Studies on the use of lactic acid

Reliable studies on the internal (oral) use of lactic acid/lactate , focusing 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 indicate it.

Current human studies (oral intake)

• Oral lactate & gastric emptying/appetite (randomized crossover) – 10 healthy men: oral administration of D/L-sodium lactate (vs. IV lactate/placebo) slowed gastric emptying , decreased ghrelin, and increased GLP-1; ad libitum food intake remained unchanged. Demonstrates 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” (high in lactate) vs. yeast bread: greater 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 and blood lactate (pilot study, n=5, 15 sessions) – did not increase blood lactate and caused moderate to severe GI side effects (including vomiting/diarrhea). Conclusion: Oral sodium lactate administration is 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, threshold, or 20-minute time trial. (Product contained lactate; isomer not specified.) 2024. ⁴

• Calcium lactate & performance/acid-base status (randomized) – pH/bicarbonate increased slightly, no performance improvement ; GI tolerability assessed. (Commercially available calcium L-lactate .) J Funct Morphol Kinesiol 2024. ⁵

Food/Nutrition (high in lactate or lactic acid-acidified)

• Acidified infant formula (sometimes with L(+)-lactic acid) – Historically and in more recent reviews: acid-acidified formulas (chemically with L(+)-lactic acid or by fermentation) inhibited pathogenic bacteria ; early/older RCTs report less diarrhea/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 : no clinically relevant D-lactate acidosis in healthy children; caution advised in short bowel syndrome . ⁸ , ⁹

• Adults: acidified milk vs. fermented yogurt (crossover intervention) – increased serum L-lactate after acidified milk; effects of both products were similar , suggesting the matrix/acidification as a driver. Nutrients 2022. ¹⁰

Regarding the isomer (“right” vs. “left”)

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

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

Mechanistic/indirect evidence (not: direct L(+) administration)

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

Safety & practical advice

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

• GI tract irritation : Oral sodium lactate frequently caused GI discomfort in a pilot study; therefore, caution should be exercised regarding dose/form when using 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 administration (hormonal/motility-related, but partly GI-limited). ² , ⁷