Sunday, April 10, 2016

It's a bit more complicated than that - fat and sugar

Ian Leslie has written an interesting long read for the Guardian: "The Sugar Conspiracy".

It's a good illustration of how science works. Science is a great idea and, I would argue, the best thing we have for finding out if something is true or not. I like Jerry Coyne's definition of science, broadly construed: "as the use of reason, empirical observation, doubt, and testing as a way of acquiring knowledge." Unfortunately, like many great ideas, it's carried out by fallible humans, and so whilst in principle, and practice, science has given us great leaps forward, that progress is often constrained by the personalities and foibles of those involved in the debate at the time. Max Planck's remark neatly sums this up: “A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.” Leslie, referencing that same remark (and showing empirical support for it), shows how nutritional advice has followed this pattern. (To see another illustration of this in practice, you should read the excellent Big Bang by Simon Singh).

However, I have a few problems with the article:

The first is that it talks favourably about the Atkins diet, deriding those who questioned it. However, the Atkins diet is a fad diet, and not a very good one.

For starters, Leslie rightly says "Controlled trials have repeatedly failed to show that people lose weight on low-fat or low-calorie diets, over the long-term.". The problem is, the Atkins diet is also a low calorie diet.

The Atkins diet advocates high fat and protein, and virtually no carbohydrates. The diet results in people eating food that leaves them feeling full for longer. Consequently, they have a reduced calorie diet because they don't eat as many calories. Whilst patients may lose weight on the Atkins diet, the diet is not risk free - for example it may lead to damage to tissue and vascular damage, and could lead to life threatening complications.

The article also seemed a bit disingenuous to claim "Only in the last few years has it become acceptable to study the effects of Atkins-type diets." Atkins first book may have been published in 1972, but it was the 2002 book "Dr. Atkins' New Diet Revolution" that really saw the Atkins diet take off (see the Google ngram graph). It didn't take long for the scientific community to look at the efficacy and safety of low-carb diets, see "Atkins and other low-carbohydrate diets: hoax or an effective tool for weight loss?" from The Lancet in 2004 and "Safety of low-carbohydrate diets" from 2005. These are both over a decade old - does that qualify as the "last few years"?

The Atkins diet also restricts intake of fruit and vegetables - diets high in fruit and veg lower the chances of a number of diseases.

On top of that, ideally the goal of a weight loss programme should be for the weight to stay off. A recent (albeit small) study showed the Atkins diet was no more effective than other weight loss programmes, but that after the 6 month trial, the 12 month follow up showed that weight had been put back on.

My second issue with the article is that it leaves one with the impression that fats are okay, and sugar is bad, and that reducing sugar is the key to resolving the obesity epidemic (and there is an epidemic - some people will try and tell you that there isn't one, but it has become harder to deny when there are more obese people than underweight people in the world) - but it's much more complicated than that. Cutting out carbohydrates is will not give a healthy, balanced diet, after all carbohydrates are the bodies preferred energy source - in fact the NHS Eat Well guide is a very good way of thinking about how much, and of what, you should be eating. However, following a diet plan can be useful, and there is also a guide on the pros and cons of a number of diets out there on the market. Indeed cutting out carbohydrates will result in less fruit and veg being consumed - something Robert Lustig does not recommend.

This leads to another grumble - Leslie should have distinguished between refined carbohydrates ("sugar") and complex carbohydrates, like starch. The article is about the refined carbs - what people put in their tea, and yet when advocating low carb diets, this can include cutting out complex carbohydrates as well. It's a distinction that should have been made.

Lastly, Taubes is lauded for his book, but he is not without his critics - some of those criticisms are the same that Leslie is making: conclusions being made with insufficient evidence, which Taubes is also guilty of when he concludes that low carb diets are the key.

Diet is not the only factor when it comes to weight management. It is emerging that the microbiome of the gut may play a part, and of course, the other important factor absent is levels of exercise. The article makes it look like cutting out carbs will solve obesity, but his isn't the case.

Whilst there are lots of factors involved in a person's weight, achieving or maintaining a healthy weight isn't complicated. You must expend more calories than you take in to lose weight. It's simple physics - whilst people may lose weight at a different rate, the body gets its energy from the food that is eaten. If more of that energy is being used than is being taken in, then weight will reduce. As Michael Pollen said "Eat food. Not too much. Mostly plants". I would add - move yourself often.

The problem though is not informing people of these things, it's actually changing people's behaviour (see page 13 of this link) so that the information is taken on board - but if the information provided is misleading, as I feel that Ian Leslie's article is, then that won't help in that regard.

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