Still no evidence that the Swedes are killing themselves with low-carb diets

I’ve had a few emails this week about a study which appeared in the British Medical Journal last year [1]. In short, it purported to show that Swedish women eating a ‘low-carbohydrate, high-protein’ diet over a period of 16 years had greater risk of cardiovascular events such as heart attacks or stroke. I was well aware of the study at the time, but chose not to write about it because, as I explain below, I believe it really is a rubbish piece of ‘research’ which tells us essentially nothing about the impact of low carbohydrate diets on health. Also, it came on the back of another study based on the Swedes that was similarly useless. One reason for writing about the more recent study now is to make clear just how rubbish it is, seeing as I’m getting asked about it. Another reason for this post is to draw attention to the utter drivel that some doctors and commentators can talk, suppoesedly in the name of science.

Let me start by describing the study before I point out what I think some of the problems are with it.

In the early 1990s a large group of Swedish women were asked to fill out a diet questionnaire asking them to remember and log how often they had eaten specific foods. After eliminating some women with evidence of cardiovascular disease or who hadn’t filled out their questionnaire properly, about 43,000 women were then followed for 16 years and monitored for cardiovascular events such as heart attacks and strokes.

On the basis of their dietary logs, the researchers assigned the women a ‘low-carbohydrate, high-protein’ score. Here, women with the lowest amount of carbohydrate in their diets and the most protein ended up with a score of 20. Women with the most carbohydrate and the least protein ended up with a score of 2. Women with a score of 16 or above were found to be at 60 per cent increased risk of cardiovascular events than those with a score of 6 or less, which led to the conclusion that ‘low-carbohydrate, high-protein’ diets are bad news. End of.

OK, here, in no particular order, are what I see as the main problems with this study:

1. It’s epidemiological

This means it looks at the association between two things (diet and cardiovascular disease). But just because two things are associated with each other, does not mean one is causing the other. This study, and the way it was reported, inferred that low-carb, high-protein diets cause cardiovascular disease, and this sort of study just can’t support that sort of conclusion at all.

2. The study used dietary recall
Do you remember what everything you ate and drank a week ago today? Most people struggle withw this sort of thing. Just imagine, now, trying to give an accurate representation of what you’ve eaten over the last 6 months. Can you see some room for inaccuracy?

Also, I don’t want to come over unduly cynical, but there’s a tendency (unconsciously or consciously) for people to under-report their consumption of foods perceived as unhealthy, and over-report their consumption of food with healthy reputations.

Oh, and the women’s diets were assessed only once during the 16-year period of the study, because we all know people never change their diets over time, right? Again, here we see enormous potential for the dietary logs not to reflect what the women actually ate.

3. The ‘low-carbohydrate’ women weren’t very ‘low-carbohydrate’ at all
Women with the highest low-carbohydrate score were, according to their dietary logs were consuming up to about 125 g of carbohydrate a day. In reality, the low-carbohydrate diets that are the whipping boys of just this sort of study often allow less than 50 grams of carbohydrate a day. In other words, this study was not able to determine the effect of genuinely low-carbohydrate diets.

Very rarely is a piece of science perfect and beyond criticism, but the failings of this study make it almost not worth the paper it’s written on. Yet, this week has seen me getting a steady stream of emails about it. Why?

Well, it turns out that this study was specifically cited in a piece run by the Guardian newspaper, in which several doctors were asked what things they wouldn’t do. You can read this piece here.

Here, you’ll find Dr Tom Smith writing the following advice to us all:

I would never go on a low-carbohydrate, high-protein diet like Atkins, Dukan or Cambridge. Why? Because although you will probably lose weight, they may kill you. Don’t take my word for it – read about the 43,396 Swedish women followed for an average of 15 years. Those who stuck to low carbs and high protein had a rising risk of dying from heart attacks and strokes, depending on how strict they were and for how long they endured them. There was a staggering 62% higher risk of such illnesses among the women eating the strictest diet over those who ate normally. Eating is for enjoyment; these diets turn food into medication, and it’s patently the wrong medicine – it is often lethal.

Notice here how Dr Tom shows no apparent appreciation of the manifold deficiencies of this study and the likely errors in it. Notice also how he seems to fail to appreciate the inability of epidemiological evidence to determine cause and effect. Notice also how Dr Tom appears to conclude causality when it is simply incorrect to do so.

But should we be too surprised? Well, my experience tells me that while we may rely doctors for our scientific and rational minds (and some of us pride ourselves on having such things), the reality is some of us have a tenuous grasp of scientific principles and methodology. But another reason for us not being too surprised is that Dr Tom has form in this area.

