Genes for Weight and Weight Gain are Different

We know from twin studies that measures of weight (e.g. BMI) tend to be highly heritable – i.e. monozygotic twins are far more likely to resemble each other in terms of weight than dizygotic twins.

We also know that the ability to gain (and lose) weight is very much determined by genetic factors – i.e. for the same degree of excess energy (or energy restriction), monozygotic twins tend to resemble each other in weight gain (or loss) more than dizygotic twins. For e.g. identical twins lose virtually the same amount of weight following obesity surgery, when surgery is performed in the same setting (Hagedorn et. al).

Given this relationship, one may easily assume that genes that control body weight are the same that control weight gain.

A new study by Jacob Hjelmborg from the University of Southern Denmark, Odense together with colleagues from Finland, Italy and the US, just published in OBESITY, suggest that this may not be the case.

Hjelmsberg and colleagues anlaysed data from the longitudinal twin study of the cohort of Finnish twins (N = 10,556 twin individuals) aged 20-46 years at baseline followed up for 15 years.

Simply stated, they found a high level of heritability of BMI levels at baseline (we knew this) and a relatively high heritability of weight gain over the observation period (this is also not new).

However, in their models, it turns out that the two phenomena only show rather modest correlation at the genetic level.

What this means is that while both baseline BMI and weight gain are genetically determined, they are probably each regulated by a different set of genes.

So, while one set of genes may determine how big you are, other genes may determine how large you can get.

We know that some people are large and just stay that way all their life without losing or gaining much. Others may start out at a given size and end up gaining a lot of weight. All depends on your genetic background (and of course how this interacts with your lifestyle and other environmental factors).

Just a reminder how complex genetics actually is.

AMS
Edmonton, Alberta