The Renal Diet: Foods to Eat & Avoid in Kidney Disease

Chronic kidney disease is one of the most common age-related diseases and is diagnosed in nearly two out of five people with diabetes. After diagnosis with kidney disease, the most important thing to do is eat well. Read on to learn more about the renal diet.

What is the Renal Diet?

In brief, a renal diet is a diet designed to go as easy on the kidneys as possible.

The kidneys are, along with the liver, a major part of the body’s filtration system. They sift through the blood and remove salt, minerals, fluid, and waste products like urea. That waste is transported to the bladder and leaves the body as urine [1].

Certain foods give the kidneys more work to do than others. After all, the more salts and waste they have to filter out, the harder they work. Plus, salt and other electrolytes raise blood pressure, which also stresses the kidneys [1, 2, 3].

Healthy kidneys don’t generally have a problem working a bit harder, but certain factors – genetics, underlying health conditions, or eating a bad diet over a long period of time – can stress the kidneys until they begin to fail [1, 2, 3].

A renal diet prevents stress to the kidneys and slows the progression of chronic kidney disease or CKD. It avoids foods that are high in salt, certain minerals, and proteins [4].

Glomerular Filtration Rate (GFR)

For a clearer picture of why some foods put more stress on the kidneys than others, we need to take a deeper dive into the anatomy and physiology of these organs.

Each kidney is made up of many small structures called nephrons. Each nephron contains a glomerulus: a tiny filter where salts, fluid, and waste leave the blood and head to the urine. The efficiency of the glomeruli is measured as the glomerular filtration rate, or GFR [5, 6].

The kidneys need to be strong – with a high, efficient GFR – to be able to process salty, high-protein foods efficiently [3].

Low GFR is often the first sign of chronic kidney disease (CKD). As GFR falls, kidney disease is considered more and more serious. CKD progresses through stages numbered 1 through 5, where stage 5 is considered kidney failure [7, 8].

Who Needs the Renal Diet?

Generally speaking, only people with chronic kidney disease need to eat a renal diet. However, people who are at risk of developing CKD should consider changing their diets to include healthier foods. People who eat healthy, varied diets – the Mediterranean or MIND diet, for example – develop CKD at a much lower rate than average [3].

Diabetes and Chronic Kidney Disease

Up to 40% of people with diabetes develop chronic kidney disease or CKD. High blood sugar causes high blood pressure and stresses the kidneys in much the same way as sodium and waste [9, 10, 11].

Therefore, people with diabetes must carefully control their blood sugar to avoid stress and damage to the kidneys. If a diabetic person develops CKD, they are usually advised to follow a modified version of the renal diet that excludes foods that raise blood sugar [11].

Genetics of Kidney Disease

Some genetic variants are associated with higher rates of chronic kidney disease than average. One of the most studied genes in this category is APOL1, which produces part of the protein that makes HDL (good) cholesterol [12].

In the APOL1 gene, the highest risk of kidney disease seems to be associated with [13, 14]:

• The minor G allele at rs73885319
• The minor G allele at rs60910145

Another well-studied gene is UMOD, which produces uromodulin, a protein made in the kidneys and excreted in the urine. More than 40 mutations in UMOD can increase the risk of kidney disease [15].

• At rs4293393, the T allele is associated with increased risk of kidney disease and the C allele is protective against kidney disease [16, 17].
• At rs13333226, the G allele is slightly protective against kidney disease [18].

Mutations in the MYH9 and SHROOM3 genes are also associated with increased risk of kidney disease.

• MYH9 produces a protein involved in cell movement. The A allele at rs11912763 and the G allele at rs5750250 are associated with increased risk of kidney disease [19, 14].
• SHROOM3 produces a protein that regulates cell shape in some tissues. The A allele at rs17319721 is associated with increased risk of kidney disease [20, 21].

If you believe that you are genetically predisposed to kidney disease, talk to your doctor about whether the renal diet could be appropriate for you.

