, insulin will kick in.
So if you do sprint intervals or any other exercise at full power like calisthenics circuits with short break time, then the body will induce a state of emergency, and it will be stressed to find ways to sustain the activity. That will burn calories, but not from your fat reserves. Therefore, focus more on cardio training if burning fat is what you want when you exercise.
Cardio training is less stressful and will not create sugar craving or make you so hungry afterward. If you follow a low-carb and low-calorie diet (which, by the way, I don’t recommend it in most of the situations), then it will be a lot more comfortable to sustain the effort.
How Many Calories Are in a Pound of Body Fat?
I said that we have a lot more fat reserves. Well, one kilogram (which is about 2 pounds) of body fat stores 7500 calories. If I make the calculations, one pound of body fat can deliver about 3500 calories. Your liver stores 400 calories in the form of glycogen. Does it make sense why doing extremely intensive training drains you out of energy in just minutes? And yet, 1 pound of body fat can sustain your aerobic exercise for hours if your body doesn’t collapse quicker.
One hour jogging can burn as much as 500-700 calories, or perhaps more depending on how fit you are. Also, think how many in a quest to burn fat actually do the right things for the purpose, as science recommends. They burn calories and train hard but wonder why they lose weight so hard. Well, if they continuously expand hundreds of calories from sugar in their training but eat a tremendous amount of carbs right after, then the body will have a hard time losing weight. Moreso if they eat processed food, overrefined sugars with a high glycemic index. In this situation, you need to charge with carbs, but only with the right ones.
High-intensity training induces carb craving, and soon after you eat them, and especially if you had more than what’s required, then it’s more likely to store those carbs as fat. Insulin has this ability to convert carbs into fat. That’s why insulin is a fat-storing hormone.
Therefore, it matters how you train to target fat loss effectively and also to eat a variety of organic and healthy foods. But eat in moderation. This is more crucial than the thermodynamic law, calories in versus calories out.
That doesn’t mean you can’t also burn fat by doing exclusively anaerobic training, and I will talk about it in the future, so stay tuned with my blog posts and in the meanwhile, here is a great calorie-burning workout: