TMAO – or trimethylamine N-oxide – has been known to be generated from dietary carnitine through metabolism of gut microbiota, and was recently reported to be an “important gut microbiota-dependent metabolite to cause cardiovascular diseases,” explained Taiwanese researchers in the Journal of Functional Foods.
While antibiotics have been found to inhibit TMAO production, concerns over side effects and resistance have limited their use. This has led researchers to examine the potential of natural alternatives.
New data indicated that carnitine-fed lab mice showed a “remarkable increase in plasma TMAO levels”, compared with lab mice fed a control (no carnitine). However, when allicin supplements were provided with the carnitine diet, TMAO levels were significantly reduced.
“Surprisingly, the plasma TMAO levels in the mice of ‘carnitine diet + allicin’ treatment group were as low as that of chow diet [control] group,” wrote the researchers. “This result indicated that the metabolic capacity of mice gut microbiota to produce TMAO was completely inhibited by allicin supplement even though provided with carnitine-rich environment in the gut.
“It means the functional alteration of gut microbiota induced by carnitine diet can be prevented by addition of another substance with antimicrobial potential derived from food, such as allicin.”
Garlic and heart health
The study adds to the body of scientific literature supporting the potential heart health benefits of garlic and the compounds it contains.
Consumer awareness of the health benefits of garlic, mostly in terms of cardiovascular and immune system health, has benefited the supplements industry, particularly since consumers seek the benefits of garlic without the odors that accompany the fresh bulb.
The benefits have been linked to the compound allicin, which is not found in fresh garlic: It is only formed when garlic is crushed, which breaks down a compound called diallyl sulphide.
The Taiwanese researchers divided male C57BL/6(B6) mice into four groups: One group received only the control chow diet; the second group received the carnitine diet (carnitine added to drinking water at a level of 0.02%); the third group received the carnitine diet with supplemental allicin; and the final group received the control diet plus the allicin supplement for six weeks.
Results showed that the second group (carnitine diet) had TMAO levels 4–22 times greater than those observed in the control group. However, these increases were attenuated in the carnitine + allicin group, said the researchers.
“Our study suggests that antimicrobial phytochemicals such as allicin effectively neutralize the metabolic ability of TMAO production of gut microbiota induced by daily intake of L-carnitine,” wrote the researchers. “It may offer an opportunity for us to take advantage of plants' delicately designed defense system against microorganisms, to protect ourselves by modulating gut microbiota to a healthier status.
“Our research also suggested that allicin and dietary fresh garlic containing allicin might be used as functional foods for the prevention of atherosclerosis,” they concluded.
Source: Journal of Functional Foods
Volume 15, Pages 408–417
“Dietary allicin reduces transformation of L-carnitine to TMAO through impact on gut microbiota”
Authors: W-K. Wu, S. Panyod, C-T. Ho, et al.