The percentage of recruit-age men who are overweight has doubled since 1960. For women, the figure has tripled. That means the percentage of recruitable youths is declining. Since the military won't waive the physical-fitness requirements for service, the Pentagon's competition with U.S. industry for healthy young workers will grow fiercer.
If the United States reinstated the draft, which isn't likely, the effects would be even more severe. And if the fertility rate declines significantly in the years ahead, it is possible that the rise in teen obesity would mean there won't be enough young people to fill essential military billets.
Fortunately, that doesn't look as though it will happen soon. Obesity will not become an immediate threat to national security because American parents continue to have more children on average than the rest of the developed world. That has allowed the number of recruitable youths - and the quality - to increase over the last half century.
Demographers don't know exactly why Americans alone among citizens in the West are having enough children to replace themselves. Higher fertility among U.S. immigrants is only part of the picture. Values matter a lot. Higher fertility rates are correlated to regions where there are higher rates of religious practice and conservative ideals.
For all these reasons, Americans are having enough children to expand the U.S. workforce and the recruitable population out to 2050, even while they contract in the rest of the developed world. Indeed, the Pentagon maintains a force younger, fitter, and better educated than the general U.S. working population, and it has been able to meet its recruitment goals despite the adverse environment of two wars.
Conversely, Russia, Germany, and Japan expect contractions in their workforces of more than 25 percent by 2050. The fertility rates and size of the childbearing cohort in some countries will be so small by 2070, a top U.N. statistician told me, that if things don't improve drastically some societies will virtually disappear.
Demographic decline is having telling effects on our allies' national defense. European nations have pulled troops off the front lines and even pooled aircraft carrier and nuclear-weapons capabilities because of a fiscal crisis exacerbated by the cost of supporting aging societies in social democracies. Japan, our closest ally in Asia, is retiring ships early for want of young sailors, and their ground forces are already too old on average to man frontline units according to U.S. standards.
What is truly worrisome is that Washington is poised to squander America's demographic advantage. The real threat to national security is not a lack of capable youth, but a loss of strategic direction and the prospect of $1 trillion in defense cuts. Much of the looming cuts are not because of strategic priorities but are an irresponsible substitute for hard choices about Social Security and skyrocketing medical-care costs.
If we put our fiscal house in order now, we can avoid the kind of draconian cuts that would compromise our military posture. This will allow Americans to seize their demographic advantage and lead the world through the turbulent decades ahead.
While the first lady rightly tells the troops to eat their vegetables, President Obama should be telling Congress to trim the fat on bloated entitlements before their misguided defense cuts truly jeopardize America's national security.
E-mail Susan Yoshihara at email@example.com.