Carboxylic acid

Other Names

No alternative names.

Synopsis

Carboxylic Acids as Dietary Supplements and Natural Ingredients: A Comprehensive Reference

1. Identity: Chemical Classification, Nomenclature, and Scope

Carboxylic acids are a class of organic compounds characterized by the presence of a carboxyl group (–COOH), and they have a rich history in medicinal and nutritional applications. The carboxyl group (–COOH) confers unique properties such as acidity and reactivity, allowing these compounds to participate in diverse physiological functions.

Carboxyl-containing compounds (CCCs) include amino acids (AAs), fatty acids (FAs), tricarboxylic acid cycle intermediates (TCAs), phenolic acids (PAs), and triterpenic acids (TTAs). Carboxylic acids include numerous important compounds that play an irreplaceable role in biological processes such as cell signaling or energy metabolism, and form a large group of substances, including phenolic acids, fatty acids and their derivatives, amino acids, triterpenic acids, intermediates of the tricarboxylic acid cycle, and bile acids.

Carboxylic acids are named systematically using IUPAC conventions, but many are far better known by their common names. Carboxylic acids are often referred to by their common names, such as lactic acid or citric acid; for example, butanoic acid is commonly known as butyric acid, derived from butter. The carboxylic acid group is always positioned at the end of the carbon chain, with the carbonyl carbon designated as carbon 1.

The principal nutritionally and clinically relevant subclasses of carboxylic acids include:

Short-chain fatty acids (SCFAs): acetic acid (ethanoic acid, C2), propionic acid (propanoic acid, C3), butyric acid (butanoic acid, C4). SCFAs are mainly produced by gut microbiome fermentation of dietary fiber and can also be produced by bacteria of the skin and vagina; acetate, propionate, and butyrate are the three major SCFAs.
Medium-chain fatty acids (MCFAs): caprylic acid (octanoic acid, C8), capric acid (decanoic acid, C10), lauric acid (dodecanoic acid, C12).
Long-chain and polyunsaturated fatty acids: eicosapentaenoic acid (EPA, C20:5 n-3), docosahexaenoic acid (DHA, C22:6 n-3), α-linolenic acid (ALA). Structurally, fatty acids consist of a hydrocarbon chain with a carboxyl group (C(O)OH) and a methyl group (CH3) at opposing ends.
Hydroxy acids: citric acid, lactic acid, malic acid, tartaric acid.
Phenolic/cinnamic acid derivatives: caffeic acid, rosmarinic acid, p-coumaric acid, ferulic acid, cinnamic acid, benzoic acid, chlorogenic acid.

2. Natural Sources

Natural carboxylic acids can be found in all plant tissues, including edible parts such as fruits, seeds, leaves, stems, and roots. Many carboxylic acids are present in the foods and drinks we ingest, including malic acid (found in apples), tartaric acid (grape juice), oxalic acid (spinach and parts of the rhubarb plant), and lactic acid (sour milk).

Various natural carboxylic acids—such as citric, lactic, acetic, and salicylic acids—were derived from plants, fruits, and fermented products. Benzoic acid and cinnamic acid are naturally present in fruits, vegetables, nuts, herbs, spices, as well as fungal and animal tissues; benzoic acid can also be produced by microorganisms during food processing; and Cinnamomum cassia (Chinese cinnamon) is the richest natural source of benzoic acid (0.336 mg/g) and cinnamic acid (0.01–1.91 mg/g).

Medium-chain fatty acids have specific food sources. Lauric acid is the primary composition (>50%) of coconut oil and is found in coconut oil, palm kernel oil, and laurel oil; it is also found in various kinds of foods such as fruits, seeds, and breast milk. Benzoic acid is present in sage (Salvia officinalis), thyme (Thymus vulgaris), and nutmeg in the range of 0.015–0.05 mg/g.

A few of the most common naturally occurring phenolic acids—caffeic, carnosic, ferulic, gallic, p-coumaric, rosmarinic, and vanillic—have been identified as ingredients of edible botanicals including thyme, oregano, rosemary, sage, and mint. Caffeic acid and chlorogenic acid are two common coffee polyphenols; ferulic acid was prepared originally from Ferula foetida regel and more recently also commercially from rice bran.

