Food Inc documentary claims that the number of FDA food safety inspections had fallen from 50,000 in 1972 to 9164 in 2006 and this information is also cited here.

However, I cannot find any official source to support this claim.

Question: Did the number of FDA food safety inspections fall from '70s to 2006?

The documentary film Food, Inc. was released in June 2009. Nicholas Kristof wrote an op-ed in the New York Times about this movie on June 20, 2009. One tidbit he omitted from his draft of the article was the statistic raised in the question, that the number of FDA food safety inspections had fallen from 50,000 in 1972 to 9164 in 2006.

He wrote about why he omitted this factoid in his blog. Before making that draft final, he asked his assistant to double-check with the FDA:

The FDA said the figures were wrong — both of them. The FDA acknowledged that the number of inspections had dropped, but said the 1972 figure was 10,610, while the fiscal year 2006 figure was 7,498 domestically and 125 abroad. The FDA said it had no idea where the other numbers could have come from.

Kristof then contacted people associated with the movie to determine the source of this information. A producer said the source of the numbers was a fact sheet from Rep. Henry Waxman, which Kristof and crew verified (i.e., they found Waxman's fact sheet online and it stated those exact numbers).

Waxman's fact sheet said the 2006 number was an estimate and that the 1972 number was based on a Washington Post article by a long-time FDA staffer and commissioner. So Kristof and crew chased this down. The article existed and contained the value on Waxman's fact sheet. That same person had also testified in Congress that there were 35,000 (not 50,000) inspections in 1972.

With conflicting values from different sources, Kristof decided not to include that factoid in his op-ed. Instead he simply wrote that the number of FDA inspections had plunged.

That depends on what you want to call a "food safety inspection"

The U.S. Food & Drug Administration conducts many kinds of inspections. And they conveniently provide a publicly available — and searchable — database of their inspections.

FDA Inspection Classification Database Search

Under "Center for Food Safety and Applied Nutrition" we find the following classifications:

• Project 03 - Foodborne Biological Hazards


• Project 04 - Pesticides and Chemical Contaminants


• Project 07 - Molecular Biology and Natural Toxins


• Project 09 - Food and Color Additives Petition Review


• Project 18 - Technical Assistance: Food and Cosmetics


• Project 21 - Food Composition, Standards, Labeling and Econ


• Project 29 - Colors and Cosmetics Technology

You can play around with that database and do queries on your own. I tried entering 2017-11-30 to 2018-11-29, selecting projects 03, 04, 09, and 21 (Ctrl + left-click to select multiple), classification "All", District "All", State "All", and I got 8,672 results.

Which one(s) of these you want to call "food safety inspection" is up to you. And even more interesting to know is what was classified as a "food safety inspection" in the 1970's. Until we know what constituted a "food safety inspection" in the 1970's, and we can map those onto these categories, any kind of comparison is impossible and your question is unanswerable.

Even more interesting to know is if you want to call any decrease of these kinds of inspections a failure or a success. Nipping dangers in the bud — so that the need for inspections decreases — is commonly considered a good thing.

Summary

For the time being your question has the answer "undetermined" or "unanswerable".

This is because we do not know what "Food Inc" means when they say "food safety inspection". We also do not know if any change in the number of such inspections is a good or a bad thing. The makers of Food Inc seem to imply that it is a bad thing, but if so that is their opinion and not an established fact.