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Most fitness watches now show a fat burning zone, usually labelled zone 2, and it sits lower than many people expect. For most adults it is a brisk walk. You breathe harder and could still chat to the person beside you, though you would not want to sing. Venables and colleagues tested 300 men and women on a treadmill and found fat burning peaked, on average, at about 61.5% of their maximum heart rate.
To get your own number, take 208, subtract 0.7 times your age, and work out 60–70% of the result. At 45 that is about 106–124 beats a minute, which for most people is a brisk 5–6 km an hour. Faster walks and jogs burn more calories in total, and over the weeks those count towards fat loss as well.
What is the fat burning zone?
It's the pace at which your body burns fat fastest. On an evening walk, that's the speed where you can still tell the person next to you about your day, though you wouldn't want to sing. Slow down to a stroll and you burn less of everything. Speed up to a run and your muscles switch more and more to carbohydrate, which releases energy faster.
Achten, Gleeson and Jeukendrup measured this in Birmingham in 2002, with trained cyclists breathing into a mask through stepped tests. Their fat burning peaked at about 74% of maximum heart rate and stayed near the peak over a fairly broad band of effort. At about 92% of maximum it had fallen close to nothing.
The same lab later tested 300 ordinary men and women on a treadmill. Their fat burning peaked lower, at about 61.5% of maximum heart rate on average. How much body fat a person carried made no difference to how much fat they burned while exercising.
What heart rate is the fat burning zone for you?
First you need your maximum heart rate. The poster in most gyms still says 220 minus your age. Tanaka's team pooled 351 studies and found 208 minus 0.7 times your age fits better, especially after 40, where the old rule guesses too low.
Say you're 42 and you walk most evenings around the colony park. Seven tenths of 42 is about 29, so your maximum works out to 208 − 29, or 179 beats a minute. Sixty to seventy per cent of that is roughly 107–125 beats a minute. On the treadmill at the society gym, that's usually a brisk walk at 5–6 km an hour.
Worked out the same way, zone 2 is roughly 112–131 beats a minute at 30, 108–126 at 40, 104–121 at 50 and 100–116 at 60. Real maximums scatter ten beats or more either side of the formula, so take these as a first guess and check them against your breathing. If you take tablets for blood pressure or the heart, ask your doctor which range to use, since some of them hold the heart rate down.
Is the fat burning zone different for women?
A little, for women. In the Birmingham treadmill study, women burned fat at a higher rate than men for their lean body mass. Their peak also came at a harder effort: about 52% of aerobic capacity against 45% for men. Men switched to carbohydrate as the main fuel earlier as the treadmill sped up. In practice, a woman walking beside her husband at the same pace may be burning a larger share of fat.
Body fat itself made no difference. People carrying more fat did not burn more fat during exercise, and people carrying less did not burn less. Fitness and how active people said they were explained part of the spread, though only about 12% of it, and most of the difference between individuals stayed unexplained.
Training changes the picture over months. Achten and Jeukendrup's review describes how regular endurance exercise brings changes in the muscles that raise fat burning. As fitness grows, a walk that once pushed you into zone 3 settles into zone 2, and you need a quicker pace or a slope to get back there.
Zone 1, zone 2 or zone 3: which burns the most fat?
Most watches split effort into five zones by percentage of maximum heart rate. The usual bands are 50–60% for zone 1, 60–70% for zone 2, 70–80% for zone 3, 80–90% for zone 4 and 90–100% for zone 5. Some brands set them a little differently, so it's worth a look at the settings page. On the usual bands, the average fat-burning peak in Venables' treadmill study lands in zone 2.
Zone 1 is an easy stroll, the kind you take after a heavy Sunday lunch. Zone 2 is a brisk walk or an easy ride on a cycle, and fat burns close to its fastest rate there. Zone 3 is a quick walk up a slope or a steady jog, where you can only talk a few words at a time. It burns more calories a minute, with a slightly smaller share coming from fat.
Achten's cyclists stayed near their peak fat burning across a fairly wide band, so zones 2 and 3 are closer than many charts suggest. Zones 4 and 5 run mostly on carbohydrate and suit short intervals. For most of the week zone 2 is the sensible pick, since you can do it again the next day.
Does burning fat during exercise mean losing body fat?
Wewege's group in Sydney tested the idea directly. They pooled 13 trials in adults carrying extra weight that compared steady moderate cardio with interval training, where much of the fuel is carbohydrate. Both cut fat mass and waist size by about the same amount over roughly ten weeks, and the interval groups trained for about 40% less time.
The reason is that the body balances its fuel across the day. After a session that burns mostly carbohydrate, the next meals refill those stores and the body leans on fat at other times. Fat comes off when the energy used stays above the energy eaten, week after week.
