The gut flora or microbiota
is undoubtedly crucial to the digestive process. However, there is growing
interest in the role of the gut microbiota as an environmental factor
influencing propensity for cardiometabolic disease. Studies have implicated the
gut microbiota in susceptibility to obesity and insulin resistance; germ-free
mice fed a high-fat, high-carbohydrate Western-style diet were protected
against diet-induced obesity, glucose intolerance and insulin resistance.
More recently, research has
linked dietary lipid intake, the gut microbiota and increased risk for
atherosclerosis.(2,3) Cholesterol-rich foods, such as egg yolks, contain
phosphatidylcholine which is hydrolysed by phospholipase enzymes to release
choline. The gut microbiota then convert choline to trimethylamine (TMA), whichundergoes
oxidation in the liver to trimethylamine N-oxide (TMAO), released into the
plasma.
In mice susceptible to
atherosclerosis fed a diet supplemented with phosphatidyl choline, there was an
increase in plasma levels of TMAO concomitant with increased atherosclerotic
plaque development. Mechanistically, increased dietary choline was associated
with suppression of multiple macrophage scavenger receptors which protect
against atherosclerosis.3 These data therefore implicate excess dietary choline
as an emerging modifiable risk factor for cardiovascular disease, mediated by
the gut microbiota.
These findings may be
relevant in the light with recent research which showed an association between
egg yolk consumption and carotid plaque burden. Individuals consuming 3 or more
eggs per week had a significantly higher plaque burden that those with reduced
consumption. This suggests that egg yolk consumption should be reduced or
avoided in high-risk individuals with established cardiovascular disease.
Consumption of a large egg (which equates to about 200 mg of dietary
cholesterol) not only increases the susceptibility of low-density lipoproteins
(LDL) to oxidation, but also increases postprandial lipaemia, and potentiates
the adverse effects of dietary saturated fat. Additionally, egg consumption
effectively halves postprandial clearance of atherogenic chylomicron remnants,
which implies a need to re-consider egg yolk consumption in individuals with
cardiometabolic disease, including those with diabetes. Indeed, in
observational studies, regular egg consumption was associated with increased
risk of new-onset diabetes, cardiovascular disease and all-cause mortality.
These epidemiological data, together with the FOCUS paper, provide a strong
rationale for a prospective randomized trial comparing the effects of
consumption of eggs or egg white-based substitutes on hard clinical outcomes.
Currently, international guidelines are inconsistent in considering the
dietary cholesterol. Currently, international guidelines are inconsistent
in their consideration of dietary cholesterol. There are also misconceptions
that because of the efficacy of statins in lowering plasma total cholesterol
and LDL cholesterol, consideration of dietary cholesterol is less relevant in
statin-treated patients. Yet even with intensive statin therapy, there remains
about 70% residual cardiovascular risk.
by
Dr.Akshaya Srikanth, Pharm.D
