My argument is that if, as seems to be the case, calorie consumption has fallen over time, increases in body weight must be due to fewer calories being expended and, therefore, that a reduction in physical activity is the most likely culprit. I appreciate that there are people who believe that a calorie is not a calorie and that changes in the diet could therefore be the issue. I tend to side with the traditional consensus view that a calorie is, in fact, a calorie, but even I wasn't so inclined, it so happens that the consumption the ingredients that some claim are uniquely fattening (notably saturated fat and sucrose) have also declined, so that line of argument seems like a dead end.
Physical inactivity is not the sole explanation for why people are expending fewer calories than they used to. It has been argued that central heating means that people burn off less energy through keeping warm. The decline of smoking has probably also had some effect; smokers weigh several kilograms less than nonsmokers on average.
There may be other factors that have affected metabolism over time, but physical inactivity remains the main contender for why obesity has risen. All sorts of evidence can be given on this count, only a little of which was documented in The Fat Lie. For example, I read an interesting post by Tim Olds at The Conversation this week:
In 1919, a young woman named E.M. Bedale started postgraduate research at University College London, an uncommon undertaking for a woman at that time. Her studies focused on energy balance in children, which led her to spend several years at a serendipitously eponymous school called Bedales in rural Hampshire.
During her two years at Bedales, Miss Bedale measured the energy expenditure and intake of the school’s students, using methods that are still considered to be gold standards today.
Her data provide a startling contrast to our time. Children from almost 100 years ago were 50% more active than kids today. They accumulated over four hours more of physical activity and sat for three hours less than today’s kids - every day.
Too historical for you? Not 'evidence-based' enough? Then how about this?
Or this...
In the 1960s, half the jobs in private industry in the United States required at least moderate-intensity physical activity, compared to less than 20% today.
Work in factories and farms has given way to office work, and that has amounted to over 400 kilojoules less each day that adults expend at work. This difference alone results in a weight increase of about 13 kilograms over 50 years, which pretty closely matches actual changes in weight.
And in the home...
In many ways, the whole ethos of ease now saturates our society, and efficiency is the hallmark of modernity.
Think about it this way - nobody is in the market for a labour-creating device. Sit-on mowers, leaf blowers, self-opening doors and automatic car windows, robot vacuum cleaners, sensor lighting, dishwashers and microwaves all yield daily microsavings in energy expenditure that add up to hundreds of kilojoules.
In 1900, the average American housewife spent an estimated 40 hours every week in food preparation. Today, that time is barely four hours — and it appears to have reached an absolute minimum.
When it comes to physical activity in one's leisure time, some interesting research was published this year in the American Journal of Medicine. I mentioned it briefly in The Fat Lie but some of the statistics are shocking and require another look. The graphic below shows the proportion of Americans who engage in no leisure activity whatsoever. Click to engorge.
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Between 1988-94 and 2009-10, the proportion of men who did no leisure-time physical activity rose from 11.4% to 43.5%. Amongst women the rate rose from 19.1% to 51.7%. These are enormous changes in a relatively short period of time.
There's more to come but this blog post is long enough so I'll come back to it in the near future.
6 comments:
Hi Chris, thanks very much for taking up the question! Very compelling and convincing, as always.
I guess my worry is partly tactical. Does adopting a scientific position on the issue make you an unnecessarily large target?
On the other hand, public health advocates will attack the man whatever you say, so who cares!
Energy in, energy out. I still think this is a bit simplistic.
There's a system to stop you feeling hungry when you've eaten a bit more than enough. If you ignore that, (which clearly we often do), there is also a system to only extract the energy we need, (plus a practical amount to store as fat), and dump the rest undigested.
Storing too much as fat will slow you down, and puts you in danger from predators. Natural selection gave us a good regulatory system. What has gone wrong with it?
Zaphod
Interesting historical stuff, but the large amount of exercise equivalent to just one biscuit leaves me unconvinced. I still err on the side of diet and I am one who doesn't think all calories are the same with regard to fat deposition. You evidence for the decrease in fat as well as calorie consumption can't be argued with, so I'm perplexed. I'll modify my stance to the following.
Whatever may be causing your middle age spread, try for a couple of months cutting down on bread, potatoes, pasta, cakes and biscuits and, when you feel hungry, eat nuts, eggs, cheese, full fat milk and peanut butter. It might help.
In fact, it doesn't take much exercise at all to burn off a biscuit. One Bourbon biscuit is 67 calories. Walking the dog (three miles at 3mph) burns 255 calories, nearly four biscuits' worth. Since moving to the countryside and acquiring a dog, a horse and a garden, I eat a lot more than I used to, and have lost about 20 pounds. It's certainly the extra exercise that makes the difference.
It's an interesting subject.
My initial response is that it's down to genetics; some people have a propensity for being plump, others don't.
But that doesn't explain the indisputable rise in what they like to call 'obesity'. And really, I only have intimate knowledge of my own metabolism.
And we are, of course, all unique. So any study based on 'averages' is going to be wrong a helluva lot more than it's right.
I personally eat whatever takes my fancy. I've never thought about calorie intake or exercise. The work I do is fairly physical, but I don't 'exercise' at all. My weight has remained constant (apart from a couple of explainable blips) for the past 45 years. Why? I've known plenty of guys who had jobs far more physically demanding than mine who were fat. So I'm sure there's more to it than just diet and exercise. There must be a genetic aspect to it somewhere. Or perhaps are those genetic profiles evolving as society is changing?
I have no answers, only questions.
Hi Dr Plotka,
I thought a chocolate hobnob could put a dent in your argument but alas, at 77 cals, not a big one. However, I give you the Sainsbury luxury range all butter chocolate chip and hazelnut cookie - a whopping 132 cals, and all of them tasting incredible.
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