Edible insects exert a high potential renal acid load to the human kidneys

ABSTRACT

The potential renal acid load (PRAL) describes the capacity of a food to produce acid or base in the human body. The long-term consumption of high-PRAL diets induces a chronic low-grade metabolic acidosis state that has been associated with inflammation and impaired kidney function. PRAL tables are available to help individuals in selecting low-PRAL foods. However, these tables do not cover novel or uncommon foods in Western societies. Entomophagy – the practice of eating insects is an emerging trend in the Western world with unclear health consequences from an acid-base perspective. Here, we hypothesized that the consumption of insects is associated with a high PRAL, and analyzed the PRAL values of n = 39 commonly consumed edible insects. Our results suggest that the majority of edible insects have very high PRAL values (of up to 43.62 mEq/100 g), indicating strong acidifying properties and likely resulting in acid retention. PRAL values of edible insects rank well above the PRAL values of other high-protein foods, including legumes, pork and beef. PRAL was moderately correlated with the protein content (r = 0.42) and phosphorus content (r = 0.50) of the examined edible insects. Our data point to a potential health concern when regularly consuming edible insects.

KEYWORDS:

• Potential renal acid load
• dietary acid load
• edible insects
• entomophagy
• nutritive value
• acid-base equilibrium
• diet
• protein

Introduction

Diet composition may alter acid-base balance in humans by providing acid or base precursors.^[1,2] High-protein foods such as meat, cheese and eggs increase the production of acid in the human body, whereas most plant-based foods decrease it by generating alkalis.^[2,3] This happens upon the metabolization of potassium salts of organic anions (mainly malate and citrate), which undergo combustion in the human body to yield bicarbonate and which consume hydrogen ions.^[4,5] The overall capacity of acid or base production of any food is called potential renal acid load (PRAL).^[1]

The long-term consumption of high-PRAL diets induces a chronic low-grade metabolic acidosis state, which has been associated with systemic inflammation and tissue damage in the human body.^[6,7] This might be particularly detrimental in individuals with chronic kidney disease and reduced buffering capacities, who benefit from a low-PRAL diet.^[8,9]

To accomplish this goal, PRAL quantification is of paramount importance. PRAL tables can assist individuals to achieve this,^[10] as they contain the PRAL values of commonly consumed foods and systematically categorize food items into alkaline and acidic foods. However, PRAL values are not yet available for all food items and non-existent for novel and previously rather uncommon foods in Western countries. One example is the group of nondairy plant-based milk alternatives, for which we recently published a systematic PRAL analysis.^[11] Another food group that has received little to no attention from an acid-based perspective in the past includes edible insects.

Entomophagy – the practice of eating insects – is an emerging trend in the Western world.^[12] Supporters of entomophagy argue that edible insects are a sustainable and healthy food choice,^[12] whereas critics raise ethical and animal welfare concerns.^[13,14] Additional arguments against entomophagy include the presence of anti-nutrients as well as potentially allergic or toxic substances encountered in insects. Although these aspects should not be ignored, entomophagy is a rising trend. This trend, however, has unknown consequences for PRAL, kidney health and the acid-base equilibrium in humans.

To the best of our knowledge, negligible work on the PRAL values of edible insects have been reported in the scientific literature. Yet, many edible insects are abundant in protein and phosphorus,^[15] which are the major PRAL contributors.^[10] Thus, questions arise as to how the consumption of edible insects affects PRAL and whether there are noticeable differences between different insect groups. At this stage, it is also unclear how the PRAL value of edible insects fares in comparison to the PRAL value of other important protein sources for humans, including legumes and traditional meat products.

In this short contribution, we hypothesized that the consumption of edible insects is associated with elevated PRAL values. To test our hypothesis, we analyzed the PRAL values of n = 39 edible insects commonly consumed around the globe.

