Somebody sent me an email asking about what I think makes people fat. I think this is the post that prompted the email so I thought it appropriate to post my response here:
At a basic level dysfunctional mitochondria i.e. an inability to burn saturated fatty acids at rest and when active and an over-reliance of the metabolism on glucose especially when at rest. What is the primary driver of obesity that makes it easy to understand: insulin. Especially given the fact that T3 degrades insulin which increases beta-oxidation which increases the structuring of water in the cell. If you are rest and you feel hypoglycemic that is a precursor to an overall stress response. You have two choices, eat more sugar which will calm the stress response, but once blood glucose drops again you must do the same thing. For a while this works but two things at this point work against you, sugar transiently works against you by shutting down efficient respiration i.e. the Crabtree effect which in turn transiently shuts down mitochondrial function though either excess superoxide formation through Complex I of the mitochondria which in turn damages the mitochondria, and by reducing the mitochondrial density of the cells and hyperinsulinemia. The problem with this is that the mitochondria play a big part in maintaining the structure of the cell. The charges on the mitochondria have a structuring effect on the water of the cell i.e. structured water which maintains the integrity of the cell, disrupting this causes de-structuring of cellular water which in essence is negative consequence. Saturated fat is hydrophillic, the way the molecule is structured invites better structuring of water in 3 dimensional space whereas the structuring of water around polyunsaturated fats and sugars which are also hydrophillic but less so then saturated fat, is more chaotic. The ability of a energy substrate to de-structure water depends on how the atoms are grouped together in the molecule and how water structures around the molecule in 3 dimensional space. The structure of the energy substrate also determines how much interference the energy substrate causes to the rest of the cell. My opinion is that saturated fat causes the least de-structuring of water in the cell in 3 dimensional space. The other choice is to prefer saturated fat as the main energy substrate as the fluxes in hormones as well as the symptoms are caused disruption in beta-oxidation/OXPHOS. This is why thyroid hormone can be helpful it stimulates beta-oxidation/OXPHOS which helps to restructure cells and promote organization in the organism.
That is the long story.
The short story is elevated insulin either from a thyroid deficiency or chronic stimulation of insulin caused by diet. I think carbohydrates and polyunsaturated fats and excess protein are responsible for causing obesity. There is usually and interplay there of give and take but for simplicity I'll keep it to that.
For thoughts on protein consider this: http://edwardjedmonds.com/energy-and-structure-protein/