SCFAs also arise endogenously. Short-chain fatty acids, in particular n-butyric acid (BA), acetic acid, and propionic acid, are naturally present in the colon as a bacterial product of dietary fiber fermentation.

3. Common Forms and Preparations

Carboxylic acids are compounds occurring naturally in different stages of life cycles (living organism-Krebs cycle; fermentation processes; and geological processes) or can be produced in laboratories or at large scale from oxidation reactions of aldehydes, primary alcohols, and hydrocarbons, oxidative cleavage of olefins, base-catalyzed dehydrogenation of alcohols, or through the hydrolysis of nitriles, esters, or amides.

The naturally occurring organic acids approved for use as food additives include acetic, propionic, butyric, lactic, citric, benzoic, and sorbic acids, which, depending on the food matrix, are used in their acid form or as sodium/potassium salts. In supplement form, carboxylic acids appear as:

Encapsulated salts: calcium, sodium, and magnesium butyrate; sodium propionate; magnesium citrate.
Microencapsulated preparations: used for butyrate to delay release and reduce malodor.
Esterified prodrugs: tributyrin (a triglyceride ester of butyrate) to improve bioavailability. Animal studies indicate that tributyrin can increase butyrate levels and improve health outcomes; oral administration of tributyrin to rats and mice induced a peak in butyrate concentration 15 to 60 minutes after administration, remaining elevated for approximately 1 hour.
Liquid forms: acetic acid as vinegar; omega-3 carboxylic acid formulations (e.g., Epanova®) as free fatty acids in oil-based softgels.
Standardized botanical extracts: standardized for phenolic acids such as rosmarinic acid or chlorogenic acid.
Medium-chain triglyceride (MCT) oils: rich in caprylic (C8) and capric (C10) acids, typically derived from coconut or palm kernel oil.

4. Traditional and Historical Use

The health-promoting properties of phenolic acids contained in plants were appreciated already in antiquity and used in folk medicine.

Acetic acid (vinegar): For centuries, vinegar (acetic acid) has been used in folk medicine as a disinfectant and digestive aid, valued for its antimicrobial properties and its ability to preserve foods. Acetic acid has been used as an antiseptic since Hippocratic medicine, mainly to treat infected wounds in patients with burns.

Salicylic acid: Salicylic acid, naturally found in willow bark, has long been recognized for its pain-relieving and anti-inflammatory effects, leading to the development of aspirin.

Citric acid: Citric acid, abundant in citrus fruits, was traditionally utilized to prevent scurvy and support immune function due to its vitamin C content.

Antimicrobial preservation: Organic acids are well-known as effective preservatives, and their antimicrobial action is due to the ability to change from undissociated to dissociated form depending on environmental pH; for example, calcium and sodium propionate prevent spoilage by inhibiting the growth of bacteria and fungi and are used as preservatives in dairy and bakery food products.

Phenolic acids in traditional medicine: The health-promoting properties of phenolic acids in plants were appreciated already in antiquity and used in folk medicine; these compounds continue to be the subject of research on their antibacterial, cardioprotective, anti-inflammatory, and anti-cancer properties. Rosmarinic acid (RosA) is a water-soluble phenolic compound that is an ester of caffeic acid and 3,4-dihydroxyphenyl lactic acid, discovered in many plants of the Boraginaceae and Lamiaceae families.

With the growth of antibiotic therapy, the use of carboxylic acids (and other chemical antiseptics) in clinical settings lost relevance; however, with the continuous emergence of multi-antibiotic/antifungal resistant strains, the search for alternatives has intensified.

5. Key Constituents and Mechanisms of Action

5.1 Short-Chain Fatty Acids (SCFAs): Acetate, Propionate, and Butyrate

The gastrointestinal tract is home to trillions of diverse microorganisms collectively known as the gut microbiota, which play a pivotal role in breaking down undigested foods such as dietary fibers; through the fermentation of these food components, short-chain fatty acids such as acetate, propionate, and butyrate are produced, offering numerous health benefits to the host.

Butyrate has been described as a potent pro-resolution molecule that has a significant role in maintaining gut immunity, supporting gut barrier function, regulation of histone deacetylase (HDAC), and numerous systemic roles. Renewed interest in SCFAs has also emerged because of their ability to alter gene expression through histone deacetylase (HDAC) inhibition.

