This article appeared in the Spring/Summer 1996, Vol. 8, No. 1, issue of the National PKU News. The information is quite applicable to MSUD. The author, Dr. Miriam Keller is a young German physician who has PKU.

For many people it would be much easier to consume the entire amount required of the formula (medical food) in just one sitting. Particularly for teens and young adults who are frequently away from home, drinking the formula is awkward and inconvenient during the day. Most families have been told, however, that it is ideal to divide the required amount into at least three portions. These portions should be consumed at intervals throughout the day. This recommendation is based on well- known principles of amino acid metabolism.

Several recent studies in Germany have confirmed the importance of consuming smaller amounts of formula at intervals, rather than in larger amounts once or twice daily. I want to summarize and explain the investigations of the University Clinic in Berlin. The team there, of which I was a part, involved a special work group [consisting] of a nutritionist, scientists and physicians dealing with the problem of PKU formulas.

Nitrogen is the most important building block of amino acids, and thus of body protein. The formula is the main source of nitrogen for persons with PKU [and MSUD]. It provides amino acids (containing nitrogen) used for making body protein. For optimal protein synthesis, the body requires the presence of amino acids at intervals throughout the day, in combination with carbohydrates or fat. But amino acids cannot be stored, and any surplus that cannot be used at the time is broken down to be used for energy. To become a source of energy, the nitrogen from the amino acids is removed and excreted in the urine.

Several studies have shown this effect. In one study, ten young people with PKU (ages 12-26 years) ingested their formula on one day in a single or only two doses. Another day, they divided the amount into three portions. On both days, they collected their urine and the amount of nitrogen excreted was measured. The amount of nitrogen in the urine is an indicator of the quantity of amino acids that cannot be used for protein synthesis, and are therefore broken down and excreted. The study showed that significantly more nitrogen was found in the urine when the formula was ingested only once a day.

In another study, the same procedure was done for a 22 year-old female patient on a strict low phe [phenylalanine] diet. On one day, the formula was divided into three portions and ingested with the main meals. On the other day, the entire daily amount was taken during breakfast. Again, nitrogen loss increased when formula was ingested in one portion. The study also used a stable isotope as a marker to measure amino acid use. Amino acids are broken down into "carbon skeletons," and finally into carbon dioxide if they cannot be used for protein syntheses. The carbon is exhaled in breathing. In this study, the isotope was ingested along with the formula. As expected, the isotope elimination rate was higher when the formula was taken in only one portion. The larger the amount of amino acids consumed in a single dose, the greater the breakdown.

Both studies show the importance of consuming the formula with food, well-distributed during the day. Consuming the formula in only one or two doses results in poorer use of amino acids for protein synthesis. Also, the person who ingests the entire daily formula during a single meal misses the benefit of amino acid supplementation for the rest of the day.

Clinics should remind their patients of these findings. Families should try to take the advice to heart. And if you have PKU [or MSUD], you should reflect on your own habits. Can you optimize your daily routine based on the findings of these studies? Do not hesitate to do the best you can for your health!


The MSUD Family Support Group is currently funding several research projects and we are proactively looking for researchers interested in developing new treatments or finding a cure for MSUD. Significant funding is necessary if we are to accomplish this goal.
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