The Gut Truth for Heart Attack Survival

The surprising role of our gut microbiome in thriving after a cardiac event

No one wants to have a heart attack, but heart attacks don’t always lead to death. For survivors of heart attacks, it’s especially important that they work to improve their health to avoid additional cardiac events.

One of the biggest recommendations for heart attack survivors is to work on an exercise regimen. It’s well documented that exercise, especially aerobic exercise, helps improve heart health after an attack and reduces the chances of another attack occurring.

But why does exercise help improve heart health?

Could it be… the gut microbiome? Is it possible that the bacteria in our lower digestive tract, our small and large intestine, are somehow playing some sort of role in improving our heart health when we exercise?

It sounds crazy; those two systems have nothing to do with each other! But scientists have found that the microbiome is connected with many wide-reaching different aspects of health. It doesn’t just help us break down food; it seems to be linked to a number of inflammation-related diseases, it affects our mental state, and it affects our hormone levels.

Researchers in Shanghai University put this to the test in mice; they gave the animals artificial heart attacks, and then tested how the microbiome influenced their recovery. In their paper, “Gut microbiome mediates the protective effects of exercise after myocardial infarction”, they posit that, well, the gut microbiome controls the benefits of post-heart-attack exercise.

Here’s what they found.

How to give a mouse a heart attack, no cats needed

In order to test heart attack recovery, the researchers needed to induce cardiac events. How do you give a mouse a heart attack?

Thankfully, you don’t need to feed them tons of sugary foods, or pop a paper bag next to their cage, or hold up a printed-out picture of a cat. All you need to do is a bit of surgery; cut and suture the artery leading into the heart, and you cut down the heart’s ability.

After recovery from the surgery, the mice in this Shanghai study were put on an exercise regimen. Time to hit the treadmill! The researchers measured how much endurance the mice had — how long they could stay on the treadmill — and how long they could go at ever-increasing speeds until they were exhausted and gave up.

After eight weeks of this recovery, the mice were sacrificed (sorry, mouse lovers; sometimes science requires sacrifice) and dissected to examine how well they recovered from the heart surgery. The researchers examined the capacity of the injured hearts of the mice, and also collected fecal samples to analyze to study their microbiomes.

By the way, when we talk about the microbiome, we’re referring to the diverse collection of many different species of bacteria that naturally live in the lower intestine. These bacteria feed off the food we eat, but they interact closely with the body, sending signals and unique molecules across the intestinal wall to communicate with the immune system, liver, brain, and other organs.

Here’s their results.

Did exercise help these mice recover from their (simulated) heart attacks?

Short answer: Yes.

Longer answer: The researchers looked at the hearts of the mice who exercised and saw significant improvements in two semi-related values of how efficient the heart is:

• Fractional shortening is how much the heart compresses when it beats. Higher is better.
• Ejection fraction is how much blood the heart can push with one pump. Again, higher is better.

They also saw a reduction in cardiac fibrosis, the amount of scar tissue that was present in the heart. Scar tissue is a great choice for a quick band-aid, but it doesn’t stretch or flex as well as normal heart muscle, so less fibrosis in the heart is better.

This info isn’t groundbreaking; we’ve known for a while that, in humans, exercise is a highly recommended activity after a heart attack. It helps the heart rebuild and become more efficient, reducing the chances of further cardiac events.

Did exercise alter the composition of the mice’s gut microbiome?

Short answer: Yes.

Longer answer: The researchers used a sequencing technique called 16S rRNA sequencing, which gives a general identification of different bacterial groups by looking at a single gene, like a barcode. It’s not as exact as other methods, but it still showed that there were significant changes in the post-heart-surgery mice who exercised, versus those who got to remain lazy and sit around.

But why? Exercising doesn’t introduce any new food; why would this alter the gut microbiome composition?

There could be several reasons at play:

• When you exercise, it moves your poop along faster through your gut, which affects your microbiome in turn.

• Exercise may reduce the amount of fat we absorb from our diet, altering the amount of available fat for microbes to eat.
• Exercise temporarily reduces blood flow to the gut, which can stress the intestinal wall cells and alter their outputs and interactions with the microbes.
• Regular exercise increases the permeability of the intestine, letting more microbe signals cross to the body.

