We inherit our
genetic code from our parents and from cradle to grave that genetic sequence is
immutable. We all know that forensic medicine can take any part of the human
body, however small, and sequence the DNA, thus obtaining our absolutely unique
genetic code. If every part of the human body contains the full sequence of DNA
inherited from our parents, then why is your ear not your nose? What makes the
different parts of our body different from one another is that the inherited
sequence of DNA is “tweaked” so that genes that are not needed are turned down
or off and those that are needed are turned up. Effectively, nature gave us a
genetic dimmer switch which cannot change the sequence of genes but which can
change the extent to which individual genes are expressed. By far the most
striking example is the queen bee. All bee larvae contain the exact same
genetic code obtained from the queen and thus they are clones. When a queen
passes her sell by date so to speak, the worker bees prepare a new queen. From
the thousand of cloned larvae, they select one and the wrap that larva up in a
secretion from their throat region. That secretion is Royal Jelly and it
contains a very unique balance of nutrients. Most importantly, it contains a
protein known as Royal Lactin[1].
The effect of this is that the larva treated to Royal Jelly emerges as a queen
bee, which, while sharing the exact same genetic code as the worker bee, is
physiologically vastly different. Indeed up to one third of all the genes that
are associated with the bee brain are differentially expressed (up or down
regulated) in the queen bee. Queen bees live for years while worker bees live
for only weeks. The queen bee will uniquely produce 2,000 eggs on a summer’s
day while worker bees are sterile. This modification of gene expression is
called epigenetics and it is of enormous importance in human nutrition.
During life in our mother’s womb, nature’s
genetic dimmer switch gets to work. Without changing a single aspect of genetic
sequence, it switches up some genes and switches down others. It does so to
make sure that the new born baby has its genetic profile made to measure for
the external environment into which it enters at birth. There are two ways to
look at this phenomenon, the first of which is physical. John Hammond, a famous
UK animal scientist reported in 1938 on a study, which crossed the very large
Shire horse with the very small Shetland horse. When a Shire stallion mated a
Shetland mare, the offspring had the physical proportions of the Shetland mare.
Vice versa, when the Shetland stallion mated a Shire mare (with help I
assume!), the offspring had the proportions of the Shire mare. Even though all
of the foals born had 50% Shire and 50% Shetland genes, their life in the womb
determined their birth size. The size of the uterus in gestation over-rode the
genetic inheritance. This was among the first studies to show that our
inherited genetic sequence is subject to significant up- and down-regulation
during pregnancy. The second factor that emerged as a major determinant of
pregnancy modulation of gene expression was diet. It began with historical
studies that linked birth weight and length to the risk of many diseases in
adulthood. Thus for example, in adulthood, the risk of developing high blood
pressure was shown to rise dramatically among those who had a lower than
average birth weight and a higher than average placental weight. When this data began to emerge in the
early 1980’s it was regarded as almost heretical by nutritional epidemiologists
for whom all chronic disease could be explained by poor eating habits. In time,
the evidence grew and animal experiments bore out the theory. Today, we absolutely
accept optimal nutrition in pregnancy is essential to minimize disease later in
life.
Pregnancy is not
the only period where nutritional factors can cause the expression of our genes
to change with life long effects. The second vulnerable period is the first 2
years of life. (This period, combined with the duration of pregnancy, is referred to these days as “The first
1000 days”). During the first 2 years of life, diet can play a role in
permanently altering both our physique and our cognitive function. If growth is
impaired during this period in any sustained manner, then the person will be permanently
stunted, that is too small for their age. Stunting is widespread in developing
countries. During the first 2 years of life, our brains grow both in size and
in complexity. In adults, the brain consumes about a quarter of all calories consumed.
In infants, this figure rises to nearly three quarters of calories consumed. If
children are inadequately nourished during this period, their cognitive
function is permanently reduced.
To understand
why nature has given us this gene dimmer switch we need to consider its
evolutionary advantages. In pregnancy, the biological profile of the mother, in
which diet plays a powerful role, lays down a permanent imprint on gene
expression. If times are frugal, the birth weight falls and the baby is
programmed for a frugal existence. If that child grows to be an adult in a very
non-frugal and obesogenic environment, then they cope poorly such that chronic
disease rates rise. Thus we adapt to the biological environment prevailing
during pregnancy in the expectation that that will prevail. In times gone by,
that adaptive mechanism had a great evolutionary advantage. As regards the
evolutionary advantage brain development in the first 2 years of life, that lies
in the ability to absorb the culture into which the child is born. Chinese babies
learn to speak Chinese and to absorb Chinese culture. Each culture needs that
time to imprint all of its values into the new born. The brain of a foal is
hard wired at birth such that instantly, the foal stands and runs with the
herd. No schooling is needed. Horses just haven’t evolved as man has with its “plastic”
infant brain.
When the human
genetic code was sequenced, the “genohype” predicted great medical miracles. We
now know that sequence is one thing but how that sequence is expressed is what
makes a huge difference and we know that a balanced optimal diet will lead to
the optimal changes I gene expression. We now also know that one of the main
public health nutrition challenges is maternal nutrition. It is a challenge
that the high priests of healthy eating are unhappy with because it distracts
them from their prevailing wisdom with which they are very happy.
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