Cellular respiration involves a break down of sugars such as glucose to yield energy in the form of ATP and water together with carbon dioxide as byproducts.
In this case, when mice are fed with glucose, cellular respiration takes place breaking down glucose to yield energy in the form of ATP, water and carbon dioxide.
Therefore, the radioactive carbon in glucose showed up in carbon dioxide, since the carbon in glucose ends up in carbon dioxide.
I think probably diet because the type of food you put in your body (if it has high calorie or sodium) can severley affect your overall health and therefore affect your bpm(beats per minute)