WASHINGTON, DC – The effects of plant-based diets and phosphorous restriction on kidney disease were the subject of two talks presented at Kidney Week 2019.

Plant-based diets may be good for people with kidney disease, said Juan Jesus Carrero, MD, PharmD, PhD, a professor of epidemiology with the Karolinska Institute in Sweden. Plant proteins had been viewed as having low biological value, he said, because when dietary guidelines were issued, it was believed impossible to acquire complete essential amino acids from plant foods. However, numerous trials and meta analyses conducted over the past 20 years have proved that theory wrong. Fruit and vegetable intake has been shown to offer numerous health benefits such as lowering the risk of chronic kidney disease (CKD), end-stage renal disease (ESRD) and death, and delaying the progression of kidney disease.

Few natural diets today provide insufficient amounts of essential amino acids in adults, Carrero said. Even vegan diets do not risk malnutrition in patients with end-stage renal disease¹, as in dialysis patients, such diets can achieve protein intake of greater than 1.1 g per day/kg². Plant proteins have had more beneficial effects than animal-based sources of protein, he added. Studies have indicated that substituting one serving of red or processed meat with plant proteins can  lower the risk of CKD by 20-30%³, and the National Health and Nutrition Examination Survey (NHANES) found that a diet with a higher proportion of protein from plant sources was associated with lower mortality⁴. Plant proteins also have been shown to reduce kidney plasma blood flow, increase kidney vascular resistance, and lower the fractional clearance of albumin.

One concern with recommending fruit and vegetable intake has been the development of hyperkalemia, Carrero said, but that assumes that plants are the main source of serum potassium.

“We often forget that many meat and dairy products have a potassium content similar to many fruits and vegetables,” Carrero said. “We tend to disregard that many fruits and vegetables have a low potassium content, and perhaps those we can be more comfortable recommending.”

While hyperkalemia is a serious event, he said, evidence so far suggests that dietary potassium can contribute more marginally than originally thought. Dietary potassium should be restricted only when necessary, and it may be better to replace rather than restrict the diet with fruits and vegetables containing low potassium---such as peas and legumes, raspberries and apples---especially if they also can provide fiber.

In a second talk on serum phosphate, Myles Wolf, MD, a professor of medicine and nephrology at Duke University School of Medicine, in Durham, N.C., noted there is a large body of evidence suggesting high serum phosphate is an independent risk factor for mortality in ESRD, in CKD and in the general population. Much of the phosphate found in plant-based sources is poorly absorbable, Wolf said, “so we can probably consume more total phosphate safely in kidney disease without exerting a big effect on serum phosphate.”

However, processed foods consumed by lower socioeconomic groups tend to have high amounts of phosphate-based food additives. Food labels aren’t always clear, and people may be consuming a whole lot more phosphate than they think.

“We think that the United States food industry is harming people of low socioeconomic status with poor access to healthy foods, who are disproportionately eating phosphate-based food additives that necessessitate a bigger FGF23 response to maintain normal phosphate levels that contributes to cardiac injury, heart disease and well-known disparities in heart failure,” Wolf said. “Kidney disease disproportionately affects these same segments in the U.S. population, and this is a real problem.”

Ways to combat this include teaching patients to read food labels to avoid products that list phosphorus, and using phosphate binders and other mediations. Tenapanor, a drug that blocks sodium absorption in the gut, has led to serum phosphate reductions of 2 or 3 mg/dL, he said. Other avenues of study aim to block Npt2a, one of the kidney transporters for phosphate reabsorption.

“One real important piece in lowering serum phosphate [that] we’re lacking is the proof that doing so improves clinical outcomes,” Wolf said. A pragmatic trial he is involved with aims to determine the best blood level of phosphate for people with kidney failure on dialysis.

Resources

1. Soroka N, Silverberg DS, Greemland M, et al. Comparison of a vegetable-based (soya) and an animal-based low-protein diet in predialysis chronic renal failure patients. Nephron. 1998;79(2):173-80.
2. Kandouz S, Mohamed AS, Zheng Y, et al. Reduced protein bound uraemic toxins in vegetarian kidney failure patients treated by haemodiafiltration. Hemodial Int. 2016 Oct;20(4):610-617. doi: 10.1111/hdi.12414 . Epub 2016 Apr 4.
3. Haring B, Selvin E, Liang M, et al. Dietary Protein Sources and Risk for Incident Chronic Kidney Disease: Results From the Atherosclerosis Risk in Communities (ARIC) Study. J Ren Nutr. 2017 Jul;27(4):233-242. doi: 10.1053/j.jrn.2016.11.004 . Epub 2017 Jan 5.