Snapshot

Foods to avoid:

• Salty, processed, fermented, or pickled foods
• Whole grains, chocolate, beans, nuts, and lentils
• Oranges, bananas, melons, and tomatoes
• Cheese

Foods to increase:

• Lots of fruits and vegetables that aren’t very high in potassium
• Fish as a source of protein and omega-3 fats
• Other sources of omega-3 fats

Make sure you get enough:

• Calcium, vitamin D, iron, and folate
• Protein
• Total calories

Renal Diet Foods

To Avoid

As we’ve already discussed, the renal diet works by avoiding stress to the kidneys. In the early stages of chronic kidney disease (CKD), that mostly means salt, potassium, and phosphorus. As CKD progresses into its later stages, that might also mean protein and even fluids.

Some of the foods that produce the most stress on the kidneys include [4, 22]:

• Salt
• Highly processed foods (lunch meat, canned soups, bottled sauces, fast food)
• Pickled foods (including tofu, olives, and relish)
• Salted or cured meats
• Beans, nuts, and lentils
• Whole grains
• Chocolate
• Oranges, bananas, melons, tomatoes
• Potatoes and sweet potatoes
• Avocado
• Milk
• More than 8 ounces of protein per day

1) Foods High in Sodium

Sodium is one half of table salt or sodium chloride. Processed foods and meat are highest in sodium, while fruits and vegetables are the lowest. It is important to minimize salt because, without proper filtration in the kidneys, sodium can raise blood pressure to dangerous levels [4, 22].

Depending on GFR and stage of disease, each person’s recommended sodium intake may be different. The American Heart Association recommends less than 2400 mg of sodium a day for everyone; those on a renal diet will need to aim for less than that. The goal is to keep blood pressure below 140/90, which may require some fine-tuning of sodium intake [22].

Besides table salt and salted snacks, some of the foods that are highest in sodium include:

• Beef and chicken broth [23, 24]
• Prepared soup mixes [25]
• Prepared gravies and sauces [26, 27, 28]
• Prepared desserts like pudding [29]
• Fermented or pickled foods like tofu, capers, and olives [30, 31, 32]
• Cured meats like bacon or salt pork [33, 34]
• Cured sausages like salami [35]
• Some cheeses like Roquefort and parmesan [36, 37]

In short, to keep your sodium intake low, avoid salted, pickled, or highly processed foods.

2) Foods High in Potassium

Potassium is an essential nutrient. Our bodies need it to keep all of its cells functioning normally. However, those with chronic kidney disease need to keep a close eye on their potassium intake because both low (< 3.5 mmol/L) and high (> 5.5 mmol/L) levels of potassium are associated with increased mortality from renal disease [38, 39, 40].

For most people, the daily recommended intake of potassium is 2.6 – 3.4 g without a set upper limit. People on a renal diet should stay below 3 – 4 g per day [38, 22].

Some of the foods that are highest in potassium include [38]:

• Apricots, raisins, and prunes
• Bananas
• Lentils
• Squash
• Potatoes
• Beans
• Instant coffee [41]

Many vegetables contain relatively high amounts of potassium. People on a renal diet can eat potatoes, squash, and other vegetables safely by taking a few extra steps to prepare them. Peel and slice the vegetables and soak them in warm water for about two hours. Then, drain them and boil them in fresh water [22].

Each person is different. Talk to your doctor to make sure that this preparation method will reduce potassium enough for your kidneys to safely handle these vegetables.

3) Foods High in Phosphorus

Phosphorus is important for the growth and maintenance of tissues, especially bones and teeth. Most adults need at least 580 mg per day to prevent deficiency, and people on a renal diet should stay below 1 g per day [42, 22].

Some foods that are high in phosphorus include:

• Whole grains, seeds, and bran [43, 44, 45]
• Cheese [46]
• Smoked salmon [47]
• Meat, especially bacon and organ meats [48, 49]
• Nuts and nut butter [50, 51]

People on a renal diet also often take phosphate binders. These medications attach themselves to phosphorus in the digestive system and prevent it from being absorbed into the bloodstream [22, 52].

