Dr Anne-Marie Minihane discusses the future of
nutrition, as new research finds that your diet can directly
influence your genes.
Current dietary advice
Current dietary advice is rather generalised and takes a type of
one size fits all’ approach. For example, all adults in the
UK are advised to eat, less than 33% and less than 10% of their
energy intake as total fat or saturated fat respectively and
consume a minimum of 0.45g of fish-oil fatty acids daily,
increasing to 1g per day if you suffer from diagnosed
cardiovascular disease (CVD). Similar generalised recommendations
also exist for other minerals and vitamins.
Undoubtedly, if we all met current dietary recommendations the
population incidence of chronic disease would fall dramatically.
However, the truth is for a number of nutrients we are a long way
from reaching such a public health Utopia. Looking at the National
Diet & Nutrition Survey in the UK (2003), it is evident that
only 40% of children and 15% of adults meet the total fat and
saturated fat recommendation, whilst only 27% eat any oily fish on
a regular basis.
Although the majority of us will gain some benefit from meeting
all recommendations, it is becoming increasingly apparent that
depending on their age, gender, health status or genetic make-up
etc, certain individuals are particularly sensitive to a lack or
excess of certain nutrients and would benefit from
increasing/decreasing their dietary intake of that component.
Therefore a more personalised approach to dietary advice is likely
to be taken in the future.
Genes, genotype and health
Apart from identical twins, we are all genetically unique with
an individual’s genetic make up influencing the amounts and
type of proteins (which regulate your metabolism) produced. This
will has a knock on effect, influencing health and risk of disease,
and how our bodies respond to changing environments such as altered
dietary patterns or drug use.
Nutrigenomics and potential role in public
health.
Over the last 10 years, the field of
nutrigenetics/nutrigenomics, (terms describing the study of how
nutrients interact with your genes) has grown. These interactions
are proving more complex than originally thought, but it is hoped
that in the future, genetic profiling may be routinely used to
detect disease risk and provide personalised diet advice in order
to motivate an individual to successfully change their diet and
increase the efficacy of lifestyle changes.
Cardiovascular disease, genotype and diet
Like most other chronic disease, CVD is partly inherited, with
40-50% of overall risk attributable to our genes. Furthermore the
response of physiological risk factors for CVD such as cholesterol
and blood pressure to altered diet, exercise or drug intake is
highly variable and in large part determined by genetic factors. It
is now well accepted, for example, that depending on genetic
make-up, a reduced fat diet can be very effective at reducing total
and LDL-cholesterol in some, but produce little effect in
others.
The identity of these genes which determine family history and
response to diet remains in part elusive but some genes are
emerging as being consistently important.
CVD risk and response to diet
Perhaps the most widely investigated gene variant with respect
to risk of disease is the apoE genotype. ApoE is a protein well
known for its role as a regulator of blood cholesterol and
triglyceride metabolism. Twenty-five per cent of individuals in the
UK who are carriers of the E4 version of this gene (as apposed to
the E2 or E3 version) are known to be at higher risk of CVD and
Alzheimer’s disease. This is thought to be attributed to
higher cholesterol levels and a greater state of inflammatory
stress.
Recent research indicates that E4 individuals are particularly
sensitive to dietary fat and show above-average reductions in blood
cholesterol levels when they follow a low-fat, low-saturated fat
and low-cholesterol diet. Furthermore, an increased antioxidant
intake is likely to counteract the impact of genotype on oxidative
stress and inflammation.
Another example is the eNOS gene. This particular gene encodes
for a protein which regulates the elasticity of your blood vessels
and blood pressure. A common variant in this gene has been shown to
be associated with increased CVD incidence and blood pressure and
reduced elasticity. However, an increased fish oil intake, which
increases vascular elasticity, has been shown to normalise the
defects in individuals with the dysfunctional version of the
gene.
There are many other examples which could be quoted that
demonstrate how dietary change can counteract the physiological
impact of a particular genotype and that highlights how a
particular dietary regime can be more important for some than
others.
The future
The science of nutrigenetics is currently in the research stage.
In the future it is highly unlikely that the whole population will
be genotyped and provided with personalised health advice based on
genetic make-up. However, it may be particularly useful as a tool
for the early detection of disease risk and lead to the provision
of a personalised health plan to those with a family history of
disease and therefore a known genetic defect.
There are, however, a number of social and ethical issues which
need to be considered before more widespread genetic profiling can
become a reality (for more information see www.hgc.gov.uk). Also the predictive
ability and the impact on health of having particular at
risk’ genotype must be kept in perspective, in order to avoid
creating a worried population. For example, the risk of CVD
associated with an E4 genotype (50% increase) is less than one
tenth that of smokers or those with diabetes (> 5 fold increased
risk).
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