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PKU dieting with unrestricted fruits and vegetables?

A very interesting article came out last year [1]. The paper reports on an experiment where PKU patient were allowed to eat unrestricted amounts of fruits and vegetables. More specifically, all fruits and vegetables with less than 0.75mg Phe per gram were counted as “Phe free”. Surprisingly, the blood Phe levels of the patients were “consistently good” despite the additional Phe consumed. The daily Phe tolerance of the patients thus appeared to increase by an average of 83mg per day, which is a 25% increase.

Here is the title and abstract of the paper. You can click here to read the full version.

Simplifying the diet for patients with phenylketonuria (PKU): unrestricted consumption of fruit and vegetables” By Carmen Rohde, Alena Gerlinde Thiele, Ulrike Mütze, Wieland Kiess, Skadi Beblo, Leipzig


Over a period of three years, the phenylalanine content in fruit and vegetables was not taken into account in the daily phenylalanine balance for patients with phenylketonuria, a congenital metabolic disorder. In spite of a significantly higher intake of phenylalanine, no worsening of metabolic control could be detected.

Can you imagine not having to count fruits and veggies? Now, that would make the diet so much easier to manage!


[1] Rohde C, Thiele AG, Mütze U, Kiess W, Beblo S (2014) Simplifying the diet for patients with phenylketonuria (PKU): unrestricted consumption of fruit and vegetables. Ernahrungs Umschau 61(12): 178–180


How much Phe in one gram of protein from fruit?

How much phenylalanine (Phe) does one gram of protein contain? It depends. For fruits, it could be as little as 20mg Phe, or as much as 39mg Phe. Indeed, as one can see from our data, the vast majority of fruits have between 20mg Phe and 39mg Phe per gram of protein.

Quick Fact Sheet for Phe from protein estimation

For those of you who don’t feel like doing the math every time, here is a small table that gives the minimum and maximum Phe for various protein contents (rounded to the nearest gram). There are two columns: the first one is for any food that does not contain aspartame. The second one (last one on the right) is for foods made of fruits only (or fruits plus Phe-free ingredients).  As you can see, if the Nutrition Fact Label states that the food contain 0g protein, then the food could contain as much as 32mg Phe in general (assuming no aspartame).  But if the ingredient lists contains only fruits plus Phe-free things like sugar, color, oil, etc., then the maximum Phe when there is 0g protein is only 19.5mg Phe.


The background for this Fact Sheet is in this document.


Great news! Our paper proposing new multipliers for estimating the PHE content of a food from it protein content has been accepted for publication in the Journal of Food Composition and Analysis. It will take a bit before the paper appears, but I will post a link to the article as soon as it is available. Meanwhile, Here is abstract:

 Phenylalanine (Phe) is a key nutrient in the dietary management of phenylketonuria (PKU). Since the protein content of many foods is readily available, estimating the Phe content of a food is facilitated by an understanding of the statistical distribution of the Phe:protein ratio in common foods. In particular, from the minimum and maximum Phe:protein ratio, one can obtain an upper bound and a lower bound on the Phe content of any given food from its protein content. Currently, the multipliers commonly used are 30 and 50. In this document, we present and compare the statistical distribution of the Phe:protein ratio in two databases, namely the USDA National Nutrient Database and the Danish Food Composition Databank. Based on this data, we suggest replacing the 30 –  50 multipliers by 20 –  65. When used to estimate the Phe content from the protein content, these multipliers yield estimates that are correct for more than 97% of the data analyzed (as opposed to less than 76. 3% for the multipliers 30 – 50). Furthermore, we confirm that the commonly used average of Phe:protein ratio for the foods in the categories of fruits (30) and vegetables (40) are more or less accurate.

Perhaps you have heard that multiplying the protein content of a food by 50 gives a maximum for the Phe content of the food. I personally heard this many times in the past. For example, if the food label states that one serving contains 1g or protein, then I was explained that the maximum Phe content is 1.5×50=75mg. Well, it turns out that many foods have more Phe than that, and so one should multiply by 65 to get an accurate maximum. The data to support that is in the paper.

The new multipliers have been incorporated into our PHE estimation app. The web browser version of the app is freely available at

My student Jieun also made an Android version, which you can download (for free!) from this webpage:


Estimating the Phenylalanine (Phe) content of “Sixlets” (using Phe:protein ratios)

I was recently asked to estimate how much Phe is in one serving (10 pieces) of Sixlets. Here is what I did.

1) I found the Nutrition Fact Label and ingredients lists (…/candy/p/8966903792)

2) I noted that the Nutrition Fact Label states that there is zero gram of protein. Due to rounding, this actually means that there is no more than 0.5g of protein per serving.

3) I looked at the ingredient list and noted all ingredients that contain protein. I then looked up the mg Phe per g protein ratio of each of these ingredients in this (free) food list I mentioned in my previous post.

I found that
1 g protein from whey contains 32mg Phe
1 g protein from cocoa contains 34mg Phe
1 g protein from carob contains 33mg Pge
1 g protein from cornstarch contains 50mg Phe

4) Since cornstarch has the highest phe:protein ratio at 50mg, then one serving of Sixlets contains no more than 0.5 x 50= 25 mg Phe. However, corn starch is ingredient #8, so there is probably a very small amount of cornstarch. Furthermore, cornstarch contains a very small amount of protein. So we can neglect the cornstarch and assume that all Phe comes from the next highest Phe:protein ratio (cocoa at 34mg).  Thus we get that one serving of Sixlets contains no more than 0.5 x 34= 17 mg Phe.

Final Answer: no more than 17mg Phe per serving.

Proposing a new concept in online learning: “slectures”

Last Spring, I proposed the concept of “slecture” as a new way for students to learn by teaching.

What’s a slecture? Simply put, a slecture is an online lecture made by students.

More specifically, the idea is to have one or more students give a second hand account of a lecture or a course they took, using text, videos, pictures, or whatever other online medium they see fit. They do so with the approval of the instructor, sometimes even with full access to the instructor’s teaching material, including lecture videos. However, the instructor does not have to review the accuracy of the material after it is produced and the students bare the blame for any inaccuracy it might contain.  Students even have the freedom to enhance the course content with their own explanations and comments, using other references if needed.

The plan was to make all slectures freely available on the  Project Rhea website. After working on this for close to a year, we now have a few nice examples to showcase on the website. Take a peek and let us know what you think!

Link to slecture page on Project Rhea.

A (free) Food List in PDF Format

Dear PKUers,

I want to share with you this food list, which my graduate student Jieun and I just published. It combines all the foods in the USDA Database, along with another (Danish) database. The focus of our food list is the Phe:protein ratio of the food, but it also lists the mg Phe per gram food (first column). Feel free to print it if you like. However, I find it easier to just search through the pdf on my computer.

Link to (free) Food List in PDF Format by Kim and Boutin