Materials and methods

Study population and design

Nutrient content of edible insects was extracted from previous publications in the field. Reviews examining the nutrient content of edible insects were identified using the following search engines: PubMed, Google Scholar and Web of Science. These databases were searched using various combinations of the following search terms: edible insects; entomophagy; consumption; nutrient content; protein. Exploratory in nature, the literature search was not designed to reflect a systematic review. Nevertheless, cross-references and reference lists of the included articles and cited reviews were manually screened for additional articles to ensure an adequate sample size. Only data from edible insects with a complete nutrient profile required for PRAL estimation (including protein, potassium, phosphorus, magnesium and calcium) was extracted. We considered only articles in English or German language. The entire review process was conducted by the authors in April 2023.

DAL estimations

We estimated PRAL (in mEq/100 g) based on the following validated formula by Remer et al.^[16]

$PRAL\left(mEq/100g\right)=\left(0.49\ast totalproteinintake\left(g/100g\right)\right)+\left(0.037\ast phosphorusintake\left(mg/100g\right)\right)-\left(0.021\ast potassiumintake\left(mg/100g\right)\right)-\left(0.026\ast magnesiumintake\left(mg/100g\right)\right)-\left(0.013\ast calciumintake\left(mg/100g\right)\right).$

The PRAL score is a validated method to calculate the estimated acid-base impact of foods. It considers ionic dissociation, intestinal absorption rates for the included micro- and macronutrients and sulfur metabolism.^[1]

Statistical analysis

We calculated PRAL values in mEq/100 g for each analyzed edible insect. We used histograms, box plots and Stata’s Shapiro – Wilk test to check whether data was normally distributed or not. For normally distributed variables, we provided the mean and its corresponding standard deviation. For non-normally distributed variables we presented medians and the corresponding interquartile ranges in parenthesis. Pearson’s product-moment correlations and Spearman’s rank-order correlations were run to assess the relationship between the content of selected nutrients and PRAL for all examined insects. Scatterplots, boxplots and heatplots were created to visualize the results. Scatterplots were supplemented with overlaid linear prediction plots for illustrative purposes (blue dashed line = line of best fit). All analyses were performed with STATA 14 statistical software (StataCorp. 2015. Stata Statistical Software: Release 14. College Station, TX: StataCorp LP).

Results

A total of n = 39 edible insects without missing information on PRAL-relevant nutrients were identified.^[15,17–22] Table 1 lists their micronutrient and protein content as well as the thereof resulting PRAL score. The majority of edible insects (n = 34/39) was characterized by a high PRAL value (>10 mEq/100 g). Only 12.82% (n = 5/39) of the analyzed insects had alkalizing properties (as indicated by a PRAL score < 0 mEq/100 g). The highest PRAL score was found for Oryctes boas (larvae), the rhinoceros beetle larvae, with a PRAL value of 43.62 mEq/100 g.

Table 1. Nutrient content and resulting potential renal acid load values of selected edible insects: an overview.

