“The Role of Epigenetics
in the Obesity Epidemic” Identical twins don’t just share
DNA; they also shared a uterus. Might that also help account for some
of their metabolic similarities? Fetal overnutrition, evidenced by
an abnormally large birth weight, seems to be a strong predictor of
obesity in childhood and later in life. Could it be you are what your mom ate? A dramatic illustration from the
animal world is the cross breeding of Shetland ponies with massive
draft horses. I mean, either way, the offspring are half pony, half
horse, but in the pony uterus they come out much smaller—
thank heavens for the poor pony. This is presumably the same reason
why the mule—donkey dad and mare— is larger than the hinny—
stallion and donkey mom. The way you test this in people
is to study the size of babies from surrogate mothers
after in vitro fertilization. Who do you think most determines
the birth weight of a test-tube baby: the donor mom who
provided all the DNA or the surrogate mom who provided
the intrauterine environment? When it was put to the test,
the womb won. Incredibly, a baby born to
an obese surrogate mother with a skinny biological mom may
harbor a greater risk of becoming obese than a baby from a big biological
mom born to a slim surrogate. The researchers conclude the
environment provided by the mother is more important than her
genetic contribution to birth weight. The most compelling data comes from
comparing obesity rates in siblings born to the exact same mother before
and after her bariatric surgery. Compared to their brothers and
sisters born before the surgery, those born when mom weighed about
100 pounds less had lower rates of inflammation, metabolic
derangements, and most critically, three times less risk
of developing severe obesity, afflicting 35% of those born
before the weight loss, compared to 11% born after. The researchers conclude these
data emphasize how critical it is to prevent obesity and treat
it effectively to prevent further transmission
to future generations. But wait. Mom had the same
DNA before and after surgery. She passed the
same genes down. How could her weight during
pregnancy affect the weight destiny of her children any differently?
Darwin himself admitted that the greatest error he
committed had been not allowing sufficient weight to the direct action
of the environment, like food, independently of natural selection. We finally figured out the mechanism
by which this can happen: epigenetics. Epigenetics—literally meaning above
genetics—layers an extra level of information on top of the DNA
sequence that can be both affected by our surrounds and potentially
passed on to our children. This is thought to explain the
developmental programming that can occur in the womb
depending on the weight of the mother, or even
your grandmother. Since all the eggs in your infant
daughters’ ovaries are already preformed before birth, a mother’s weight status during
pregnancy could potentially affect the obesity risk of her grandchildren
too. Either way, you can imagine how this could result in an
intergenerational vicious cycle where obesity begets obesity. Is there anything
we can do about it? Well, breastfed infants may be
at lower risk for later obesity, though the benefits may be
confined to exclusive breastfeeding, as the effect may be
due to growth factors triggered by exposure to the
excess protein in baby formula. The breastfeeding data
is controversial though, with charges leveled
of a white hat bias. That’s the concern that public health
researchers might disproportionally shelve research results that doesn’t
fit into some goal for the greater good— in this case preferably
publishing breastfeeding studies showing more positive results—
but of course that’s coming from someone who works for
an infant formula company. Breast is best regardless;
its role in the childhood obesity epidemic just remains
arguably uncertain. Prevention may be the key.
Given the epigenetic influence of maternal weight during
pregnancy, a symposium of experts on pediatric nutrition
concluded that planning of pregnancy, including prior
optimization of maternal weight and metabolic condition,
offers a safe means to initiate the prevention rather than
treatment of pediatric obesity. Easier said than done, but overweight
moms-to-be may take comfort in the fact that after the weight
loss in the surgery study even the moms who gave birth to kids
with three times lower risk were still, on average, obese themselves,
suggesting weight loss before pregnancy is not
an all-or-nothing proposition. Video source: https://www.youtube.com/watch?v=5ZCaOPapdLw
