Eric Ravussin, Ph.D.

Now, when you have this metabolism, you produce heat. If you have no exercise, no external work, all the energy which is provided in generating this ATP is lost as heat. And this is direct calorimetry. And I was fortunate when I did my PhD back in Lausanne, Switzerland, to have access to both indirect and direct calorimetry. You can really do fantastic studies.

Now, when you have this metabolism, you produce heat. If you have no exercise, no external work, all the energy which is provided in generating this ATP is lost as heat. And this is direct calorimetry. And I was fortunate when I did my PhD back in Lausanne, Switzerland, to have access to both indirect and direct calorimetry. You can really do fantastic studies.

We did a study of measuring in vivo what we call the PO ratio. How many oxygen do you need to generate one ATP and all these kind of things by the combination of these two techniques. Now, going to indirect calorimetry, this is an easier one than direct.

We did a study of measuring in vivo what we call the PO ratio. How many oxygen do you need to generate one ATP and all these kind of things by the combination of these two techniques. Now, going to indirect calorimetry, this is an easier one than direct.

Now, we can do that in humans. I was fortunate to be at a place which had one of the two direct calorimeter. At the time, there was one in Bethesda. It doesn't exist anymore. The one in Switzerland doesn't exist anymore. I wish I had a picture to show you, but this is a basically, I would say, 1.2 meters by 1.2. It's a little bit bigger than a cubic meter box.

Now, we can do that in humans. I was fortunate to be at a place which had one of the two direct calorimeter. At the time, there was one in Bethesda. It doesn't exist anymore. The one in Switzerland doesn't exist anymore. I wish I had a picture to show you, but this is a basically, I would say, 1.2 meters by 1.2. It's a little bit bigger than a cubic meter box.

And you recover all the heat, and you have dry heat by convection, and you have a layer, a gradient layer, capturing the heat production. You collect the evaporative heat losses from perspiration, expiration, and so on. And you merge all that, and you have a complete heat balance of the person. And we measure these two kinds of heat, and this is basically equal to your metabolic rate.

And you recover all the heat, and you have dry heat by convection, and you have a layer, a gradient layer, capturing the heat production. You collect the evaporative heat losses from perspiration, expiration, and so on. And you merge all that, and you have a complete heat balance of the person. And we measure these two kinds of heat, and this is basically equal to your metabolic rate.

You generate energy by oxidation of substrate, and the byproduct is heat. And without exercise or external work, energy in is equal energy out. And this is what we measured, and I did a lot of these studies during my PhD. But then at that time, we decided to build a metabolic chamber, which is like an hotel room in which you can live one day or two days.

You generate energy by oxidation of substrate, and the byproduct is heat. And without exercise or external work, energy in is equal energy out. And this is what we measured, and I did a lot of these studies during my PhD. But then at that time, we decided to build a metabolic chamber, which is like an hotel room in which you can live one day or two days.

And I think you stayed for two days in one of these rooms at Pennington in Baton Rouge. And here we measure oxygen consumption and CO2 production. Oxygen is used to oxidize a substrate. It produces CO2 and water. And knowing oxygen consumption, CO2 production, you can calculate the energy expenditure or the energy generated by this oxidative process.

And I think you stayed for two days in one of these rooms at Pennington in Baton Rouge. And here we measure oxygen consumption and CO2 production. Oxygen is used to oxidize a substrate. It produces CO2 and water. And knowing oxygen consumption, CO2 production, you can calculate the energy expenditure or the energy generated by this oxidative process.

And you can also calculate the substrate that you oxidize. If the ratio between the VCO2, the CO2 production and the oxygen consumption is one, you oxidize carbohydrate. If it's 0.7, you oxidize fat. And protein is something in between, 0.82, depending of the protein.

And you can also calculate the substrate that you oxidize. If the ratio between the VCO2, the CO2 production and the oxygen consumption is one, you oxidize carbohydrate. If it's 0.7, you oxidize fat. And protein is something in between, 0.82, depending of the protein.

Yeah, when I was at NIH, we did a lot of reliability testing in the same person. Or you can calibrate the system. You calibrate the system with standard gas that you know the exact concentration to calibrate the analyzers. But you can also mimic someone by burning alcohol or propane. And you can vary the rate of burning. And this is what we did when we did this study with four different chambers.

Yeah, when I was at NIH, we did a lot of reliability testing in the same person. Or you can calibrate the system. You calibrate the system with standard gas that you know the exact concentration to calibrate the analyzers. But you can also mimic someone by burning alcohol or propane. And you can vary the rate of burning. And this is what we did when we did this study with four different chambers.

We validated the chambers once against the other one, and we accepted to have 3% deviation for CO2 or oxygen. Based on stoichiometry, you know exactly how much alcohol or propane you burn. You know how much CO2 should be produced and how much oxygen has been consumed. And this is what we did. And you are right. They are very, very precise. And you don't have the inconvenience of the mask.

We validated the chambers once against the other one, and we accepted to have 3% deviation for CO2 or oxygen. Based on stoichiometry, you know exactly how much alcohol or propane you burn. You know how much CO2 should be produced and how much oxygen has been consumed. And this is what we did. And you are right. They are very, very precise. And you don't have the inconvenience of the mask.

I mean, you couldn't measure with a mask for 24 hours or two days.

I mean, you couldn't measure with a mask for 24 hours or two days.