Name	Stage/Part	Protein	Calcium	Potassium	Magnesium	Phosphorus	PRAL
Acheta domesticus ^[Citation15]	Adult	64.38	132.14	1126.62	109.42	957.79	38.76
Acheta domesticus (cricket) ^[Citation17]	Adult	62	132.14	1126.62	109.42	957.57	37.59
Acheta domesticus ^[Citation15]	Nymph	67.25	120.09	1537.12	98.69	1100.44	37.26
Allomyrina dichotoma ^[Citation18]	Larva	54.18	12.34	1249.1	283.56	860.69	24.63
Anaphe venata (African silkworm) ^[Citation17]	Larva	58	40	1150	50	730	29.46
Bee brood ^[Citation17]	Immature stages	40	59.48	1159.48	90.95	771.55	20.66
Blatta lateralis ^[Citation19]	Nymph	19 *	38.5	224	25	176	9.97
Bombyx mori ^[Citation15]	Larva	69.84	102.31	1826.59	287.86	1369.94	37.74
Bunaea alcinoe ^[Citation18]	Larva	46.57	27	91.25	19.53	128.5	24.80
Chilecomadia moorei ^[Citation19]	Larva	15.5 *	12.5	259	27.8	225	9.60
Cirina forda (Westwood) ^[Citation21]	Larva	33.12	7	2130	32.4	1090	10.90
Galleria mellonella ^[Citation15]	Larva	41.25	58.5	532.53	76.14	469.88	23.67
Gryllus bimaculatus ^[Citation19]	Adult	58.32	240.2	1079.9	146.7	1169.6	42.24
Hermetia illucens (soldier fly)^[Citation17]	Larva	49	934	453	174	365	11.34
Imbrasia epimethea (mopane caterpillar) ^[Citation17]	Larva	62	224.73	1258.06	402.15	666.67	15.25
Imbrasia ertli ^[Citation20]	Larva	48.66	50	1095	231	546	14.39
Imbrasia truncata (mopane caterpillar) ^[Citation17]	Larva	65	131.61	1348.44	192.02	841.42	27.96
Macrotermes bellicosus ^[Citation18]		27.5	43.2	209	54.9	710	33.37
Macrotermes nigeriensis ^[Citation15]	Adult	23.47	0.1	336	6.1	1.49	4.34
Macrotermes subhyalinus ^[Citation20]	Larva	38.42	40	476	417	438	13.67
Musca domestica (house fly) ^[Citation17]	Adult	62	76.5	303	80.6	372	34.69
Nasutitermes spp ^[Citation18]	Adult	58.2	26	54	14	38	28.09
Nudaurelia oyemensis (caterpillars) ^[Citation15]		61.08	149.46	1107.53	265.59	870.97	30.05
Oryctes boas ^[Citation18]	Larva	14.74	9.39	782	17.4	1443	43.62
Oryctes owariensis ^[Citation18]	Larva	55.28	54.51	1610	369.75	142.17	−11.78
Periplaneta americana ^[Citation17]	Nymphe/Adult	66.00	38.50	224.00	25.00	176.00	33.00
Protaetia brevitarsis ^[Citation18]	Larva	44.23	258.56	2001.4	327.6	1140.4	9.96
Rhynchophorus ferrugineus ^[Citation19]	Larva	28.42	38	568	120	239	7.23
Rhynchophorus phoenicis ^[Citation17]	Larva	33.00	54.10	1025.00	131.80	352.00	3.54
Rhynchophorus phoenicis ^[Citation20]	Larva	20.34	186	1972	30	314	−23.03
Ruspolia differens (brown) ^[Citation15]	Adult	44.3	24.5	259.7	33.1	121	19.55
Ruspolia differens (green) ^[Citation15]	Adult	43.1	27.4	370.6	33.9	140.9	17.31
Sitophilus zeamais ^[Citation18]		16.49	17.6	710	105	1198	34.54
Teleogryllus emma ^[Citation18]	Adult	55.65	193.54	895.5	152.48	1085.4	42.14
Tenebrio molitor ^[Citation17]	Larva	48	47.18	895.01	210.24	748.03	26.32
Usta terpsichore (mopane caterpillar) ^[Citation17]	Larva	76	391	3259	59	766	−9.47
Usta terpsichore (mopane caterpillar) ^[Citation20]	Larva	44.1	355	2958	54	695	−20.81
Zonocerus variegatus ^[Citation22]		30.73	328	1905.01	123.6	181.77	−25.70
Zophobas morio (superworm) ^[Citation17]	Larva	45	81.02	750.59	118.29	562.95	22.99

PRAL = Potential Renal Acid Load; PRAL in mEq/100 gram; all micronutrients are displayed in mg/100 gram; Protein in g/100 mg; nutrient content based on a dry mass if not specified otherwise; * based on fresh weight

Two other insects also had PRAL values > 40 mEq/100 g: Gryllus bimaculatus with a PRAL value of 42.24 mEq/100 g and Teleogryllus emma (larvae) with a PRAL value of 42.14 mEq/100 g. The lowest PRAL values were found for Zonocerus variegatus (−25.70 mEq/100 g), Rhynchophorus phoenicis (−23.03 mEq/100 g), and Usta terpsichore (larvae, mopane caterpillar) with a PRAL value of −20.81 mEq/100 g. The median PRAL value of the entire sample was 22.99 (23.40) mEq/100 g.

