Abstract
The capability of any food to alter net endogenous acid or base production can be estimated using the potential renal acid load (PRAL) estimation method. The PRAL of edible mushrooms has been rarely examined; thus a quantification study of nā=ā37 edible mushroom species was performed. Results revealed a heterogeneous picture: although the most commonly consumed mushrooms (e.g., Agaricus bisporus, Lentinula edodes, and Pleurotus ostreatus (white)) have alkalizing properties, several acidifying species (Volvariella volvacea, Pleurotus flabellatus) were identified, which may be attributable to their high phosphorus content.
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Diet composition alters humansā acidābase balance by providing acid or base precursors1,2. The majority of plant-based foods generate alkalies, whereas animal-based high-protein foods, such as meats and cheese, have acidifying properties2,3. The capability of foods to endogenously alter net acid or net base production after intestinal absorption and metabolism of the respective nutrients is termed potential renal acid load (PRAL) and can be calculated from foodsā nutrient content1.
The long-term consumption of high-PRAL diets promotes a subclinical low-grade metabolic acidosis state, which has been associated with systemic inflammation and tissue damage in the human body2,4,5. Low-PRAL diets, on the other hand, have been related to improved metabolic parameters and improved anaerobic exercise performance6,7,8. Replacing sulfur-rich animal protein āa major PRAL contributorāwith high-quality plant protein may thus be beneficial to human health5.
Edible mushrooms are commonly consumed in many countries and are traditionally known as a good protein source9,10. They are also low in fat and high in potassium. Mushroomsā PRAL has been rarely examined, and the original PRAL reference list by Remer et al. only contains a single and not closer specified mushroom type called ācommon mushroomsā11. Due to the high heterogeneity and variability in mushroomsā nutrient content9, a more sophisticated PRAL assessment of edible mushrooms was deemed necessary.
Based on a scientific literature review, we identified a total of nā=ā37 edible mushrooms without missing information on PRAL-relevant nutrients. Table 1 displays their nutrient content and the estimated PRAL scores based on a dry matter basis9,12,13,14,15,16.
The mean PRAL score of all examined mushrooms was ā10.83āĀ±ā28.73āmEq/100āg. Approximately 40.5% (nā=ā15/37) of mushrooms displayed acidifying properties (PRALā>ā0āmEq/100āg). The highest PRAL values were found for Volvariella volvacea (41.50āmEq/100āg), Pleurotus flabellatus (35.21āmEq/100āg) and Craterellus aureus (31.02āmEq/100āg). Among those with alkalizing properties (PRALā<ā0āmEq/100āg) the following mushrooms were noticeable: Craterellus aureus (ā73.92āmEq/100āg), Russula lepida (ā51.94āmEq/100āg) and Heimiella retispora (ā48.54āmEq/100āg).
Mushroomsā mean protein content was 20.14āĀ±ā6.59āg/100āg. Mushrooms were also characterized by a high potassium (mean: 2264.88āĀ±ā1095.50) and phosphorus content (median: 699 (395.69)) in mg/100āg. As shown in Fig. 1, potassium and phosphorus content were strongly correlated with PRAL (Pearsonās r: ā0.80 and Spearmanās rho: 0.62, respectively; pā<ā0.001 for both), whereas no significant association was found for protein content.
The PRAL values of edible mushrooms varied substantially and although the sampleās mean generally indicated alkalizing properties, several acidifying candidates were identified. When specifically glancing at some of the most commonly consumed mushroom types in the Western world (Agaricus bisporus, Lentinula edodes, and Pleurotus ostreatus (white)), all were characterized by negative PRAL values.
In terms of protein and amino acid composition, mushrooms have been proposed as suitable substitutes for animal-based foods (e.g. meat)17. Their PRAL values, however, have been rarely explored and received little attention in the past.
Thus, the herein presented PRAL tables could be helpful for individuals who wish to alkalize their diet and could be of great support for nutritionists who intend to optimize the PRAL of their patients.
