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How to estimate the Phe content of a food from its protein content: Part 4

May 10, 2013

This blog entry is the last in a series of four posts that introduce this simple web app which estimates the phenylalanine (Phe) content of a food from its protein content.


In Part 1, Part 2, and Part 3, I explained how the rounded protein content listed on the package of a food can be used to estimate the Phe content of the food. More specifically, I showed how to obtain a lower bound and an upper bound on the Phe content using the rounded protein content, the rounding error, and the multipliers 20-64.5. As you may have noticed, the upper bound (the maximum) can sometimes be quite far from the lower bound (the minimum), and so it may be hard to guess what the true Phe content of the food really is from this estimate.

But there are many ways to obtain a more accurate estimate.

The first thing one can do is check which of the ingredients contains Phe (if any).

If the protein content is listed as 0g (meaning that the true protein content is between 0g and 0.5g), then it is possible that no ingredient contains any Phe. If that’s the case, then you’re lucky because you will know for sure that the food is free of Phe. For quick reference, we  put a list of Phe-free foods and ingredients in pdf format towards the bottom of our web app (right below Question 2). Feel free to share!

Another interesting (lucky!) case is when the only ingredients containing Phe are fruits. An example of this would be fruit juice, or roll up fruit snacks without gelatin.

One remarkable thing about fruits is that their Phe:protein ratio tends to be lower than for other foods. In our study, my graduate student Jieun Kim and I found that the vast majority of fruits have between 20mg Phe per gram protein, and 39mg Phe per gram protein. Therefore, for a fruit-based food, the multiplier 64.5 can be replaced by 39.

This is why we added “Question 2” to our app. If you state that the only Phe containing ingredient in the food are fruits (by clicking “yes” for Question 2), then the maximum Phe content is obtained by multiplying the maximum protein content by 39 (instead of 64.5). This gives a smaller range of possible Phe, and thus a more accurate estimate.

I guess that’s all I have to say about this first app for now. I hope my explanation was clear.

Look out for another, more sophisticated (and more accurate!) app coming soon.

From → PKU

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