Protein and micronutrient content varied substantially across the examined edible insects (Table 1). Mean protein content of the examined sample was 45.90 ± 16.82 g/100 g. As for the micronutrients, we observed a mean phosphorus content of 619.54 ± 404.43 mg/100 g. Median magnesium, calcium and potassium content were as follows: 105 (158.92) mg/100 g, 54.51 (122.06) mg/100 g, and 1025 (977.84) mg/100 g, respectively. Usta Terpsichore (mopane caterpillar) with a PRAL value of −9.47 mEq/100 g, had the highest potassium content with 3259 mg/100 g. Other edible insects with a remarkable potassium content were Bombyx mori (1826.59 mg/100 g) and Protaetia brevitarsis (2001.4 mg/100 g). Oryctes boas (larvae) and Bombyx mori yielded the highest phosphorus content. Box plots were constructed to visualize the large variety in the micronutrient content of edible insects. Figure 1 displays their phosphorus and potassium content, whereas Figure 2 shows their magnesium and calcium content.

Figure 1. The phosphorus and potassium content of edible insects.

Micronutrients shown in mg/100 g edible portions. Based on n = 39 observations.

Figure 2. The magnesium and calcium content of edible insects.

Micronutrients shown in mg/100 g edible portions. Based on n = 39 observations.

Figure 3 displays a scatterplot, visualizing the significant association between PRAL and edible insects’ phosphorus content. In a similar style, scatterplots were constructed for potassium (Figure 4) and protein (Figure 5). Correlation coefficients may be obtained from the respective figure legends. Finally, Figure 6 summarizes the results of all bivariate correlation analyses in a heatplot (based on n = 38 observations). Significant associations were marked with an asterisks.

Figure 3. Scatterplot showing the positive association between PRAL and phosphorus content of edible insects.

Phosphorus content in mg/100 g; PRAL in mEq/100 g. The Pearson’s product-moment correlation coefficient was 0.50 (p = .001). Based on n = 39 observations (red dots). Blue dashed line = line of best fit.

Figure 4. Scatterplot showing the inverse association between PRAL and potassium content of edible insects.

Potassium content in mg/100 g; PRAL in mEq/100 g. The Pearson’s product-moment correlation coefficient was -0.47 (p = .002). Spearman’s rho was -0.23 but not statistically significant (p = .16). Based on n = 39 observations (red dots). Blue dashed line = line of best fit.

Figure 5. Scatterplot showing the positive association between PRAL and protein content of edible insects.

Protein content in g/100 g; PRAL in mEq/100 g. The Pearson’s product-moment correlation coefficient was 0.42 (p = .009). One outlier (protein content per 100 g: >70 g) in the sample was removed for analytical purposes. Based on n = 38 observations (red dots). Blue dashed line = line of best fit.

Figure 6. Heatplot summarizing all bivariate correlation analyses.

Significant associations are marked with an asterisk. One outlier (protein content per 100 g: >70 g) in the sample was removed for analytical purposes. Based on n = 38 observations.

Discussion

While traditionally common in tropical and subtropical regions, entomophagy is now also a rising trend in the Western world.^[17] Supporters of entomophagy argue that insects are an important source of animal protein, with a crude protein proportion ranging from 40% to 75% based on a dry weight basis.^[17] Entomophagy advocates also argue that edible insects contain more crude protein than conventional meat. They are also considered a good source of vitamins. Edible insects generally have a high protein digestibility that can exceed 90%^[23] - a fact that should be considered in the discussion about the PRAL values estimated in this study.

As displayed in Table 1, some insects are also abundant in phosphorus – another main PRAL contributor besides protein. For the aforementioned reasons, one would intuitively expect high PRAL values from a 100 g portion of any edible insect. Then again, some insects are at the same time rich in potassium, which is the most important alkali precursor. One particular example is Bombyx mori, with approximately 1800 mg potassium/100 g. In light of these specific nutrient content patterns and with regard to the absolute nutrient content dimensions, we deemed it necessary to precisely estimate the PRAL values of edible insects.

