Plant-Based Milk Alternatives and Risk Factors for Kidney Stones and Chronic Kidney Disease

Abstract

Objective:

Patients with kidney stones are counseled to eat a diet low in animal protein, sodium and oxalate and rich in fruits and vegetables, with a modest amount of calcium, usually from dairy products. Restriction of sodium, potassium and oxalate may also be recommended in patients with chronic kidney disease (CKD). Recently, plant-based diets have gained popularity due to health, environmental and animal welfare considerations. Our objective was to compare concentrations of ingredients important for kidney stones and CKD in popular brands of milk alternatives.

Design and Methods:

Sodium, calcium and potassium content were obtained from nutrition labels. Oxalate content was measured by ion chromatography coupled with mass spectrometry.

Results:

Calcium content is highest in macadamia followed by soy, almond, rice and dairy milk; it is lowest in cashew, hazelnut and coconut milk. Almond milk has the highest oxalate concentration, followed by cashew, hazelnut and soy. Coconut and flax milk have undetectable oxalate levels; coconut milk also has comparatively low sodium, calcium and potassium, while flax milk has the most sodium. Overall, oat milk has the most similar parameters to dairy milk (moderate calcium, potassium and sodium with low oxalate). Rice, macadamia, and soy milk also have similar parameters to dairy milk.

Conclusion:

As consumption of plant-based dairy substitutes increases, it is important for healthcare providers and patients with renal conditions to be aware of their nutritional composition. Oat, macadamia, rice and soy milk compare favorably in terms of kidney stone risk factors with dairy milk, whereas almond and cashew milk have more potential stone risk factors. Coconut milk may be a favorable dairy substitute for patients with CKD based on low potassium, sodium and oxalate. Further study is warranted to determine the effect of plant-based milk alternatives on urine chemistry.

Introduction

Patients with kidney stones are counseled to eat a diet low in animal protein, sodium and oxalate and rich in fruits and vegetables, as well as a modest amount of calcium, usually from dairy.^{1, 2} Recently, plant-based diets have gained popularity; the US nondairy milk market grew by 50% in 2018.³ Unfortified nondairy milks have less calcium than dairy, although many commercially-available non-dairy milks are calcium-fortified. Prospective data from the Health Professionals Follow-up Study and Nurses’ Health Studies showed that increased calcium intake from dairy or non-dairy dietary sources is associated with a lower risk of incident symptomatic kidney stones.⁴ However, there is concern that some nut-based milks may have high oxalate content.⁵ This could have implications for patients with kidney stones.

Besides kidney stones, the micronutrient distribution of the various milk alternatives may affect those with chronic kidney disease (CKD). For example, in this patient population, sodium and potassium restriction is often recommended, although our understanding of the effect of dietary potassium in CKD is currently evolving. Additionally, urinary oxalate excretion declines with waning kidney function, which can raise plasma oxalate levels and may lead to further decline in kidney function.⁶

Our objective was to evaluate the concentrations of ingredients which promote (sodium, oxalate) or inhibit (calcium, potassium) stones in milk alternatives. In addition, we compared the concentration of ingredients that should be monitored in CKD (sodium, potassium, oxalate).

Methods

Market statistics were used to identify representative dairy and non-dairy milks, including brands with significant market share that were available locally for oxalate measurement. Sodium, calcium and potassium content were obtained from nutrition labels. To ensure complete extraction of oxalate, milk products were acidified with hydrochloric acid (1M final concentration) and vigorously mixed for 5 minutes at room temperature. Oxalate content of acidified milk extracts was measured by ion chromatography coupled with mass spectrometry (ICMS) using 13C2-oxalate as an internal standard and an AS22 (2 × 150 mm) anion exchange column and MSQ mass spectrometer (Thermo Fisher Scientific Inc., Waltham, MA), as previously described.⁷

Results

Table 1 shows the results. Calcium content is highest in macadamia followed by soy, almond, rice and dairy milk; it is lowest in cashew, hazelnut and coconut milk. Almond milk has the highest oxalate concentration, followed by cashew, hazelnut and soy. Coconut and flax milk have undetectable oxalate levels; coconut milk also has comparatively low sodium, calcium and potassium, while flax milk has the most sodium. Overall, oat milk has the most similar parameters to dairy milk (moderate calcium and potassium, modest sodium and low oxalate). Rice, macadamia, and soy milk also have similar parameters to dairy milk.

