Part One
You may have heard the news that the nation’s doctors have had a change of heart about physical activity and no longer believe it to be a sensible way of staying slim. Don’t be too quick to put your feet up. All is not as it seems.
The doctors responsible (or, arguably, irresponsible) for this claim are Aseem Malhotra, Tim Noakes, and Stephen Phinney. Malhotra is a Croydon-based cardiologist who rose without trace several years ago, first attacking junk food and then climbing aboard the anti-sugar bandwagon. Now the scientific director of the wacky pressure group Action on Sugar, he explicitly tells people to eat more saturated fat and implicitly tells people not to bother exercising – unusual advice from someone who looks after people’s hearts for a living. Last year, he wrote an article for the British Medical Journal which was investigated and corrected after it made insupportable claims about the safety of statins. It turned out that Malhotra had brushed aside concerns raised by one of the peer reviewers. His Action on Sugar briefing papers have also contained very questionable assertions.
Malhotra’s co-author, Tim Noakes, is a South African paleolithic diet advocate currently promoting a new diet book. He disputes the evidence that high cholesterol is a risk factor for heart disease and is currently being investigated by the Health Professions Council of South Africa for ‘disgraceful conduct on social media’ after telling a mother on Twitter to wean her infant on to a low-carb diet. (Noakes appears to be taking this in his stride.) Stephen Phinney, the other co-author, is a scientific advisory board member of Atkins – as in the Atkins Diet – and has written several books extolling the low-carb way of life.
They are not, in short, typical doctors. Together they wrote a short editorial for the niche British Journal of Sports Medicine, in which they made the striking and unambiguous claim that ‘physical activity does not promote weight loss’. They then praised the alleged virtues of fat and called for legislation to clamp down on carbohydrates, especially sugar.
The idea that burning off calories does not help prevent weight gain
is idiosyncratic to say the least, but the media haven’t misrepresented
them. That is what they say in their article and there is no reason to
think they don’t believe it. Malhotra has previously boasted of having convinced
the Minister for Public Health that ‘physical inactivity is not linked
to obesity’. Their evidence for this claim seems to boil down to the
fact that obesity has risen in recent decades despite levels of physical
activity remaining the same. Therefore obesity must have risen because
people are eating more calories.
The trouble is, it is not a fact. As Public Health England
noted in a major report last year, ‘People in the UK today are 24 per
cent less active than in 1961’. British Heart Foundation figures show
that British adults are walking less (from 255 miles per year in 1976 to 181 miles in 2012) and the proportion of British children who walk to school has dropped from 70 per cent in 1980 to less than 50 per cent today.
At work, we are less physically active than ever. Jobs in agriculture
declined from 11 per cent to two per cent of employment in the
20th century while manufacturing jobs declined from 28 to 14 per cent.
Less than one in five adults report doing any moderate or vigorous
physical activity at work. Outside of work, 53 per cent of us take part in no sports or exercise at all.
You don’t need to be a social historian to see that Britons are
leading increasingly sedentary lifestyles. Only a minority of households
owned a car in 1965. Today, only a quarter do not. In Britain, as in
all western countries, there have been what the World Health Organisation
describes as ‘decreased physical activity levels due to the
increasingly sedentary nature of many forms of recreation time, changing
modes of transportation, and increasing urbanisation’.
If Malhotra et al’s theory seems counter-intuitive it is for the
simple reason that it doesn’t stand up. They provide no new research in
their ‘study’ and only cite one article
in support of their claim about physical activity. That, too, is an
opinion piece from the fringes of the scientific debate and has been widely criticised. The phrase ‘overwhelming evidence’ can be overused, but it can certainly be applied to the countless studies
showing that physical activity helps prevent weight gain – and to the
data showing that rich westerners burn fewer calories than their
grandparents.
Why claim something that can so easily be challenged by reference to
laboratory, animal and observational trials? Why fly in the face of
empirical evidence and lived experience?
The answer, I think, lies in political pragmatism. Governments are
not yet ready to pass laws forcing people to exercise, so it makes sense
for the likes of Action on Sugar to focus on the food supply where
regulation is more likely. A soda tax is more realistic than a sofa tax.
If politicians view obesity as a cultural symptom of greater wealth and
structural changes in the labour market, they will be less likely to
support taxes, advertising bans, graphic warnings and all the other
interventionist policies that you would expect from a campaign group
which claims that ‘sugar is the new tobacco’.
This, admittedly, requires a certain amount of self-delusion, since
the cold facts show that physical activity is not the only thing that
has declined since 1980 – sugar consumption has too.
But what are activists to do? Bore people with all of the science?
Leave them alone? Of course not. Better to trust the media to be
suitably deferential to them on account of their PhDs. The media did not
let them down last week. The closest Malhotra came to being challenged
was when the National Institute for Clinical Excellence said that an
obesity strategy that ignored physical activity would be ‘idiotic’.
