Nutrition Guide: What foods should you avoid if you have alkaptonuria?

October 16, 2025 •

4 min read

Alkaptonuria (AKU) is a rare inherited metabolic disorder, affecting approximately 1 in 250,000 to 1 million people worldwide, that prevents the complete breakdown of two amino acids: phenylalanine and tyrosine. For individuals with this condition, understanding what foods should you avoid if you have alkaptonuria? is a critical part of managing their health and preventing complications from the resulting build-up of homogentisic acid (HGA).

Quick Summary

Individuals with alkaptonuria must follow a controlled diet to limit the intake of amino acids phenylalanine and tyrosine, which can accumulate as homogentisic acid. This requires avoiding or carefully restricting high-protein foods like meat, fish, and dairy, particularly when taking the medication nitisinone.

Key Points

High-Protein Foods: People with alkaptonuria should strictly limit or avoid foods high in protein, including meat, dairy, eggs, nuts, and legumes, as they are rich in phenylalanine and tyrosine.
Aspartame: The artificial sweetener aspartame should be avoided entirely, as it is a source of phenylalanine.
Nitisinone Considerations: Dietary restrictions are critical for patients on nitisinone therapy to manage tyrosine levels and prevent eye complications like keratopathy.
Professional Guidance is Key: Working with a metabolic dietitian is essential for creating a safe, balanced, and personalized dietary plan to prevent malnutrition.
Medical Foods: Specially formulated protein-free amino acid supplements are often prescribed to ensure adequate nutritional intake for patients following restricted diets.
Risk of Malnutrition: Unsupervised low-protein diets pose a significant risk of malnutrition and other adverse health effects.

Understanding Alkaptonuria and Dietary Impact

Alkaptonuria (AKU) is caused by a deficiency of the enzyme homogentisate 1,2-dioxygenase (HGD), which is necessary to break down homogentisic acid (HGA). Without proper function of this enzyme, HGA accumulates in the body's tissues, leading to a condition called ochronosis, which can cause dark-colored urine and severe, early-onset arthritis.

Since HGA is a metabolite of the amino acids phenylalanine and tyrosine, controlling the intake of these two protein building blocks is the primary focus of dietary management. A low-protein diet has been a traditional approach, especially for children with AKU, though compliance can be difficult and nutritional risks exist.

Modern treatment often involves the medication nitisinone, which significantly reduces HGA production. However, nitisinone treatment can cause a secondary rise in tyrosine levels, which, if not controlled through diet, can lead to painful eye complications (keratopathy). A registered dietitian specializing in metabolic disorders is essential for creating a safe and effective dietary plan, especially when medication is involved.

High-Protein Foods to Avoid or Limit

For those managing alkaptonuria, especially on nitisinone therapy, reducing the intake of foods high in protein is paramount. High-protein foods are naturally rich in phenylalanine and tyrosine and must be avoided or strictly limited under medical supervision.

Meat and Poultry: Beef, pork, lamb, chicken, and turkey are all significant sources of both amino acids. Processed meats, sausages, and deli cuts are also high in protein.
Fish and Seafood: Almost all types of fish and seafood contain high levels of protein, making them unsuitable for an unrestricted AKU diet. This includes common choices like salmon, cod, shrimp, and tuna.
Dairy Products: Milk, cheese, yogurt, and ice cream contain concentrated protein, particularly whey and casein, which must be limited.
Eggs: A staple of many diets, eggs are another high-protein food that must be avoided or severely restricted. Both the yolk and the white contain significant protein.
Legumes: Lentils, beans, peas, and chickpeas are plant-based protein sources that are high in the target amino acids. Soy products, including tofu, tempeh, and edamame, are also high in protein and must be managed carefully.
Nuts and Seeds: Almonds, peanuts, cashews, sunflower seeds, pumpkin seeds, and sesame seeds are all rich in protein and should be limited. Peanut butter should also be avoided.
Artificial Sweeteners: The artificial sweetener aspartame metabolizes into phenylalanine in the body and should be strictly avoided. This includes many diet sodas, sugar-free gum, and packaged low-calorie foods.

Navigating a Low-Protein Diet: Food Comparisons

Adjusting to a low-protein diet can be challenging, but understanding food comparisons can make it easier to plan meals. This table contrasts foods that should be avoided with suitable, low-protein alternatives.


