Over the last few years there has been something of a diet revolution going on in Sweden. It appears that increasing numbers of Swedes are eschewing the conventional advice to eat a low fat, high carbohydrate diet, and instead are opting for something altogether lower in carb and higher in fat – the so-called ‘low-carb/high-fat (LCHF) diet. Interest in this way of eating was particularly sparked by Dr Annika Dahlqvist, and more recently has been championed by Dr Andreas Eenfeldt over at dietdoctor.com.
So significant has this shift been, that it’s reported that about a quarter of Swedes have given LCHF a go, and the country has suffered from something of a butter shortage lately.
However, not everyone is happy about this dietary trend. Just this week saw the publication of a study in Nutrition Journal which laments it [1]. The study, conducted by Swedish researchers, assessed trends in food consumption in the north of Sweden, along with weight and cholesterol levels, from 1986 to 2010.
First of all, though, let’s be clear on two things:
1. The data regarding dietary intake was self-reported – something which is known to be fraught with inaccuracy.
2. The data is epidemiological in nature, which means it can never tell us anything more that the associations between things, and certainly not that one thing is causing another.
Anyway, the researchers point our attention to the fact that fat intakes fell from 1986-1992. At this time, by the way, and through the study period as a whole, average weight was climbing. So what does that say, on the face of it, for the effectiveness of low-fat eating for weight control?
But then fat intakes started to rise in 2002 for women and 2004 for men. The concern that comes loud and clear in the paper is that this was paralleled by a rise in cholesterol levels which the authors describe as a ‘deep concern’. However, by their own admission, cholesterol levels didn’t start to climb until 2007. The inference is that increased fat intake led to the rise in cholesterol. But are we really expected to believe that it took 3-5 years for cholesterol to rise in response to an increase in saturated fat intake? That doesn’t seem quite right to me.
Also, while overall fat and saturated fat were increasing, other changes in the diet were occuring too. For example, the Swedes drank progressively more wine, and ate more rice and pasta too. But there is no mention in the study that there is a possibility that these foodstuffs might contribute to changes in cholesterol levels (or weight).
Another problem is that this sort of study is based on averages from a population. We cannot tell, therefore, what’s happening on an individual level. Is it possible, for instance, that those who adopted a LCHF diet lost weight while those who did not gained, overall? We’ll never know. Even if we did, it would not matter much seeing as, as we discussed before, this was a big old epidemiological study anyway, which will really never enlighten us about anything much at all.
And why does any rise in cholesterol matter anyway? Well, in the minds of the researchers, raised cholesterol will inevitably translate into an increased risk of cardiovascular disease.
The authors also cite this evidence:
Evaluations of 14 randomized trials of statins have concluded that a reduction of LDL cholesterol by 1 mmol/L leads to a 12% reduction in all-cause mortality and a 19% reduction in CHD mortality [2]. The suggestion here, if cholesterol-lowering is good, raised cholesterol must be bad.
There’s a couple of problems with this thinking, though. First of all, the study they quote was based on data obtained from studies of cholesterol-lowering drugs (statins). Lowering cholesterol with drugs is not the same as lowering it through diet, and one cannot extrapolate from one to the other.
Secondly, there’s a very good chance, in my opinion, that statins don’t even work through cholesterol reduction. For example, they reduce the risk of stroke, even though cholesterol does not appear to be an important risk factor for stroke. They also appear to reduce the risk of heart disease in people with normal or low cholesterol levels. Further evidence for the fact the statins probably do not work through cholesterol reduction comes from a ton of evidence which shows that many approaches which improve cholesterol do not have broad benefits for health including fibrates, resins, torcetrapib, ezetimibe, hormone replacement therapy and, last but by no means least, dietary change (lower fat or fat modification).
But let’s get back to basics for a moment. Does saturated fat cause cardiovascular disease? Major recent reviews of the evidence suggest not [3-5]. It should be noted that this evidence is epidemiological in nature, so we can’t be certain that saturated fat does not cause problems from this evidence. However, the lack of an association between saturated fat and cardiovascular disease strongly suggests that eating more of it is unlikely to be a problem.