Fasted cardio follows the same rule. Achten and Jeukendrup's review notes that a carbohydrate snack before exercise lowers fat burning during the session. In Schoenfeld's trial, young women on a diet did an hour of steady cardio three times a week, fasted or after a meal, and both groups lost the same amount of fat.
How much cardio does it take to lose fat?
Quite a lot, if cardio is doing the job by itself. In its 2009 position stand, the American College of Sports Medicine found that 150–250 minutes a week of moderate activity gave modest weight loss. Going past 250 minutes a week was linked with clearer loss and with keeping it off.
Donnelly's Midwest Exercise Trial 2 shows what that takes. For ten months, 141 sedentary young adults exercised five days a week, mostly walking or jogging on treadmills, and ate as they normally did. Those burning 400 calories a session lost 3.9 kg on average, and those burning 600 lost 5.2 kg. The group that didn't exercise gained half a kilo.
Swift's review puts the usual result from guideline amounts of cardio at about 2 kg, with big differences between people. That's why walking pairs so well with eating a little less, say one roti fewer at dinner or tea without sugar. Zone 2 adds to the gap without leaving you ravenous or too stiff to go out again the next evening.
Which activities keep you in zone 2?
Walking is the easiest way in. For most untrained adults, 5–6 km an hour on flat ground does it, the pace of someone who has somewhere to be. On a treadmill, add a slight incline once flat walking stops lifting your heart rate. Outdoors, a route with a gentle slope or a flyover footpath does the same job.
An exercise cycle at the society gym works well if your knees grumble on long walks. Pedal at a resistance where you can talk in sentences, and keep the pedalling smooth rather than grinding. Someone carrying a lot of extra weight will reach zone 2 at a slower pace than a lean friend, and that's fine, because the heart rate is what counts.
The stairs in an apartment block are the quickest route to zone 3, so keep them for a short, harder day rather than your daily session.
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How do you do a 30-minute zone 2 walk?
Spend the first five minutes at an easy stroll so your heart rate climbs gently. Then speed up until talking takes a little effort. For most people that's around 5–6 km an hour, which works out to a kilometre every 10–12 minutes.
Hold that pace for 30 minutes and check your breathing every ten minutes or so. If a slope pushes you past zone 2, shorten your stride and keep going. End with five minutes of slow walking, then stretch your calves and hamstrings against a wall or a park bench for a minute.
Cushioned shoes help. From April to June, carry water and walk in the shade or after sunset. On smoggy winter mornings, the treadmill at the society gym or the stairwell of your building can stand in for the park.
How can you find zone 2 without a heart rate monitor?
The talk test is free and surprisingly accurate. Walk or jog with a friend, or talk to yourself if you're alone. At zone 2 you can tell someone you'll pick up the dhaniya on the way home, all in one breath, while singing feels like hard work.
Persinger and colleagues checked this against lab measurements on a treadmill and an exercise cycle. The point where speech first became awkward lined up closely with the ventilatory threshold, the top edge of steady moderate effort. Reed and Pipe's 2014 review found it held up for walking, jogging, cycling, elliptical trainers and stair climbing.
A wrist tracker is useful for trends over weeks. It can lag behind on intervals or jump on a bumpy road, so when the watch and your breathing disagree, go with your breathing.
Why does zone 2 work best alongside strength training?
The 2009 American College of Sports Medicine review found that resistance training made little difference to scale weight in weight-loss trials. It did add fat-free mass and increase the fat lost. Muscle that is worked regularly tends to be kept even when food is short, and a body that keeps its muscle keeps more of its daily calorie burn.
That is why doctor-led programmes that aim for up to 20% of body weight off, with the muscle kept, never stop at walking. They begin with a home blood test and a doctor's review of the person's usual week. Then they add two short strength sessions and a protein food at every meal, such as dal, paneer, eggs, curd, chicken or fish.
A home session can be simple: squats to a chair, rows with a filled water can, wall push-ups and step-ups on the bottom stair, for about 20 minutes. The WHO's 2020 guidelines ask for strength work on two or more days a week, on top of 150–300 minutes of moderate activity.
What does a week of fat burning zone training look like?
Start with 20–30 minutes of brisk walking on five days a week, and stay at that until it feels easy. Then build towards four zone 2 sessions of 40–50 minutes, plus two 30-minute strength sessions with dumbbells, bands or your own body weight. Keep one day light, with a stroll or some stretching.
After a few weeks, swap one steady walk for intervals. Warm up for ten minutes, then go hard for one minute and easy for two, six times. On a treadmill that means jogging the hard minutes and walking the easy ones.
Every fortnight, add five or ten minutes to your zone 2 walks until you pass 250 minutes a week. Measure your waist every two weeks along with the scale, since walking plus strength work often shrinks the waist first.