What is the contribution of the major nutrients -- glucose, fat and protein -- to the human body's energy requirements, in normal conditions?
For some tissues, the fuel preference is known qualitatively -- the brain runs on glucose, the heart preferentially oxidizes fatty acids, etc. I'm looking for quantitative data on the consumption (oxidation) rate of the major nutrients, on the whole-body level. Molar amounts per unit time, or energy per unit time, or relative contributions to the total.
To get a rough idea, I looked at glucose and triglyceride turnover in blood. This article estimates blood glucose turnover at about 8 g / hour, or 190 g / day. If we assume that blood glucose transport equals amount of oxidized glucose, then this corresponds to 3200 kJ / day, or about 1/3 of the daily energy requirement. Similarly, this article estimates blood triglyceride half-life at about 1h; with a blood triglyceride content about 5 g, this yields about 90 g / day, or 3300 kJ / day from fat.
So with this rough estimate, sugar and fat appears about equally important, but about 1/3 of the daily energy requirement is missing. And I would imagine my quick calculation is inaccurate in many ways... Anyone know of better estimates? Some literature on the subject?
(I'm aware of the the dietary reference intake data, but diet composition may not equal the proportions of nutrients oxidized due to all sorts of interconversions.)