4) High-protein Foods

Protein may or may not be limited in a renal diet depending on the person and the stage of chronic kidney disease [22].

Too much protein can result in large amounts of urea building up in the kidneys. This condition is called uremia; its symptoms include fatigue, nausea, and lack of appetite. On the other hand, some protein is absolutely required to build and maintain tissues. This balancing act is very important to get right [22, 53].

If your doctor advised a renal diet, you will work together to determine the ideal protein intake for you. For dialysis patients, recommended intakes range from 0.6–1.3 g per kg of body weight per day. For a 150 lb person, that would be between 40.8 and 88.4 g (1.4 and 3.1 oz) per day [22].

5) Excessive Fluids

People don’t usually need to limit their water intake on a renal diet. The exception is for stage 5 chronic kidney disease (CKD) or renal failure. People who reach this stage of CKD have very low kidney function and produce very small quantities of urine. They are usually restricted to 600-1000 mL of fluids per day [22].

To Eat

Looking at a long list of foods you can’t eat can be daunting, so let’s talk about the foods that you can – and should! – put in your grocery cart.

Grocery List

Some of the best foods for people on a renal diet include [4, 22]:

• Apples, berries, cherries, grapefruit, pineapples
• Leafy greens, sprouts, leeks, endives, parsley, chives
• Beets, carrots, onions, radishes, turnips, jicama
• Garlic and ginger
• Sweet and hot peppers
• Mushrooms
• Cauliflower
• Spaghetti squash, summer squash, zucchini
• Bread (not whole grain, which is high in phosphorus)
• Low-salt dry and cooked cereals (not whole grain)
• Popcorn, rice cakes, tortillas
• Non-dairy creamers, rice milk
• Vegetable oils (olive and canola)
• Most spices (in moderation)
• Jam and jelly

If you have mild, early-stage CKD, your diet will not be limited to only these foods. Talk to your doctor about your allowances for sodium, phosphorus, and potassium to make sure you’re eating the ideal diet for you.

Healthy Fats

People eating a renal diet are often advised to add polyunsaturated fatty acids (PUFAs), especially omega-3 fatty acids, to their diet. Omega-3 fats may help prevent uremic pruritus, a terrible itchy feeling on the back, abdomen, head, and arms that develops in the later stages of chronic kidney disease (CKD). Omega-3 fats have also been associated with reduced rates of cardiovascular disease in people with CKD [54, 55].

To increase your omega-3 intake, try getting some of your protein from oily fish like salmon, herring, and mackerel. Be careful with salmon, however, as it can contain as much as 371 mg of phosphorus in a 100 g serving, where the other fish have much less. By contrast, beef steak contains a little over 300 mg of phosphorus in a 100 g serving [56, 57, 58, 59].

As always, the best thing to do when in doubt is to ask your doctor about what’s safe and appropriate for you.

Common Deficiencies

Because of the strict limits on potassium and phosphorus, it can be very difficult for people on a renal diet to get enough of some other vitamins and minerals. Some of the nutrients that may need to be supplemented include [22]:

• Calcium (foods high in calcium tend to also be high in phosphorus)
• Vitamin D
• Iron
• Folate

Iron is especially tricky because phosphate binders can also decrease the absorption of iron supplements. Eat foods high in iron to prevent anemia. Some good choices include spinach, shellfish, and beef, but be mindful of your protein limits, if any [22].

Total Calories

Because of the restriction on salt, some people find that a renal diet doesn’t taste very good and, as a result, eat less food. Getting enough calories can be difficult for such people, but low caloric intake can lead to energy deficit and malnutrition. It is very important to meet your caloric needs, even if you don’t find that food tastes very good [22].

The approximate caloric needs of a person with chronic kidney disease are 30 kcal per kg per day. For a 150 lb person, that’s about 2040 calories [22].

