Saturday, January 18, 2014

Diet Fizzy Drinks

As I said in the last blog post. I was recently involved in an online discussion about the advice given by Change 4 Life. Some people expressed disbelief that Change 4 Life (which is an NHS healthy lifestyle campaign) would advise people to swap sugary drinks for diet drinks with artificial sweeteners. They found this incredible because they said artificial sweeteners "are disastrous for your health".

Is that really true? Are artificial sweeteners disastrous for your health? Where is the evidence?

The people I was talking with had probably seen articles and websites such as this one which claims a whole host of terrible effects of aspartame including "Aspartame poisoning is commonly misdiagnosed because aspartame symptoms mock textbook ‘disease’ symptoms, such as Grave’s Disease." The website has lots of links to the author's book and to a "detoxification programme" she hopes to sell you.

These kinds of articles are so widespread that has a whole page about aspartame written by David Hattan  Acting Director of the Division of Health Effects Evaluation in the United States Food & Drug Administration (USFDA) Center for Food Safety and Applied Nutrition. You can (and should) read it yourself. he gives a detailed rebuttal of many of the most common claims of the risks of aspartame, and concludes "The legitimate attempts that have been made to confirm and replicate allegations of adverse reactions from aspartame ingestion have not been successful and the USFDA continues to consider this to a be among the most thoroughly tested of food additives and that this information continues to confirm the safety of aspartame."

But we never trust just one source of information, so let's keep checking. Wikipedia has a page about aspartame and it also has a page just about the controversy over aspartame's safety with 69 separate references, many of them to peer reviewed journals. The articles seem to confirm Hattan's claim that aspartame has been very thoroughly and repeatedly tested, due to the ongoing public concern, but that the evidence seems to be that it is a very safe additive.

But let's still not rest there. We can use Google scholar to check the primary evidence ourselves. I used the search terms "aspartame safety" which returned 13,100 results. The first was called
Effect of aspartame loading upon plasma and erythrocyte amino acid levels in phenylketonuric heterozygotes and normal adult subjects You need to know that phenylketonuria (PKU) is a genetic disorder which makes the body unable to process the amino acid phenylalanine, present in aspartame but also found found naturally in other foods such as breastmilk. If you have two genes for PKU you have the condition and you would definitely know about it - untreated it causes learning disability. But what if you only have one PKU gene? Then you wouldn't have the condition, but maybe it would make you more susceptible to ill-effects from aspartame, especially if you were consuming a lot of it. It's a reasonable hypothesis, they tested it, and found that if you have one gene for PKU you are slightly less able to process shedloads of aspartame than someone with no PKU genes, but you can still process it adequately, and so aspartame is as safe for you as for anyone else. Without paying moeny you can only read the abstract for this article, which is all I have done. The article was published in 1979 (that's pretty old) in The Journal of Nutrition which Wikipedia tells me is a peer reviewed journal (that's good - you can only publish an article there if other nutrition experts have read it and think it's good science) with an impact factor of 3.916 which isn't bad for a niche journal.

How safe is it for anyone else? The second hit on Google scholar addresses that. It's a review paper which is good because systematic reviews are at the top of the hierarchy of evidence. I keep telling you that you shouldn't trust just one source of evidence, even a well-conducted scientific study. A systematic review gathers together all the scientific studies on a particular topic, weights them according to how well-conducted and therefore reliable they are, and weighs up the balance of evidence from all the available research. So a good, recent systematic review is about as dependable evidence as you can ask for. This review is called Aspartame: review of safety and again all you can see is the abstract unless you pay for the full paper. It was published in 2002 which isn't bang up to date but it's not really old either. It was published in Regulatory Toxicology and Pharmacology which Wikipedia tells me is a peer reviewed journal with an impact factor of 2.132 which isn't terriible for a niche journal. The review concludes "The safety testing of aspartame has gone well beyond that required to evaluate the safety of a food additive. ... it is clear that aspartame is safe, and there are no unresolved questions regarding its safety under conditions of intended use." Seems conclusive ... until I spotted that the email address for the lead author is - she works for the NutraSweet company, who make artificial sweeteners. Obviously, that seriously undermines the trust I want to place in this review. That doesn't mean I automatically believe the opposite of what this review says, just that it carries very little weight in making up my mind whether I believe aspartame is safe or not.

I could keep on looking, but even discounting that last research paper all the dependable evidence seems to be pointing in the same direction - aspartame is a very safe food additive. All the evidence in the opposite direction seems much less reliable - unscientific and trying to sell you detox programs and books.  Change 4 Life are probably right to advise people to stop drinking sugary drinks (which are empty calories) and switch to diet drinks instead (which are safe and won't make you fat). If you don't drink sugary drinks but instead prefer to drink water, then just keep doing that.

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