Protein is one of the three macronutrients — the other two being carbohydrates and fats — that your body requires in large amounts to function optimally.
While a high-protein diet has several advantages for fat loss, blood sugar control, and healthy aging, a low-protein diet may be necessary for some instances.
This article explains what to eat and avoid on a low-protein diet and provides a 3-day sample low-protein diet menu.
What is a low-protein diet?
Protein is a macronutrient that plays several important functions in the body.
The functions of protein include (1):
- growth and maintenance of tissues
- production of enzymes and hormones
- provides structure for bones, tendons, ligaments, and skin
- maintains proper cell acid-base and fluid balance
- supports immune health
- transports and stores nutrients
Amino acids are the building blocks of protein.
There are hundreds of amino acids found in nature but your body only needs 20, nine of which you must get from foods since your body cannot make them (2).
As a vital component of life, protein is found in most foods, with dairy products, meats, seafood, beans, seeds, and nuts being the richest sources.
The recommended dietary allowance (RDA) of protein for a healthy adult is 0.36 grams per pound (0.8 grams per kg) of body weight per day (3).
While the definition of a low-protein diet varies, it generally refers to an amount of protein below the RDA, usually 0.27 grams per pound (0.6 grams per kg) of body weight per day, but sometimes lower.
Uses and benefits
Many people including older adults and those who are physically active or trying to lose weight may benefit from consuming a high-protein diet.
Others, however, including those with advanced kidney disease or certain inborn errors of metabolism may benefit from following a low-protein diet.
Advanced kidney disease
Kidney or renal disease is a chronic condition where the function and health of your kidneys progressively decline over time.
There are five stages of kidney disease, with stages 3-5 being classified as advanced kidney disease.
A key responsibility of the kidneys is to filter urea, a waste product that forms in the blood when you metabolize protein.
In advanced stages of kidney disease, the kidneys cannot effectively filter urea from the blood, which allows it to build up in the body where it can further impair kidney function and damage other organs.
Restricting protein may help alleviate this strain, potentially slowing the progression of kidney disease and the need for dialysis (4).
As such, current clinical practice guidelines recommend that adults with advanced kidney disease follow a low-protein diet providing 0.25–0.27 grams per pound (0.55–0.60 grams per kg) of body weight (5).
In people with advanced kidney disease and diabetes, the guidelines recommend a higher intake of 0.27–0.36 grams per pound (0.6–0.8 grams per kg) of body weight due to protein’s beneficial role in blood sugar control.
However, it’s unclear whether restricting protein in people with advanced kidney disease will reduce their risk of dying from the disease or some other reason (6).
Protein metabolism disorders
A low-protein diet may also be necessary for certain for those with certain disorders that affect protein metabolism, including phenylketonuria (PKU) and homocystinuria (HCU).
These conditions cause changes in the enzymes that the body needs to break down certain amino acids, which can consequently build up in the body and cause health problems.
People with these conditions don’t need to necessarily restrict protein but instead the amino acids that the body cannot metabolize.
Downsides and risks
A low-protein diet contains inadequate amounts of protein necessary to support normal bodily functions.
- decreased muscle size and strength
- weakened immune health
- increased risk of falls and fractures
- skin, hair, and nail problems
- fatty liver
- weakness and fatigue
- decreased metabolism
- development of other nutrient deficiencies, such as iron, calcium, vitamin D, and vitamin B12
Because of these effects, you should only follow a low-protein diet under medical supervision and with the guidance of a registered dietitian.
In some instances, the potential benefits of a low-protein diet may not outweigh its risks and downsides.
Foods to eat and limit
While most foods contain protein, many plant-based sources tend to be low in protein.
Here is a list of low-protein foods:
- Non-starchy vegetables, such as asparagus, beets, broccoli, leafy greens, mushrooms, onions, peppers, squash, and tomatoes
- Fruits, such as apples, bananas, berries, cherries, grapes, peaches, oranges, watermelon, etc.
