Studies on the use of lactic acid

Robust studies on the internal (oral) use of lactic acid/lactate, with a focus on dextrorotatory L(+)-lactic acid ("right-handed lactic acid"). Important note: Many human studies test mixed lactate (D/L) or lactate-rich foods instead of isolated L(+)-lactic acid. Where the isomer type is specified, we will note it.

Current Human Studies (Oral Intake)

• Oral Lactate & Gastric Emptying/Appetite (randomized crossover) – 10 healthy men: oral administration of D/L-sodium lactate (vs. i.v. lactate/placebo) slowed gastric emptying, decreased ghrelin, increased GLP-1; ad-libitum food intake unchanged. Shows a direct GI effect of oral lactate. Clin Nutr 2022 (Corrigendum 2024). ¹

• Sourdough Bread Rich in Lactic Acid (randomized, double-blind, crossover, n=44) – "Whole-meal sourdough" (lactate-rich) vs. yeast bread: more satiety, slower gastric emptying, more favorable early glucose/C-peptide response, no significant reduction in ad-libitum energy intake. Postulated active substance: (L-)lactic acid from fermentation. Curr Res Food Sci 2024/25. ²

• Oral Sodium Lactate & Blood Lactate (Pilot, n=5, 15 sessions) – did not increase blood lactate and caused moderate to severe GI side effects (incl. vomiting/diarrhea). Conclusion: oral Na-lactate administration unsuitable for studying systemic lactate effects. J Appl Physiol 2024. ³

• Oral Lactate as a Sports Supplement (randomized, placebo-controlled crossover pilot RCT, n=15) – no ergogenic effects on VO₂peak, thresholds or 20-min time trial. (Product contained lactate; isomer not specified.) 2024. ⁴

• Calcium Lactate & Performance/Acid-Base Status (randomized) – pH/bicarbonate slightly increased, no performance improvement; GI tolerance recorded. (Commercially usually calcium L-lactate.) J Funct Morphol Kinesiol 2024. ⁵

Foods/Nutrition (Lactate-rich or Lactic Acid-acidified)

• Acidified Infant Formulas (partially with L(+)-Lactic Acid) – Historically and in recent reviews: acid-acidified formulas (chemically with L(+)-lactic acid or by fermentation) inhibited pathogenic germs; early/older RCTs report fewer diarrheas/vomiting vs. non-acidified formulas (details vary). Review/classification 2013; evidence review article 2014. ⁶, ⁷

• Safety: Fermented/Acidified Formulas & D-Lactate – Randomized safety study with L. reuteri-containing formula and Rapid Review: in healthy children no clinically relevant D-lactic acidosis; caution with short bowel syndrome. ⁸, ⁹

• Adults: Acidified Milk vs. Fermented Yogurt (Crossover Intervention) – increased serum L-lactate after acidified milk; effects of both products similar, suggesting matrix/acidification as the driver. Nutrients 2022. ¹⁰

On the Isomer ("right" vs. "left")

• In sourdoughs, L-lactic acid usually predominates over D-lactic acid (proportion depends on starter cultures/process). This supports that lactate-rich sourdough products predominantly provide right-handed lactic acid. ¹¹

• In acidified infant formulas, (depending on product/region) explicitly L(+)-lactic acid is used for pH reduction (chemically acidified) – however, many clinical studies do not always specify the isomer content. ⁶

Mechanistic/Indirect Evidence (not: direct L(+) administration)

• Lactulose (not lactate, but fermented in the colon to lactic acid/SCFA) acidifies the intestinal content; thereby ammonia "trapping" (NH₃→NH₄⁺) – an established mechanism in HE therapy. This supports the principle "colon acidification = less ammonia absorption" (indirect parallel, no direct L(+) administration). ¹², ¹³

Safety & Practical Notes

• Short bowel/organic acidosis: In structural intestinal diseases, there have been historical reports of D-lactic acidosis under diets/probiotics rich in D-lactate; in healthy infants/children, no clinically relevant risk has been shown. ⁹

• Irritability of the GI tract: Oral sodium lactate frequently caused GI discomfort in a pilot series; therefore, caution with dose/form for isolated lactate salts. ³

Conclusion

Direct human studies with isolated L(+)-lactic acid are rare; the best evidence for internal use currently comes from lactate-rich foods (e.g., sourdough bread) with acute effects on satiety/gastric emptying, from acidified dairy products/formulas (historically: infection/GI outcomes) and from oral lactate administrations (hormonal/motility-related, but sometimes GI-limited). ², ⁷