Scientists Told Me to Stop Working Out So Hard if I Want to Burn Fat

This test says that I—and maybe you—have been doing cardio wrong since forever.

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Mar 1 2018, 9:53pm

Grant Stoddard

Last December while researching a Tonic story about the accuracy of the caloric data that’s summarily shat out by cardio machines, I was told by Dori Arad, the director of the Metabolic, Body Composition, and Sports Performance Clinic at Mount Sinai, that my abs remain covered by a blanket of adipose tissue because I’m exercising at the wrong intensity.

That nugget, at face value, may not be surprising to you and it wasn’t to me either. It was what he said next that blew my mind. Arad told me that it was possible, indeed likely, that I couldn’t shift my belly fat, not because I wasn’t putting in enough effort, but because I was putting in too much. Arad answered my next question before I could blurt it out: “We have a test that can show the exact intensity of work at which your body is using the maximum amount of fat as fuel,” he said. “You can use the results of the Fatmax test to help you burn the greatest percentage of fat whenever you are performing cardiovascular exercise.” I was, to put it mildly, all in.

Proteins, fats and carbohydrates in our food are broken down into amino acids, fatty acids, and glucose respectively. Glucose is stored as glycogen in the liver and in muscle tissue, ready to provide the body with energy at a moment’s notice. Fat is also tapped for energy at moderate intensities but when the going is either easy or tough, it’s glycogen that the body turn to in greater measure. It’s quick, it’s dependable, and using it obviates the hassle of breaking into the gelatinous stash that many of us would rather be used for fuel.

But before I get smart about getting rid of it, a kindly word about body fat: Without a certain amount it, we’d die. The amount referred to as “essential fat” is around 2-5 percent for men and 10-13 percent for women. Beyond its role in keeping us alive and able to reproduce, we’d all be pretty miserable without carrying a sufficient amount of body fat around. It acts as an insulating layer, reducing heat loss through our skin; it acts as padding—making being a novice snowboarder or a BDSM bottom possible—as well as protects major organs like our kidneys. And in the event that food becomes scarce and/or glycogen stores are depleted, it stores excess food energy that can be tapped into.

That reserve fuel tank is found between the dermis and muscle tissue throughout the body, though it accumulates in certain areas depending both on genetics and gender. In women, more fat accumulates in the buttocks, hips, and thighs to support pregnancy and provide energy for milk production. In men, fat accumulates around the belly where it serves no physiological purpose at all. (After menopause, fat accumulation in women tends to shift from the lower body to the abdomen too.)

The one potentially useful thing that belly fat does do is indicate that another wholly more dangerous type of fat is likely also building up around our vital organs or viscera. As I’ve mentioned already, to an extent organs benefit from the body’s bubble wrap but too much “visceral fat” is associated with a number of chronic diseases and increased mortality rates due to something called lipotoxicity. So while the prospect of looking less horrid while naked led me to take a Fatmax test, putting the resulting data to use could also help me ward off diabetes, heart disease, high blood pressure, dementia, depression, arthritis, stroke, sexual dysfunction, sleep disorders and death, which is a nice bonus.

Clinic Coordinator Kaitlyn Bishop shows me into a small room and begins affixing, strapping, and wrapping data-collecting equipment to, on, and around me while I saddle up on a cycle ergometer.

“When we exercise we know that the energy type that we use varies depending on the intensity of the work,” she explains as she hands me a clip to place on my nose. “When we start exercising, we’re going to be using that fast energy, a little more carbohydrate. As it goes on, start to burn fat and, as it gets harder and our body needs faster energy and we’ll eventually go back to using carbohydrates.”


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Bishop explains that the format of today’s test is a graded exercise test in three-minute stages with every stage getting harder by 30 watts. She tells me that she’s allowed for as many as 11 stages but gives no indication as to whether she thinks that I could complete them all.

“Hopefully, as we move you up in intensity by stage, we’re going to see a nice bell curve representing fat oxidation,” she says. “At the top of that curve, we’re going to try and capture the work rate and the heart rate at which you achieved peak fat oxidation and that will be your Fatmax.”

