Saturday, 19 July 2014

*How* does insulin cause weight gain?

The question of exactly how insulin causes weight gain is not intuitively obvious enough and so it needed testing, and thats exactly what this paper did....

Adipose Weight Gain during Chronic Insulin Treatment of Mice Results from Changes in Lipid Storage without Affecting De Novo Synthesis of Palmitate

They infused mice throughout the day with mini-pumps containing extra insulin. This lasted for 7 days until the mice were sacrificed and their fat stores examined. All mice were put on a low fat chow diet.

First to note, is that there was a non-significant increase in food intake in the insulin treated mice, although there was a slight trend to the upside.

LI= low insulin group,  HI= high insulin group

Surprisingly they did not detect any increase in the de novo synthesis rate of palmitate in the insulin treated groups. So the lipogenesis pathway was essentially unaffected by the insulin treatment. This could have been because the palmitate de novo pathway was already running at maximum capacity, amoung other possible reasons they present in the discussion.

Second, the insulin treatment mice had a persistent decrease in their blood sugar levels, this may have been what caused them to eat *non-significantly* slightly more.

Did the insulin treated mice increase their fat stores? yes....

Only the increase in the high insulin group's fat stores was deemed statistically significant. The punchline however is that the newly formed fat in the high insulin group came almost exclusively from newly synthesized triglyceride ( subQ depot ).  There was a slight decrease in lipolysis as well which also contributed to the net fat gain.

 Our findings indicate that insulin treatment likely reduced whole body fat oxidation rather than increasing de novo fatty acid synthesis, and altered TG deposition and lipolytic rates in different depots, but the whole-body macronutrient energetics responsible for insulin-induced increased gain in weight and adipose fat remain to be fully explained.

So... there you have it. Atleast in this model. Insulin causes fat gain by diverting fatty acids that would otherwise have been oxidized for energy to instead be assembled as triglyceride and deposited into your adipose tissue.

The applicability of this to real life weight gain in humans is (probably ) not a straight forward translation,, but I think you can rest assured that, in situations of large amounts of insulin floating around, your likely to find excess triglyceride accumulating in your subcutaneous fat.

Is our food more insulinogenic now than it was 50 years ago? And is everyone carrying more triglyceride than we were 50 years ago?.....................