How The Body Uses Carbohydrates
However, once you begin moving quickly, you suddenly present your body with a fuel paradox. Though fat is plentiful on your body , and provides many calories for exercise energy, it simply doesnt provide that energy as quickly as carbohydrates. When the body needs to get from point A to point B quickly, or needs to hoist a heavy object overhead, it needs immediate energy, and thats where carbohydrates come in. They may not provide as much energy, but they certainly provide it far faster than fat.
So as you progress from a standstill, to a walk, to a jog, to an all-out sprint, your body begins to tap into carbohydrates more and more, while reducing its use of fat as a fuel. Of course, during this entire progression, youre burning more overall calories too. So while the percentage of fat used as a fuel is decreasing, the total fat calories you burn might still be increasing.
Your Body’s Energy Systems
Your body can use all three macronutrients as energy sources to fuel your workouts. However, not all of those macronutrients are created equal when it comes time for them to be broken down into adenosine triphosphate, or ATP, which is the fuel actually utilized in your cells.
Both the energy systems and the fat-burning process in the human body are complex, variable operations and scientists are still unraveling some mysteries of the fat-burning process, in particular. However, a few key principles stand out as useful information for your weight loss journey.
Your body burns carbs first. As noted by Len Kravitz, PhD, an exercise researcher at the University of New Mexico, in general, carbohydrates are the first and preferred fuel your body uses to power a workout. That’s because they can readily be broken down into ATP via both anaerobic and aerobic metabolism. Even if you’re doing a so-called “aerobic” workout like dancing, walking, jogging or swimming, your initial efforts will use anaerobic energy sources, because it takes a couple of minutes for your heart and lungs to be ready to provide the oxygen needed for aerobic metabolism.
There’s no single answer. However, your body’s switch from burning carbs to fat as the preferential fuel source can vary quite a bit depending on many factors, not all of which are entirely understood. As noted in the aforementioned sources, your body composition, level of fitness, diet and overall health all play a role.
Know Your Heart Rate Zones
Youve probably noticed that after logging a workout, your Fitbit app shows you a colorful graph depicting how much time you spent in three heart rate zones. Knowing a little bit about how these zones were created can help you make the most of them.
Target heart rate zones are calculated using maximum heart ratethe highest number of times your heart can safely beat in one minute. To keep things simple, Fitbit uses the common formula of 220 minus your age to estimate your maximum heart rate. So a 35-year-old would have a max heart rate of 185 .
If your birthday is entered into your Fitbit account profile, then the app will default to this formula to calculate your max heart rate. However if you already know your max heart rate or want to target a specific number, you can click Account on your Fitbit app dashboard, choose HR Zones, and then turn on Custom Max Heart Rate, and fill in a custom max heart rate there.
Once Fitbit knows your max heart rate, it will create three simplified zones for you. Each one represents an intensity levelor percentage of your max heart ratethat taps into a different energy system in the body, producing specific results. Heres a breakdown:
PeakIntensity: Vigorous Benefit: Increases performance speed
Intensity: Hard Benefit: Builds cardiovascular fitness and muscle strength
Fat BurnIntensity: Moderate Benefit: Builds aerobic endurance and teaches the body to burn fat as fuel
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The Endurance Athlete’s Adaptation Conundrum
The body adapts to certain circumstances by responding in the reverse manner. Not drinking enough water? Your body tries to retain it. What actually occurs in weight training is a breakdown of muscle tissue, leading the body to adapt by building muscle. When you burn calories doing aerobic training, your body adapts by slowing your metabolism and allowing your body to store more fat. As an endurance athlete, your goal is to become very efficient at aerobic exercise. As it becomes easier for you to perform, you’ll burn fewer calories and lose less weight.
Those who first get into triathlon from, say, a running background often find swimming and biking difficult. They will probably lose some weight initially because their body isn’t used to these activities and is burning greater calories than normal as it exerts more effort. After racing and training for a few years, however, running, biking and swimming will burn much fewer calories then it used to. More calories are burned doing activities the body is not used to.
The work required to run five miles will become less and less as you get fitter. In order to improve, you either go further or you run those five miles faster. In weight training, as you get better, you add more weight or more reps and there is literally no finish line.
Chart And How To Calculate
There is an equation for figuring out a persons maximum heart rate and fat burning heart rate. The fat burning heart rate is based on the maximum heart rate.
It is important to note that these equations are not suitable for determining safe heart rates for children.
To calculate the maximum heart rate, a person should subtract their current age from 220. For example, a 40-year-olds maximum heart rate would be 180 beats per minute.
To calculate the fat burning heart rate zone, a person should determine the upper and lower limits. The upper limit is 70% of the maximum heart rate. The lower limit is about 50% of the maximum heart rate.
Using the same example, a 40-year-olds fat burning heart rate is between 90 and 126 beats per minute.
