A low-protein diet puts less strain on the kidneys. As a result, this type of diet can benefit people with kidney-related disorders, such as kidney disease or phenylketonuria.

When a person eats protein, the body produces a compound called urea. If the kidneys are not functioning well, urea can build up in the blood and cause fatigue and a loss of appetite. By making key changes, a person can develop a satisfying and diverse low-protein diet plan that works for them. In this article, we discuss the benefits and risks associated with a low-protein diet. We also list some of the best foods to eat and avoid when limiting protein intake.

Who should follow a low-protein diet?

The Dietary Guidelines for Americans 2015–2020 recommend that most adults consume at least 10% of their daily calories in the form of protein. A low-protein diet involves eating less protein than this each day.

Some people cannot tolerate high levels of protein. If the body cannot process protein or its waste, these substances build up and cause symptoms ranging from nausea and vomiting to brain damage. For these people, following a low-protein diet will reduce the risk of negative health effects. Doctors may recommend that people with the following health conditions adopt a low-protein diet:

Kidney disease

By reducing protein intake, people with kidney disease who are not on dialysis can reduce stress on their kidneys and prevent the buildup of urea in the bloodstream. The body produces urea, a compound, during the digestion of protein. In people who do not have kidney problems, urea leaves the body through the urine, without causing issues. However, when the kidneys do not function correctly, urea builds up in the blood and causes symptoms such as nausea, fatigue, and loss of appetite.

A 2018 review of 17 studies reports that very low protein intake may slow down the progression of advanced kidney failure. The National Kidney Foundation advises that limiting protein intake can extend the amount of time before a person needs dialysis. Those already receiving dialysis treatment should not follow a very low-protein diet.

Diabetic nephropathy

A review of several studies reports that a low-protein diet may improve the symptoms of diabetic nephropathy, which refers to diabetes-induced kidney damage. The research did not uncover adverse effects of the diet, such as worsening of other diabetes symptoms.

Phenylketonuria

Phenylketonuria (PKU) is a rare disorder that occurs when the body does not produce the enzyme needed to break down an amino acid called phenylalanine. Amino acids are the building blocks of protein. For a person who has PKU, eating foods rich in protein can cause phenylalanine to build up in the body. If people with PKU do not receive treatment, it can lead to intellectual disability and other neurologic symptoms, such as hyperactivity, poor coordination, and seizures. The main treatment for PKU is a lifelong, very low-protein diet. People with the condition should consume only the minimal amount of phenylalanine necessary for healthy growth and development.

Homocystinuria

Homocystinuria is an inherited disorder that affects the body's ability to process methionine, another amino acid. A buildup of methionine causes problems with vision and bone health. As with PKU, treatment involves a very low-protein diet.

General benefits of a low-protein diet

Authors of a review of research suggest that a low-protein diet may also provide some benefits for people without kidney problems. They report that in middle-aged (but not older) adults, restricting protein intake may reduce the risk of:

• Cancer
• Diabetes
• Heart disease

Other research, published in the journal Cell Reports, indicates that a diet low in protein and high in carbohydrates may help protect brain health and reduce cognitive decline. However, the scientists only conducted this research in mice and cannot be sure of the effects in humans. Authors of a 2015 study report that a low-protein, high-carbohydrate diet may be just as effective at increasing a person's lifespan as following a calorie-restricted diet, possibly because of benefits to heart health and digestion. However, they only tested this in mice.

Foods to eat

Replacing some meat with vegetables and grains is an effective way to reduce protein intake. Vegetables and grains should form the main body of meals, with a supplementary protein source.

A person following a low-protein diet can get most of their calories from the foods below, which are relatively low in protein.

Low-protein foods

The following are low-protein foods:

• All fruits, except dried fruits
• All vegetables, except peas, beans, and corn
• Many sources of healthful fats, such as olive oil and avocados
• Herbs and spices

Many other types of food are low in protein, and a person should use moderation when incorporating them into the diet. Some of these foods include:

• Sugar
• Candies that do not contain gelatin
• Tea and coffee, without dairy milk
• Jams and jellies
• Mayonnaise
• Butter
• Many sauces and dressings, including tomato sauces and salad dressings

Moderate-protein foods

On a low-protein diet, people should eat foods that contain moderate amounts of protein sparingly. Examples include:

• Bread
• Crackers
• Breakfast cereals
• Pasta
• Oats
• Corn
• Rice

Low-protein versions of many of these products are available online or in pharmacies.

