Experts have long been aware that countries hit by famine have their population growth slow or even come to a halt. If the famine is of short duration, the lack of population growth will rebound with a correlating spike in the birth rate once food is again available.
Nature is very adaptable that way and tends to find ways to compensate after tragedy. We saw it with Bengal in 1943, China from 1958-1961, and Ethiopia from 1983-1985. The population growth in these countries ground to almost a complete stop during the rough years but was then followed by rising birthrates within a few short years.
But there's more than one way to starve. In urban centers throughout America, women are throwing themselves into workouts. They're exercising often and they're exercising hard. According to a study performed by University of Pittsburgh researchers, women who are big into workouts are having trouble getting pregnant. So what's the connection between an urban lady's exercise program and third-world famine? Not enough calories to sustain a pregnancy.
In the Pittsburgh study, experts employed monkeys to prove their theory that hard workouts can bring on a state of infertility. The researchers gave monkeys the equivalent of marathon training. As the monkeys stepped up their activity levels, but researchers kept their intake of calories at the same level, the monkeys ceased to menstruate.
The researchers found that normal menstruation could be restored by adding 31%-81% more calories, even though the level of energy expended stayed the same. The greater amount of food they were fed, the sooner the monkeys' menstrual cycles were restored to normal.
What is it that occurs when women don't get enough calories? The part of the brain called the hypothalamus signals the body to cease ovulation and menstruation. The body groks that its owner isn't feeding it enough calories to produce a baby. According to the medical director of the UK-based Midlands Fertility Services, Dr. Diane Lockwood, "Women who are very thin have higher risks of miscarriage and babies born prematurely. There is overwhelming evidence that thin women have underweight babies."
Okay, so too thin is no good. What's the limit on thinness before it sends your fertility plummeting? According to the National Institute of Clinical Excellence, women who want to conceive should have a body mass index (BMI) of somewhere in the neighborhood of 19-30. The Duchess of Windsor famously said, "One can never be too rich or too thin," but then again, she wasn't responsible for providing an heir to the throne, now was she?