While less extensively studied compared to butyrate, acetate holds notable interest due to its lower toxicity to epithelial cells, its ability to stimulate bacteria that produce butyrate through cross-feeding, and its anti-inflammatory and protective properties; receptors such as GPR43, pivotal in maintaining calcium homeostasis, are receptive to acetate and propionate.

Butyrate can promote the growth of intestinal epithelial cells, strengthen intestinal tight connections, and regulate the activities of gut microbiota.

5.2 Omega-3 Long-Chain Polyunsaturated Fatty Acids (EPA and DHA)

Omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) may reduce the risk of atherosclerotic cardiovascular disease events through various mechanisms, including triglyceride (TG) lowering, membrane stabilization, and antithrombotic, anti-inflammatory, or antiarrhythmic properties.

It is generally believed that omega-3 FA supplementation can increase mitochondrial β-oxidation and thereby reduce endogenous triglyceride synthesis; omega-3 FA supplementation also increases plasma lipoprotein lipase activity to play a protective role in cardiovascular protection.

5.3 Phenolic Carboxylic Acids

The anti-inflammatory properties of rosmarinic acid are thought to be based on the inhibition of lipoxygenase and cyclooxygenases, and interference with the complement cascade and the inhibition of expression of inflammatory cytokines; caffeic acid also inhibits 5-lipoxygenase (5-LOX) and protein kinase C (PKC) activity, in addition to antioxidant activity.

Phenolic acid molecules with alkoxy or alkyl substituents might enhance their compatibility with biomolecules (like enzymes or receptors) by increasing their lipid solubility or by stabilizing hydroxyl radicals, thus amplifying their anti-inflammatory potential. Phenolic acids with catechol-like configurations, exhibiting two adjacent hydroxyl groups, are characterized by their robust antioxidant capabilities, enabling them to effectively neutralize free radicals and display pronounced anti-inflammatory properties.

A review of the literature revealed that rosmarinic acid exhibited the highest antioxidant activity among the selected natural carboxylic acids, with potency decreasing in the order: rosmarinic acid > caffeic acid ≈ chicoric acid > p-coumaric acid > cinnamic acid > benzoic acid.

5.4 Antimicrobial Mechanisms

Carboxylic acids are much more effective as antimicrobials than strong inorganic acids whose toxic effects are largely exerted on the cell exterior; the toxicity of carboxylic acids is determined by their pKa, the pH of the milieu, and their lipophilicity; the dissociation of the acid in the cytosol results in intracellular acidification that consequently reduces the activity of pH-sensitive enzymes involved in central carbon metabolism, RNA and DNA synthesis, cell wall assembly, and transfer RNA aminoacylation.

5.5 Biological Buffering and Metabolic Intermediacy

Carboxylic acids help regulate pH levels in biological fluids by acting as buffering agents maintaining acid-base balance; lactic acid, for example, is involved in temporary muscle fatigue and pH control during anaerobic respiration. Many metabolic intermediates and waste products are carboxylic acids or their derivatives; uric acid is a waste product of nitrogen metabolism in humans, and benzoic acid and its salts are used by the liver to detoxify substances via conjugation with glycine.

Amino acids, the building blocks of proteins, contain both an amino group (–NH2) and a carboxylic acid group (–COOH); the carboxyl group allows amino acids to participate in peptide bond formation, leading to the formation of proteins, enzymes, and structural components in cells.

6. Scientific Evidence by Area of Health Use

6.1 Cardiovascular Health — Omega-3 Fatty Acids (EPA and DHA)

The cardiovascular effects of long-chain omega-3 fatty acids (themselves carboxylic acids) represent one of the most extensively studied areas in supplement medicine.

In the Vitamin D and Omega-3 Trial (VITAL), 840 mg/day of EPA and DHA resulted in a 28% reduced risk for heart attacks, a 50% reduced risk for fatal heart attacks, and a 17% reduced risk for total coronary heart disease events; in the ASCEND trial (A Study of Cardiovascular Events in Diabetes), cardiovascular disease death was significantly reduced by 19% with 840 mg/day of EPA and DHA; however, the primary composite endpoints were not significantly reduced in either study.

Based on results from REDUCE-IT, the addition of 4 g/day of EPA should be considered for statin-treated patients who have cardiovascular disease or diabetes and elevated triglycerides.

