"How Our Gut Bacteria Can Use Eggs to Accelerate Cancer"
We are walking communities comprised not only
of a Homo sapiens host, but also trillions of symbiotic
commensal microorganisms within the gut
and on every other surface of our bodies.
There are more bacterial cells in our gut
than there are human cells in our entire body.
In fact, only about 10% of the DNA in our body is human.
The rest is in our microbiome,
the microbes that we share this walking community we call our body.
What do they do?
Our gut bacteria microbiota, or gut bacteria microbiome,
serve as a filter for our largest environmental exposure:
what we eat.
Technically speaking, food is a foreign object
that we take into our bodies by the pound every day.
And the microbial community within each of us
significantly influences how we experience those meals.
Hence, our metabolism and absorption of food occurs
through this filter of bacteria.
But if we eat a lot of meat, poultry, fish, milk, cheese, eggs,
we can foster the growth of bacteria that convert the choline and carnitine
in those foods into TMA, trimethylamine,
which can be oxidized into TMAO and wreak havoc on our arteries,
increasing our risk of heart attack, stroke, and death.
We've known about this troublesome transformation
from choline into trimethylamine for over 40 years.
But that was way before we learned about the heart disease connection.
Why were they concerned back then?
Because these methylamines might form nitrosamines,
which have marked carcinogenic activity, cancer-causing activity.
So where is choline found in our diet?
Mostly from meat, eggs, dairy, and refined grains.
The link between meat and cancer probably wouldn't surprise anyone.
In fact, just due to the industrial pollutants alone, like PCBs,
children probably shouldn't eat more than like five servings a month
of meats like beef, pork, or chicken combined.
But what about cancer and eggs?
Studies going back to the '70s hinted at a correlation between eggs
and colon cancer, but that was just based on so-called ecological data,
showing that countries that ate more eggs
tended to have higher cancer rates,
but that could be due to a million things.
It needed to be put to the test.
This started in the '80s,
and by the 1990s, 15 studies had been published,
10 suggesting a direct association between egg consumption
and colorectal cancer and five showing no association.
By 2014, there were dozens more studies published,
confirming that eggs may indeed be playing a role in the development
of colon cancer, though no relationship was discovered
between egg consumption and the development
of precancerous polyps,
which suggests that eggs might be involved more
in the promotional stage of cancer growth, accelerating cancer growth,
rather than initiating the cancer in the first place.
Which brings us to 2015.
Maybe it's the TMAO made from the choline in meat and eggs
that's promoting cancer growth.
And indeed, in the Women's Health Initiative study,
women with the highest TMAO levels in their blood
had approximately 3 times greater risk of rectal cancer,
suggesting TMAO levels may serve as a potential predictor
of increased colorectal cancer risk.
Though there may be more evidence for elevated breast cancer risk
with egg consumption than prostate cancer risk,
the only other study to date on TMAO and cancer
looked at prostate cancer and did, indeed, find a higher risk.
Diet has long been considered a primary factor in health.
However, with the microbiome revolution of the past decade,
we have begun to understand how diet can affect the back and forth
between us and the rest of us inside, and the whole TMAO story
is like a smoking gun in gut bacteria-disease interactions.
Since choline and carnitine are the primary sources
of TMAO production, the logical intervention strategy
might be to reduce meat, dairy, and egg consumption.
And if we eat plant-based for long enough,
we can actually change our gut microbial communities,
such that they may not be able to produce TMAO even if we try.
The theory of "you are what you eat"
is finally supported by scientific evidence.
We may not have to eat healthy for long, though.
Soon we may yet be able to "drug the microbiome"
as a way of promoting cardiovascular health.