On Fat Balance

The role of dietary fat in adipose tissue metabolism

My latest musings on adiposity come courtesy of this paper. The authors try very hard in this paper to argue that polyunsaturated fats in the diet are "good" while saturated fats are "bad". However, if one reads past their bias, there are a few very interesting lines that caught my eye.

the rate of fat oxidation must be set largely by the gap between total energy expenditure and energy intake in the form of protein and carbohydrates, rather than by the amount of fat consumed on a given day.

This is as I was arguing before back in this post that ultimately, the rate of fat oxidation is determined by the absence of both Carbs and protein in the diet. The paper tries very hard to argue that the fate of dietary fats is almost always that of storage, but this runs counter-intuitive to the macroscopic affects observed when one consumes a diet of mostly lipid compared to mostly carb. It was known back in 1964 that a diet of mostly lipid produces greater fat loss than a diet of mostly carb.

Next, we move on to the idea that the composition of dietary fats strongly influences the composition of the lipid membrane present in fat cells. That is, a diet high saturated fats makes lipid membranes mostly saturated, and a diet high in polyunsaturated fats makes lipid membranes mostly unsaturated. The next quote was particularly interesting........

The amount of insulin bound and the translocation of GLUT4 transporter induced by this hormone increases with the content of polyunsaturated fatty acids in membrane phospholipids.

Whoa! This is big. What this is basically saying is that a diet high in polyunsaturated fats favors lipid membrane compositions that are more unsaturated and thus increases the insulin sensitivity of fat cells! Oppps! When I read this quote my brain was immediately backflashed to the video of urgelt talking about how farmers feed pigs polyunsaturated fats to "fatten" them up! There was also this very interesting post by that paleo guy about a very similar thing, i.e. feeding lots of polyunsaturated fats to animals increases obesity!

The message is clear to me, stay the fuck away from vegetable oils!

In a slightly divergent topic, I found this paper that ties together some theories of mine.

Higher fasting plasma concentrations of glucagon-like peptide 1 are associated with higher resting energy expenditure and fat oxidation rates in humans

This rather nicely ties together the ideas that a higher respiratory quotient ( i.e. high carb burning ) is positively associated with increases in fat gain, and also that a reduced incretin response to food is almost straight up causative of obesity. OK, so, glp-1 increases fat oxidation, meanwhile a high carb burning metabolism and rapid consumption of glycogen stores ( at rest ) results in hunger and fat gain.

The connection is this paper. To quote.......

Only GLP-1-(23), however, significantly increased the rate of glucose storage as glycogen

Bingo! So glp-1 increases glycogen synthesis, and probably also inhibits glycogen breakdown, under conditions of higher glp-1, glycogen stores are preserved and thus the metabolism runs on fat ( as it should! ).

Now it is slightly easier to understand why Carbohydrate balance predicts weight and fat gain in adults, My ( educated ) guess is that people with a higher carbohydrate balance have this BECAUSE their glp-1 is higher, and higher glp-1 encourages fat oxidation over carb oxidation and thus helps resist obesity.