Methylmalonicaciduria (MMA), also known as methylmalonic acidemia, is the most common and rare disease of organic acid metabolism disorder in China. The prevalence of MMA in China varies widely in different regions, ranging from 1/4000 to 1/50,000, with an average of about 1/1.5 million.

Since methylmalonic acid is a metabolite of methylmalonyl coenzyme A in the catabolic pathway of isoleucine, valine, methionine (methionine), threonine, cholesterol, and odd-chain fatty acid catabolism, we generally have to pay attention to the intake of related nutrients in the course of the treatment of MMA, especially the control of protein-rich foods, such as isoleucine, valine, methionine, threonine, and so on.

(i) Levels of isoleucine, valine, methionine and threonine in common foods

In general isoleucine is mainly derived from liver, eggs, duck eggs, soybeans, black beans, corn, black rice, brown rice, almonds, peanuts, wheat, fish, dairy products and other foods; valine is mainly derived from meat, dairy products, dry legumes, nuts in in, etc.; methionine is mainly derived from soybeans, black beans, green peas, eggs, duck eggs, fish, pork, beef, etc.; threonine is mainly derived from animal liver, meat, eggs, mushrooms and so on.

(ii) Dietary treatment considerations

Dietary treatment for patients with simple MMA is especially important, mainly to adjust the intake of natural protein according to the patient’s condition and blood ammonia. However, we should pay attention to the following matters while restricting natural protein so as not to affect growth and development.

1. While strictly controlling natural food, special formula without isoleucine, valine, methionine and threonine can be supplemented under guidance, so as to ensure the intake of energy and protein.
2. in order to ensure adequate energy intake, foods with relatively low protein content, such as lotus root powder, maltodextrin, sugar, fruit puree, melon and fruit vegetables, etc., can be chosen while increasing the intake of fats and oils appropriately.
3. Commercially available low-protein foods, such as low-protein rice, low-protein flour, low-protein cookies, and raw flour, can be chosen to make fancy staple foods or snacks to increase energy intake.
4. Considering that isoleucine, valine and methionine are essential amino acids that cannot be restricted for a long period of time, it is necessary to monitor the levels of isoleucine, valine and methionine on a regular basis to avoid deficiency.
5. Pay attention to height and weight measurements to monitor growth and development.

Overall, protein intake is especially critical for children with MMA and has different requirements in different disease states and at different ages. However, whether it is special formula, natural food, or processed low-protein food, the family members of the child should learn how to calculate the protein in food under the guidance of the doctor and dietitian, so as to ensure that the child can complete the appropriate protein intake at home according to the doctor’s instructions, and follow up with pediatric endocrinologists and clinical dietitians on a regular basis for adjusting the treatment and nutritional program.