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

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.

https://engineering.purdue.edu/brl/PKU/method_0.html

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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.

How to estimate the Phe content of a food from its protein content: Part 3

This blog entry is the third 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.

https://engineering.purdue.edu/brl/PKU/method_0.html

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A little word about precision and round-up.

In the  previous post, I explained how to use the protein content listed on the Nutrition Fact Label of a food to obtain an upper bound and a lower bound on the Phe content of the food. The explanation assumed that the protein content was rounded up to the nearest gram, and so the true protein content could have been up to 0.5g more/less than the stated protein content.

However, the protein content is not always rounded up to the nearest gram. Sometimes, in particular on the label of some food produced in Asia, the protein content is rounded to the nearest 0.1g. For example, a package of ramen noodles might state that it contains 1.4g of protein per serving. In that case, you can simply enter 1.4 into our app, and it will automatically take into account the higher precision of the protein content. More specifically, it will multiply 1.35 by 20 to find the minimum Phe, and it will multiply 1.45 by 64.5 to find the maximum Phe.

As you might have learned in high school chemistry, the last digit of a rounded up number indicates the precision of the measurement.  So while a rounded up protein content of  1g would indicate a true protein content between 0.5 and 1.5, a rounded up protein content of 1.0 would indicate a true protein content between 0.95 and 1.05.

Try it! Enter “1.0” for the protein content in our app and check the result. You will get a different maximum and minimum Phe content then if you had entered “1”.

More in Part 4.

How to estimate the Phe content of a food from its protein content: Part 2

This blog entry is the second 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.

https://engineering.purdue.edu/brl/PKU/method_0.html

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In the previous post, I explained how the 20-64.5 multipliers can be used to obtain an upper bound (i.e., a maximum) and a lower bound (i.e., a minimum) for the Phe content of a food from its protein content. However, in the previous computation, we assumed that the protein content was known exactly. Unfortunately, on the Nutrition Fact Label, the protein content is rounded up to the nearest gram. This means that, if the protein content listed is 1g, then the true protein content can be anywhere between 0.5g and 1.5g.

In that case, one can find out a lower bound on the Phe content by multiplying the minimum possible protein content, namely 0.5g in our example, by the multiplier 20. So we have 0.5g x 20=10, and thus the Phe content cannot be less than 10mg.

Now to find an upper bound on the Phe content, you have to multiply the maximum possible protein content, namely 1.5g in our example, by the multiplier 64.5. So we have 1.5 x 64.5= 96.75m and thus the Phe content cannot be more than 96.75mg.

Now image that the protein content listed in the nutrition fact label is 0g. Because the number is rounded up to the nearest gram, then the true protein content can be anywhere between 0g and 0.5g. In that case, we find the minimum Phe by multiplying zero by 20, which gives zero, and thus it is possible that the food contains zero Phe. To find the maximum Phe, we multiply 0.5 by 64.5, which gives 32.25, and thus the maximum Phe content is 32.25mg.

If you want to to this automatically, you can use our app at https://engineering.purdue.edu/brl/PKU/method_0.html. Just enter the protein content in grams in the first box, and click “no” and “no”  for Question 1 and Question 2. (I will explain why we ask Question 2 in a future post.) Then click “show results” and a box will pop up with the minimum and maximum Phe value. 

To be continued in Part 3.

How to estimate the Phe content of a food from its protein content: Part 1

This blog entry is the first 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.

https://engineering.purdue.edu/brl/PKU/method_0.html

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Phenylalanine (Phe) is an amino acid that is present in all proteins we consume. Generally speaking, the more protein a food contains, the more Phe it contains. But exactly how much Phe does one gram of protein contain? Actually, it depends on the food. For example, if you look up “coconut milk” in the USDA database, you will see that one gram of coconut milk contains 0.02g of protein and 1mg of Phe. This gives a Phe to protein ratio equal to 1/0.02=50mg Phe per gram protein. On the other hand, an apple contains 0.0026g protein and 0.06mg Phe per gram of apple. This gives a Phe to protein ratio equal to 0.06/0.0026, which is approximately 23 mg Phe per gram protein. As you can see, the proteins in an apple contain much less Phe (less than half!) than the proteins in coconut milk.

