Hello.
I am debating the best way to normalize indirect calorimetry data when comparing normal mice (about 30g) vs obese mice (about 60g) Using body weight is not correct since fat has a very low energy expenditure (EE) so obese mice would present a lower EE/g than the real value. On the other hand, I consider that normalizing the data only with the lean mass is also incorrect. Normal mice present about 10-15% of fat and obese mice around 50%, I think it would be a mistake to consider that half of the body weight would not participate in the energy expenditure. There is the option of showing EE data without controlling for the animal weight, but bigger mice would have higher EE. I was looking for a formula combining lean and fat mass for data normalization but I could not find it. Have you heard about any consideration about normalizing indirect calorimetry data when comparing normal/lean mice vs obese mice?
Thank you very much.
Best regards.
In metabolic studies with farm animals often the metabolic bodyweight is used. This is the bodyweight to the power 0.66 or 0.75. Did you consider that option also?
Thank you for your answer Dr. Kan. In mice studies bodyweight to the power 0.75 is also used, however I think that formula would work if mice lean and fat mass are proportionally altered among mice independent of the used diets. In the case of obesity studies in mice, lean mass do not really changes, regardless the diet all mice, with the same age, fed low fat or high fat diets will have about the same lean mass. On the contrary, fat mass it the responsible for body weight increase in these type of studies. Anyway, I will use that correction factor if I can´t find a combination with both lean and fat mass.
Thank you very much. Best regards.
Actually using the same scaling exponent on total weight would be problematic because, as you said, fat is metabolically "inactive".
I would rather apply a correction to use the structural mass. I mean removing the fat mass for all individuals and then apply the exponent (0.66 or 0.75) to correct energy expenditure by body mass.
Not a perfect solution, but without specific data exploring the scaling exponent of mice with different fat% i believe that it would be the best way to make comparison