Obesity rates have tripled since the 1980s, much faster than the rate of possible genetic changes in societies. This shows that there is an important environmental element in relation to obesity. But, we also have studies that show that identical twins tend to be more similar in body weight than non-identical twins. This shows that body weight has a genetic component. In addition, there is evidence that the influence of genetics may change with age. For example, in the case of intelligence, genes seem to be a stronger determinant of intelligence in adults than in children.
A new study has shown that this also applies to body weight. The researchers found that the extent to which the environment or genetics may influence obesity changes throughout life. According to the study, during childhood, genetics had little association with obesity rates, but this association increased with age (from adolescence to age 69).
A similar pattern was observed in relation to body weight and social background of people. People with deprived social backgrounds had higher weight from adolescence onwards. Although there was no significant difference in the weight of infants and children of people with different social backgrounds.
However, as people age, researchers also noticed differences in their weight that could not be explained by genetics or social background. This means that none of these factors are good predictors of a person’s body weight. The researchers used data from the UK Medical Research Council’s National Health and Development Study to conduct their study. In this study, a group of 5362 people were followed up from the time of birth in 1946 until today.
The researchers used this data to study the association between genes and social deprivation with body weight from age two to age 69. They study social deprivation because it is thought to be an important environmental risk factor for obesity and is likely to play a role in other forms of health inequality.
The researchers expressed a person’s genetic risk as a “polygenic score,” which is a summary of all the genes in a person that are associated with higher body weight. To define social background, they used participants’ social class at age four, which was determined by their father’s social class.
The researchers found that people with more genes associated with obesity were more overweight. Those who were in the top 25% of obesity risk were 11.2 kg heavier at the age of 63 than those in the bottom 25% of genetic risk. People who grew up in the most deprived homes were, on average, 7.4 kg heavier at age 63 than people from the most privileged backgrounds.
Although these are large differences in body weight, the results show that genetics and social background are not good predictors of whether a person will become obese in the future.
While the difference in weight increased significantly as participants aged, genetic risk predicted only 10% and social background only 4% of these differences. Therefore, there are still many issues with body weight that cannot be explained by genetics or social deprivation, and there are other factors that have an important impact on our body weight.
Prediction of body weight
It is important to note the limitations of the new study. The researchers focused on only one generation whose experiences are very different from other generations. For example, people born in 1946 experienced rationing in early childhood. Recent generations also have much higher levels of obesity (especially in childhood) than previous generations. It is interesting to see in future studies whether the results of the present study are repeated in recent generations.
The researchers also looked at only a portion of a person’s genetic risk and the most abundant genes associated with body weight. However, there are also rare genes that may have a large effect on body weight, so it is important to investigate these in future studies. Finally, measuring social exclusion is challenging. Wide differences in how social advantage and genetic risk are measured make it difficult to compare their effects on body weight.
We have no control over our genetics and the social background we are born into. However, these factors may still affect us almost 70 years after birth.
The fact that we may be affected by factors beyond our control can help us to think about why it is difficult for some people to lose weight or avoid gaining weight. These findings may also help us understand why obesity policies that typically rely on individual willpower have been less effective than changing the food environment.
New research also shows that genes and social background are not fateful. This thought can give us strength as we strive to maintain a healthy weight.
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