You’ve probably seen graphs on cardio equipment demarcating where users’ fat burning zone lies. While these charts are well meaning, it turns out that the point at which we use fat, like calories more generally, varies widely from person to person. Sports physiologist Asker Jeukendrup writes that while the average Fatmax is 65 percent of maximal heart rate, it can be as low as 50 percent and as high as 80 percent. His recommendation is that everyone interested in putting more fat in their fuel max subject themselves to the exact test I’m getting ready to take. As my baseline readings appear on various screens around me I start to worry that my Fatmax is on the higher end and the prescription for melting my belly off is greater exercise intensity and not, as I hoped, much less.

“Are you ready?” Bishop asks, after confirming that a physician is standing by in the event that I keel over.

I have electrodes on my body, a blood pressure cuff on my left arm, and a mask over my muzzle that’s transporting my breath along a tube. It’s from my breath that my oxygen consumption and carbon dioxide production can be confirmed.

Unable to talk—and instructed not to try—I give Bishop the thumbs up and start pedaling at a prescribed 50 RPM. The hardest thing about the first stage is getting the cadence right but after the blood pressure cuff tightens around my left arm for the first time, I’m in the groove. It’s at stage three that I really start to feel myself beginning to work heard and by stage four (150 watts), I begin to sweat. With Bishop’s encouragement I get through stage five before, at 210 watts, I both succumb to the workload and also notice that the electrodes are beginning to slide off of my body. After my warm down, Kaitlyn wryly chides me for using lotion on my body—an earlier email had instructed me not to use any for this very reason.

Because Fatmax is a relatively new protocol and no standardized software is available, Bishop has to plug in every bit of data she collected individually. I receive the results the following day: a PDF of tables, charts, and graphs all pertaining to what I have to do to make my body cannibalize my fat and use it as fuel most effectively.

On page seven of the thorough report, she’s highlighted three numbers that amount to news I can use. At the point at which my body was deriving a whopping 77 percent of its fuel from the wobbly matter making my pants tight, my heart rate was 95 bpm, my oxygen consumption was 16.55 mL/kg·min and the workload was 60w. This meant that I was burning most fat near the very beginning of the test—the easiest part. That’s good news for the lazy man. The bad news is that I’ve been performing cardiovascular exercise at a much higher intensity all these years. In short, I’ve spent countless hours burning zero fat calories while trying to burn fat.

I should mention that while I’m somewhat preoccupied with the idea of one day having a hard body, I, like everyone else, have plenty of good reasons to perform cardiovascular exercise at higher intensities. It’s at these higher workloads that cardiovascular health and overall fitness are most effectively improved. What’s more, some people may actually burn more total fat as fuel despite working an intensity beyond their Fatmax.

For example, someone who runs at 400 kcal per hour might derive 75 percent of their energy from fat meaning that, over the course of an hour, they’d burn 300 fat-derived calories. If they upped their calorie burn rate to 750 kcal an hour, however, the percentage of fat burned may drop to 60 percent of that 750, but they’ll still burn 150 total fat calories more than they would have when exercising moderately for the same duration.

It was found that I burn the most fat when my heart rate is 95 bpm. If I had to get my heart beating at 130 bpm to burn the maximum amount of fat, I’d be simultaneously be increasing the number and size of blood vessels in the muscles, improving lung ventilation, getting more oxygen to your muscles and the efficiency with which waste products are taken away. While becoming fitter and leaner happens at the same time for some people, they don’t for me.

“Working out at higher intensities is extremely beneficial for health and fitness,” Arad says, after reviewing my results. “But in your case you are burning very little fat in that zone. To lose body fat and improve your fitness, you may want to do exercise in both of those zones separately.”

Seeing as I’d been exercising in a way that left my fat unmolested all my life, I decided to drop into a lower gear and shift some blubber. In my report, Bishop had included some sample aerobic exercise sessions for optimal fat utilization based on the data she’d collected. The following day I went to the gym, eager to put her math to fat scorching use. I jumped on a stationary bike and tried to maintain a heart rate of 95 bpm. At this rate, I should burn 331 kcal in 60 minutes with 255 of those calories (77 percent) coming from fat.

Thing is, the low Fatmax point that’d I’d hoped for makes my war on adipose tissue feel impossibly easy, like I’m pushing against an open door. The elderly YMCA members to my left and right are giving me funny looks and I imagine that they either think that I’m very stoned or that I’m somehow mocking them. After realizing that doing this for an hour a day will bore me to death, I pull out my phone, buy a Fitbit on Amazon and resolve to make a moderate hour-long walk part of my fat-torching regimen.

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