While covering an unexplored field, this brief communication does likely not cover all edible mushrooms in the sense of a systematic review. Further to that, nutrient and mineral contents of mushrooms on a dry matter basis were used. This may have led to an overestimation of PRAL when considering fresh mushrooms, which usually have a moisture content of up to 90%18. Although drying is one of the most significant preservation methods employed for the storage of mushrooms19, they are not exclusively consumed as dried foods. The nutrient content of mushrooms, however, is mostly reported based on a dry matter basis20. While such data was employed for comparative purposes here, we clearly acknowledge the potential limitations of this approach. To ensure a transparent comparison, we also provide PRAL values of selected mushrooms based on fresh edible 100āg portions in Table 2 (which is based on data from the U.S. Department of Agriculture21).
Fresh weight-based PRAL values expectedly were much smaller, yet nutrient mushroom content data based on fresh weight is rarely reported in the scientific literature. While potentially less accurate, dry weight-based PRAL data may still be of importance to differentiate between alkalizing and acidifying mushroom species.
Finally, we highlight that some important edible mushrooms, such as Cantharellus cibarius, were not included in this analysis because publications that included all PRAL-relevant nutrients for the aforementioned species could not be identified. The same applied to mycelial extracts, for which PRAL-relevant nutrient profiles were only available in a limited number of publications22.
Nevertheless, the present results were deemed important. This analysis highlights the heterogeneous PRAL of mushrooms and proposes several mushroom types that allow for two important goals at the same time: substituting animal protein with plant protein while simultaneously optimizing PRAL without diminishing protein intake quantity and quality.
Methods
Data gathering
This brief communication is part of a series of short contributions covering the PRAL value of novel, underexplored, or uncommon food groups5,23. The nutrient content of selected edible mushrooms was extracted from previous publications, which were identified using PubMed and Google Scholar. The literature search strategy included the following search terms: edible mushrooms; nutrient content; nutritional value; protein; and minerals.
Due to the exploratory character of this brief communication, the literature search was restricted to the aforementioned databases and not designed to reflect a systematic review. Cross-references and reference lists of the identified articles were screened for additional articles to increase the sample size for analysis. Only data from edible mushrooms with a complete nutrient profile required for PRAL estimation (see below) was extracted. Publications that did not contain all PRAL-relevant nutrients were not eligible. Only sources that normalized the nutritional composition of mushrooms according to their dry matter content were included in the primary analysis. Articles that provided the nutritional content in other units (e.g., ppm) were not considered. The search was restricted to English language publications from the last 10 years and the entire review process was conducted by the author in June 2023.
PRAL estimation
PRAL (in mEq/100āg) was estimated based on the commonly employed formula by Remer et al.24; it is shown in Eq. (1) below:
The PRAL score is a validated method and considers ionic dissociation, intestinal absorption rates for the included nutrients as well as sulfur metabolism1,5,23.
Statistical analyses and procedures
PRAL values were calculated in mEq/100āg dry mass of each edible mushroom. The ShapiroāWilk test was used to determine whether data was normally distributed or not. The meanāĀ±āSD was provided for normally distributed variables, whereas medians and interquartile ranges were provided for non-normally distributed variables. Pearsonās product-moment correlations and Spearmanās rank-order correlations were run to assess the relationship between the content of selected nutrients and PRAL. Nutrient-dependent scatterplots and heat plots were created to graphically display the results. Data was analyzed with STATA 14 statistical software (StataCorp. 2015. Stata Statistical Software: Release 14. College Station, TX: StataCorp LP).
Reporting summary
Further information on research design is available in the Nature Research Reporting Summary linked to this article.
Data availability
All data generated or analyzed during this study are included in this published article.
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Storz, M.A. Quantifying the potential renal acid load of edible mushrooms. npj Sci Food 8, 17 (2024). https://doi.org/10.1038/s41538-024-00259-w
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DOI: https://doi.org/10.1038/s41538-024-00259-w