Biological Pathway of Lipid Hypothesis?

Question

I've read a lot on both sides of the debate of low carb vs low fat diets trying to make some sense of what is being proposed. The lipid hypothesis runs roughly along the lines that we have lots of observational epidemiological evidence that eating a high fat diet correlates heart disease/obesity/enter disease of choice.An alternative hypothesis is that high carbohydrate diets cause these things. Since the studies haven't been done, there is not the correlation to point to. This hypothesis is believable (to some people) due to the well-understood biological pathway: Carbohydrates turn to glucose, which causes an insulin release, and insulin regulates fat storage, so high carbohydrate diets lead to weight gain (see a biochemsitry textbook for a more detailed explanation).My question is: Does the lipid hypothesis have any biological pathway for which there could be proposed a causal relation rather than just a correlation? Of all the speakers/writers on this topic, the low carb advocates always clearly describe the causal relation, whereas the low fat advocates never say *why* eating fat should cause weight gain.Note: I'm not interested in discussing the merits of the studies, but rather the proposed causal mechanism.

Answer 1

Hello there,

As far as your discussion on high fat diets correlating to heart disease, I believe that would be due to the high fat diet containing excess saturated fat. Saturated fat is much worse for your body, especially cardiovascular system (and increases LDL) than is unsaturated fat.

As far as your actual question goes: A low carb advocate would say that your body is producing less insulin and must rely on the glycogen stores in a starvation state.

After the glycogen stores are depleted, your body undergoes Beta Oxidation (the Beta carbon cleaved on a fatty acid) where it uses your fat stores for energy.

Per gram, fat contains far more energy than does a carbohydrate (9kcal vs 4kcal).