Reporter's notebook: What I learned about my body after being in a metabolic chamber

— -- ABC News' Mara Schiavocampo shared her experiences after spending a day inside a metabolic chamber at Mount Sinai St. Luke’s Hospital in New York City. Schiavocampo's journey, which aired on "Good Morning America," was the first time that TV cameras were allowed to peek into a metabolic chamber, which is used to monitor your total energy expenditure and better understand how your body uses energy in everyday tasks such as resting, eating and exercising.

Three weeks ago I spent an entire day inside a vacuum-sealed metabolic chamber at Mount Sinai St. Luke’s Hospital in New York; 23-hours trapped inside a room the size of a prison cell. Why? It’s the most cutting edge way to measure how your body burns calories, and just might provide a glimpse into the future of weight management. The room has previously only been available for research purposes, and I’m one of the first people to ever use it commercially.

After analyzing the data for weeks, I finally got the results. As someone who spends a lot of time reading about health and wellness, I wasn’t expecting to learn much. Instead, I was shocked by the results. Here’s what I learned about the way I burn energy:

1. For me, good old-fashioned cardio beats high-intensity interval training (HIIT)

High-intensity interval training, or HIIT, is one of the hottest new fitness trends. This is a training method where high-intensity intervals are followed by brief periods of rest. For example, you might sprint for one minute, then walk for a minute, and repeat this cycle for 30 minutes. It’s widely believed to be one of the most efficient ways of exercising, burning more calories in less time. The chamber found that I burned more calories during a moderate steady run (10.7 per minute) than during a HIIT workout (seven calories per minute). Of course, this isn’t a conclusive finding about HIIT’s effectiveness, but it surprised me because I felt like I was working much harder during HIIT.

2. Afterburn? Not so much.

Afterburn is a phenomenon where your body continues burning calories at an elevated level after you’ve completed a workout. I always thought I was burning higher levels of calories for hours, even days, after an intense workout. Not so much. The chamber found that my body returned to pre-exercise calorie burning levels within 15 minutes of completing my workout. Bummer.

3. Carbs burn fast

The one thing that didn’t surprise me was seeing just how quickly my body burned through carbs. To test this, I spent six hours in a different, smaller chamber, and ate a high carb breakfast of a muffin and sugary coffee drink. My body torched those 750 calories in four hours, compared to the estimated six hours it would have taken to burn off a high-protein meal. This confirmed what most of us know instinctively; protein keeps you full longer.

The chamber measures oxygen consumption and CO2 production to provide the most accurate measure of calorie burn available today. So we also decided to compare the results from the chamber with the estimates provided by online calculators and fitness trackers. Unfortunately, those weight loss tech tools often missed the mark. Here are some of my findings from the metabolic chamber compared to what was calculated with the other gadgets I have used.

1. BMI

BMI, or Body Mass Index, is one of the most widely accepted measures of weight-related health. There are tons of online calculators that use a standard equation to determine BMI, most using your height, weight, age and gender. But just how accurate are they? According to online calculators, my BMI is 25.6, in the overweight category. But the data analysis used by doctors at Mount Sinai St. Luke’s also factored in my body fat percentage, finding that my real BMI is 23.4, right smack in the middle of the healthy range. Why? BMI doesn’t take muscle into account, and muscle is heavier than fat. It was a reminder for me not to get too caught up with numbers.

2. Metabolism

Resting Metabolic Rate (RMR) is the number of calories your body needs to just to live, doing things like breathing or digesting food. Online calculators showed my RMR varying widely, from 1,345 to 1,670 calories a day. Turns out my real RMR, according to the chamber, is 1,800 calories a day, which means I can eat a lot more than I previously thought! Doctors told me that it also means by eating too little I was slowing my own metabolism.

3. Fitness Trackers

While in the chamber, I wore three fitness trackers. Over the course of the 23 hours, the chamber showed I burned 3,240 calories. So how did the fitness trackers compare? Not so great. One overestimated by 200 calories, another by 300 calories, and another said I burned 624 more calories than I actually had.

The bottom line: The chamber reminded me how different we all are, which is why broad weight loss plans often don’t work for many people. But it also reaffirmed my belief in focusing on overall health, as opposed to getting caught up in numbers, and my commitment to honoring my body with the joy of fitness and a diet of mostly whole, unprocessed foods.