Medications to Avoid

Some drugs are processed in the kidneys and excreted in the urine. These drugs can stress the kidneys and should be avoided if you are eating a renal diet. They include:

• NSAIDs like ibuprofen and naproxen [60]
• Some antibiotics such as vancomycin [61]
• Some diuretics such as furosemide [62]
• Some ACE inhibitors [63]

Make sure to follow your doctor’s recommendations to protect your kidneys.

Challenges

It can be difficult to follow a renal diet. Some of the challenges laid out for people with chronic kidney disease (CKD) include:

• Guilt, anxiety, and depression: it’s hard to go out or eat in with friends and have to eat completely different foods from everyone else. Some people become anxious and depressed, while others break their diets in social settings [22].
• Health literacy and available information: much of the information presented online is either inaccurate or too difficult to understand. It’s important to find high-quality sources or speak to your doctor directly about what’s best for you [64, 65].
• Cost: the renal diet is more expensive than the average American diet. This may make it inaccessible to some people with CKD unless they receive subsidies or stipends [66].
• Protein balance: the true benefit of low-protein diets is still being debated. Finding the correct protein intake for each person can be a serious challenge, especially since low protein can lead to wasting and other health problems [53].

Your doctor or another health professional may have some resources to help you adhere to the diet and maintain your kidney function. Reach out for support if you’re having difficulties!

New & Evolving Perspectives

The renal diet of today is not the same as the renal diet of just a few decades ago, and it is likely to continue changing in the near future. Even now, different people may say “renal diet” and mean different things. It’s easy to get confused, and this confusion is probably part of why some people don’t follow their diets as well as they should for optimal health [67, 64].

Alternative Diet Plans

One possible alternative to a strict renal diet is the “six-tip diet.” Adherents only need to follow six tips to keep the diet [68]:

1. Do not add salt during cooking or at the table
2. Avoid salami, sausages, cheese, dairy products, and canned food
3. Replace noodles and bread with special low-protein/hypoproteic food (prescribed food)
4. Eat meat, fish, or eggs at one meal per day (in prescribed amounts)
5. Eat 4-5 servings per day of fruit and vegetables
6. Once or twice a week, eat normal (not low-protein/hypoproteic) noodles with legumes

According to the main study that developed this diet, people with stage 3-5 CKD saw improvements to their lab tests when they were assigned to the six-tip diet. Many people find this plan easier to follow than the conventional renal diet, and more people tend to stick to it than to a low-protein diet [68].

In earlier stages of chronic kidney disease (CKD) or in people at risk of CKD, the Mediterranean or DASH (Dietary Approach to Stop Hypertension) diets could be enough to halt the progression of the disease without resorting to a strict renal diet [22].

Talk to your doctor about whether an alternative diet might be appropriate for you. Do not switch to any restrictive diet without seeking medical advice, especially if you’re already on a diet recommended by a doctor.

For Dogs & Cats

Kidney disease isn’t just a problem for humans, but for our animal companions as well. The biggest challenge of renal diets for dogs and cats is that these animals need much more meat – and, thus, protein – in their diets than we do [69].

Commercial food is specially formulated for pets with chronic kidney disease (CKD). However, some pet owners want more control over what their companions eat. If you design your pet’s diet, researchers have a few tips for managing CKD [70].

Renal Diet Tips for Pets

• To prevent nausea and distension of the stomach, feed less food with a higher energy density. In practical terms, that means more fat and fewer carbohydrates and protein [70].
• Omega-3 fatty acids maintain a better glomerular filtration rate (GFR) than saturated fats. Some dogs with CKD may actually see increased kidney function when fed omega-3s. Using fish as a protein source may help [70].
• To reduce the amount of acid secreted in the stomach, reduce the percentage of protein relative to fat [70].
• To prevent oxidative stress in the kidneys, supplement with vitamin E, vitamin C, and beta-carotene [70, 71].

Watch for signs of electrolyte imbalance. Unlike humans, cats (and dogs, to a lesser extent) may actually become deficient in potassium because of CKD. Cats with low potassium will have weakened muscles and may not be able to lift their heads when sitting upright [70].