How to find your fat-burning zone
If you want to burn as much body fat as possible while you exercise, ignore the charts at your gym showing generic “fat-burning zones.” Instead, try these do-it-yourself hacks to learn how to help your body incinerate more fat when you work out.
“Our bodies are quite good at maximizing fat oxidation” during exercise, if we let them, said Isaac A. Chávez-Guevara, a lecturer in the Department of Health Sciences at the Autonomous University of Ciudad Juárez, who led new research on fat burning.
Encouragingly, the key to burning fat during exercise is to exercise far more gently than many of us might expect.
Why fat burning matters
“There are good reasons” to want to find your fat-burning zone, Chávez-Guevara said, and they have little to do with weight loss and appearance. Fat tissue, even in people of normal weight, can have undesirable metabolic consequences. Fat cells often release substances linked to inflammation and insulin dysfunction that contribute to diabetes, heart disease and other conditions, he said.
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So, in general, reducing body fat improves health. And exercise, in the right doses, may help us shed fat. Exercise requires fuel. It can come from whatever foods you’ve recently eaten or from the fat or carbohydrates stored in our bodies’ tissues.
Whether you burn primarily fat or carbohydrates during exercise depends mostly on your workout’s intensity. In broad terms, the harder you exert yourself, the more your body relies on carbs.
What may surprise some people is that the lighter the workout, the more your body uses fat to fuel it, making easy exercise the key to your fat-burning zone.
Three ways to find your fat-burning zone
Your goal is to find the pace of exercise at which most of the calories you’re burning come from fat. Exercise scientists define a person’s “fat-burning zone” as the level of exercise that keeps your heart rate within about 10 percent of that pace. To find your own fat-burning zone, consider one of these three approaches.
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Visit a lab. For the most precise measurement, visit a physiology lab for exercise and metabolic testing. Some hospitals, universities and even fitness centers provide such tests for a fee. The costs may be covered by insurance if your doctor recommends the testing.
DIY with a heart-rate monitor and math. You could also estimate your particular fat-burning zone by walking on a treadmill and doing a little math, Chávez-Guevara said. First, figure out your maximum heart rate. The commonly used equation of 220 minus your age is “not very accurate,” Chávez-Guevara said. Instead, try wearing a heart-rate monitor or smartwatch and walking or jogging on a treadmill at a pace that starts off feeling easy. Increase the speed every three to five minutes, until the pace feels quite draining and your heart rate plateaus. This is your maximum heart rate (or close to it).
Next, calculate 60 percent of that number and aim to work out near that heart rate, Chávez-Guevara said. In a new review he and his colleagues published in Sports Medicine, they collated data from 64 past studies involving almost 7,500 men and women with obesity who’d completed exercise testing and found those who exercised at between 57 and 66 percent of their maximum heart rates burned the highest percentage of fat. Similar heart rates would probably maximize fat burning in most people without obesity, Chávez-Guevara said.
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You do need to keep moving for more than a few minutes at that pace to burn a meaningful amount of fat, though, he continued. In his group’s research, 40 minutes of easy walking seemed to be near the sweet spot for fat burning.
Exercise a little easier. You could also let your body be your fat-burning guide. In past studies, people asked to walk at speeds they felt they could maintain for at least 45 minutes usually settled into a pace squarely in their fat-burning zone.
That pace also tended to be slower than many of us might expect, hovering at about 2.5 to 3 miles an hour for many people, Chávez-Guevara said, or barely 20 minutes per mile. “Most people can manage that,” he said, even if they’re new to exercise.
Ignore the fat-burning zone charts at the gym
You may be tempted to just use the fat-burning charts posted online or in many gyms. But they’re too generic to be useful, a small new study finds.
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In the study, researchers at the Icahn School of Medicine at Mount Sinai in New York gathered data from 26 men and women, representing a range of ages, weights and fitness levels, who’d completed an exercise test at the institution’s physiology lab. The test used heart rate and breath monitors to pinpoint the intensity and heart rate at which each person burned the highest percentage of fat and, from there, their fat-burning zones.
Then the scientists compared those zones to the ones advised on typical health-club charts.
There wasn’t much agreement. Some people’s measured fat-burning zones fell within the numbers on the generic charts, said Hannah D. Kittrell, a PhD candidate at Icahn Mount Sinai, who led the study. But others differed by as much as 10 beats per minute.
“That might not sound like much,” Kittrell said. But 10 beats per minute could be the difference between walking and jogging for some people, meaning someone who uses the charts to set the pace of their workout could wind up exercising too hard or too lightly to maximize their fat burning.
Food and timing can affect fat burning
Whatever method you choose to find your fat-burning zone, try to watch what you eat after you exercise, so you don’t immediately replace whatever fat you’ve just burned, Chávez-Guevara said.
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Many questions also remain at least partially unanswered about how fat-burning zones differ for people who are lean vs. those with obesity; the roles of gender, fitness and diet in fat burning; and whether the time of day matters. Some research indicates you might burn more fat with the same walk in the afternoon rather than the morning.
But those are marginal concerns, Chávez-Guevara said. In general, if your primary goal is to drop a little body fat, go easy.
Do you have a fitness question? Email YourMove@washpost.com and we may answer your question in a future column.
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