Recipe ideas

When following a low-protein diet, it can be helpful to think of vegetables and grains as the main components of a meal. A person should consider meat, pulses, and soy products to be side dishes or condiments.

The National Institutes of Health (NIH) report that most people, whether they have kidney disease or not, can meet their protein needs with just 2 servings of meat or meat substitutes each day. A serving is 3 ounces, or the size of a deck of cards.

Examples of satisfying low-protein meals include:

• A sandwich with very thinly sliced meat, lots of vegetables, and mayonnaise
• Fried white rice with vegetables and a small portion of meat, tofu, or shellfish
• Low-protein pasta with tomato sauce and roasted vegetables
• A burrito, made with a low-protein tortilla, vegetables, salsa, homemade guacamole, and a small portion of beans
• Vegetable curry with low-protein rice or a small portion of regular rice
• Homemade vegetable soup

Low-protein snacks include:

• Fresh fruit
• Raw vegetable sticks with salsa or homemade guacamole
• Homemade muffins, made with a low-protein baking mix
• Baked sweet potato fries with a spicy mayonnaise dip
• A fruit smoothie made with water or a low-protein dairy alternative, such as rice milk
• Homemade fruit juice popsicles

Other tips for a low-protein diet

Here are some other strategies for keeping protein levels low without compromising on flavor:

• Use unsweetened rice milk or another low-protein milk substitute in recipes that call for dairy milk
• Bulk up soups with small amounts of rice or pasta
• Increase the vegetable content while decreasing the meat content in recipes. For example, diced mushrooms can be a good meat alternative in spaghetti bolognese
• Add a small amount of egg to salads to make them more filling
• Top meals with a little parmesan cheese to increase the flavor without adding too much protein
• Make a meal more filling by adding some healthful fats, such as from avocado or a drizzle of olive oil

When grocery shopping, always check labels carefully for protein contents and ingredients.

Foods to avoid

Protein is an essential nutrient, so even people on a low-protein diet need to consume a certain amount of protein to stay healthy. However, high-protein foods should make up only a small part of the daily caloric intake. Anyone on a low-protein diet should limit or avoid the consumption of:

• Meat
• Poultry
• Fish and shellfish
• Eggs
• Dairy, including milk, cream, and cheese
• Beans, peas, and lentils
• Soy foods, such as tofu and tempeh
• Nuts, nut butters, and seeds
• Gelatin

Plant-based dairy alternatives often contain less protein. Learn about plant-based alternatives to dairy products, including milk, cheese, and butter here.

Staying healthy on a low-protein diet

As protein is vital for health, it is important to consult a doctor or dietician before restricting protein consumption to below 10% of the daily calorie intake. Typically, people should only restrict their protein intake to this extent when a doctor advises them to do so. Following a low-protein diet requires careful planning. Otherwise, it could lead to nutritional deficiencies and other health issues, including muscle loss and poor immune function.

Also, protein restriction is not suitable for everyone. For example, research suggests that older adults may need extra protein, due to the muscle wastage associated with advancing age. Furthermore, sticking to this type of diet can prove challenging for many, but with some planning, a low-protein diet can be healthful and satisfying.

A person on a low-protein diet may need to take certain supplements to stay healthy. Vitamin B12, for example, is only present in animal products and fortified foods. People who restrict their intake of meat and fish may not get enough B12 from food sources, so they may need to take supplements or eat foods fortified with this vitamin, such as some cereals and plant-based milks.

Discuss the use of supplements with a doctor or dietician before beginning a low-protein diet and stay in regular contact with health-care professionals. Researchers suggest follow-up visits every 3 to 4 months when on this diet.

Summary

People with kidney-related health conditions may need to follow a low-protein diet. The diet involves restricting the intake of high-protein foods and focusing on eating plenty of fruits, vegetables, and healthful fats. Doctors do not usually recommend a low-protein diet for people without health conditions because of the risk of nutritional deficiencies and other health issues. Anyone considering this type of diet should consult their doctor first. With planning, a low-protein diet can be varied and healthful.