People interested in increasing their endurance and cardiovascular strength often train at higher levels. Sometimes called the cardio zone, people training for performance increases often train at 7085% of their maximum heart rate.
The following chart shows the breakdown of heart rates based on a persons age.
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How The Fat Burning Zone Works
Your body gets most of its fuel by burning a combination of fat and carbohydrates. The more active you are, the greater percentage of carbs it burns as opposed to fat. Why is this the case?
Carbohydrates are a less dense form of energy than fats, which makes them easier to break down. When the intensity level of your exercise increases, your heart rate rises and your body needs energy more quickly, so it turns to the source that can be accessed faster.
For this reason, lower intensity workouts burn a higher percentage of fat compared to carbs than higher intensity efforts do. That is why the heart rate zone for burning fat is also categorized in the chart above as light exertion level. The 70% of max HR number comes from it being strenuous enough exercise to burn fuel, but not too strenuous to burn carbs instead of fat.
The Link Between Heart Rate And Fat Loss
During a workout or ride, your body requires more energy. Thus, your heart pumps faster and harder to send oxygen to your muscle cells to break down more glycogen and fat to fuel your muscles.
While 1 gram of carbohydrate contains 4 calories of energy, 1 gram of fat contains 9 calories. This makes glycogen a less dense form of energy storage that is readily broken down into glucose, as compared to fats.
As such, glycogen is your bodys first source of energy during exercise. Since high-intensity workouts require more energy quickly, you tap on glycogen rather than fat in your body for fuel. Your body only taps on to the next fuel, fat, when you start to run out of glycogen.
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Other Factors To Consider
Exercise is not the only way to burn excess fat. You can also get your body to shed fat by eating a balanced diet, watching your portion sizes, drinking plenty of water, and getting enough sleep. The more avenues you use, the faster you drop the extra weight.
Plus, burning fat or losing weight is not the only goal of cardiovascular exercise. Working out regularly has been found to lower your resting heart rate, which also reduces your risk of dying early from cardiovascular disease.
So What Is The Fat Burning Zone
The fat burning zone that most people talk about is the heart rate range in which your body is burning the most body fat to fuel your workouts and the least carbohydrates from your muscles and liver. On first glance that sounds great, right? Your goal is to burn body fat, after all! Well, theres a little bit more to the equation than just that.
While more of your calories burned in this low-intensity zone come from fat, the overall number of calories you burn is much lower when youre working much less hard. Imagine going for a 30-minute leisurely walk vs. a 30-minute run. During your 30-minute walk you might burn 100 calories, and 70 of those will be from fat. During your run you may be burning only 50% fat and 50% glycogen , but if you burn 300 calories total you will still burn 150 fat calories.
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The Fat Burning Zone Has No Afterburn Effect
When you exercise at low exercise intensities, you burn very few calories after the exercise is completed. When you exercise intensely such as during a HIIT workout, there is a metabolic disturbance that burns calories after the workout is completed. This is known as the afterburn effect.
Estimates of the afterburn effect vary wildly depending on the exercise method, the intensity of the workout, and even how its measured.
In a study by Dr. Christopher Scott and the University of Southern Maine, the total calorie burn of low intensity exercise vs. high intensity exercise was examined. A low intensity exercise group cycled at a steady rate of 3.5 minutes. The higher intensity exercise group required three 15 second sprints as fast as the subjects could run.
What was the difference in calorie burn? Quite substantial.
The cycling group burned 29 calories vs. 4 calories for the sprinting group during the exercise. But when you take into account the calories burned after exercise, or the afterburn effect, the numbers look much different 39 calories burned for the cycling group vs. 65 calories burned for the sprinting group. A surprising 95% of the total calorie burn occurred after the sprinting exercise!2 Keep in mind the cycling group exercised for almost 5x longer than the sprint group .
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Eat For How You Want To Feel
It starts with mind and body chemistry the combination of hormones and neurotransmitters that naturally occur in your body. By eating the right mix of beneficial fat , lean protein and complex, low-glycemic-index carbohydrates , Dr. James says you can support that biochemistry to encourage your system not just to burn fat, but also to give you more focus and energy more consistently throughout your day.
“Everyone has their own unique biochemical individuality, so no one diet will work for everyone,” Dr. James says. “I encourage my patients to start with a healthy balance of key macronutrients, and then fine-tune that based on how certain foods and the timing of certain foods make them feel.”
To find the perfect combination for your biochemical individuality, you’ll need to do a little self-sleuthing. Dr. James recommends keeping a journal to document how exercise and meals make you feel. “For example, do you thrive with fruit, whole-grain cereal or bread in the morning?” he asks. “Are you a person who does better with morning exercise or evening exercise?”
“We need to keep track of what we are doing and how we feel,” he says. Try starting with the options developed by Dr. James at www.gaiam.com/energymeals. “Then follow the signs. With a little observation, you can dial in to your best course of eating.”
