Tuesday, 28 April 2009

Saturated fat: Why all the fuss?

I'm just finishing a text book I forgot to finish a year or so back. Got into the chapter on heart disease.

It reminded me why I get a little frustrated with current nutritional and health advice and why I think the public gets so confused and follows so many fashions. In my view it's because so much of the evidence we hear about comes from correlations. Correlations are not actual scientific fact they're part of the evidence that informs us where best to focus our research. They give a hint as to where the solution may be found. However they do not ever provide fact and during my A levels and degree we were all lectured to death never to confuse correlation with fact and never to present it as such. 

So that's why I find it hard to take everything I read as cut and dried. As perfect truth. It's the reason so many explanations keep changing. One day you'll hear that anti-oxidants are great or saturated fat is bad and the next you hear others pointing out that both anti-oxidants can inflict damage on cells and that saturated fats are more stable than other fats and thus can be beneficial. 

The reason being the initial advice wasn't based on sound well researched fact where each point in the chain towards the cause has been tested and verified. No, it's mainly a set of correlations, often from a very big study with lots of funding, paid for by an influential body and with enough people studied , usually tens of thousands, to make the results sounds water tight. 

So what triggered off this rant? 
In truth it's been building for years, I've only just got round to it, but right now it was a paragraph that mentioned that 
much research has found the highest correlation of  coronary heart disease in those whos diets obtain a large part of their energy from saturated fat 
They then go on to test your interpretation of this statement to make sure that you answer that this means getting a lot of your energy from saturated fat means you're more likely to have heart disease.

While that's a fair thing to say it often ignores a lot and not once is there any question that this data is from a correlation. The question being, is it saturated fat that is bad and that's what's being shown? or is it that saturated fat content is high in foods that contain ingredients which may cause heart disease? or diets with a high level of energy from saturated fat are common in people with a lifestyle that promotes heart disease?

I find no real discussion of the credibility of the information in the first place. I'm not questioning the fact of the main statement i.e. that high saturated fat is linked to problems, I am questioning the interpretation and particularly the way it is presented and assessed. I find no space to query or critique this view, which during my psychology and sociology a levels  I was encouraged to. Yet in biology and physiology the idea of encouraging critique in exams and the subject itself doesn't seem to be allowed. 

This idea that saturated fat is the main problem has been around for decades yet I find as much evidence questioning it's label as a bad boy as I do supporting it. Thus I find it like a jigsaw where the piece doesn't quite fit. I've heard lots of theories, often political, why saturated fat gets the blame. Those that influence me the most are the ones that take into account the facts that we do know instead of the correlations we assume. 

Take this suggestion. I read recently that saturated fats are in fact more stable than poly or mono unsaturated fats meaning they'll be less affected by free radicals and other damage both in storage, during cooking and within the body than mono and poly unsaturated fats. That makes sense because that is the very definition of a saturated fat. It means that all its carbon atoms have solid double joins to the hydrogen ions in it's fatty acid chains. That's a technical answer but that's the point. It matches up technically. Data was also presented to show that these fats were in fact the most stable in various situations and thus should be nutrients that cause little harm to the body. 

I'll leave it to real experts to explain the efficacy of the last statement but atleast the answer used facts to make a point. It was also something that should be relatively easy to test and prove, atleast that in certain solutions and situations you could prove that the fats were inert or that they were unstable and would be less susceptible to free radical damage. 

So that's a small example of why saturated fats themselves may be mis labelled because they are just associated with bad things but may not be the cause. 

Another problem is that correlations can only predict the things you measure. There is a growing list of things that are now measured in relation to health. The point being that our ability to measure certain things is improving all the time but also means we can't measure alll the things we want to measure. Thus again we'd find that we label saturated fats as bad simpy because we're able to measure them among lots of other things. Yet  for many years things such as stress levels, levels of sleep deprivation and other things that have been more recently shown to be important factors would not have been included in the older types of research. Also the difference between man made, hydrogenated fats and natural saturated fats was not known or recorded in a lot of these studies. Again I believe more recently it's the amount of calories from hydrogenated fats that's even more important. 

Let's switch our focus though. There is plenty of evidence that lack of activity is our big concern. There are enough people across the world who have lived long, health and productive lives on a diet relatively high in saturated fat because that's what their culture has survived on for generations. Their lives have adapted and generally include a lot of activity and it's the activity that is linked to clearing up the metabolic waste that excess calories creates. It's also this extra activity and the metabolic demands it puts on our bodies that uses up a lot of these extra calories that these people consume. 

In essence the picture here is that many people in westernised nations have reduced their activity whilst maintaining their food intake. This has simply lead to a gradual and regular surplus of calories. Remember there's a limit to the number of calories stored in the body as carbohydrate but not as fat. So it's obvious that any one who eats a bit too much will have excess fat travelling around their body. So fat gets the blame because it contains more calories, weight for weight than carbohydrate and protein and so it's more likely to lead to an excess. 

We've already mentioned that there are man made fats and that the last hundred years have seen a huge rise in foods that are quite removed from what we've evolved to eat. They often contain, or atleast many years ago they contained, saturated, particularly hydrogenated, fats. Now remember that saturated fats from natural sources will contain vitamins and nutrients that we've evolved to survive on. Our bodies often store things in our fat cells for use later and so do animals. Thus this fat can be a vital source of our daily requirements. However the man made fats, those that have been highly processed are just more likely to have lost a large amount of these.  A diet missing important nutrients, no matter how small the amount that's required, is bound to lead to problems. So again you see how the simple statement that high saturated fat diets lead to heart disease does not tell the whole story.

There's been so much written for and against saturated fats that I could go on all day but I'll leave it there. What I'd rather do is encourage people to expect more of those who report scienctific information and also look a bit further into what's presented to see the quality of information that's behind the data. Always remember correlations are useful but not proof of anything. When I've looked further I've generally found that the actual researchers acknowledged that correlations weren't sufficient evidence and indicated need for further research. It often seems that political needs drive the adoption of these correlations as fact. 

Given the vast and growing amount of conflicting information that's out there I think it's also a very good reason for the scientific community to provide a way for everyone to search, visualise and understand it all in better more open ways. Right now there's just too much that's unavailable to most of us because we don't have the time or resources to trudge through it all and then make sense of it. Surely the technology should be helping us. 

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