Examining the fetal origins of obesity

The figures and trends behind the obesity epidemic are alarming: More than one-third of all adults in the United States are obese, as are 34% of women aged 20-39, and 17% of youth aged 2-19, according to data for 2011-2014 from the National Health and Nutrition Examination Survey.

In our ob.gyn. practices, many of us have witnessed the significant climb in national obesity rates over the past several decades. We’ve seen a continued increase in the prevalence of obesity among childbearing women, and a steady increase in the incidence of high-birth-weight babies. The percentage of women weighing 200 pounds has more than doubled since 1980, and up to 3-4 times as many children and teens in various age subsets are obese today as in the 1970s.

Dr. Michael G. Ross

The obesity epidemic is often attributed to a high-fat and/or calorie-dense diet and decreased activity levels. However, this is only part of the picture. There has been growing recognition in recent years that obesity may be programmed by the in utero and newborn environment, particularly as it relates to nutritional permutations. We now have evidence, in fact, that developmental programming is likely a primary cause of the obesity epidemic.

Exposure to maternal obesity and being born with a low birth weight – especially a low birth weight paired with rapid catch-up growth – are both associated with a significantly increased risk of childhood and adult obesity.

Research has demonstrated that newborns may be programmed, in both of these scenarios, with an increased appetite and a predisposition to storing calories as fat. In addition, data are accumulating that exposure to bisphenol A and other endocrine-disruptive chemicals, other environmental toxins, and corticosteroids may exert similar programming effects.

This window into the origins of obesity has significant implications for the practice of ob.gyn., where we have the opportunity to address the programming effects of the in utero and early life environment. Most importantly, we must counsel women before pregnancy about the importance of losing weight, guide them during pregnancy to achieve optimal pregnancy nutrition and weight gain, and prepare them to adopt optimal newborn feeding strategies that will guard against overconsumption.

Programming of obesity

The current obesity epidemic is only minimally due to genetics. Although select genetic mutations may be associated with obesity, these mutations account for an exceedingly small proportion of the obese population. Instead, much of the obesity epidemic involves epigenetic change – in this case, largely epigenetic deregulation of gene expression – and more broadly what we call gestational, or developmental, programming.

Developmental programming is a process by which a stress or stimulus at a critical or sensitive period of development has long-term effects. The major part of the developmental process pertaining to cell division occurs during intrauterine life; more than 90% of the cell divisions necessary to make an adult human occur before birth. Although there are important effects of the early newborn period, developmental programming is therefore largely gestational programming. Depending on when an in utero stress or perturbation occurs, it may permanently change cell number and/or cell differentiation, organ structure, metabolic set points, and gene expression.

Dr. Mina Desai

The late physician Dr. David Barker got us thinking about in utero programming when he demonstrated an association between low birth weight, rapid weight gain in early life, and adult cardiovascular mortality. His theory about how nutrition and growth before birth may affect cardiovascular health later on, as well as other adult chronic diseases and conditions, became known as the Barker Hypothesis.

Many studies, both animal research and human epidemiological studies, have since confirmed and expanded our understanding of this phenomena. Research has demonstrated associations, for instance, between low birth weight and later risks of insulin resistance, diabetes, fatty liver, and the often-underlying metabolic syndrome.

Obesity is also central to the development of the metabolic syndrome, and we now have irrefutable evidence to show that low birth weight infants have a higher risk of obesity than do normal weight infants. We also know, as Dr. Barker and his colleagues had surmised, that the greatest risks occur when there is rapid catch-up growth of low-birth-weight infants in the early years of life.

Moreover, we now understand that maternal obesity has programming effects that are similar to those of an in utero environment of undernutrition and growth restriction. In the past several decades, the marked increase in maternal obesity has resulted in this programming process having an ever-increasing impact.

Both animal and human studies have shown that infants born to obese mothers have the same increased risks for adult chronic disease – including the risk of becoming obese – as those of low birth weight infants. This increased risk is often, but not always, associated with high birth weight, and it is independent of whether the mother has gestational diabetes mellitus (GDM). Having a high birth weight is more likely in the setting of maternal obesity and itself raises the risk of eventual obesity (as does GDM), but an infant’s exposure to maternal obesity in and of itself is a risk factor.