Excess carbs coverted to fat?
Thanks to reader LynMarie for prompting me to exhume this post that has been in the "draft" hopper for months! I'll probably update with some comments at a later time, but wanted to get this article/link out there.
This is a repeated mantra in the LC community ... if only it were true to any significant extent.
We've heard it from Taubes, and Sisson, and -- the worst offender -- Nora Gedgaudas who goes so far as to claim that all fat in the body comes from glucose! I even emailed her once about this and she stuck by this claim -- "I didn't make it up"
The model of the human macronutrient energy economy that emerges from the study of McDevitt et al is consistent with previous work (2,3,8,9). In the hierarchy of fuels, dietary carbohydrate appears to have a higher priority for oxidation than does dietary fat; when both are present, carbohydrate is chosen. The 2 major macronutrient energy sources (carbohydrates and fats) are not, however, interconvertible energy currencies. Fat cannot be converted to carbohydrate in animals because animals lack the enzymes of the glyoxylate pathway, and carbohydrate is not converted to fat because of a functional block of uncertain cause.
What are the implications of this model? Some conclusions should not be drawn. First, these results do not mean that extra carbohydrate energy represents "free" energy in terms of body fatness. By sparing fat in the body's fuel mixture, surplus carbohydrate energy will make people fatter, even though it is not directly converted to fat. The absence of significant de novo lipogenesis is bad news for high-carbohydrate dieters for another reason, in that the high thermogenic cost of de novo lipogenesis cannot be invoked as an energy-dissipating feature of such diets. Second, the effects of carbohydrate-rich diets on macronutrient balances should not be confused with their potential effect on plasma lipids and atherogenesis. High-carbohydrate euenergetic or hyperenergetic diets consistently induce hypertriglyceridemia, the public health consequences of which remain controversial (10).
My personal feeling on carbs/insulin/fat accumulation is that insulin is not so much a storage hormone as it is an energy "traffic cop". Net storage is but the byproduct of excess consumption.