Red meat, gut bacteria and heart disease

Red meat intake has been associated with elevated risk of cardiovascular disease and cardiovascular death.1-5 For example, combined data from the Nurses’ Health Study and Health Professionals Follow-up study, comprising over 120,000 people, estimated that each serving (100 grams) of red meat raises the risk of cardiovascular death by 18 percent

Two widely accepted factors that are thought to link red meat to increased cardiovascular disease risk are the high saturated fat and heme iron contents of red meat. Saturated fats are known to elevate total and LDL cholesterol levels, and excess iron is associated with oxidative stress, which promotes atherosclerosis.6-9 However, scientists have theorized that these factors alone do not explain the contribution of red meat to cardiovascular risk.3 Additional properties of red meat are likely involved.

Fascinating new research presents a new potential mechanism by which red meat may increase cardiovascular risk – by modulating the species of bacteria that populate our digestive tract!

We are now learning that our intestinal flora interacts with the cells of the intestinal wall to exert profound effects on our health. Beneficial microbes produce vitamins, protect us against pathogenic microbes, promote healthy immune function, facilitate energy extraction from food, and break down fiber and resistant starch into beneficial short chain fatty acids, which protect us against colon cancer. Importantly, what we eat determines which species of bacteria thrive in our digestive tract. Healthful, fiber-rich plant foods provide an energy source (“prebiotics”) for beneficial bacteria to grow.10,11

Is the reverse true? Do unhealthy foods promote proliferation of unhealthy gut bacteria?

Carnitine is an amino acid involved in energy production, and it is abundant in animal products, especially red meat; there is little or no carnitine in plant foods, and the human body can produce adequate carnitine from other amino acids, lysine and methionine. Studying mice, the scientists found that carnitine was metabolized by intestinal bacteria, producing trimethylamine-N-oxide (TMAO), a substance previously shown to contribute to atherosclerotic plaque development by slowing the removal of cholesterol from the arterial wall. They then sought to confirm these findings with human subjects. When analyzing the blood levels of carnitine and TMAO in human subjects, they found that the combination of high carnitine and high TMAO was associated with increased likelihood of cardiovascular disease or cardiovascular events (heart attack and stroke). When they gave humans carnitine supplements, they interestingly found that omnivores produced far more TMAO in response to carnitine than vegans and vegetarians. In addition, the species of gut bacteria in omnivores were different from those in vegetarians and vegans. These results suggest that regularly eating carnitine-containing foods promotes the growth of gut bacteria that can metabolize carnitine into a heart disease-promoting substance.12-14  

Our overall dietary pattern determines the bacteria that live in our gastrointestinal tract, and this research indicates that eating red meat regularly promotes the growth of bacteria that produce harmful substances from the components of red meat. It also indicates that those of us that regularly consume a healthful diet of whole plant foods have a healthier microbial profile, and we are less susceptible to the disease-promoting effects of high-carnitine meats. Future studies will continue to uncover more of these intriguing links between diet, gut bacteria, and health. 

Carnitine content of animal foods:15

Food Carnitine (mg)
Beef steak (3 ounces) 81
Ground beef (3 ounces) 80
Pork (3 ounces) 24
Milk (whole; 1 cup) 8
Fish (cod; 3 ounces) 5
Chicken breast (3 ounces) 3
Cheese (1 ounce) 1

This new research highlights an additional way that red meat likely increases heart disease risk, but certainly the high amount of carnitine in red meat does not exonerate fish, chicken, eggs and dairy products. We already have plentiful evidence that excessive consumption of animal products in general are associated with increased risk of death from all causes. Animal products overall are micronutrient-poor, void of phytochemicals and antioxidants, contain pro-inflammatory fats, increase cholesterol levels, calorically concentrated, promote weight gain, and most importantly elevate IGF-1 which increases heart disease and cancer risk.

