The best solution to the obesity epidemic is to encourage would-be mothers to increase their levels of physical activity so that they can prepare their metabolism for pregnancy and have leaner, healthier children.

18 Apr


calorie intake doesn’t explain obesity: active mothers and their leaner offspring ate more food and calories than the fatter inactive mice. Once again, I wasn’t the first to discover this. In the 1950s, nutrition scientist Jean Mayer demonstrated that active animals, whether mice, rats or humans, ate more food and stayed leaner and healthier than sedentary ones. By 2014, I had conducted an extensive literature review that turned my intuition into a theory that revealed the missing heritability and a new way of understanding why so many children today are obese. The answer was a combination of a mother’s body composition and physical activity during pregnancy. When pregnant women are physically active, the increased energy demands redirect nutrients to her muscles and away from her fetus. This competition between the mother’s muscles and the developing fetus’s fat cells produces leaner, healthier babies. Their genes and food intake are irrelevant to the process. This competition doesn’t happen in inactive mothers. Without having to struggle for energy and nutrients, the fat cells in the fetus increase in both size and number, increasing the birth weight of the infant – a factor strongly related to adult obesity and type II diabetes. This is passed on down the line, with future generations becoming fatter and increasingly inactive and unhealthy. This is an example of non-genetic evolution, where traits are transmitted to offspring with no underlying change in their genome.

, a 1995 study of babies born
through egg donation found that the only discernible factor
influencing their birth weight was the surrogate mother’s body mass.
The egg donor’s body mass, her own birth weight and the birth weight
of her other children bore no relationship to the birth weight of
the infant produced from the donated egg (Early Human Development,
vol 42, p29).

The genes from the egg donor’s biological mother played no
detectable role in the birth weight of the infant. This helps to
explain why, despite many billions of research dollars, the search
for the “genes that make us fat” will continue to disappoint
(Journal of Physiology, vol 592, p 2381).

The idea that the nine months we spend in the womb affects our
health has been around for centuries – it was discussed by the
Ancient Greek physician Hippocrates, for example. More recently the
“thrifty phenotype” hypothesis developed in the 1990s found that an
impoverished uterine environment can programme a fetus’s metabolism,
predisposing it to obesity and diabetes. However, this doesn’t
explain why childhood and adult obesity exploded during the late
1970s, when food was abundant. This is where my theory transforms
our understanding of childhood obesity.

For most of human history, survival required huge amounts of
physical exertion. Hunting, gathering, chopping wood and carrying
water provided a dose of physical activity that made deliberate
exercise unnecessary. Yet over the past century, socio-environmental
changes slowly eliminated physical labour. At first, technological
advances coupled with a healthier food supply led to the birth of
children that were the fittest in human history. But by the middle
of the 20th century, the advent of labour-saving devices, the rising
popularity of the car and passive, sedentary entertainment led to
people becoming fatter and more inactive.

From 1965 to 2010, the amount of energy expended in the home by
women in the US decreased by almost 2000 kcal per week. At the same
time, the amount of time they spent watching TV and using computers
doubled (PLoS One, vol 8, e56620). My research has found that obese
women in the US get less than one hour of vigorous physical activity
per year. Not surprisingly, just as non-exercising mice produce
grandchildren that are bigger and fatter, so too do US women.

By the late 1970s, a tipping point was reached in which mothers were
so inactive that the evolution of human energy metabolism was
markedly altered. As a result, fetuses grew so large that the need
for caesarean sections rose significantly. The increased use of
surgical interventions during pregnancy allowed both the larger
babies and the mothers that produced them to survive and reproduce.
Thus, natural selection was rendered artificial selection, and the
number of metabolically compromised children and adults increased in
the global population.

Non-genetic evolution is the primary determinant of obesity, not
gluttony, fast food or genes. The best solution to the obesity
epidemic is to encourage would-be mothers to increase their levels
of physical activity so that they can prepare their metabolism for
pregnancy and have leaner, healthier children.

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