The STRENGTH trial evaluated the effects of a carboxylic acid formulation of EPA and DHA (4 g/day) in 13,078 patients with elevated triglycerides and cardiovascular disease risk; similar to previous mixed omega-3 fatty acid formulations, this well-conducted trial did not show any reduction in risk of cardiovascular events.

The cardiovascular outcome trials have yielded highly inconsistent results, perhaps attributable to variations in dosage, formulation, and composition; in particular, clinical trials using icosapent ethyl (IPE), a highly purified ethyl ester of EPA, reproducibly reduced cardiovascular events and progression of atherosclerosis compared with mixed EPA/DHA treatments.

Moderate- and high-quality evidence suggests that increasing EPA and DHA has little or no effect on mortality or cardiovascular health (evidence mainly from supplement trials); previous suggestions of benefits from EPA and DHA supplements appear to spring from trials with higher risk of bias.

Evidence strength: Mixed to moderate. High-quality RCTs demonstrate triglyceride-lowering effects, and select EPA-only formulations show significant cardiovascular event reduction, but mixed EPA/DHA carboxylic acid formulations have not consistently reproduced these results in large outcomes trials.

6.2 Glycemic Control — Acetic Acid (Vinegar)

There is considerable support for vinegar having a positive acute effect on blood glucose levels when combined with carbohydrate-rich meals; conversely, there are few chronic interventions analyzing the impact of vinegar intake on blood glucose.

A pooled analysis of studies revealed a significant mean glucose and insulin area under the curve (AUC) reduction in participants who consumed vinegar compared with the control group (standard mean difference = −0.60, 95% CI −1.08 to −0.11, p = 0.01, and −1.30, 95% CI −1.98 to −0.62, p < 0.001, respectively); the findings suggest that vinegar can be effective in reducing postprandial glucose and insulin levels, indicating it could be considered as an adjunctive tool for improving glycemic control.

In one human study, three levels of vinegar (18, 23, and 28 mmol acetic acid) were served with white wheat bread containing 50 g available carbohydrates; a significant dose-response relation was seen at 30 minutes for blood glucose and serum insulin responses—the higher the acetic acid level, the lower the metabolic responses—and the rating of satiety was directly related to the acetic acid level.

Sustained dietary supplementation of acetic acid led to significantly lower fasting blood glucose in the type 2 diabetes group compared with placebo, without having a significant effect in healthy individuals, people with overweight or obesity, or those with metabolic conditions.

Proposed pathways by which vinegar may improve blood glucose include the inhibition of α-amylase action, increased glucose uptake, and mediation by transcription factors; daily vinegar intake in amounts of approximately 10–30 mL (~2–6 tablespoons) appears to improve the glycemic response to carbohydrate-rich meals; however, there is a paucity of studies investigating chronic effects of vinegar intake.

In a randomized controlled clinical trial in diabetic patients, results showed a significant decrease in fasting blood glucose (FBG), HbA1c, total cholesterol, LDL, LDL/HDL ratio, cholesterol/HDL ratio, and an increase in insulin hormone in the apple cider vinegar group. One mechanism of action of apple cider vinegar is the effect of acetic acid on disaccharidases and inhibition of their activity, reducing blood glucose; another mechanism is the inhibition of α-amylase; additionally, apple cider vinegar reduces the rate of gastric emptying, causing a reduction in blood glucose.

Evidence strength: Moderate for acute postprandial effects, particularly in subjects with type 2 diabetes. Long-term chronic evidence remains limited in quality and quantity. Clinical trial sizes are generally small.

6.3 Gut Health, Intestinal Barrier, and Microbiome — SCFAs

Medical literature extensively documents the supplementation of SCFAs, particularly butyrate, in the treatment of gastrointestinal, metabolic, cardiovascular, and gut-brain-related disorders.

Short-chain fatty acids, including butyrate, are one of the key metabolic end products that has been a major focus of microbiome understanding; butyrate has reportedly been described as a potent pro-resolution molecule with a significant role in maintaining gut immunity, supporting gut barrier function, regulation of HDAC, and numerous systemic roles.

