Interesting question. In answer to your query, here are a few facts about childhood obesity:
1. Early onset obesity is defined as occurring before the age of 10 - ie you were severely obese in childhood before turning 10.
2. Your BMI has to be 3 standard deviations above the norm.
If there were 100 people that fell within this group, approximately 7 of them would have a genetic mutation in the form of a single point genetic mutation - in other words, 7% of childhood obesity can be directly attributable to your "bad genes".
What about the other 93%? Well, the majority of obesity is still due to a combination of:
1. Too much food intake
2. Lack of physical activity
How do we know that genetics has a role to play in obesity?
We know this as not everyone who grew up in urban or rural environments become obese, which suggests that genetics play a role as well.
Genetics in obesity
Recognized forms of obesity attributable to genes include:
- A deficiency of the leptin and melanocortin-4 receptors
- Mutations in the melanocortin-4 receptor gene
- People with 2 copies of the FTO gene (fat mass and obesity associated gene) have been found to weigh 3–4 kg more and have a 1.67-fold greater risk of obesity compared with those without the risk allele.
Finally, obesity is also a feature in a few rare and inherited syndromes such as:
- Prader–Willi syndrome
- Bardet–Biedl syndrome
- Cohen syndrome, and
- MOMO syndrome
