We often think that life is unfair when we see certain people consume a lot of food but still maintain lean figures. On the other hand, some people who limit their food intake are unable to lose excessive weight. Life becomes even more unfair.
Michael Cowley, director of Monash Obesity and Diabetes Institute (MODI), was quoted by ABC Science as saying that it was thought that between 60 and 70 per cent of our body weight is determined genetically, yet scientists are now unsure.
The explanation lies in the knowledge that the scarcity of food in our ancestors' time encouraged the evolution of the body's ability to store fat quickly and use the fat (cellular energy) very efficiently.
But now we are faced with plenty of food rich in fats and carbohydrates, and some of us seem to have the genes that haven't had time to evolve a response to the plentiful offer of food. So the cellular energy from the food eaten is stored quickly but only used efficiently, leaving excessive fats in store.
This food intake and genetic situation meets with the decrease of physical work that most of us have to do. Clothes washing, for example, used to take hard labour. But now all it takes is the push of a button.
"The result is that in our modern environment most of us stack on the kilograms," stressed Prof. Cowley.
It is true that how much we eat and the amount of physical activity we do determine our weight together with the genes. However, there are overweight people who eat less and exercise more but do not lose weight. Possibly, once again, they are genetically programmed to use energy more effectively.
Meanwhile, other people stay slim as their genes influence appetite, making them eat less and stop when they are full. The genes also allow less fat storage but more energy use, ensuring that they stay lean. "It's just luck of the draw," concluded Cowley, who later recommended healthy eating and regular exercise in spite of what the genes determine.
Prof. Lesley Campbell from the Garvan Institute of Medical Research in Sydney was also quoted by Fact Check as saying, "There is good evidence that between 40 and 70 per cent of a person's weight is inherited."
She went on to say that obesity had high heritability and was not a matter of choice or weak will, and that obesity did not always appear to cause medical consequences. In up to 30 per cent of people, obesity itself isn't a disease.
"One-third of people who are obese don't have metabolic problems, and it doesn't necessarily make you sick," said Prof. Campbell.
While obesity is also frequently linked to diabetes, scientists at Sydney's St. Vincent Hospital found in a 2012 study that a unique group of obese individuals exhibited better insulin sensitivity than expected for their body fat levels.
Once again, it's just luck of the draw.