High-Protein Foods to Avoid	Low-Protein Alternatives	Notes
Meat & Poultry: Chicken, Beef, Pork	Specialty Products: Low-protein meat substitutes.	Many patients use specialized protein-free amino acid formulas prescribed by their doctor.
Dairy: Milk, Cheese, Yogurt	Dairy Alternatives: Unfortified almond milk, coconut milk, or rice milk.	Always check labels, as some plant milks contain added protein.
Seafood: Fish, Shrimp	Fruits & Vegetables: Most fruits, many vegetables (like leafy greens, peppers, zucchini) are very low in protein.	Focus on fruits and vegetables for bulk and nutrients.
Legumes: Lentils, Beans, Tofu	Refined Grains: White rice, white bread, and low-protein pastas.	Whole grains are higher in protein and should be limited.
Nuts & Seeds: Almonds, Peanuts	Healthy Fats: Olive oil, canola oil, and avocados.	Small portions of low-protein nuts may be allowed, but always consult your dietitian.
Aspartame: Diet Drinks	Sugar-based drinks: Regular soda (in moderation), fruit juices, water.	Check all food labels carefully to identify hidden aspartame.

The Role of Medical Foods and Dietitian Guidance

Due to the significant restrictions required, a low-protein diet can place individuals at risk for nutritional deficiencies and inadequate caloric intake. To counter this, many patients rely on medical foods—prescribed amino acid formulas that are free of phenylalanine and tyrosine.

Working with a specialist dietitian is critical for several reasons:

Personalized Meal Planning: A dietitian can help create a balanced diet plan that meets the individual's specific nutritional needs while controlling protein intake.
Monitoring Nutritional Status: Regular monitoring is necessary to ensure the patient is not developing deficiencies in protein, vitamins, or minerals.
Compliance Support: Low-protein diets can be complex and socially challenging. A dietitian provides guidance and support to improve long-term adherence.

Risks of Unsupervised Dietary Management

Attempting a strict low-protein diet without professional medical and dietary supervision carries significant risks:

Malnutrition: Inadequate intake of essential amino acids and micronutrients can lead to poor growth in children and severe nutrient deficiencies in adults.
Weight Changes: Research has shown that some AKU patients on unsupervised low-protein diets experienced unintentional weight gain, potentially due to over-consumption of fats and carbohydrates.
Poor Compliance: Strict, unguided dietary restrictions often lead to poor long-term adherence, undermining the intended therapeutic effect.

Conclusion

Managing alkaptonuria effectively requires a meticulous and personalized dietary strategy focused on restricting the intake of phenylalanine and tyrosine. The list of foods to avoid, which includes high-protein items like meat, dairy, eggs, legumes, and nuts, serves as a fundamental guide. However, a successful approach relies heavily on professional guidance from a dietitian, particularly when patients are on medication like nitisinone, to prevent malnutrition and manage side effects. Through careful planning and specialized medical foods, individuals can navigate this dietary challenge to help minimize the long-term impact of the disorder.

For more information on alkaptonuria and ongoing research, you can refer to relevant medical literature and patient resources, such as those published by the National Center for Biotechnology Information (NCBI) on PubMed Central (PMC), like this study on nutritional status in AKU patients.

Frequently Asked Questions

A controlled diet is crucial because alkaptonuria is a metabolic disorder that affects the body’s ability to break down the amino acids phenylalanine and tyrosine. By limiting the intake of these amino acids, the production and accumulation of homogentisic acid (HGA) can be reduced, helping to minimize long-term damage.

Common foods high in these amino acids include meat, poultry, fish, eggs, dairy products (milk, cheese, yogurt), legumes (beans, lentils), and nuts.

No, many common vegetarian protein sources, such as soy products (tofu, edamame), legumes (beans, lentils), and nuts, are high in phenylalanine and tyrosine and must be limited or avoided under professional guidance.

Nitisinone, a drug used to treat AKU, reduces HGA but causes a significant increase in circulating tyrosine levels. Patients on this medication require a more carefully managed, lower-protein diet to control tyrosine and prevent side effects like painful eye conditions (keratopathy).

Yes, but only under strict medical supervision from a metabolic dietitian. While protein restriction in early life may be beneficial, it must be carefully monitored to ensure normal growth and development and to prevent malnutrition.

No, following a strict low-protein diet without a doctor's guidance can be dangerous. It can lead to insufficient intake of essential nutrients and calories, causing malnutrition. Professional dietary supervision is necessary to create a safe and effective meal plan.

A low-protein diet for AKU typically includes plenty of fruits and vegetables. Many refined starches, such as white rice, white bread, and low-protein pastas, are also staples. Patients may also use specially formulated low-protein products and medical foods.