Meat Your Veggies

Diet plays a crucial role in the prevention and management of kidney diseases, including CKD and urinary stone disease.^1,2 In CKD, the dietary recommendations often include modulation of certain nutrients, including protein, phosphorus, potassium, and sodium, and preferring healthy dietary patterns.¹ In urinary stone disease, dietary recommendations depend on the type of kidney stone and include an adequate fluid intake, adequate calcium intake from foods, and increasing citrate intake through a diet high in fruits and vegetables while limiting animal-based protein and excessive oxalate intake.² Therefore, increasing fruits and vegetables is a key recommendation for managing both types of diseases.

In CKD, the recommendation to increase fruit and vegetable intake is primarily to limit metabolic acidosis by consuming base-producing foods and additional potential benefits, including lowering BP, increasing dietary fiber intake with benefits to the gut microbiome, and reducing mortality.^1,3 While it may sound like an easy-to-follow recommendation, the intake of fruits and vegetables has been consistently reported below the recommendations in people with CKD. In an analysis of the National Health and Nutrition Examination Survey from 1988 to 2018, people with CKD were more likely to consume a diet low in fruits and vegetables than those without CKD.⁴ In a cohort of almost 10,000 people undergoing hemodialysis from ten European countries and Argentina, the median intake of fruits and vegetables was eight (interquartile range, 4–14) servings per week, equivalent to approximately one serving of fruits and vegetables per day.⁵ This low consumption may reflect the restrictive nature of the kidney diet in CKD, which historically has emphasized limiting a variety of fruits and vegetables because of their potassium content and a potentially higher risk of hyperkalemia in people with advanced CKD.¹

People with urinary stone disease are recommended to increase their fruit and vegetable intake, particularly in those individuals with hypocitraturia.² Because fruits and vegetables are the major contributors of alkali in the diet, dietary patterns emphasizing a higher consumption of fruits and vegetables, such as the Mediterranean and Dietary Approaches to Stop Hypertension diets, are recommended to limit the risk of kidney stone formation.² However, people with urinary stone disease are also likely to consume inadequate amounts of fruits and vegetables despite the known potential benefits. Some barriers to an adequate fruit and vegetable consumption include food insecurity, inadequate access, taste preference, food literacy, concerns regarding preparation time, and rapid spoilage. Therefore, alternatives that can help overcome these barriers to improve the intake of fruits and vegetables are needed.

Plant-based meat alternatives may help overcome some of these barriers by facilitating the exchange of foods that people readily consume (i.e., animal-based products) and providing a similar product in appearance and taste. Plant-based meat alternatives generally contain lower sulfur-containing amino acids while simultaneously providing some alkali precursors such as potassium, calcium, and magnesium, which may help decrease acid production and benefit people with CKD and urinary stone disease. However, some limitations of consuming plant-based meat alternatives, particularly those with almond or soy as the primary protein source, include a higher oxalate—a potential problem for people with hyperoxaluria—and higher sodium and phosphate-containing additives than their animal-based meat counterparts.¹ To date, there are limited data on the effect of plant-based meat alternatives in people with CKD and urinary stone disease.

In this issue of CJASN, Ward et al.⁶ performed a pilot secondary analysis of The Study With Appetizing Plantfood—Meat Eating Alternatives Trial. This secondary analysis of the randomized, single-site crossover trial aimed to investigate the effect of consuming plant-based meat alternatives compared with animal-based meats on urinary markers related to acid load, including urinary sulfate, ammonium, phosphorus, pH, and citrate. Healthy adults (N=36 completed the study) eating an omnivorous diet that included at least one serving of animal-based meat a day were randomized to consume at least two servings a day of animal-based meat or plant-based meat alternatives that resembled beef, pork, and chicken products for 8 weeks for each phase. Using fasting spot urine samples and after adjusting for urinary creatinine, the authors reported that the consumption of plant-based meat alternatives resulted in lower urinary sulfate, ammonium, phosphorus, and urinary nitrogen and higher pH and citrate-to-creatinine ratio compared with animal-based meats. Finally, despite a similar overall nutrient intake, when they estimated the amino acid consumption as part of their total diet for both periods, the intake of acidic amino acids was lower after the plant-based meat alternatives. Overall, the authors concluded that plant-based meat alternatives may provide a way to reduce dietary acid load.

