There is a debate about whether genetics or the environment is more to blame for being overweight or obese.
Since the 1980's, the rate of obese people has tripled. Our genetics could change, but this is much quicker than that.
Studies show that identical twins are more similar to non-identical twins in their body weight.
There is evidence that genetics can change as people get older. Genes are more powerful predictors of intelligence in adults than in children.
This is true of body weight as well. A person's environment or genetics may have an effect on whether they become obese.
As people got older, the study showed that genetics had a stronger correlation with weight gain.
The same pattern was found when it came to a person's weight and social background. From adolescence onwards, we found that people from disadvantaged background had a higher body mass index. There wasn't much difference in infancy or childhood.
We noticed that people's weight could not be explained by genetics or social background. Both of those factors are not good predictors of body weight.
We used the data from the National Survey of Health and Development. There was a sample of 5,362 people who were born in 1946.
We used the data to find out how genes and social disadvantage affect body weight. Social disadvantage is thought to be an important environmental risk factor for obese people and may contribute to other forms of health inequalities.
A Polygenic Score is a summary of all the genes a person has that are linked with higher body weight.
The participants' social class at four years old was used to capture the social background. The social background of the participants was categorized by their father's class on a scale from professional to unskilled.
We found that people with a lot of genes related to weight gain. At age 63, those in the top 25 percent of the genetic risk were more likely to be overweight than those in the bottom 25 percent.
By age 63, people from the most disadvantaged homes were 7.4 kilograms heavier than those from the most advantaged homes.
Genetics and social background are not good predictors of whether or not a person will become obese. The genetic risk only predicted 10 percent of the weight differences as participants got older.
This shows us that genetics and social disadvantage are not the only factors that affect our body weight.
We need to note the limitations of our work. The experiences of the one generation are very different from those of other generations.
People who were born in1946 would have been exposed to rationing. Most notably in childhood, more recent generations have higher levels of obese people. It will be interesting to see if the results of our study are the same in the future.
We only looked at the most common genes associated with body weight. It will be important for future research to investigate the effects of rare genes on a person's weight.
It's difficult to measure social disadvantage. It's not easy to compare the influence of social advantage and genetic risk on body weight.
We don't have a say over our genetics or social background. These factors may be affecting us when we are 70 years old.
Some people find it hard to lose weight or avoid gaining it due to factors outside their control. It may help us understand why policies to tackle obesity have relied on people's will power instead of making changes to the food environment.
Genetics and social background are not destiny according to our research. When we try to maintain a healthy body weight, this could help to empower us.
Neil Davies is a Senior Research Fellow at the University of Bristol and he is one of four people.
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