John,
With the recent litigation over certain classes of drugs, proves whatever policies they have in place, to be protective, are ineffective. Which in my book makes them WASTEFUL. However, that shouldnt mean the maintenance engineers should lose thier paychecks. 
On the food side, if their charter is to keep us healthy, why do they allow corporate farms to grow nutrient deficient foods.
It makes no sense to have a society that values education yet government agencies that refuse to learn.
Adam
Having dealt directly with the FDA concerning petitions for both drugs and foods, I don't believe that their role is as broad as keeping us healthy.
Rather, it's to protect us against drugs and foods which have not been proven to be safe!
The generally accepted concept of keeping us healthy is too broad and beyond their capability.
For example, the Clinton Administration opened the doors for the introduction of "health foods and healthy suppliments" without the level of proof of safety formally required. That's the main reason we've seen the steroid and steroid derivative suppliment problems over the last few years.
In the case of both new drugs and foods, the responsible agency,the FDA, has always taken a very conservative position, requiring a lot of proof before approving any new substance for consumption.
The way they are forced to operate, is to require proof of safety from the petitioner for a new drug or food. Their budget isn't nearly sufficient to actually do all the testing themselves. Animal safety tests for a new drug cost million of dollars for each species and each type of test--such as carcenogenisity, birth defect possibilities, toxicity, etc.
In the case of the recent heart drug related tragedies, the drug company obviously cooked the results and fooled the FDA examiners.
In addition to their traditional duties, much of the FDA's budget is now expended on inforcement of the Public Health Security and Bioterrorism Preparedness and Response Act of 2002. All incoming drugs and foods must be registered prior to entry, including manufacturing method, location, ports of entry, destinations, etc.
Both the FDA and USDA are involved in monitoring incoming shipments for contamination and inclusion of toxic, dangerous or radio active contents. They don't have nearly enough staff or budget to inspect every shipment.
A large part of the USDA's budget is involved in basic agricultural research for the general good. Food safety, plant and animal genetics, crop agronomy,new crop variety development,and animal disease prevention are only a few of the areas in which they provide most of the scientific work that is done in the entire U.S. Private companies don't do this type of basic research because the pay back is too small. The USDA actually does a lot of basic research hoping to interest private industry in picking up on their ideas. It's one way the government tries to stimulate opportunities for investment in the agriculture areas.
There has been a lot of speculation that the FDA and USDA should be merged into a single super-agency. This might save a little money, but not much, since the two groups have almost no overlap--each is assigned tasks exclusive to each agency.
As you can see, insuring the relative nutritional content of one food versus another is way down the list for both the FDA and USDA--especially in a country where starvation isn't a major problem.
This has been boring enough I think.
John