One of Twitter’s odder subcultures warns you of its obsessive presence with the hashtag #LCHF. It stands for ‘low carb, high fat’ and its followers have remarkably strong feelings about carbohydrates. Why? Mostly because they used to be fat and then they gave up carbs. They are no longer fat and so, QED, carbs are the cause of obesity and people shouldn’t worry about calories or physical activity. Silly old scientists won’t admit this profound but hidden truth because they have been bought off by Big Grain or Big Pharma or something, but who needs scientists when you have personal testimony?
This rebadged version of the Atkin’s Diet works for many people, at least in the short term, but the conclusions of some of its disciples are based on magical thinking, rather like a cargo cult. People lose weight when they cut out the carbs because they are cutting out a lot of calories. Carbs are easily accessible and energy-dense. That has been their selling point for thousands of years. In a typical meal, the meat provides the protein, the vegetables provide the vitamins and minerals, and the carbs provide the calories (plus fibre, protein, B vitamins and flavour). People in every society on Earth bulk out their meals with bread, potatoes, rice, pasta, noodles or whatever source of cheap carbohydrate is available to fill their stomachs and give them energy. If you cut these foods out of your diet or replace them with vegetables, there is a very good chance that you are going to lose weight.
A low carb diet is not an alternative to cutting down on calories. It is a way of cutting down on calories. It doesn’t guarantee weight loss because you could still gorge yourself on cheese and bacon, but it is so restrictive that you are likely to substitute lower calorie food in practice. In its purest form, it is a highly restrictive diet. A diet which forbade you from eating any food that begins with a letter between N and Z in the alphabet would have much the same effect.
The same magical thinking can be seen in the LCHF view of diabetes. It is well known that obesity increases the risk of developing Type 2 diabetes, perhaps by a factor of seven. In recent years, it has also become accepted that the disease is reversible in some patients through intense weight loss. Since a highly restrictive diet like LCHF can lead to rapid weight loss, there are low carb enthusiasts who have seen their diabetes go into remission. With a little cargo cult science, it is easy to come to the conclusion that a low carb lifestyle is the cure for Type 2 diabetes and, by association, that carbohydrates are the cause of Type 2 diabetes.
This is not the conclusion that mainstream scientists have come to. Rather boringly, they prefer the more obvious interpretation that obesity is a risk factor for Type 2 diabetes, that obesity is caused by excess calories, and that both obesity and diabetes can be addressed by creating a calorie deficit. This is not just their opinion. It is based on empirical evidence. For example, the Scientific Advisory Committee on Nutrition found no association between carbohydrate intake and body mass in its latest evidence review and, with regards to diabetes, it concluded…
No significant association was found between total carbohydrate intake as g/ day and incidence of type 2 diabetes mellitus (RR 0.96, 95% CI 0.86, 1.08 for each 70g/ day increase; p=0.5).
Now, I am as happy as the next man to believe that a scientific consensus can be wrong, but if it is a choice between trusting nutritional scientists on the one hand and a bunch of keyboard warriors and diet book salesmen on the other, I will go with the consensus.
You might also be expected to go with the consensus if you were a BBC executive commissioning a documentary about carbohydrates, especially if your programme was called ‘The Truth About Carbs’ rather than, say, ‘A Theory About Carbs’. But no. ‘The Truth About Carbs’, which was broadcast on BBC1 last week, was presented by Dr Xand van Tulleken, a medic who has written a diet book. He used to weigh 19 stone because, as he asserted it at the start of his programme, he loved eating carbs.
So began an hour of television which purported to show the benefits of a low carb diet but which actually showed the benefits of a reduced-calorie diet that is high in vegetables. First, van Tulleken split carbs into three categories of his own making: ‘beige carbs’ (pasta, rice, etc. which were portrayed as bad), ‘white carbs’ (refined sugar, which were portrayed as unspeakably bad), and ‘green carbs’ (fruit and veg, which were portrayed as being acceptable because they contain fibre).
He then tried to convince the viewer that beige carbs are really white carbs in disguise by having a dietitian explain how much energy is released into the human body by ingesting the likes of a jacket potato or a bowl of rice. The normal way of doing this would be to give the calorie count, but low carbers don’t believe in counting calories and so sugar cubes were used instead. Sugar cubes are often used to illustrate the amount of refined sugar that is added to fizzy drinks, but in this instance the sugar was neither refined nor added, nor even in the food. It was the amount of glucose produced naturally by the human body as part of the digestive process; a rather different proposition.
Members of the public were asked how many ‘sugar cubes’ were in various food products. The big reveal came when the dietitian explained that a jacket potato releases twice as much energy in the form of glucose as a chocolate muffin. ‘There’s 19 sugar cubes in this jacket potato,’ she declared, not entirely truthfully. A bowl of rice was shown to be even worse, with 20 quasi-sugar cubes. The effect on the members of the public was immediate and predictable. ‘It’s grains of sugar that we’re eating!’ said one. ‘I’m not eating rice no more,’ said another.
I don’t want to sound like a Reithian paternalist, but it seems irresponsible of the BBC to give its viewers the strong impression that a chocolate muffin is a healthier option than a bowl of rice. Aside from the other nutritional considerations, a chocolate muffin has at least 50 per cent more calories than a bowl of rice, and yet this went unmentioned by van Tulleken who concluded the segment by saying:
‘The thing that this really rams home for me is that there is a huge amount of energy in a potato, and that pile of glucose that your body will turn the potato into will be stored as fat unless you burn it off.’
There are about 250 calories in a jacket potato. Regardless of whether you consider this to be a ‘huge amount’ (it is only a tenth of an adult male’s recommended intake), energy from any type of food will be ‘stored as fat unless you burn it off’. This basic truth was never alluded to in The Truthiness About Carbs. How could it be? If van Tulleken had acknowledged the laws of thermodynamics he would have debunked his own programme.
The BBC’s intrepid truth-seeker then travelled north to visit Dr David Unwin who lives the low carb life and recommends his patients do likewise. Although the documentary offered no hint that Unwin was anything other than an ordinary family doctor, he is a controversial figure by his own admission. A low carb manifesto he co-authored in 2016 was widely criticised by scientists and was such an embarrassment to its publishers at the National Obesity Forum that its trustees issued a statement to ‘make it completely and transparently clear that they were not given the opportunity to see the document, or give any input into it’. Several of them resigned on principle. It would have been interesting to see Unwin respond to his critics. Instead, van Tulleken asked him softball questions like this:
Van Tulleken: ‘Is it fair to say that almost everyone in the UK is eating more carbs than they need and more carbs than is good for them?’
Unwin: ‘I think that’s probably fair.’
The less said about the rest of the programme, the better. Suffice to say that van Tulleken underwent a colonoscopy while interviewing a bowel cancer specialist and came away with the conclusion that low carb diets reduce bowel cancer risk despite the specialist saying nothing of the sort. He then got a chef to cook some redcued-calorie meals for a group of overweight people in Merseyside, telling him that their ‘lives depend on you seducing them with low carb food.’ Sure enough, after two weeks on a reduced calorie diet that was high in fruit and vegetables, they were healthier and had lost weight. Van Tulleken treated this as a near-miraculous demonstration of the dangers of carbohydrates. Eating well, he concluded, is about ‘counting the carbs, not the calories’.
Whatever public service broadcasting is, The Truth About Carbs was the opposite. Scientifically illiterate, wilfully misleading and ludicrously one-sided, it ensured that no matter how little the viewer knew about nutrition when they tuned in, they would know less about it by the time it was over.