Table 1.

Nutrition information of plant-based and dairy milks listed in descending order of measured

	Sodium (mg/cup)	Calcium (% RDA/cup)	Potassium (mg/cup)	Mean Oxalate (mg/cup)
Silk Almond Milk Original	150	30%	0	27.1 ± 0.49
Forager Cashew Milk	10	2%	94	17.2 ± 0.96
Pacific Foods Hazelnut Milk	115	10%	NS*	11.3 ± 0.52
Silk Soy Milk Original	90	30%	380	9.6 ± 0.39
Pacific Foods Hemp Milk	130	20%	145	4.5 ± 0.08
Oatly Oat Milk	100	25%	390	3.5 ± 0.05
Milkadamia Macadamia Milk	115	35%	10	1.1 ± 0.13
Rice Dream Enriched Rice Milk	100	30%	NR**	0.71 ± 0.08
Barber’s Dairy Pure Whole Milk	120	30%	380	0.54 ± 0.14
Barber’s Dairy Pure Fat Free	130	30%	410	0.50 ± 0.03
Good Karma Flax Milk	190	25%	20	<0 43***
So Delicious Coconut Milk oxalate content	25	10%	0	<0 43***

RDA: Recommended Dietary Allowance. Calcium content was reported by manufacturers as a percentage of RDA; absolute values of calcium were not available for all products.

^*not a significant source of potassium

^**Not reported; USDA reports the potassium content of rice milks is 65 mg

^***oxalate content below the limits of detection

Discussion

Our results suggest that oat, rice, macadamia and soy milk may be appropriate substitutes for stone-formers. For patients with CKD, coconut milk compares favorably with dairy milk based on the lowest sodium, potassium, and oxalate levels. Macadamia milk is another option for patients who are restricting potassium and oxalate, but has a higher sodium content than coconut milk.

There are many reasons why plant-based milk alternatives are attractive to consumers, making their effect on kidney stone risk and CKD an important clinical question. Approximately 2/3 of the world population has a reduced ability to digest lactose after infancy.⁸ In addition, many studies have linked dairy with common malignancies including breast and prostate cancer,^9–12 possibly mediated by IGF1.^{12, 13}

Others avoid dairy due to concern for animal rights or environmental impact, including carbon emissions, land and water use, and reduced biodiversity. A recent study found that replacing half of all animal-based foods (e.g., dairy, meat and fish) with plant-based foods would save 224 million metric tons of carbon per year, equivalent to 47.5 million passenger vehicles.¹⁴ Modeling studies have projected substantial increases in kidney stones due to climate change¹⁵; therefore, substitution of dairy by plant-based milks with favorable stone risk profiles is an attractive solution to reduce future stone risk at the individual and societal level.

Limitations of this study include the lack of data on citrate, a stone inhibitor. In addition, data were not available for the magnesium, chloride, phosphorus and sulfate content for all of the products examined in this study, and some products only list the %RDA for calcium, not the exact content. Also, we only examined one product per category, while many formulations are available with potentially different nutritional parameters. Finally, we do not have data on 24-hour urine chemistry, stone formation or CKD progression among consumers of these products, which are important areas for further study.

Strengths are that this is the first report synthesizing kidney stone- and CKD-related nutrients for dairy versus plant-based milks. In addition, oxalate is not reported on nutrition labels and very little has been published regarding oxalate content of plant-based milks.

In conclusion, as consumption of plant-based dairy substitutes increases, it is important for healthcare providers and patients with renal conditions to be aware of their nutritional composition. Oat, macadamia, rice and soy milk compare favorably in terms of kidney stone risk factors with dairy milk, whereas almond and cashew milk have more potential stone risk factors. Coconut milk may be a favorable dairy substitute for patients with CKD based on low potassium, sodium and oxalate. Further study is warranted to determine the effect of plant-based milk alternatives on urine chemistry.

Practical Application

Oat, macadamia, rice and soy milk compare favorably in terms of kidney stone risk factors with dairy milk, whereas almond and cashew milk have more potential stone risk factors. Coconut milk may be a favorable dairy substitute for patients with CKD based on low potassium, sodium and oxalate.