Put it all together, and the mice who exercised saw significant changes in the blend of bacteria that made up their gut microbiome.

If you disrupt the microbiome, does that alter the benefits of exercise?

Now we get into the cool, newer findings.

Imagine that you and a friend both recently had heart attacks. You decide that you’ll exercise together, keeping each other accountable to get into better health and avoid future heart attacks.

But your friend recently got a nasty ear infection, and is on a dose of antibiotics for a couple of weeks.

It turns out that this minor detail will have a significant impact on your recovery. You are both exercising, but you’ll see health benefits — while, for your antibiotic-consuming partner, the benefits are either absent, or severely reduced.

In this study, the researchers found that post-heart-surgery mice who consumed antibiotics, killing off their gut microbiome, didn’t get the same exercise-driven benefits as their bacteria-filled companions. The antibiotics didn’t evoke any change in the mice who were lazily sitting around after their heart surgery, but they did eliminate those benefits shown in the post-heart-surgery mice who exercised.

Even just taking a quarter of the antibiotic dose was enough to remove the beneficial effects of post-heart-attack exercise, suggesting that it doesn’t take a huge disruption to the microbiome to negate these benefits.

If you put the microbiome of a well-exercised mouse into another mouse that hasn’t done any exercise, does it get benefits?

Have we just found a hack for lazy people?

The answer appears to be a partial yes. If you take the microbiome from a mouse that has been regularly exercising and you transplant it into a mouse that hasn’t been exercising, the recipient does show some cardiac improvements. With the exercise-trained microbiome, lazy mice still get improvements to their heart health.

Unfortunately, not all the benefits carry over; the lazy mice don’t have the increased muscle tone and endurance of their exercise-trained counterparts.

Still, it seems like just getting the right microbiome gives the same reduction of scar tissue in the heart as exercising — without doing any exercise! This could be huge for heart attack victims who can’t bring themselves to set foot in the gym, or who want a boost to accompany their training regimen.

Are there limitations to this study?

Remember, just because it’s published, it doesn’t mean that it’s guaranteed. And there are certainly a few limitations with this study that should jump out to anyone who regularly reads my articles:

Mouse study. When we are studying a phenomenon, it’s best if we can do it in our own species. We can cure a lot of diseases in mice that we can’t yet treat in humans, because there are subtle but important differences between humans and mice. And to further reduce our confidence, these mice didn’t even get a humanized microbiome, where we transplant a human microbiome into them. They’re mice, with mouse microbiomes, and the human microbiome may not work the same way in its interactions with our heart.

16S rRNA sequencing. As mentioned above, 16S rRNA sequencing is like barcoding; it provides a general identification of the bacteria, but it’s not detailed enough to accurately identify them all the way to the exact species or subspecies level. This paper didn’t go too deep into identifying the exact microbes that were responsible for the exercise-linked heart improvements, so this is less of an issue in this case.

Limited number of individuals. Each experimental group in this study only contained about a dozen mice; that’s a pretty small sample, so the effects could be lost at a larger scale.

Heart damage was induced surgically. Real-life heart attacks may cause more damage or induce damage in other areas that aren’t represented by this study.

What you should take away

We’ve long known that exercise is vital for helping us recover from heart attacks. Exercise reduces the amount of scarring on heart tissue and improves its functionality, letting it pump more efficiently and heal from the heart attack damage.

But now, scientists are finding that this improvement may be due, at least in part, to activities of the gut microbiome. Researchers are still not fully certain what the exact mechanism is that leads to interaction between the bacteria in the gut and the heart, but this is definitely a promising avenue of research that deserves more investigation.

What will come next? The research team will likely focus next on identifying the specific microbes, as well as the molecules produced by these microbes. A future treatment could just give people the molecules, not the bacteria themselves, for heart recovery.

Maybe this will become a recommended treatment, prescribed by doctors, to help heart attack victims recover and come back to full strength!

In the meantime, we know that exercise does help get the right microbiome for recovery. It might be more work than a pill, but it’s the best option open for us… right now.

Thanks for reading. Next, check out whether carbonated (sugar-free) water is actually good or bad for our teeth.

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