Malnutrition is associated with over a third of children’s deaths and is the single most important risk factor in many diseases. It can also cause obesity later in life. In the womb and during the first couple of years, the body adjusts to a poor diet by squirrelling away whatever it can as fat (an energy reserve). It never loses its acquired metabolism. This explains the astronomical obesity rates in countries that have switched from poor to middle-income status.
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Source: The Economist