September 13, 2008

The food tastes too good

May contain nutsWhy are people getting obese? Could it be that they eat too much? Of course. And since it cannot be their fault it must be some food additive making them! Svenska Dagbladet runs a story Smakämne ökar risk att bli fet that claims the culprit is MSG, sodium glutamate.

The source is a study that examined Chinese villagers, comparing the users of MSG with the non-users. The users where heavier, and SvD claims that when controlling for caloric intake, MSG appears to produce obesity.

There are just a few major problems with this story. First, the article erroneously suggests that MSG is something "western", while it is actually quite the reverse. Much of the bad press of MSG is due to "Chinese restaurant syndrome", which has been attributed (with no demonstrated causal link) to MSG. In fact, of the villagers in the study 82.4% were adding MSG to their food.

(In this paper it is mentioned that 20% of test subjects react more weakly to the MSG taste than the rest; maybe this correlates with the ~80% use?)

Second, as junkfood science points out, the statistical method looks iffy. If there was a simple causal link the heavy users would be on average heavier than the nonusers (when controlling for food and exercise), but instead they found more obese people in the heavy user category than in the nonuser category (the averages did not differ much). Maybe some people are vulnerable to MSG, but there are strong confounders here. For example, heavier people tend to eat more, and would hence eat more MSG per day than small eaters.

Third, the news stories all love to depict MSG as something nasty and unnatural. SvD quotes a representative of a consumer organization denouncing it as dangerous and says food producers should remove it. Of course they will, if it gives them bad press. The trouble is that MSG is quite natural and easy to add by adding tomatoes or parmesan cheese. Hmm, are Italians or people eating Italian food overly obese? And if you want to just add the amino acid, just write "hydrolyzed soy protein" on the label - it is 100% true. If that sounds too chemical, just add soy sauce, it is nearly the same thing.

Fourth, if glutamate in food was a danger we would all be dead. Glutamate is the main neurotransmitter in the brain, and even a slight excess of that in the tissue would likely crash the whole system. But glutamate is also a very common amino acid used in most proteins, making the total intake several times the amount used in the brain. (see this review and this article).

The real issue is of course that glutamate, and the umami taste in general, makes food taste good and makes people want to eat it more. It especially seems to be a way of getting people to accept a novel food. This has been used to get patients to eat healthier food and improve the appetite of elderly.

Now, what is the effect of appetizing food? We tend to eat more, even when we are less hungry. The real issue here is that we have become so good at making cheap and yet tasty food that we tend to overeat. MSG is not the villain, it is just another tool in the toolbox of skilled cooks in their attempt to make what we eat taste well. We could easily get rid of obesity by mandating that food should be bland, expensive and ideally slightly spoiled. Clearly we want another solution. I'm going to ponder what to do over lunch.

Posted by Anders3 at September 13, 2008 02:03 PM