"Vegetarians and Stroke Risk Factors —Animal Protein?"
In 2014, a study on dietary protein intake and stroke risk
found that greater intake was associated with lower stroke risk,
and furthermore it was the animal protein that appeared
to be particularly protective.
Might that help explain
why vegetarians were recently found to have a
higher stroke rate than meat-eaters?
Animal protein consumption increases the level of a cancer-promoting
growth hormone in the body known as IGF-1, insulin-like growth factor one,
which can accelerate the progression of precancerous
changes to invasive cancer.
High blood concentrations are associated with an increased risk
of breast, prostate, colorectal, and lung cancers,
potentially explaining the association between dairy milk
and prostate cancer risk, for example.
But there are also IGF-1 receptors on blood vessels; so, maybe IGF-1
promotes cancer but also brain artery integrity?
People who have strokes appear to have lower blood levels of IGF-1,
but it could just be a consequence of the stroke rather than the cause.
There weren’t any prospective studies over time —until 2017,
and indeed higher IGF-1 levels were linked to lower risk of stroke,
but is it cause and effect?
In mice the answer appears to be yes,
and in a petri dish IGF-1 appears to boost production of elastin,
a stretchy protein that helps keep our arteries elastic.
Higher levels are associated with less artery stiffness,
but acromegaly patients, like Andre the giant,
those with excessive levels of growth hormones like IGF-1
do not appear to have lower stroke rates, and a more recent study
of dietary protein intake and risk of stroke, looking at a dozen
studies of more than a half million people, compared to only
7 studies with a quarter million in the previous analysis,
found NO association between dietary protein intake and the risk of stroke.
In fact, if anything dietary plant protein intake
may actually decrease the risk of stroke.
However, those with high blood pressure who have low IGF-1 levels
do appear to be at increased risk of developing atherosclerosis,
thickening of the artery walls leading up to the brain,
but no such association was found in people with normal blood pressure.
So, there may be a cautionary lesson for vegans here.
Yes, a whole food plant-based diet to down-regulate IGF-1 activity
may slow the human aging process, not to mention reduce the risk of
some of the common cancers that plaque the Western world.
But, perhaps, the ‘take-home’ message should be that people
who undertake to down-regulate IGF-1 activity by cutting down
on animal protein intake as a pro-longevity measure should take
particular care to control their blood pressure to preserve
their cerebrovascular health, the health of their arteries in their brain.
In particular, they should keep salt intake relatively low
while ensuring an ample intake of potassium
to keep their blood pressures down.
So, that means avoiding processed foods and avoiding adding salt,
and in terms of potassium-rich foods, beans, sweet potatoes,
and dark green leafy vegetables.
So, might this explain the higher stroke risk found among vegetarians?
No. Why? Because dairy and egg whites are animal proteins too.
Only vegans have lower IGF-1 levels in both men and women;
so, low IGF-1 levels can’t explain why higher rates of stroke
were found in vegetarians.
So, what is it already?
I think the best explanation for the mystery is something called
homocysteine, which I’ll cover, next.