Are the authors aware of this evidence? Maybe, maybe not. What they do is, first of all, cite the deeply flawed work of Ancel Keys. Then they go on to state this:
However, a recent review on the role of fats and fatty acids on human health concluded that the relationship is more complex [6]. Trans fatty acids increase the risk, fish or n-3 long-chain polyunsaturated fats decrease the risk, but the data are conflicting or insufficient to convict or free total fat intake or other fat fractions with respect to CVD risk. Thus, further research is needed, especially focusing on long-term dietary intake.
Notice, absolutely no mention of saturated fat here at all.
And what of the more reliable intervention studies? What happens when individuals adopt a diet lower in fat or change fat consumption in a supposedly healthier direction? Well, a recent huge meta-analysis [7] of this evidence showed:
Reduction of dietary fat, modification of dietary fat, or both did not reduce the risk of death due to cardiovascular disease.
Reduction of dietary fat, modification or dietary fat, or both did not reduce overall risk of death.
The authors of this study report that there was evidence that reduction and/or modification of fat led to a significant reduction in risk of ‘cardiovascular events’ (basically a collection of fatal and non-fatal heart attacks and strokes). However, there’s a couple of things worth bearing in mind here:
First of all, dietary fat change did not lead to a significant reduction in risk of either heart attack or stroke when taken in isolation. Also, some of the studies used in the analysis did not just employ changes in dietary fat, but other strategies too (for example, nutritional supplements were given to the treated group). This obviously makes it impossible to discern what elements of the treatment were effective. Crucially, when such studies were removed from the analysis, overall risk of cardiovascular events was not lowered at all.
In other words, the best available evidence (intervention studies) tells us that modifying our diet in the way that the Swedish authors would us believe is healthy has, in fact, no benefits for health. Of course, the natural logical conclusion to draw from this is that a move to a higher fat diet is not inherently harmful.
Of course you won’t learn any of this from the ‘study’ itself, nor the way it’s been reported. Here’s a typical example. And here’s a quote from the study’s lead author from the article I’ve linked to – Professor Ingegerd Johansson of the University of Umea:
…these results of this Swedish study demonstrate that long-term weight loss is not maintained and that this diet increases blood cholesterol, which has a major impact on risk of cardiovascular disease.
The first idea simply cannot be concluded from this study. And there’s a pile of evidence to suggest that the second assertion is just plain wrong. And this from a professor, no less. Someone needs to give this professor a lesson in science.
References:
1. Johansson I, et al. Associations among 25-year trends in diet, cholesterol and BMI from 140,000 observations in men and women in Northern Sweden. Nutrition Journal 2012, 11:40
2. Baigent C, et al: Cholesterol Treatment Trialists’ (CTT) Collaborators. Efficacy and safety of cholesterol-lowering treatment: prospective meta-analysis of data from 90,056 participants in 14 randomised trials of statins. Lancet 2005, 366:1267–1278.
3. Mente A, et al. A Systematic Review of the Evidence Supporting a Causal Link Between Dietary Factors and Coronary Heart Disease. Arch Intern Med. 2009;169(7):659-669
4. Siri-Tarino PW, et al. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease Am J Clin Nutr 2010;91(3):535-46
5. Skeaff CM, et al. Dietary fat and coronary heart disease: summary of evidence from prospective and randomised controlled trials. Annals of Nutrition and Metabolism 2009;55:173-201
6. Food and Agriculture Organization of the United Nations (FAO): Fats and fatty acids in human nutrition. Report of an expert consultation. Rome: FAO Food and nutrition paper 91; 2010. ISBN ISBN 978-92-5-106733-8.
7. Hooper L, et al. Reduced or modified dietary fat for preventing cardiovascular disease.
Cochrane Database Syst Rev. 2011 Jul 6;7:CD002137
