Nutrient imbalances are factors in:
aging
alcoholism/substance abuse
behavioral disorders
cancer
cardiovascular disease (CVD)
chronic fatigue
deafness
diabetes
immune disorders
macular degeneration
multiple sclerosis
neurological disorders
osteoporosis
Parkinson’s disease
stroke.
Diseases that are known to involve interactions
between multiple genetic and environmental factors
such as diet include:
many cancers
diabetes
heart disease
obesity
some psychiatric disorders.
Inherited mutations in genes can increase one’s
susceptibility forcancer. The risk of developing can-
cer can be markedly increased if there is a gene-diet
interaction. Studies of twins show that the likelihood
of identical twins developing the same cancer is less
than 10%, indicating that the environment plays an
important role in cancer susceptibility. There are var-
ious examples of the effects of diet on cancer risk:
High consumption of red meat has been shown to
increase the risk of colorectal cancer.
The incidence of colon cancer among Japanese
increased dramatically after the 1960s as the Japa-
nese diet became westernized.
Dietary fiber has a protective effect against bowel
cancer.
Some studies have shown a relationship between
dietary fat and breast cancer.
Among people with high blood pressure only
about 15% have sodium-sensitivehypertension. For
the other 85%, eliminating salt from the diet has no
effect on their blood pressure. Nutrigenomics is
addressing why some people can control their hyper-
tension with diet, whereas others require drugs.SNPs
The DNA sequence of the human genome varies
by only 0.1% between individuals. However that small
variation is very important for disease susceptibility.
These variations in the DNA sequences of genes are
called polymorphisms. Some polymorphisms affect
the functioning of the proteins encoded by the genes.
The most common type of variation is a change in just
one nucleotide or unit of the DNA sequence, called a
single nucleotide polymorphism or SNP. Some of the
differences in individual responses to components of
food are due to SNPs, which may change the way a
proteininteracts with metabolites in the body.
MTHFROne of the best-known examples of a
gene-nutrient interaction is the MTHFR gene that
encodes the enzyme methylene tetrahydrofolate
reductase. MTHFR regulates folic acid and maintains
blood levels of homocysteine. A specific SNP in the
MTHFR gene is found in 10% of northern Europeans
and 15% of southern Europeans. People with this
SNP in both copies of their MTHFR gene have ele-
vated levels of homocysteine in their blood, particu-
larly if their intake of folic acid is low. This condition is
associated with CVD. However it is not yet known
whether folic-acid supplementation will prevent CVD
in these individuals a recent study in theBritish Med-
ical Journalsupported the use of folic acid supple-
ments for those with elevated homocysteine levels.
This SNP in MTHFR is also associated with a reduced
risk for colon cancer, but only if folic-acid intake is
normal. However there is no evidence that treatment
with folic acid, or eating foods such as beans, peas,
green leafy vegetables, and fortified grains that pro-
vide folic acid, will prevent colon cancer. There are
numerous genes associated with the development of
CVD and a multitude of dietary nutrients that interact
with these genes. Researchers have also found genetic
differences in folic-acid metabolism among black
American and Mexican women and MTHFR SNPs
have been associated with other disorders including
severe migraines and depression.
LIPID METABOLISMOne of the first applications of
nutrigenomics was to examine the differences among
individuals and populations in the blood levels of
lipids—triglycerides and HDL (‘good’) and LDL
(‘bad’) cholesterol—and the effect of high-fat diets
on these levels. High levels of HDL cholesterol are
associated with a reduced risk for CVD. Dietary
changes have a modest beneficial effect on blood-
lipid levels in the majority of people. However some
people experience no effect and others experience the
opposite effect from the same dietary modifications.
SNPs in genes that are directly or indirectly involved inNutrigenomics