Slayer's Den

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The Calories-Out Study​

What if we just kept our diets the same but did a buncha cardio? Would we lose fat? How much? What about muscle? Check out this study.​

In the simplest terms, choose one of these options to lose fat:

1. Eat fewer calories than your maintenance intake (calorie deficit via diet)
2. Expend or burn more calories (calorie deficit via exercise)
3. Eat a little less than maintenance AND burn more calories with exercise

Yes, hormones, sleep, nutrient timing, and other things play their parts, but calories play the lead role in any fat-loss drama.

Most of us choose number three when it's time to drop fat: we adjust the "calories-in" and the "calories-out." But what would happen if we stuck to maintenance calories and just achieved an energy deficit through exercise alone? What if that exercise was only cardio? And what if we got ourselves into a 1000-calorie deficit by doing two hours of daily cardio for 93 days?

Well, we probably wouldn't do that! Luckily, some researchers did do it, and there's a lot we can learn from their insane study.

The Calories-Out Only Study​

This study was crazy-strict. The researchers recruited seven pairs of moderately overweight, sedentary identical twins to live in a research facility for several months. Every meal was prepared for them and they were watched by two researchers every time they ate to make sure they were consuming the exact number of calories needed for the study.

During the baseline testing period, the 14 subjects underwent every test imaginable to figure out their maintenance intake, plus underwater weighing, skinfolds, blood work, biopsies… you name it.

Remember, the goal was to get them into a caloric deficit, but not from cutting calories. Their diet wasn't a "diet" – it was maintenance intake and customized to each guy. Macros were 50% carb, 15% protein, and 35% fat.

For exercise, the subjects peddled a stationary bike (light to moderate intensity) for two total hours per day: one workout in the morning and one in the afternoon. The researchers made sure they were each burning 1000 calories from exercise per day. They did this for 10 days in a row, had a day off from training, and repeated it several times. It came out to 93 days of being in a negative calorie balance.


Body Fat Measurement1920×785 286 KB

Did They Die?​

No. On average, they lost about 11 pounds with no discernable loss of muscle. Some lost only 2 pounds; some lost up to 17.5, but the average was 11.

What Can We Learn?​

Cardio does work. Sure, it has its limitations and drawbacks, but it does work despite all the social media influencers saying, "Cardio don't work!" Well, obviously, it does. Hey, I wish they'd all gained fat and lost muscle too, so I'd have an excuse to avoid cardio, but that didn't happen.

Based on CICO math (calories-in calories-out), the researchers expected more fat loss. They ran the numbers and figured the average loss would be 14 pounds. So why only 11?

According to Dr. Bill Campbell, the subjects' metabolisms probably adapted as the study went on. Just like with diet, the body adapts to aerobic exercise. Sometimes this happens because "the body adapts to increased physical activity by reducing energy spent on other physiological functions, particularly non-exercise activity thermogenesis or NEAT," Dr. Campbell says.

This is something that competitive bodybuilders notice: the more they increase their cardio, the less they feel like moving around outside the gym. In the case of this study, their 1000-calorie deficit may have become an 800-calorie deficit because they sat around more in off times, burning 200 fewer calories. The cardio still worked, but the calories-out math shifted. Your body, that sneaky guy, fights you like a ninja when you're trying to lose fat.

Some of the subjects lost 2-3 pounds while some lost 15-17. They all did the same exercise and ate the same diets. This reminds us not to compare our results with the results of others. Although the genetically identical twins had similar rates of fat loss, even they weren't the same. For example, one twin lost 13 pounds while his brother lost 9. Same workouts, same foods, same genetic code 2, but different results.

Calories-out only fat loss plans can work. Eat what you normally eat and just move around a whole lot more. But that's tricky to do outside the lab.

I suspect many people don't see any fat loss because all they do is add cardio without knowing much about what they're eating. The cardio is great, but if they've been slowly gaining fat for years then they've probably been consuming a small calorie surplus. The calories they burn with cardio just puts them back at maintenance intake, but they're maintaining an overweight body. (Try my 5/2 Protein Diet 5 if that's you.)

Should I Do Two Hours of Cardio Per Day?​

Nope, but a little helps. Dr. Campbell suggests a "sequential fat-loss strategy." This is a fancy way of saying not to fire all your fat-loss bullets at once.

First, take care of the "calories-in" side of the equation: drop 300 to 500 calories per day by eating less. Your body will eventually adapt and slow down the rate of fat loss. NOW fire another bullet: add some cardio as a new stimulus.