The multi-million-pound diet industry is, largely if not wholly,
based on the conceit that there is more to weight loss than calories in
and calories out. Supposed diet gurus will be ignored by right-thinking
people, but the line between these people and the medical establishment
is becoming increasingly blurred.
It’s difficult to say which is more depressing – three medics making a
highly doubtful claim which, if acted upon, would probably harm
people’s health, or the media taking a one-page editorial from an
obscure journal and reporting it as news. Since most people don’t take
health reporting too seriously, the damage to the public is likely to be
negligible. It is more likely to be a blow to the reputation of the
‘public health’ lobby, but given the say-anything, do-anything mentality
of some self-styled public health experts, it is a blow that is well
deserved.
Part Two
Last week I mentioned a widely reported article in the British Journal of Sports Medicine which claimed that ‘physical activity does not promote weight loss’. The article
was taken down by the journal last week due to ‘an expression of
concern’. It remains offline as I write this, but the controversy
rumbles on. At the risk of further upsetting the low-carb community (who
seem particularly antagonistic to the doctrine of ‘calories in,
calories out’), I am returning to it today.
Let’s start by looking at a series of blog posts
by Jason Fung of Intensive Diet Management that have been doing the
rounds on social media. He, too, argues that ‘there is no measurable
association between obesity and physical activity’. In his first post,
he argues that people are exercising more than ever and yet are becoming
fatter and fatter. The positive correlation between obesity and
exercise, he says, shows that physical activity really doesn’t make much
of a difference.
I once met somebody who wondered whether artificial sweeteners caused
obesity, based on the fact that their use had risen more or less in
line with obesity rates in recent decades. It seems pretty obvious that
this is a case of reverse causation. Artificial sweeteners are a
response to obesity, not a cause of obesity, just as the rise of jogging
and gym membership is a response, not a cause.
To be fair, Fung is not claiming that exercise causes
obesity, only that it is not a solution. He cites figures showing that
Brits are exercising more than they used to – or, more precisely (and
this is crucial), that more Brits are exercising than they used to.
Forty-two per cent of British men met the government’s physical activity
recommendations in 2008, up from 32 per cent in 1997. At the same time,
the male obesity rate rose from 17 per cent to 24 per cent.
But, leaving aside the question of whether people accurately report
how much they exercise, why would we expect the minority who exercise to
have an effect on the majority who don’t? There is nothing incongruous
about obesity rising even if one in ten men are exercising more than
they used to. Moreover, there is a conflation between physical activity
and leisure-time exercise that is often made by those who downplay the
benefits of physical activity.
Office jobs, computers, cars and gadgets have created a more
sedentary society which requires fewer calories to be burned. People can
offset their less active working and domestic environments by eating
fewer calories or burning more calories in their leisure time, but not
everybody does. Hence the rise in obesity in recent decades. It cannot
be assumed that those who engage in leisure-time exercise are more
physically active than previous generations, and it certainly cannot be
assumed that the leisure-time exercise of a minority makes the sedentary
majority less likely to become obese.
The evidence is quite clear that, on average, calorie expenditure has declined over the years in developed countries. Public Health England
(who say that the ‘link between physical inactivity and obesity is well
established’) report that ‘People in the UK today are 24% less active
than in 1961’. The World Health Organisation
has remarked on the ‘trend towards decreased physical activity levels
due to the increasingly sedentary nature of many forms of recreation
time, changing modes of transportation, and increasing urbanization.’ Harvard School of Public Health
says that ‘Physical activity levels are declining’ and that ‘this
decline in physical activity is a key contributor to the global obesity
epidemic’.
Even this demonstrable fact is disputed by the revisionists. Fung
cites a study of hunter-gatherers as evidence that modern man burns the
same number of calories as our ancestors. There are a number of problems
with this interpretation (see here for a few) and other studies of hunter-gatherers
have found significantly higher energy expenditure, but it is not
necessary to speculate about prehistoric man for us to see that calorie
consumption has fallen over time.
In his 1946 essay, The Politics of Starvation,
George Orwell noted that the average Briton was eating ‘about 2,800 or
2,900 calories a day’ despite rationing and a shortage of food that was
on the verge of leading to civil unrest. This would be enough to fatten
up most Britons today, which is why we are advised to eat just 2,000-2,500 calories a day.
This was not journalistic licence on Orwell’s part. Two years later, the British Medical Journal published a study
which found that the average Briton lost weight if he consumed fewer
than 2,900 calories. Unless you believe that human metabolism has
evolved dramatically in the last 70 years, the only explanation for our
grandparents eating more yet staying slimmer is that they burned more
energy in their daily lives.
Few people joined a gym in the 1940s. They didn’t need to. Today,
there are lots of gyms and lots of obese people, but this is not proof
that physical activity is useless in preventing weight gain. Asking
whether leisure-time exercise leads to weight loss is a much narrower
question than asking whether physical activity is linked to obesity, but
to answer it we need to look at the people who are exercising, not at
the whole (largely sedentary) population. In the next post, we will do
just that.
