New Delhi, Oct. 28 -- For decades, India fought one great battle-hunger. We built ration shops, expanded food programmes and ensured no child went to bed hungry. Those efforts worked. In one generation, poverty at the $3-a-day line has plunged from nearly half the population in 2004 to below 5% today. Millions of families that once struggled for daily calories now have full plates. But victory over scarcity has brought a new problem.

As India has grown richer, a different epidemic has quietly spread-obesity. Far more Indians today fall ill or die from over-eating and inactivity than from hunger. What was once a symbol of prosperity has become a threat to health, productivity and growth.

In just a few decades, India has moved from scarci...