A simple trick to estimate the phenylalanine (Phe) content of sweets with gelatin

PKUers: ever found yourself having to say no to a bite of candy because you don’t know its Phe content? Frustrating, isn’t it?

Of course, we all know that any sugar-free candy with aspartame is an automatic “no=no” because of the high Phe content of aspartame (about 50%). We also know that hard candy, “suckers,”  and any other sweets made of Phe-free ingredients (e.g., sugar, corn syrup, arabic gum, flavor) are free of Phe.

The sweets I am concerned about are the ones that contain gelatin in addition to Phe-free ingredients. Such sweets are allowed on the PKU diet, but only in limited amounts, depending on their actual Phe content. Two examples of these are Altoids mints and Jello.

Since gelatin is high in Phe, any sweet containing gelatin could potentially be quite high in Phe, but not necessarily so.  It all depends on how much gelatin it contains. Unfortunately, neither the gelatin content nor the Phe content are listed on the Nutrition Fact Label.

Having been annoyed by this problem several times, I decided to find a solution. Sitting down with my PhD student Jieun Kim, we  worked out a few simple tricks to estimate the Phe content using the nutrition facts and the ingredient list.

The first trick we found is that, as long as no part of any ingredient was removed in the preparation process, then the rank of gelatin in the ingredient list corresponds to a number of gram that contains less than 20mg Phe. For example, if gelatin is the 3rd ingredient in the ingredient list of a certain type of mint, than 3 grams of mint contain less than 20mg Phe. Similarly, if gelatin is the 1st ingredient in the list, than 1 gram of mint contains less than 20 mg Phe. Generally, if gelatin is the k-th ingredient in the list, then k grams of mint contain less than 20 mg Phe. Simple, isn’t it?

Applying this trick to Altoids mints, we find that 4 grams of mint (about 6 pieces) contain less than 20 mg Phe, since gelatin is the 4th ingredient in the list. So there shouldn’t be any issue with eating a couple of mints!

Note that this trick provides a very conservative estimate of the Phe content. In other words, the actual Phe content tends to be much lower than 20mg.  So technically, it is not a Phe estimate but an  “upper bound” on the Phe content.

DISCLAIMER: Neither the author nor Purdue University assumes responsibility for damages resulting from using this Phe estimation trick. Please talk to your doctor or dietician before making any change to your diet.

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