Therefore, it is impossible to know exactly how much Phe a food contains solely from its protein content. However, it is possible to find an estimate for the Phe content. More specifically, it is possible to find a range of Phe values that contains the true Phe value. The idea is to multiply the protein content of the food by the maximum possible Phe per protein ratio, and by the minimum possible Phe per protein ratio, to obtain the maximum and the minimum possible Phe values, respectively. Let me explain.

Suppose that some food contains 1.2g of protein. First make sure that the food does not contain any aspartame. (As we all know, aspartame is a big “no no” for people with PKU.)

Step 1: Multiply the protein content in grams by 64.5. Here we have 1.2 x 64.5= 78.48. The result, 78.48 in this case, is the maximum Phe content of the food. In other words, the Phe content of the food cannot be higher than 78.48mg.

Step 2: Multiply the protein content in grams by 20. Here we have 1.2 x 20= 24. The result, 24 in this case, is the minimum Phe content of the food. In other word, the Phe content of the food cannot be lower than 24mg.

Where do the multipliers 64.5 and 20 come from? My graduate student Jieun Kim and I chose them because, according to our study, the vast majority of foods without aspartame (more than 97%) have a Phe:protein ratio above 20 and below 64.5.

Some of you may have been told by their dietician to use the multipliers 30 and 50 instead of 20 and 64.5. Indeed, the “traditional multipliers”, which have been used for decades by dieticians, are 30-50. However, we found that these traditional multipliers are only accurate for about 67% of all foods and ingredients without aspartame. Thus, we prefer the more accurate 20-64.5 multipliers.

To be continued in Part 2.

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Our Goldie Blox arrived today!

Our Goldie Blox arrived today!

First time I see the word “engineering” in a children’s book, let alone a book for girls. Thanks Goldie Blox for thinking outside the box!

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

In yesterday’s post, I explained a simple trick to estimate the Phe content of sweets using the rank of gelatin in the ingredient list. Today I am going to give you another trick that my PhD student Jieun Kim and I developed.

It is also very simple trick: all you need to know is the size of a serving and the protein content of one serving. However, it requires a division, and thus you might need a calculator. On the other hand, you can generally expect a more accurate result than when using yesterday’s rank-based trick.

So here is the trick:

  • Find the serving size in grams on the Nutrition Fact Label.
  • Find the protein content of one serving on the Nutrition Fact Label. (We are assuming that it is rounded up to the nearest gram.)
  • Then divide the serving size in grams by the protein content in grams plus 0.5 : (serving size in grams)/(protein content+0.5). Let’s call the number you get after dividing “X”.
  • Then X grams of sweet contains less than 20 mg Phe.

For example, let’s look at Altoids mints. One serving of Altoids is 2 grams, and the protein content of Altoids is 0 grams (rounded to the nearest gram).  So we divide 2 by 0.5, which gives us X=4. Therefore 4 grams of Altoid mints (about 6 mints) contains less than 20 mg Phe. This happens to be the same result as we we obtained using the previous trick. However, usually the result will be different (and more precise).

Let’s look at another example: Jell-O Gelatin Snack. In that case, one serving is 96 grams, and the protein content in one serving is 1 gram (rounded to the nearest gram). So we divide 96 by 1.5, which gives us X=64. Therefore, 64 grams of Jell-O (about 2/3 of a serving) contains less than 20 mg Phe.

Note that this trick applies if the only ingredient containing Phe is gelatin. In particular, it does not work if the sweet contains aspartame.

I hope my explanation was clear. Let me know if you have any questions.

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.

Copyrights 2013, all rights reserved.

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.

Copyrights 2013, all rights reserved.