Short-chain carboxylic acids are of interest for their effects in the brain, including memory enhancement and neuroprotection in rodent experiments; animal and human ingestion studies of prebiotic fibers associated with brain health, such as inulin and resistant potato starch, found selective increases in the production of colonic butyric acid and acetic acid.

The liver receives a significant amount of SCFAs, including butyrate, from the intestines via the portal vein, and recent studies suggest that butyrate has the potential to prevent various liver diseases such as NAFLD, NASH, inflammation, malignant neoplasms, and liver trauma; butyrate also shows promise in improving metabolic diseases, like insulin resistance and obesity, while preventing fatty liver disease.

Evidence strength: Preclinical and early-phase human data are encouraging for gut barrier function and inflammation. Larger, well-controlled RCTs in humans remain necessary to confirm therapeutic benefit across most gastrointestinal endpoints.

6.4 Metabolic Health — SCFAs and Glucose/Lipid Metabolism

Propionate attenuated high-fat diet-induced insulin resistance and improved insulin sensitivity, and the mechanism of action may relate to stimulating odd-chain fatty acid (OCFA) production; acetate and propionate also improved insulin sensitivity and glucose tolerance.

Short-chain fatty acids have many health benefits, including anti-inflammatory, immunoregulatory, anti-obesity, anti-diabetes, anticancer, cardiovascular protective, hepatoprotective, and neuroprotective activities. However, much of this evidence derives from animal studies or in vitro models. Some analyses have found that acetate, propionate, butyrate, and mixed SCFAs had no effect on blood glucose and insulin in humans; significant heterogeneity, risks of bias, and publication biases were identified in several study categories, and caution is urged when interpreting these results; further high-quality research is required to determine the effects of SCFAs on glycemic control.

Evidence strength: Preliminary to mixed in humans. Animal and in vitro evidence is strong for metabolic benefits; human RCT evidence is inconsistent and limited in scale.

6.5 Anti-Infective Potential — Carboxylic Organic Acids

Carboxylic organic acids, including acetic, propionic, citric, and lactic acid, are intermediates of central carbon metabolic pathways long known to have potent antimicrobial potential, mainly at acidic pHs.

The food industry has been leveraging those properties for years, using many of these acids as preservatives to inhibit the growth of pathogenic and/or spoilage fungal and bacterial species.

Short-chain fatty acids such as butyrate are known for their health benefits, including anti-microbial and anti-inflammatory effects, which prompted investigation of potential disease-alleviating properties of butyrate treatment during acute murine Campylobacter jejuni-induced enterocolitis.

Evidence strength: Strong evidence for food-preservation antimicrobial activity. Clinical evidence for anti-infective applications in humans is early-stage, primarily from in vitro and animal models.

6.6 Anti-Inflammatory and Antioxidant Effects — Phenolic Carboxylic Acids

Phenolic acids comprise a class of phytochemical compounds extractable from various plant sources and are well known for their antioxidant and anti-inflammatory properties.

Rosmarinic acid has a wide range of pharmacological effects, including anti-oxidative, anti-apoptotic, anti-tumorigenic, and anti-inflammatory effects; the anti-inflammatory effects of rosmarinic acid have been revealed through in vitro and in vivo studies of various inflammatory diseases like arthritis, colitis, and atopic dermatitis; available clinical research data are limited in quantity.

Animal studies investigating intraperitoneal administration of caffeic and rosmarinic acid (5 and 10 mg/kg) showed that caffeic acid at 5 mg/kg resulted in a 66% reduction of leukocytes migrating to the pleural cavity, and at 10 mg/kg a reduction of 92.9%, compared with the control group. These are preclinical findings.

Despite the passage of years, phenolic acids continue to be the subject of research on their unique antibacterial, cardioprotective, anti-inflammatory, and anti-cancer properties.

The reported beneficial antioxidant, anti-inflammatory, and anticancer effects of caffeic acid and p-coumaric acid may be related to their prooxidant-antioxidant balance in the presence of glutathione (GSH).

Phenolcarboxylic acids such as caffeic acid, chlorogenic acid, p-coumaric acid, and ferulic acid exert beneficial effects on human health through prevention of degenerative pathologies such as cardiovascular diseases and cancer.

Evidence strength: Strong mechanistic and in vitro/animal evidence. Human clinical trials are sparse; most findings for phenolic carboxylic acids in disease prevention are preliminary and require confirmation in adequately powered RCTs.

