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World Kidney Day 2020: Plant-based nutrition offers hope for both prevention and treatment of kidney disease.

Maintaining healthy kidneys is often overlooked in the fight against chronic diseases. Yet, chronic kidney disease (CKD) currently affects approximately one in ten adults worldwide and its burden is increasing. By 2040, it is projected to become the fifth most common cause of years of life lost globally. [1]

Without appropriate treatment strategies, CKD progresses to end-stage kidney failure requiring dialysis or transplantation to sustain the individual’s life.In high-income countries like Australia, the cost of dialysis and transplantation on the health care budget is immense, while in low-income countries most people with kidney failure have inadequate, if any, access to such lifesaving treatments.

For these reasons, World Kidney Day this year focuses on the importance of preventative interventions to avert the (a) onset and (b) progression of kidney disease. [1] As a nephrologist, I would argue there is nothing more powerful than optimal plant-based nutrition to help achieve these goals.

Primary prevention of CKD: averting the onset of CKD

The two most common causes of CKD are diabetes and high blood pressure (hypertension), which are together responsible for up to two-thirds of cases. Each of these diseases causes chronic damage to the blood vessels and internal structures of the kidney over time. In fact, up to 30% of people with diabetes will develop CKD within 20 years of their diagnosis. [2] In order to prevent CKD, we must therefore first address these two chronic diseases.

Fortunately, there is now established evidence that dietary change is a powerful strategy to treat both diabetes and hypertension, as it addresses their root cause: the highly processed, energy dense, nutrient-poor standard Western diet. Research shows that shifting to a more whole food, plant-based diet can not only prevent but even reverse these conditions.

Type 2 diabetes

Looking at type 2 diabetes first, a recent meta-analysis of 9 prospective studies found a healthy plant-based pattern of eating reduced the risk of developing type 2 diabetes by 30%. [3]. This is almost certainly an underestimate of the true reduction because the studies analysed adjusted for body weight (BMI), which is a mediator of dietary effect. Several controlled trials have also demonstrated reversal of established diabetes with dietary change alone. One such trial compared an unrestricted low-fat fully plant-based diet to a control group on a calorie restricted American Diabetic Association diet. [4] After 22 weeks, a larger proportion of the low-fat plant-based group were able to reduce their glycaemic therapy (43% vs. 26%). In addition, hemoglobin A1c decreased 0.96% in the plant-based group compared to 0.56% in the control. Given the starting mean A1c of 8.0%, this reduction represents substantial improvement in their disease.

Hypertension

Several dietary factors also impact blood pressure and rates of hypertension. Specifically, low sodium, high potassium (e.g. plant intake), low alcohol and weight loss all substantially reduce blood pressure [5], and the combination has been demonstrated in controlled trials to be very effective. [6] For example, amongst those with a systolic blood pressure >150 mmHg, the low-salt DASH diet (rich in fruits, vegetables and whole-grains) compared to a high-salt standard American diet had a mean reduction in systolic blood pressure of 20.8 mmHg. [7] This is more effective than any single drug therapy, without the harmful side effects.

Further benefits

Moving beyond the prevention and treatment of diabetes and hypertension there is even further evidence that a healthy diet helps to prevent CKD. Observational studies have shown a diet encouraging the consumption of plants is inversely associated with the development of CKD [8] and the initiation of dialysis [9], despite statistical adjustment for diabetes, obesity and hypertension. I have explored some of the specific mechanisms through which a plant-based diet improves kidney health further below.

Secondary prevention: slowing CKD progression

Diet is critical in the management of all CKD, irrespective of whether the disease is due to diabetes and hypertension, or other conditions such as auto-immune diseases, polycystic kidneys or malformations from birth. In all cases, a standard Western diet contributes significantly to chronic kidney damage and therefore plays a major role in the progressive worsening of kidney function and the development of end-stage kidney failure.

Protein: the plant advantage

One of the most important dietary factors for kidney health is protein intake. From animal studies it has been known for decades that a diet high in protein increases the workload for the kidneys (hyperfiltration). [10] Initially the kidney compensates well, but this extra stress has serious long-term consequences, ultimately resulting in progressive damage. Human studies support this animal research. Observational studies demonstrate a clear linear relationship between protein intake and risk of progression to kidney failure. [11] Furthermore, controlled trials show a low protein diet results in a slower decline in kidney function over time compared to a high protein diet. [12,13,14]

Unfortunately, the standard Western diet typically is very high in animal product derived protein, with average intakes close to two-times the recommended daily requirements (0.6-0.8g per kg of body weight per day). [15] Not only is protein intake on a whole food plant-based diet naturally lower (whilst remaining sufficient), but the proteins also come directly from plant origins. This is important because at least some animal proteins appear to be more detrimental to the kidney than plant proteins. [10] In fact, one study found that replacing just one daily serve of red meat with soy and/or other legumes could reduce the risk of reaching end-stage kidney disease by 50%. [16]

Dietary acid: the facts

Another important aspect of dietary effects on kidney function is acidosis. Every piece of food we eat is made up of acid and base pre-cursors that affect the acid-base balance in our blood. Animal-derived and refined foods are generally net acid-producing, whilst fruits, vegetables and legumes are net alkali-producing. In CKD, the kidney’s ability to maintain normal acid-base balance in the blood becomes impaired and acidosis can develop. Chronic acidosis is not only associated with a loss of bone mass, impaired heart function and increased risk of death, but also contributes to worsening kidney function. [17] It is therefore unsurprising that high dietary acid load (i.e. high consumption of animal foods) has been shown to significantly increase the risk of kidney failure [18] and markers of kidney disease progression. [19]

Tertiary prevention: preventing CKD complications

Lastly, in addition to slowing kidney function decline, a whole food plant-based diet addresses many complications seen in advanced kidney disease such as:

Cardiovascular disease

It is a sad fact that for people with CKD the risk of dying from cardiovascular disease is 20 times greater than the risk of requiring dialysis or transplantation. Plant-based diets are associated with a significantly lower risk of cardiovascular disease in both observational studies [20] and controlled trials. [21,22] A meta-analysis of 6 cohort studies of people with CKD found those eating a healthy dietary pattern (higher intake of plants) was associated with a 27% reduction in overall death. [23]

High phosphate levels

In kidney disease phosphate can build up in the blood and cause harm to bones and blood vessels, leading to an increased risk of death. Whole plant foods help combat this as they contain phytates that bind to dietary phosphate, thereby significantly reducing its gut absorption compared to highly processed and animal foods. [24]

Uremic toxins

Numerous organic solutes, which are normally removed from the blood by the kidney, accumulate in CKD and contribute to various symptoms, heart disease and risk of death. Due to changes in gut bacteria, two of the most well studied toxins, indoxyl sulfate and p-crestyl sulfate, have been found to be approximately 60% lower in vegetarians compared to omnivores. [25]

Summary

If we, as a global society, are to successfully manage the worldwide rising levels of CKD we will need to focus on holistic preventative strategies. Plant-based nutrition is not only an effective tool for primary prevention of kidney disease onset, but it can also play a powerful role in both secondary and tertiary prevention due to its ability to slow disease progression and avert severe complications. This World Kidney Day, I encourage everyone to raise awareness of both kidney disease and this underutilised approach to reduce its increasing impact on society.