Gut bacteria and heart attacks

Atherosclerosis is a disease in which plaques build up inside of arteries, which can result in heart attacks, strokes, and other diseases.
It is thought that atherosclerosis arises from the endothelial dysfunction that leads to inflammation in the form of an accumulation of immune cells and therefore, a deposition of low-density lipoproteins and eventually the formation of fatty streaks.

            @ Medical News Today

            @ Medical News Today

For the last decades, cholesterol was the villain in this process as the plaques have high concentrations of cholesterol and the immune cells which resides in the plaques are loaded with it.
However, as the old mantra goes: "correlation does not prove causation". In fact, there seems to be hardly any evidence that high cholesterol intake causes it! (more to this topic here)


What actually causes plaque formation is inflammation. In many blogs, I show how the Microbiome regulates inflammatory levels.
But recently the importance of the gut microbiome has been directly connected to atherosclerosis by a research group from Cleaveland, Ohio [1,2].
A study published in the renowned journal Nature found the molecule trimethylamine-N-oxide (TMAO) to be highly associated with cardiovascular diseases [1]. The molecule is synthesized in our intestines when we eat choline-rich food (choline is found in high concentration in red meat). The researchers wanted to know if our microbiome is responsible for the conversion and treated mice with antibiotics to kill their gut bacteria. And as they expected, a suppression of the microbiome inhibited TMAO synthesis and prevented the mice from developing atherosclerosis on a high choline diet.

Mice succesptible for atherosclerosis (Apoe -/-) were treated with antibiotics (Abx) and stained for foamy macrophages as indicator for atherosclerosis [1]

Mice succesptible for atherosclerosis (Apoe -/-) were treated with antibiotics (Abx) and stained for foamy macrophages as indicator for atherosclerosis [1]

Interestingly, the antibiotic-treated mice had more aortic lesions on a normal diet compared with their microbiome-containing counterparts. But as soon as the mice were set on a high choline diet, the size of the aortic lesions in untreated mice was much higher versus the antibiotics-treated once.
This shows us that with a healthy diet our microbiome suppresses inflammations inside the body but that a diet-induced shift can convert friends to foes.

Size of aortic lesions in mice treated with antibiotics (+Abx) and untreated (-Abx). On a normal diet (control) and on a high choline diet [1].

Size of aortic lesions in mice treated with antibiotics (+Abx) and untreated (-Abx). On a normal diet (control) and on a high choline diet [1].

Does this mean meat is bad?

No, Not in general. What is bad is to have the wrong composition of microbes, as the next study shows us:
The same research group persuaded vegans to eat a steak (which by itself is impressive) and compared their TMAO levels over time with omnivorous subjects [2]. Astonishingly, omnivorous subjects produce significantly more TMAO than vegans after eating a steak.

TMAO concentration after eating a steak. Omnivores vs vegans [2].

TMAO concentration after eating a steak. Omnivores vs vegans [2].

To prove it to be a microbiome-dependent process the subjects were given broad-spectrum antibiotics for a week to suppress their gut microbes and repeated the experiment. As the researchers expected: they could not detect any increased TMAO levels in the plasma of the subjects after antibiotic-treatment. After discontinuation of the antibiotics, they repeated the experiment one more time and could even detect a higher increase in plasma TMAO levels than before the antibiotic treatment.

                                                                           Modified after [2]

                                                                           Modified after [2]

This study indicates two things:

  • The microbiome of people who eat meat it different to the microbiome of vegans.
  • Eating meat once in a while does not necessarily have negative effects on our health. On the contrary, it can even promote your health! (Learn More)
                                                               [1]

                                                               [1]

 

References

  1. Wang et al., Gut flora metabolism of phosphatidylcholine promotes cardiovascular disease, Nature, 2011
  2. Koeth et al., Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis, Nat Med, 2013