6.7 Cancer-Related Research — Butyrate as HDAC Inhibitor

The action of butyrate as a histone deacetylase inhibitor (HDACi) has led to a number of clinical trials testing its effectiveness as a potential treatment for cancer; butyrate is a short-chain fatty acid formed by bacterial fermentation of fiber in the colon and serves as an energy source for colonocytes.

Butyrate's diverse mechanisms of action, including the inhibition of histone deacetylases and modulation of cellular metabolism, contribute to its multifaceted therapeutic potential.

Evidence strength: Mechanistic basis is established; clinical application for cancer treatment is investigational. HDAC inhibitor drug derivatives have been approved, but butyrate itself as a dietary supplement for cancer prevention or therapy is not supported by sufficient clinical evidence.

6.8 Neuroprotection and Brain Health — SCFAs

Short-chain fatty acids from gut microbiota play a role in gut-brain communication. These carboxylic acids are of interest for their effects in the brain, including memory enhancement and neuroprotection in rodent experiments.

Animal and human ingestion studies of prebiotic fibers associated with brain health, such as inulin and resistant potato starch, found selective increases in the production of colonic butyric acid and acetic acid; similarly, intermittent fasting in MPTP-induced Parkinson's disease mice resulted in higher butyric acid as well as increased levels of brain-derived neurotrophic factor (BDNF).

Evidence strength: Largely preclinical (animal and indirect human data via dietary fiber studies). Direct human RCT evidence for brain-health benefits of carboxylic acid supplementation is at an early stage.

7. Body Systems and Health Areas Associated with Carboxylic Acids

Gastrointestinal system: SCFAs (butyrate, acetate, propionate) maintain gut epithelial integrity, support colonocyte energy supply, and modulate microbiome composition.
Cardiovascular system: Omega-3 fatty acids (EPA, DHA) lower triglycerides, reduce inflammation, and modify platelet function; select data support cardiovascular event reduction.
Metabolic/endocrine system: Acetic acid modulates postprandial glycemia and insulin sensitivity; propionate and acetate influence insulin resistance via GPR receptor pathways.
Immune system: SCFAs attenuate inflammatory response by decreasing the production of pro-inflammatory mediators and enhancing the production of anti-inflammatory mediators.
Hepatic system: The liver receives a significant amount of SCFAs from the intestines via the portal vein, and butyrate has the potential to prevent various liver diseases such as NAFLD, NASH, and inflammation.
Central nervous system: SCFAs participate in gut-brain signaling; preclinical evidence points to neuroprotective effects.
Antimicrobial defense: Carboxylic organic acids disrupt microbial membrane integrity at physiological pH ranges.
Antioxidant/cellular defense: Phenolic carboxylic acids (caffeic, rosmarinic, ferulic) scavenge reactive oxygen species via catechol-type hydroxyl group chemistry.

8. Dosage Forms and Dosages Reported in Studies

The following dosages appear explicitly in research literature, cited directly from those sources:

Omega-3 carboxylic acid formulations (EPA+DHA): 4 g/day of Epanova (omega-3 carboxylic acids) was tested in the STRENGTH trial, a randomized, double-blind, parallel-arm, placebo-controlled study. 840 mg/day of EPA and DHA was used in the VITAL trial.
Acetic acid / vinegar: Daily vinegar intake in amounts of approximately 10–30 mL (~2–6 tablespoons) appears to improve the glycemic response to carbohydrate-rich meals. Three levels of vinegar (18, 23, and 28 mmol acetic acid) were tested with white wheat bread in human subjects.
Apple cider vinegar: Consuming 30 mL of ACV per day for 12 weeks, along with dietary restriction, significantly reduced total cholesterol and LDL, and increased HDL compared to subjects who had only dietary restriction.
SCFAs (general): A dosage of 0.5 to 10 grams of SCFA per day administered three times daily for at least one week has been described in one approach for gastrointestinal use.
Caffeic and rosmarinic acid (animal study): Intraperitoneal administration of caffeic and rosmarinic acid at 5 and 10 mg/kg was studied for anti-inflammatory and nociceptive response in rats.
EPA (REDUCE-IT trial): In REDUCE-IT, a 25% decrease in the primary endpoint of major cardiovascular events was seen with 4 g/day of EPA (icosapent ethyl) in patients with elevated cardiovascular risk.

