It seems like an obvious question to pose, but perhaps it’s not just bacon, as biologist and blogger Beth Skwarecki raised in a thought-provoking post on May 27, 2014. The post, entitled “Think you know why obesity rates are rising? You’re probably wrong”, pointed to this report, which debunked a bunch of common misconceptions about why people today are fatter than ever before.

Is a population’s obesity driven by a lack of exercise? More expensive food? Working longer hours than ever before? The answer to all of these is apparently no, which is probably unexpected for most of us. The report found that rising obesity rates in the US are actually correlated with a reduction in work hours, increased fruit and veg availability, and – the most amazing part – increased exercise.

What the report concludes from these findings is not that our health beliefs about the relationships between fruit and veg and exercise and obesity are totally irrelevant. Instead, it is trying to emphasise that understanding the role of the environment in the obesity epidemic is about looking at changes in time over entire groups of people more than changes between groups of people with different health behaviours. There have always been differences in weight determined by lifestyle differences among the population – but the current global data shows that everyone is gaining weight, not just people who eat too much bacon. So, we learn more about the obesity epidemic by looking at the factors that affect us all.

What are these factors, then? The (slightly cringe-inducing) No Time To Weight 2014 report by Obesity Australia clearly wishes to dispel the notion that obesity is a entirely a matter of personal accountability. Perhaps this focus is not surprising, given that the organisation’s stated mission is to ‘drive change in the public perceptions of obesity’. So, perhaps we should view their finding that ‘up to 90% of the population [is] predisposed genetically to being overweight and obese’ with a little skepticism, especially as this central tenet of their report is based on just one study (which I couldn’t track down) despite the fact that there is plenty of research in the area at the moment.[1]

The figure of 90% seems a little high – but perhaps the magnitude is irrelevant. What we want to know is if it’s a population-level change. Why would this genetic predisposition have changed since the 1980s, when the obesity epidemic began?

The answer might be found in epigenetics, an accelerating field of research that looks at environmental influences which can switch our genes on or off. It is becoming increasingly clear that a mother’s nutrition in pregnancy can promote metabolic disease in her children and even grandchildren. As the No Time To Weight report explains;

If a woman’s diet is too low in calories or protein, epigenetics set an unfavourable hunger and satiety balance in the offspring, causing them to experience accelerated weight gain. Conversely, if a woman is obese, diabetic, or consumes a diet too high in calories during pregnancy, the tendency towards obesity persists in the offspring.

No Time To Weight, Obesity Australia, 2014, p. 14.

Studies like this one have shown that healthy eating during pregnancy might be important in the prevention of long-term risk of obesity for up to two generations. So if mothers are overweight, their children and grandchildren have a higher chance of being overweight – it’s easy to see how obesity could then spiral down the generations. It is also apparent that undernutrition in pregnancy gives the baby a predisposition to being overweight – you just can’t win! It makes sense though – the baby is programmed to make up for lost time and gain weight, so hormones are regulated in a way that increases hunger and inhibits satiety – and these effects echo down two generations. If we consider the beginning of the obesity epidemic in OECD countries to be in the 1980s, looking back two generations takes us to 1930 – right in the middle of the Depression. Could we be facing the consequences of post-war food stress now?

The No Time To Weight report also emphasises that

Prevention is best done early (prior to conception, during pregnancy, or at the latest prior to a child’s third birth-day) so that epigenetic “set-points” for the regulation of appetite and fat mass are optimised.

No Time To Weight, Obesity Australia, 2014, p. 14.

At the latest, prior to a child’s third birthday? That’s earlier than I tend to think about obesity being a problem – but it fits within broader research indicating that the early few years of development have long-lasting consequences.

So, epigenetics may help explain why the relationship between lifestyle and obesity isn’t always as predictable as we expect – but it’s no reason to discard the logic of balancing energy intake with energy expenditure. Even the authors of NTTW – who are apparently on a mission to open our minds to non-lifestyle causes of obesity – note that early intervention must be coupled with a broader societal program for healthy food choices and opportunities for increased energy expenditure. Epigenetics apparently don’t give us a  free reign to eat whatever we like once we’re past the age of three and not pregnant.

We also shouldn’t forget about the intersections between poverty, race, and obesity, a crucial mediating layer between lifestyle and genetics. For any given genetic makeup and ethnic background, there are complex structural and psychological causes underlying people’s abilities and decisions about their lifestyle, and therefore health – a vast field of study barely touched upon in this article.

Perhaps the most important take-home message is that obesity is not just about lazy people who are more prone to the temptation of unhealthy food than the rest of us. Being obese is not a moral failing – and limiting ourselves to narrow conceptions of causation is not only a step away from the truth, it is unhelpful. We have to understand the aetiology of obesity in all its complexity to find a solution that can turn the tide of this epidemic.

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References

Leung J. No Time To Weight: Obesity, a National Epidemic and its Impact on Australia. Obesity Australia, 2014.

Slomko H, Heo HJ, FH E. Epigenetics of Obesity and Diabetes in Humans. Endocrinology. 2012;153(1025-1030).

Sturm R, An R. Obesity and economic environments. CA: A Cancer Journal for Clinicians. 2014;64(5):337-50.

Yura S, Fujii S. Obesity in offspring with maternal undernutrition during pregnancy. 0047-1852 (Print).

 

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