L-Carnitine: The Controversy

June 02, 2013

L-Carnitine: The Controversy 

 Reference:  Mayo Clinic Proceedings 2013Nature Medicine Harvard ReviewHuffington Post

What is carnitine?  Easy.  It’s a taxi cab.  It’s a shuttle.  It is the chemical that binds fatty acids and escorts them into the hearts’ mitochondria.  The heart prefers to run on fatty acids so carnitine is an extremely critical ingredient.  In a heart attack, it rapidly becomes depleted.  The heart then can’t transport its vital energy source and you go into a terrible spiral of energy failure and death.   That makes it a life-saving chemical, poised at the junction of energy production and heart function. 

 What’s the controversy?  In the journal Nature Medicine, this spring was an article published showing a potential link with eating red meat, a rich source of carnitine and atherosclerosis.  It’s all about trimethylamine-N-oxide (TMAO).   Our guts contain bacteria that change carnitine into TMAO. The level of TMAO correlates with our risk for atherosclerosis.  Hence, the very organ we protect with carnitine becomes vulnerable to the one disease that damages it the most, artery blockage by atherosclerosis.   The more red meat one eats, the higher the level of carnitine, the higher the level of TMAO.  

The study in Nature Medicine was well done and suggests a bit of a conundrum. What we have here is a classic example of conflicting data that leaves us puzzled.  It suggests that eating red meat is dangerous.  That made the news!   Every mainstream news media outlet carried the headlines.  I like the analysis in the Huffington Post the most. 

 The fact is, it’s not that simple.  Recent well-done reviews of many studies comparing causes of heart disease to meat consumption have not shown any connection with saturated fat and artery disease.  It’s not the fat and it’s not the cholesterol.  Hmmm. So, what is it?   Here is where it gets interesting.  The Nature Medicine article found that vegans didn’t have the same effect.  It appears that the bacteria in our gut depend on what we eat.  We are in relationship with our gut bacteria and each of us have our own unique set, in part based on what we routinely eat.   If you eat red meat regularly, you nourish more bacteria that are programmed to make TMAO.  Vegans don’t have those same bacteria.  They also don’t get heart disease.  The researchers even gave antibiotics to meat-eaters whose bacteria were making lots of TMAO and sure enough, the TMAO levels plunged.  Then they gave carnitine to vegans and nothing happened.  No TMAO.  So, it may not be the carnitine itself but the combination of all of the above.   And red meat may not be bad clinically anyways. To top it off, the Mayo Clinic Proceedings looked at all the recent research on carnitine.  People who take it regularly have dramatic reductions in all cause mortality (27%).   Doesn’t sound like poison to me. 

 WWW. What will work for me?   I’m still taking carnitine.  The Mayo Report is pretty convincing.   I think this is a first class example of a fascinating tidbit that we don’t know how to fit into our everyday world.  The sound byte summary makes it sound dangerous.  I like 27% reduction in all cause mortality.    (Editor's Note:  Jan 2022:  Dayan Goodenowe has convincingly showed that acetyl-carnitine dramatically improves mitochondrial function.)

 Pop Quiz


1.  L-Carnitine is a chemical that dissolves fat.  T or F                         Answer:  False.  It is the chemical that transports fat into heart cells where it can be burned into energy. 

 2.  Heart cells prefer to burn fat for energy.  T or F                           Answer:   Bingo. 

 3.  The Nature Medicine Study shows that bacteria in meat-eaters guts turn l-carnitine into a chemical called TMAO that is strongly linked to causing heart disease.  T or F                     Answer:   True. 

 4.  Vegans, fed l-carnitine, don't make TMAO,  T or F                        Ansswer:  True 

 5.   Sounds like some combination of bacteria, canitine, diet, and maybe something else is what's to blame for heart disease.  T or F                           Answer:   Stay tuned.  Fascinating story 6.  Red meat causes heart disease.  T or F                            Answer:   True

Column written by Dr. John E Whitcomb, Brookfield Longevity, Brookfield, WI