The nutrition transition, first laid out by Barry Popkin in 1993, describes the shifts in dietary patterns of populations in the modern age.
Simplified into three steps, this transition follows a linear genealogy: first, there are the periods of famine, then there are those of receding famine, and finally, there is the era of nutrition-related chronic diseases. These diseases – i.e., metabolic syndrome, hypertension, atherosclerosis – are traditionally associated with increased affluence. Similarly, the leap from famine to receding famine has historically been a result of economic improvement. As nations have grown in wealth, they have generally become more able to cope with years of bad harvest, by participating in regional or global food markets.
Today, in the United States, we find ourselves in the third and final stage of the nutrition transition. Progression to this stage was largely mediated by the dramatic change in diet and the mechanization of food production that had occurred in the western world during the 20th century. By reducing fiber and whole grain intake, while simultaneously increasing consumption of refined carbohydrates (primarily sugar), animal products, and hydrogenated fats, the West has created a recipe for tasty foods and bigger bodies. Having moved from the cornfield to the cubicle, our more sedentary economy exacerbates the deleterious health effects of the new diet, thus resulting in the increased prevalence of metabolic diseases.
What was once an exclusively Western phenomenon is now a global one—the developing world is well on its way through the transition. However, for these nations, the nutrition transition no longer tracks the same economic trajectory that the Western world established. In other words, while the West’s growth in waistline has been coupled with a growth in the economy, for much of the developing world, the spread of metabolic syndrome has been facilitated by globalization, not necessarily rises in wealth.
And the rise of metabolic diseases is occurring faster than ever. The rate of change in obesity is currently greater in low- and middle-income countries than in higher-income countries, possibly reflecting a “catch-up effect”; developed-world rates appear to be plateauing. Looking specifically at sub-Saharan Africa, over the past 20 years, the prevalence of type-2 diabetes and cardiovascular disease has increased 10-fold. The trend towards an obese profile is alarming, given that many developing nations in Africa do not have the healthcare capacity to care for these newly emerging chronic diseases in addition to their current endemic or infectious disease burden.
The region of southern Africa is of particular interest because it so clearly demonstrates some of today’s biggest nutritional challenges. One can easily map the nutrition transition model directly onto southern Africa using data from the FAO and WHO. At one pole, you have Zimbabwe, a nation with 33.4% of its total population currently undernourished. At the other pole, there is South Africa, a nation with 33% of its total population currently obese. And in between these two poles – geographically and epidemiologically – there lies Botswana, with 24.1% of its population undernourished and 12.9% obese.
However, a more critical look at the data reveals that even in South Africa – the richest and most obese country of the region – there exists a double burden of nutritional disease. In 2005, a national study of 1-9 year olds revealed that 20% of the children were stunted, 10% were underweight, 10% were overweight, and 4% obese. In the southern African region, it is not at all inconceivable that maternal overweight and child undernutrition coexist in the same community or even the same household, as has been demonstrated in a study in Benin.
One of the most compelling explanations for this particular phenomenon – and for the rapid rise of obesity in the developing world in general – comes from epigenetics. Epigenetics is the study of how our environment can turn our genes on and off, and it is best understood in terms of the pre-birth intrauterine environment. Prenatal development is highly sensitive to nutritional inputs. If a mother does not consume enough energy due to a food shortage or mineral imbalance, then the fetus will adopt a metabolic coping mechanism, sometimes referred to as a “thrifty phenotype”. The fetus will manipulate its genetic expression profile in order to promote insulin resistance. This is beneficial during periods of starvation because it maintains nutrition of the brain (which almost exclusively utilizes glucose as its energy source) by elevating the blood sugar level without degrading body protein stores. However, in times of nutritional abundance, insulin resistance often tends to lead to hyperglycemia and type-2 diabetes.
Fetal imprinting – a term used to describe the epigenetic remodeling that occurs in the prenatal stage – appears to persist throughout an individual’s lifetime, and may even be carried through for several more generations, even when the nutritional insult is removed. This may explain why the developing world, so recently plagued by widespread undernutrition, now appears to be even more susceptible to obesity and other associated metabolic diseases.
Numerous studies have verified that stunted children have a significantly increased risk of developing obesity later on in life. This risk is especially heightened in today’s globalized environment, where the so-called “Western lifestyle” has been exported along with its products, and undernutrition is generally attributed to a lack of income, not a scarcity of food supply. Popkin (mentioned earlier, the father of the nutrition transition) claims that the globalization of modern food processing, marketing, and distribution is the leading reason why the developing world is now battling the once-called ‘diseases of the affluent.’ Multinational or regional supermarkets are increasingly replacing small-scale public markets that specialize in predominantly unprocessed foodstuffs. While the supermarket in a developing nation represents a mark of modernity, of increased access to food and a diversity of options, it also tends to over-represent the once-Western/now-global dietary preferences, in all their sugary glory.
The WHO factsheet on cardiovascular disease is, to say the least, disheartening (pun unintended). Cardiovascular diseases are the number one cause of death globally. In 2012, an estimated 17.5 million people died from them, representing 31% of all global deaths. More than three-quarters of these deaths took place in low- and middle-income countries. The rapid rise of obesity and its associated metabolic diseases in the developing world may indeed be the most significant global health threat today. Combating obesity will necessitate a shift away from our current high-fat, high-carb diet, and in the wake of new genetic research – which reveals that the undernourished are predisposed to obesity later in life – the shift in global diet may be all the more crucial.
Image courtesy Wikimedia Commons.