- Grains, such as bread, rice, pasta, and oats
- Oils, such as canola or olive oil
- Certain plant-based dairy alternatives, including almond or oat milk
- Beverages, including coffee, tea, and juice
Because these foods are low in protein, you can generally enjoy these foods without having to worry about your portion sizes.
But when it comes to animal-based products and certain plant foods, you will have to be more cautious.
High-protein foods to limit include:
- Meats, including beef, goat, lamb, and pork
- Poultry, including eggs, chicken, turkey, and waterfowl
- Seafood, including fish and shellfish
- Dairy, including cottage cheese, milk, and yogurt
- Soy products, including natto, soy milk, tofu, and tempeh
- Legumes, including chickpeas, peas, navy beans, and other beans
- Nuts and seeds, including almonds, chia seeds, flaxseeds, pecans, and walnuts
You don’t necessarily need to avoid these foods, but you should limit your serving size and decrease the frequency in which you consume them.
For example, have 2 ounces (57 grams) of chicken breast instead of the standard 4-ounce (113-gram) serving.
3-day sample low-protein diet menu
The sample diet menu may also contain fewer calories than your body needs to maintain your weight.
It’s important to consume enough calories each day so that the limited amounts of protein that you do consume can be used for its normal functions such as immunity and supporting muscle health rather than being used as energy.
Also, remember that it’s OK to eat high-protein foods as long as you limit your portion and the frequency in which you consume them.
Here’s a 3-day sample low-protein diet menu that contains under 50 grams of protein per day:
- Breakfast: 1/2 cup oats topped with 1 cup blueberries and mixed with 1 cup almond milk
- Lunch: grilled cheese and 1 cup of tomato soup
- Snack: 2 tbsp of hummus with raw veggies for dipping
- Dinner: 2 ounces baked salmon, 1 cup white rice, and asparagus
- Breakfast: 1/2 cup cottage cheese with tomato slices on 2 slices of white toast
- Lunch: veggie burrito bowl with 1/2 cup of black beans
- Snack: apple slices and 2 tbsp of peanut butter
- Dinner: veggie pasta
- Breakfast: 1 cup of high-fiber cereal with 1 cup of almond milk
- Lunch: garden pasta salad with rotini
- Snack: 2 cheese sticks, 1 ounce of almonds, and an orange
- Dinner: 1 cup of chicken noodle soup and a green salad
Keto acid analog supplements
Supplementation with keto acid analogs can be beneficial to ensure you’re getting enough essential amino acids, especially for very low-protein diets containing around 0.14 grams per pound (0.3 grams per kg) of body weight (5).
There are nine essential amino acids that you must get from food since your body cannot produce them.
Animal-based foods are particularly rich in these essential amino acids so diets that restrict them, such as low-protein and vegan diets, tend to contain low levels of these amino acids.
Keto acid analogs don’t increase blood urea levels so they can be used to help you meet your protein needs while reducing kidney strain.
There are a variety of different keto acid analog supplements that are formulated for those with advanced kidney disease on low- and very-low protein diets.
While these keto acid analog supplements can also be useful for helping people with PKU and HCU meet their protein needs, some of the products contain the amino acids that those with these conditions must avoid.
The bottom line
A low-protein diet generally restricts protein to 0.27 grams per pound (0.6 grams per kg) of body weight per day, but sometimes lower.
It’s commonly prescribed for people with advanced kidney disease to slow its progression and delay the need for dialysis.
A low-protein diet may also be recommended for people who cannot process certain amino acids, including those with PKU and HCU.
Due to its downsides and risk of adverse health effects, you should only follow a low-protein diet under medical supervision and with the guidance of a registered dietitian.
Keto acid analog supplements are useful to help people with advanced kidney disease who are following a very low protein diet meet their protein needs, but they may contain amino acids that must be restricted by those with PKU and HCU.