Part Three
Now let’s look at the effect of exercise on individuals. Fung – who
coined the term ‘Calorie Reducation as Primary’, or CRaP, to describe
‘current obesity thinking’ – is unequivocal. In a series of blog
posts entitled ‘The Myth about about Exercise’, he writes: ‘There are many benefits to regular exercise. Weight loss, though, is not one of the benefits‘ (italics in the original).
He cites three studies which found that burning off a certain number
of calories did not result in a commensurate loss of body weight. He
rightly attributes this to a degree of compensatory eating. In other
words, exercise creates appetite which can lead to more calories being
consumed.
But, in making this point, he downplays the conclusions of the
studies themselves, all of which also make it clear that the
participants who exercised lost a significant amount of weight.
The first of these studies concluded that ‘physical activity expressed as energy expended per week is positively related to reductions in total adiposity’. The second found
that people who exercised most intensively did not lose more weight
than people who trained less intensively, but the crucial fact remains
that all the subjects who trained lost more weight than those who
didn’t. All exercise groups had a significant reduction in waist
circumference. Similarly, the third study concluded that ‘supervised exercise, with equivalent energy expenditure, results in clinically significant weight loss’.
By the time he gets to his third ‘Myth of Exercise’ post,
Fung has almost given up on his claim that ‘there is no measurable
association between obesity and physical activity’ and is instead
arguing that exercise is merely less effective than dietary change.
He cites a 2007 study
involving people who exercised for around 45 minutes a day. After a
year, their body mass index (BMI) had dropped by 0.5 and 0.6 (for men
and women respectively) while the BMI of the control group either rose
or stayed the same. Moreover, those who exercised the most lost the most
weight.
Fung views this amount of weight loss as trivial, saying: ‘Colour me
unimpressed. Exercise is just not that effective for weight loss.’
That’s a matter of opinion, but it’s rather different to claiming that
weight loss is not one of the benefits of exercise.
Endless chub rub (chafing between the inner thighs). Miles upon miles on the dreadmill. But so worth it, right? Average body fat loss for men … 5 pounds. Average weight loss for women … zero.
What Fung doesn’t mention is that this study was not aimed at achieving weight loss and there is no evidence that the participants wanted or needed to lose weight.
The men had a healthy average BMI of 23.4 before they started training and the women were a slender 21.1. Both groups consumed significantly more calories while training, mainly from carbohydrates, and both groups actually did lose weight. The men lost an average of 2.7 kg and the women lost 0.9 kg, though the latter was not statistically significant. Both groups also lost fat as a percentage of body weight (from 16.6 to 13.4 per cent for men and from 24.9 to 23.6 per cent for women) although there were were too few participants for these results to reach statistical significance.
The literature on physical activity is very large and Fung is entitled to select any part of it to make his case, but if these studies debunk the claim that exercise helps people lose weight then you can only wonder what the rest of the literature says.
Unsurprisingly, other studies make the case for physical activity even more convincingly. Listing a few in chronological order:
• A randomised control trial published in 2000 found that ‘weight loss induced by increased daily physical activity without caloric restriction substantially reduces obesity’.
• A 2003 study from the US found that ‘moderate-intensity exercise sustained for 16 months is effective for weight management in young adults.’
• A 2004 study of overweight women from Singapore found that an eight-week exercise programme ‘significantly reduced body weight, body mass index, percentage body fat and waist circumference’.
• A 2005 review concluded that ‘Regular exercise can markedly reduce body weight and fat mass without dietary caloric restriction in overweight individuals.’
• A 2009 study of middle-aged women found that ‘body mass, body composition, waist circumference, and high-density lipoprotein cholesterol changed favorably’ after a 30 minute, five days a week exercise routine.
• A 2009 study of younger women found that physical activity was ‘associated with a reduction in long-term weight gain, and greater duration is associated with less weight gain’. Moreover, it found that ‘sedentary behavior independently predicted weight gain.’
• A 2012 study found that a moderate-intensity exercise programme reduced BMI by 2.4 per cent amongst post-menopausal women, rising to 10.8 per cent if combined with a reduced calorie, low-fat diet.
• A 2013 study from the US concluded that ‘supervised exercise, with equivalent energy expenditure, results in clinically significant weight loss’.
I could cite many more studies (and have before) but there is no point in labouring a point that should be obvious: if you burn off calories they cannot turn into body fat.
The simple, unavoidable fact of human physiology is that you can’t lose weight without creating a calorie deficit. Whether you do this by eating less, moving more or a combination of the two is a matter of preference. Some people may find it too difficult to change their diet while others may find it too difficult, or too time consuming, to start exercising. Some find it easy to cut out alcohol or sugar, while others find it easier to play more sport.
Since nobody denies that physical activity has health benefits that extend beyond weight management, it could be argued that a calorie burned is better than a calorie foregone, but the crucial thing is to eat fewer calories than you burn. If your preference is for radical dietary change then by all means make your case – but don’t let your interest in ‘calories in’ blind you to the importance of ‘calories out’.
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