Our results suggest that edible insects generally exert a high PRAL to the human kidneys. The high potassium content found in edible insects may not compensate for the high protein and phosphorus content from an acid-base perspective. Instead, it substantially contributes to the overall daily potassium intake and could be of particular risk in patients with chronic kidney failure who are usually instructed to play close attention to their potassium intake.

Since edible insects are more and more commonly consumed in Europe and North America,^[12] we believe that entomophagy advocates should be aware of this phenomenon, and should take into account the high PRAL exerted to the human kidneys when eating insects. To the best of our knowledge, we are the first group to glance at edible insects from an acid-base perspective.

While the estimated PRAL values were rather inhomogeneous in the herein presented sample, our results suggest that the majority of edible insects have very high PRAL values (of up to 43.62 mEq/100 g). To the best of our knowledge, PRAL values of this level are unprecedented and rank well above the PRAL values of other unprocessed high protein foods. Green beans, for example, are alkaline, with a PRAL value of −3.1 mEq/100 g. Pork and beef, on the other hand, are acidifying, and yield PRAL values of approximately 8 mEq/100 g each. Edible insects have an even higher PRAL value and should thus be considered with great caution by individuals who wish to adopt an alkaline or near-alkaline diet.

The capacity of the human’s body to buffer the acid load from diet is generally limited. In healthy people with a normal kidney function, acid retention occurs once the amount of acid that gets excreted out in the urine is > 0.4–1 mEq/kg of body weight per day (eg, 40–70 mEq/day for a 70 kg adult).^[7] Western diets are usually characterized by a total dietary acid load ranging from 50 to 100 mEq/day, and frequently lead to acid retention with subsequent low-grade metabolic acidosis.^[2] In light of this phenomenon, it is important to recognize the high PRAL values of edible insects – even when considering low intake quantities (e.g. 50 or 100 g/day). Adding edible insects to the menu might therefore result in even greater PRAL values and greater acid retention.

Our data generally suggest that insects are not suitable for individuals with reduced buffering capacities (e.g. older adults or patients with impaired kidney function,^[24] who should instead rely on high quality plant-based protein with alkalizing properties. As a logical consequence, a high concomitant intake of alkaline plant foods would be required to offset the acid burden from edible insects – even in healthy adults.

This short contribution draws upon a number of strengths but has also limitations that warrant a further discussion. To the best our knowledge, we are the first group to report PRAL values of edible insects. While the sample size is moderate, we were not able to identify a larger number of insects with a complete nutrient profile required for PRAL calculation. Cross-sectional in nature, our data offer no insights how the addition of edible insects to menus would alter overall PRAL scores. Future studies should therefore quantify this in greater detail and should also consider urinary PRAL markers. Despite these limitations, we deem our analysis to be important and call for additional studies in this particular field.

Conclusion

The consumption of edible insects exerts a high PRAL to the human kidneys. This likely results in acid retention in individuals with an otherwise low alkali intake. Future studies are warranted to obtain a deeper understanding of this underexplored topic. In the meantime, our data point to a potential health concern when regularly consuming edible insects.

List of abbreviation

PRAL

=

Potential Renal Acid Load

Authors’ contributions

MAS performed the literature research, analysis and interpreted the data. MAS is the guarantor of this study, designed the idea, and validated data. Writing original draft: MAS. Writing – review and editing: MAS, RH. Illustration: MAS. Supervision: RH. All authors reviewed and approved the final manuscript. All authors agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Availability of data and materials

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Ethics approval and consent to participate

Not applicable. The present work is a secondary data analysis of publicly available data. It does not contain any human participants.

Acknowledgments

This work been approved by all co-authors.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors received no financial support/funding. We acknowledge support by the Open Access Publication Fund of the University of Freiburg.