This study had several strengths, which include an adequate intake of study foods, an overall high adherence to both treatments, and an overall similar nutrient intake during both periods. However, several limitations should be mentioned, some of which were highlighted by the authors. First, this was a sample of primarily female, college-educated individuals. Considering the aforementioned barriers to fruit and vegetable intake, these sociodemographic factors are important. Second, this study was not powered to detect differences in urinary biomarkers. Third, the investigators used a single fasted spot urine sample per time point. Therefore, clinicians should use caution when extrapolating the results to other individuals, including people with CKD and urinary stone disease.

The authors should be commended for their analysis, providing data on healthy individuals that may help generate hypotheses in people with CKD and urinary stone disease. Looking ahead to future trials on the impact of plant-based meat alternatives in these clinical populations, some considerations should be highlighted. First, multiple 24-hour urine collections should be preferred over single-spot urine samples due to the high interindividual and intraindividual variability that limits their reliability.⁷ Furthermore, plant-based meat alternatives may also be studied in other areas of interest in CKD and urinary stone disease. For example, a key limitation for the consumption of plant-based meat alternatives is that some products use phosphate-containing additives, which are recommended to be avoided in CKD-mineral and bone disorder because they may have a higher phosphorus bioaccessibility (i.e., the amount of phosphorus available for absorption), contributing to a higher phosphate load.¹ This is an important area of emerging research as the common notion for the differences in phosphorus bioaccessibility relies on the type of food, with lower phosphorus bioaccessibility in plant-based foods because of the phytate-bound phosphorus, moderate bioaccessibility in animal-based foods, and higher bioaccessibility in foods with phosphate-containing additives.¹ Therefore, studies evaluating the difference in phosphorus bioaccessibility in these plant-based meat alternatives compared with animal-based meats are needed.

Finally, another area of interest for CKD and urinary stone disease is the gut microbiome modulation.^3,8 In fact, the parent The Study With Appetizing Plantfood—Meat Eating Alternatives Trial study showed that plant-based meat alternatives lowered the concentration of the microbial metabolite trimethylamine-N-oxide (TMAO), a detrimental metabolite causally linked to cardiovascular disease and CKD.⁹ In CKD, there are changes at the composition, function, and metabolite levels, often termed dysbiosis of CKD.⁸ This dysbiosis is characterized by an increased relative abundance of microorganisms with the capacity to produce microbially derived uremic toxins primarily derived from aromatic amino acids (i.e., indoxyl sulfate and p-cresyl sulfate) and components in animal-based foods (i.e., carnitine and phosphatidylcholine leading to higher TMAO through partial or total microbial metabolism) and lower production of the beneficial short-chain fatty acids.^3,8 Increasing dietary fiber intake is a commonly proposed intervention to alleviate this imbalance in the metabolites derived from the gut microbiome.³ Fermentable dietary fibers serve as energy source for gut bacteria, and studies have shown that increasing dietary fiber intake enhances gut microbiota diversity while reducing gut-derived uremic toxins such as indoxyl sulfate, p-cresyl sulfate, and TMAO.^3,8 Similarly, dietary fiber intake correlates with a lower risk of kidney stones.¹⁰ Therefore, incorporating plant-based meat alternatives, which contain fiber, may promote beneficial changes in the gut microbiome, but this should be prospectively studied in these clinical populations.

In conclusion, the authors should be commended for highlighting the potential benefit of using plant-based meat alternatives in people with CKD and urinary stone disease to increase the intake of plant-based foods. However, clinical trials in these populations are needed to establish if consuming plant-based meat alternatives leads to beneficial outcomes in the context of the overall dietary pattern in people with CKD and urinary stone disease.

Supplementary Material

cjasn-19-1362-s001.pdf ^{(1.3MB, pdf)}

Disclosures

Disclosure forms, as provided by each author, are available with the online version of the article at http://links.lww.com/CJN/C38.

Funding

None.

Author Contributions

Conceptualization: Annabel Biruete.

Writing—original draft: Annabel Biruete, Nooshan Mirmohammadali.

Writing—review & editing: Annabel Biruete, Nooshan Mirmohammadali.