Spectator Health

The dodgy science behind the claim that exercise doesn’t help you lose weight

27 April 2015

2:00 PM

27 April 2015

2:00 PM

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.

Curiously, the authors’ poorly referenced, 1,000-word opinion piece became a national news story. The op-ed was (wrongly) described as a ‘scientific study’ by the Independent and the trio were (questionably) described as ‘international experts’ by the BBC. Indeed, the Beeb’s claim that ‘Physical activity has little role in tackling obesity – and instead public health messages should squarely focus on unhealthy eating, doctors say’ made it sound as if this was the consensus view of the medical profession rather than the eccentric opinion of three Atkins evangelists, one of whom is a lobbyist for a pressure group.


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.

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