 

References:

1. Sinha R, Cross AJ, Graubard BI, et al: Meat intake and mortality: a prospective study of over half a million people. Arch Intern Med 2009;169:562-571.
2. Bernstein AM, Sun Q, Hu FB, et al: Major dietary protein sources and risk of coronary heart disease in women. Circulation 2010;122:876-883.
3. Pan A, Sun Q, Bernstein AM, et al: Red Meat Consumption and Mortality: Results From 2 Prospective Cohort Studies. Arch Intern Med 2012.
4. Ascherio A, Willett WC, Rimm EB, et al: Dietary iron intake and risk of coronary disease among men. Circulation 1994;89:969-974.
5. Larsson SC, Virtamo J, Wolk A: Red meat consumption and risk of stroke in Swedish men. Am J Clin Nutr 2011.
6. Tholstrup T, Hjerpsted J, Raff M: Palm olein increases plasma cholesterol moderately compared with olive oil in healthy individuals. Am J Clin Nutr 2011;94:1426-1432.
7. de Oliveira Otto MC, Alonso A, Lee DH, et al: Dietary intakes of zinc and heme iron from red meat, but not from other sources, are associated with greater risk of metabolic syndrome and cardiovascular disease. J Nutr 2012;142:526-533.
8. Ahluwalia N, Genoux A, Ferrieres J, et al: Iron status is associated with carotid atherosclerotic plaques in middle-aged adults. J Nutr 2010;140:812-816.
9. Brewer GJ: Iron and copper toxicity in diseases of aging, particularly atherosclerosis and Alzheimer's disease. Exp Biol Med 2007;232:323-335.
10. Neish AS: Microbes in gastrointestinal health and disease. Gastroenterology 2009;136:65-80.
11. Backhed F: Host responses to the human microbiome. Nutr Rev 2012;70 Suppl 1:S14-17.
12. Koeth RA, Wang Z, Levison BS, et al: Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med 2013.
13. Wang Z, Klipfell E, Bennett BJ, et al: Gut flora metabolism of phosphatidylcholine promotes cardiovascular disease. Nature 2011;472:57-63.
14. Woolston C: Red meat + wrong bacteria = bad news for hearts. 2013. Nature. http://www.nature.com/news/red-meat-wrong-bacteria-bad-news-for-hearts-1.12746. Accessed April 12, 2013.

15. Linus Pauling Institute: Carnitine. http://lpi.oregonstate.edu/infocenter/othernuts/carnitine/
 

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Comments (9) Read through and enter the discussion with the form at the end
Dan - April 15, 2013 2:55 PM

What is your take on research that contradicts these findings?

A meta-analysis of 20 studies including 1,218,380 individuals in Circulation did not find a correlation between intake of unprocessed red meat and coronary heart disease (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2885952/).

A just-released review of 13 studies in Mayo Clinic Proceedings found that L-carnitine supplementation improved cardiac health in patients after a heart attack (http://www.mayoclinicproceedings.org/webfiles/images/journals/jmcp/jmcp_pr88_4_2.pdf).

question - April 15, 2013 3:44 PM

"each serving (100 grams) of red meat raises the risk of cardiovascular death by 18 percent." Each serving what? Each serving per day?

AmyLu - April 15, 2013 4:47 PM

Did the study specify whether the red meat included was antibiotic-free, or whether it contained antibiotics?

Ginny's - April 15, 2013 5:12 PM

Is this the same as L-carni tine that people take for heart health?

Cheryl - April 15, 2013 5:20 PM

Geez, that picture made me feel a wave of nausea for a few seconds.
Back when we ate meat my husband had leaky gut syndrome. It went away after we went vegan. He ate meat one time, several months ago, and it was back for the following week. He has never eaten meat since then.
Thank you so much for sharing this info with us.
To a previous poster: it said each serving. meaning each serving that is eaten.

David - April 15, 2013 8:58 PM

I have followed ETL for over a year now. Before, I ate red meat frequently but have since cut way back. (I probably eat about 4-6 oz of red meat a month) What does the research say about the length of time it may take to reverse the negative effects of carnitine, from years of eating red meat?

David - April 15, 2013 9:17 PM

Was the study done on beef from cows that were fed corn, or does meat from grass fed cows have beef that is lower in carnitine?

Deana Ferreri, Ph.D. - April 16, 2013 9:05 AM

Yes, each serving per day.

GIGI - June 12, 2013 10:42 AM

From August 2012 to November 2012, my A1C has dropped from 10.5 to 7.1, I've lost 55 lbs and my blood pressure is perfect. I seem to be stuck at this point- it's June 2013- so 8 months of staying just about the same. (I need to lose another 50 pounds.
My physician and my endochronologist don't want me to go off my meds. After knowing my feeling about meds, my physician did allow me to cut my 80mg of diovan in half (daily) and my lipitor to every other day). My endochronologist let me gradually reduce my nightly insulin to 0, but doesn't want me to go off metformin. It seems that I would do better to drop it all. Is there any info that I can give to my docs to help them see? My A1C has dropped from 10.5 to 7.1, I've lost 55 lbs and my blood pressure is perfect.

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