I don't have any statistics on this, but your statement does not match my observations. Even within the US, the exact same product in a Kentucky supermarket will often cost twice as much in a California supermarket. I shop in both and my food costs are dramatically lower in KY.
In Central America, I found local food prices to be highly correlated with affluence. Food (both served and in markets) in Costa Rica is significantly more expensive than just north in Nicaragua. Rural Panama is a lot cheaper than Panama City. Honduras is generally expensive; Guatemala is generally cheap; but there are zones of relative expense within those countries. Food in general is dramatically cheaper south of the US border, especially if you shop in public markets.
I have not been to India but I am told by friends that food prices are significantly below US prices.
In Central America, I found local food prices to be highly correlated with affluence. Food (both served and in markets) in Costa Rica is significantly more expensive than just north in Nicaragua. Rural Panama is a lot cheaper than Panama City. Honduras is generally expensive; Guatemala is generally cheap; but there are zones of relative expense within those countries. Food in general is dramatically cheaper south of the US border, especially if you shop in public markets.
I have not been to India but I am told by friends that food prices are significantly below US prices.