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Things You Can Control
Happily, there are a number of things you can do to improve your body’s ability to burn fat as fuel. As exercise physiologists with the University of New Mexico point out, blending interval training and endurance training helps improve your body’s ability to metabolize fat as fuel.
Regular, progressive resistance training also improves that ability. Building lean muscle not only boosts your overall metabolic rate, but also helps improve post-workout fat oxidation and your overall EPOC, or the elevated level of energy your body consumes after each workout as it works to return you to a resting state. Mixing low-intensity “recovery” workouts in with your harder workouts for example, going for a relaxed stroll or taking an easy bike ride to loosen up tired legs also helps support your body’s overall fat metabolism.
Nail Every Workout With Target Heart Rate Zones
Now that your heart rate zones are set and you know what they mean, you can work out at the right intensity again.
Using your Fitbit tracker, start a workout as you normally would. As you begin moving, no matter which PurePulse-enabled tracker you own, youll see a visual representation of your zones.For instance, in the picture above the heart is in the cardio zone. Want to work on speed? Pick up the pace. Looking to blast fat? Ease up to drop back into your Fat Burn zone. When you adjust your pace on the fly, your Fitbit tracker responds instantly.
If you see the outline of a heart but no dashes, your heart rate is below 50 percent of your max, meaning youre not in a zone. And thats totally ok! If you want to get a cardiovascular boost, just increase your intensity. Here are four ways to upgrade your walk to a workout.
Heart rate reading seem off? Follow these guidelines to increase PurePulse accuracy.
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When Does Body Start Burning Fat During Fasting
Youre looking to lose some weight, but the diets youve tried havent worked. Sure, the pounds come off while you limit your eating, but they latch right back on once the diet ends. Youve heard intermittent fasting could be good for burning fat, but how long does it take for this to happen in the body?
You must be on an intermittent fast for at least 12 hours for the most efficient fat-burning. For some, its 14 hours, and for others, it could take even longer. It all depends on how much glycogen is in your body, as you have to burn this first, then your system uses fat.
If this is going to be your first intermittent fast, then we recommend you keep reading. In this article, well discuss everything you need to know to burn fat while fasting. From how the process works, how quickly your body torches fat, and even if you can take supplements for more fat-burning on a fast, youre not going to want to miss it.
Putting It All Together
Regardless of their names, exercising in both zones leads to weight loss. Ironically enough, the cardio zone, with its higher intensities will help you burn more calories in a shorter duration. For the purpose of losing weight, it matters little whether the calories burned during exercise come from fat or carbohydrates. Focus on a challenging workout and do the satisfying number crunching over your post-workout protein shake.
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Fat: The Most Efficient Energy Source
The most efficient energy source is fat. One pound of stored fat can provide 3,600 calories of energy, which is far more than most people burn in a single day. In comparison, a pound of storage protein or carbohydrate provides less than half that much energy. Because fat provides so much energy, the body relies primarily on fat during rest and during relatively slow and easy physical activity. From an evolutionary survival standpoint, that makes sense, since most people can only store about 2,000 calories of carbohydrate on their entire body. If you burned carbohydrate as your primary fuel, youd have to be finding food and eating all day long. Furthermore, if your burned protein as your primary fuel source, your body would have to break down muscle and other organs to get the protein fuel–or youd have to be rooting around for nuts, seeds, eggs, and meat all day long.
Fat Burning Heart Rate
You might have seen the “fat burning zone” written on treadmills, cycle ergometers, ellipses and other equipment. Have you ever wondered where does comes from? Well, we have the answer for you! The fat burning zone is simply the range of heart rates that is ideal for fat loss. It can be calculated as a 60-80% of your maximal heart rate.
If you want to find out more about other heart rate zones, check out the target heart rate calculator.
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Build A Progressive Workout
Not everybody can jump right into high-intensity training in fact if you’ve been inactive for some time, the best advice is to start gradually and work your way up to higher intensities and durations as your body adapts. But everybody can find some way to add more physical activity into their life, whether that means parking at the far end of the parking lot and walking to the store, taking a quick 10-minute stroll during your lunch break, swimming an extra lap in the pool or just kicking the speed on any of those up a notch.
Here’s some more good news, based on the evolving understanding of how the human body works: Every little shred of physical activity you can squeeze into the day helps. As noted in the 2015-2020 edition of the Department of Health and Human Services physical activity guidelines for Americans, previous editions of those guidelines which form the core of health-based exercise recommendations for many institutions stated that physical activity should last at least 10 minutes to count toward your “quota” of aerobic activity for the day.
But now, the HHS acknowledges that any length of activity counts toward that total even if it’s just five minutes. If you’re looking for a good first goal to set, meeting the HHS minimum recommendations for physical activity is a good place to start.