Shaun Ward MSc ANutr
The kidneys are vital organs that perform many important functions such as filtering blood, producing hormones, removing waste, and maintaining fluid balance.
Unfortunately, people with compromised kidney function are forced to implement some form of renal or kidney diet to reduce the amount of waste in their blood that consequently places unnecessary stress on this organ.
This is because avoiding or limiting certain foods in the diet has proven to decrease the accumulation of waste products in the blood, improve kidney function, and prevent any further damage .
Therefore, following such a specialized diet may help to restore kidney function and slow the progression of complete kidney failure. The renal diet fits perfectly into this dietary category.
How The Renal Diet Works
The renal diet is low in sodium, phosphorous, and protein, and in some circumstances, limits the consumption of potassium and calcium.
More specifically, limits on sodium and potassium are generally placed at ~2,000mg per day, and ~1,000mg per day for dietary phosphorus.
Sodium is a mineral found naturally in many foods.
It represents one of the 3 major electrolytes in the diet (alongside potassium and chloride) and is responsible for controlling the transportation of fluid in and out of tissues and cells.
This makes sodium very important in regulating blood pressure, blood volume, nerve function, muscle contraction, and the acid-base balance of blood.
However, an excessive intake of sodium is not ideal for people with kidney disease because their kidneys cannot adequately eliminate the excess sodium and fluid from the body.
As a consequence of this, sodium and fluid may accumulate in the bloodstream and various tissues and lead to thirst, edema, high blood pressure, heart failure, and a shortness of breath.
Potassium is a mineral that is contained in certain foods we eat and is also stored in the body to aid various metabolic processes.
It plays a role in maintaining a sufficient heartbeat, the contraction of muscle tissue, and for maintaining fluid and electrolyte balance in the bloodstream.
When the kidneys are impaired, they struggle remove excess potassium, causing an accumulation of potassium in the body.
This can lead to a clinical issue called hyperkalemia which causes muscle weakness, irregular heartbeats, reduced pulse, and potentially even heart attacks.
Despite what may be said by many people, protein does not damage healthy kidneys.
Under normal physiological circumstances, the kidneys can easily deal with and excrete the waste products from protein metabolism. Then, with the help of additional renal proteins, the waste turns into urine.
However, this is not the case for an individual with dysfunctional kidneys, as damaged kidneys will not sufficiently remove protein waste.
Fluid control is important for people with kidney issues as normal fluid consumption may cause fluid build-up in the body and potentially become dangerous.
The Potential Benefits of The Renal Diet
The low protein and phosphorus intake on the renal diet has demonstrated a benefit for preventing proteinuria, hyperphosphatemia, and hyperparathyroidism, which would all otherwise contribute towards cardiovascular damage and increased mortality risks in patients with kidney issues.
It does so by reducing nitrogenous waste products and parathyroid hormone levels, which can help ameliorate insulin sensitivity and promote metabolic control.
It May Reduce Cardiovascular Complications
The risk of death from cardiovascular events has been estimated to be ~16 times higher when someone has serious kidney disease .
This is because chronic kidney disease results in more inflammation and oxidative stress, which are risk factors for cardiovascular disease and atherosclerosis .
Moreover, it is well known that sodium restriction, which leads to a reduction in volume expansion, is a key factor for improving the response to anti-hypertensive treatment in kidney failure patients .
It May Reduce Phosphate Issues
Kidney failure patients often report disturbances to calcium-phosphate metabolism, leading to hyperphosphatemia (positive phosphate balance) and high parathyroid hormone levels.
The implementation of a renal diet that is low in dietary phosphate is regarded as the primary prevention and treatment of hyperparathyroidism and hyperphosphatemia in people with kidney issues .
Restriction of dietary phosphate allows for a reduced burden to be placed on the kidneys, and reduces the time it takes to reverse kidney disease.
Many successful results in terms of phosphate control and the prevention of hyperparathyroidism have been obtained from a ketogenic diet (low in phosphate) .
Such a diet allows for the correction of phosphorus and parathyroid hormone levels in the blood of kidney disease patients .
It May Prevent Proteinuria
Proteinuria and albuminuria are the strongest risk factors for cardiovascular events in patients with kidney disease .
To counter this problem, protein-restricted diets are key to reduce urinary protein excretion and the risk for proteinuria and albuminuria .
It May Reduce Inflammation
Chronic inflammation is present in ~40% of patients with major kidney problems and may be a driver of many chronic diseases.
In another prospective studies, low protein, low phosphorus diets such as the renal diet can significantly reduce inflammatory biomarkers such as TNF-alpha .
In addition, long-term effects of protein restriction in chronic kidney disease patients have been reported to lower C-reactive protein levels .
This may also be due to the fiber, vitamin C, and vitamin E content of the renal diet, which are all closely associated with a lower risk of elevated C-reactive protein levels. As you may be aware, these are all nutrients which contribute to the anti-inflammatory effects seen with other diets, such as a plant-based diet .
Many experts even recommend a low protein, vegetarian based diet to treat chronic uremia because of how much it has been observed to lower oxidative stress and reduce clinical complications .
The renal diet is great for people with kidney problems that are looking to avoid common symptoms of poor kidney health.
Carefully regulating the intake of protein, sodium, and phosphorus on this diet will improve common cardiovascular, inflammatory, and blood issues during a time where the kidneys are impaired.
However, it is important to categorize the renal diet as a “specialized diet” that is not suitable for healthy individuals without kidney issues.