9. Safety Considerations and Interactions

9.1 General Safety Profile of Food-Grade Carboxylic Acids

The EFSA Panel considered that ester-linked esters of acetic, lactic, citric, and tartaric acids have very low acute oral toxicity, and no relevant adverse effects were noted in short-term and subchronic toxicity studies; in vitro genotoxicity studies did not show any genotoxic potential. These compounds are extensively hydrolysed in the gastrointestinal tract into their individual hydrolysis products, which are all normal dietary constituents; no adverse effects relevant for humans have been identified from available toxicological data.

9.2 SCFAs — Gastrointestinal Tolerance and Alkalosis Risk

When a subject receives a dosage of between about 500 to 1,200 mg of SCFAs at a time, special precautions to prevent alkalosis are generally unnecessary; however, when a subject is taking more than 1,200 mg of SCFAs in a single dosage, the problem of alkalosis may arise, as the buffering effect of SCFAs may increase the pH of stomach contents to between about 3 to 5, counteracting the normal action of hydrochloric acid and potentially giving rise to uncontrolled intestinal fermentation.

It is important to consider both the beneficial and possible adverse effects of butyrate administration.

9.3 Omega-3 Fatty Acids

Large randomized clinical trials with omega-3 fatty acids have produced discordant outcomes despite similar patient profiles, doses, and triglyceride-lowering effects. The mixed results regarding the effects of EPA and DHA on primary and secondary prevention of cardiovascular disease from previous studies may be due in part to methodological limitations such as using composite endpoints, short intervention duration, low omega-3 fatty acid supplementation dose, and high background fish intake.

9.4 Acetic Acid — Dental and Gastrointestinal Cautions

The concentrated acid form of acetic acid (undiluted vinegar) can be corrosive to tooth enamel and irritating to the upper gastrointestinal tract lining if ingested undiluted or in excessive quantities. Sustained dietary supplementation of acetic acid led to significantly lower fasting blood glucose in type 2 diabetes patients, without having significant effect in healthy individuals. This indicates that glucose effects may be population-specific.

9.5 Immunomodulatory Effects and Autoimmune Considerations

C3–C8 carboxylic acids and their physiologically acceptable salts may act as immunomodulators useful for treating autoimmune-related diseases, and may also be used as dietary supplements with immunomodulating activity; propionic acid and butyric acid in particular have an influence on bowel physiology and the microbiome, thereby having an impact on the composition of the microbiome.

9.6 Phenolic Acids — Prooxidant Considerations

Systemic effects observed from phenolic acids may result from the action of phenolic acids as metabolites of polyphenols, and not strictly from parent phenolic compounds ingested with food. The reported beneficial antioxidant, anti-inflammatory, and anticancer effects of caffeic acid and p-coumaric acid may be related to their prooxidant-antioxidant balance in the presence of glutathione (GSH). This dual redox behavior means that the net effect may vary significantly by dose and cellular context.

9.7 Antimicrobial Use and Antibiotic Resistance Context

With the continuous emergence of multi-antibiotic/antifungal resistant strains, the search for alternatives to conventional antibiotics has intensified, with carboxylic organic acids among the candidates under investigation. Research in this area remains largely preclinical.

10. Evidence Limitations and Research Gaps

While much of the evidence supporting the nutritional benefits of carboxylic acid-containing compounds is robust in some areas, the effects of individual carboxylic acids can vary, and continued research is needed to fully understand their specific roles and potential therapeutic benefits.

Over the last decade, clinical research has focused on a number of in vitro (in human cells) and in vivo (animal) studies aimed at exploring the health protective effects of phenolic acids against the most severe human diseases; clinical data in humans for many phenolic carboxylic acids remain sparse.

Although uptake and metabolism of butyrate are well characterized, there are still significant gaps in the knowledge base around the intracellular handling of butyrate, where assumptions or dated evidence are relied upon.

As evidence is very uncertain in some SCFA areas, caution is urged when interpreting results; further high-quality research is required to determine the effects of SCFAs on glycemic control.

References

Health Conditions

Health conditions that Carboxylic acid may help support.

No conditions available.

Body Systems

Body systems that Carboxylic acid may help support.

No body systems available.