There’s been much talk in the media lately about processed foods and the perils of eating too much sugar, with some suggesting this is the cause of the current obesity crisis. The desire to identify the cause of weight gain is not a new one – in the 80s it was dietary fat that got all the blame. But in reality, the causes of weight gain are many and complex.
Obesity rates have risen sharply in recent decades, for which many blame the ‘obesogenic’ environment we live in. Processed foods – high in calories which tend to come mostly from sugar – are cheap and widely available, and there’s less need to be physically active, due to the automation of many jobs and the rise of screen-based entertainment. However, if that were the case, wouldn’t we all be overweight?
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What’s actually happened, though, is that the distribution of body weight has shifted. People have become heavier overall, but the change is greatest at the upper end: a much larger proportion of people now have ‘morbid’ obesity – a very high body mass index (BMI) that comes with a host of associated health problems. This suggests that if an obesogenic environment does exist, its main effect is to make people who were already predisposed to obesity become disproportionately heavier.
In 2007, the late Prof Jane Wardle proposed a behavioural susceptibility theory of obesity to explain how genetic and environmental factors interact and cause people to gain weight. She believed that genetically predetermined differences in appetite could play a key role in determining who gains weight. Individuals whose genes make them highly responsive to food cues are more likely to overeat when palatable food is readily available, and so will tend to eat more often. Those whose genes make them less responsive to feelings of ‘satiety’ or fullness are more likely to overeat in response to larger portion sizes, and so will tend to eat larger meals. These differences begin to have an effect on weight very early in life.
The differences in average food intake between people who are overweight and those who aren’t are quite small (less than 70 calories a day, according to some studies – about the same as a digestive biscuit), but just a small number of extra calories each day adds up over months and years. So rather than trying to pinpoint a single cause of obesity or identify a quick fix such as cutting out sugar, people may find it more useful to think more broadly about how they respond to food, and identify strategies to help take control of their eating.
This is an extract from issue 327 of BBC Focus magazine.
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