Last year, I wrote about him specifically because I’d heard similar utter nonsense spout from his mouth at a scientific meeting. You can read about this here. In short, he lauded quite useless epidemiological evidence again in his ‘theories’ about Alzheimer’s disease. I wonder if Dr Smith is aware that a major theory regarding the development of dementia concerns what is being termed ‘type 3 diabetes’ which, in all likelihood, is driven by the over-consumption of carbohydrate. I’m wondering also if Dr Smith might personally (and professionally) benefit from cutting back on carbs for the sake of his mental faculties.

References:

1. Lagiou P, et al. Low-carbohydrate-high protein diet and incidence of cardiovascular diseases in Swedish women: prospective cohort study. BMJ 2012;344:e4026

8 Responses to Still no evidence that the Swedes are killing themselves with low-carb diets

  1. Modesty 26 January 2013 at 8:27 pm #

    Of course not, they’re slowly but surely getting healthier. But the governmental advisory bodies etc are getting worried, being afraid that they’ve been wrong all the way. Being a Swede living in England I’m following the lchf movement and pleased to see that they are moving their goalposts steadely forward. Just wish more Brits would become more aware.

  2. Margaret Buhagiar 26 January 2013 at 8:29 pm #

    I love your last sentence !!! I must say that i have been no carb ,no grain diet just fresh meat fresh eggs fresh chicken and very very fresh vegetables as my husband is a crop farmer and I have not lost and ounce for the last 4 weeks !! Hurray !!!!

  3. Dr. Bill Wilson 26 January 2013 at 8:46 pm #

    I am not familiar with Dr. Tom Smith so I looked up some of his medical advice that he has published in his column. An otherwise healthy young woman with PMS on an SSRI wrote in complaining that she was tired all the time and was gaining a lot of weight.

    He didn’t think that had anything to do with the SSRI and suggested that she go to her physician for a complete medical workup. Although one could argue that this is good advice, I disagree with his approach.

    Fatigue and weight gain are very common side effects of SSRI medications, so the first thing I would recommend is to stop the medication. Yet I wouldn’t leave her high and dry with her PMS. In my experience, avoiding excessive fructose mainly from sugar and HFCS and high glycemic carbohydrates mainly from grains is a very effective treatment for PMS. Patients with PMS typically crave sweet and starchy foods and we now know such cravings are an early symptom of a type of food-induced brain dysfunction called Carbohydrate Associated Reversible Brain syndrome or CARB syndrome. Because of these cravings women with PMS end up eating more of the very food that is frying their brain.

    I have found the amino acid L-glutamine to be a very effective and safe way to reduce such cravings. To me it makes a lot more sense to stop a drug with potentially serious side effects and to initiate safe dietary changes and supplements before putting an otherwise healthy young lady through a big medical workup. So I do agree with you—I am not impressed with Dr. Tom Smith’s medical advice.

  4. Chloe 26 January 2013 at 9:41 pm #

    Great! A friend of mine who I am trying to ‘convert’ to low carb living sent me this study last week. I’ll get her to read this now! :-)

  5. Diane Smith 26 January 2013 at 10:38 pm #

    Strangely, the same Guardian newspaper, also ran this article by Dr Aseem Malhotra, who states that the evidence shows that it is sugar, not fat, that is causing heart disease and obesity. No wonder people are confused! Perhaps Dr Smith should read this!
    http://www.guardian.co.uk/commentisfree/2013/jan/24/defence-of-sugar-confection-scientists

  6. Pat Jones 27 January 2013 at 7:57 pm #

    I know this is unrelated but I have a dear friend who had a mini stroke before Christmas and is on Amlodipine which seems to be causing her problems. Can you give any advice on this or suggest an alternative drug please.

  7. Lorraine 29 January 2013 at 8:05 pm #

    Quote from an article in The Atlantic:
    “But let’s face it — most of us know in our hearts that eschewing a breakfast of whole grains and fruit crowned with a dab of yogurt for a greasy pile of sausage, bacon, and eggs is not the road to health”

    I also read that the researchers did state in their paper that their study does not explain a causal relationship between the increased fat intake since 2004 and the increased cholesterol values after 2007. This wasn’t highlighted in the media.

  8. Vic Shayne, PhD 2 February 2013 at 2:17 am #

    You describe a case of post hoc ergo propter hoc — that is, the faulty logic that just because something exists it is the cause of something. So-called “scientific” findings are fraught with this error in thinking. Unfortunately, the medical field is filled with such assumptions. They are quick to attribute illnesses and symptoms to causes without having any proof. It’s a sad system.

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