Why do first world countries spend a much smaller percentage of their budget on food than third world countries?

I heard that in countries like the USA, Australia, Great Britain, and some EU countries, no more than 15 percent of monthly earnings is spent on food as a percentage of income, while in countries like Vietnam is about 40 percent. Why is that? It's logical that if wages in such countries are several times lower, then the costs of food production, transportation, rent, and supermarket employee salaries are lower And this means that food should cost the same amount of times cheaper in proportion to the lower expenses, the same amount of times less the income. For example, if salaries in the US usually 6-7 times higher than in Vietnam, so why, with such high labor costs, does the US produce food at only 3 times higher the price? How can the US, with such higher wages, produce food at a rate three times cheaper than Vietnam relative to income?