Dietary guidelines are put out by the HHS and Department of Agriculture. Not FDA. I don't think FDA has much, if anything, to do with them.

The latest were published in 2005 (the 2010 version is still in preparation).

http://www.health.go...A_ExecSummary.htm

[...]

The Committee's findings support the development of Dietary Guidelines that convey the following nine major messages:

* Consume a variety of foods within and among the basic food groups while staying within energy needs.
* Control calorie intake to manage body weight.
* Be physically active every day.
* Increase daily intake of fruits and vegetables, whole grains, and nonfat or low-fat milk and milk products.
* Choose fats wisely for good health.
* Choose carbohydrates wisely for good health.
* Choose and prepare foods with little salt.
* If you drink alcoholic beverages, do so in moderation.
* Keep food safe to eat.

[ I think most of us would agree with those bullets, at least in moderation. ]

This list makes a major departure from previous editions of Dietary Guidelines for Americans in that it does not include a message specifically directed toward sugars. This does not mean that the current Committee views the topic of sugars to be unimportant. On the contrary, the Committee provides a strong rationale for limiting one's intake of added sugars (that is, sugars and syrups that are added to foods during processing or preparation or at the table). The Committee's intent is to make this point clearly under the new topic "Choose Carbohydrates Wisely for Good Health" and also under the first and second topics, which address energy needs and controlling calorie intake, respectively.

On fats it says ( http://www.health.go...t/PDF/D4_Fats.pdf ):

QUESTION 1: WHAT ARE THE RELATIONSHIPS BETWEEN TOTAL FAT INTAKE AND HEALTH?

Conclusion

At low intakes of fat (< 20 percent of energy) and high intakes of carbohydrates (>65 percent of energy), risk increases for inadequate intakes of vitamin E, α-linolenic acid, and linoleic acid, and for adverse changes in HDL cholesterol and triglycerides. At high intakes of fat (> 35 percent of energy), the risk increases for obesity and CHD. This is because fat intakes that exceed 35 percent of energy are associated with both increased calorie and saturated fat intakes. Total fat intake of 20 to 35 percent of calories is recommended for adults and 25 to 35 percent for children age 4 to 18 years. A fat intake of 30 to 35 percent of calories is recommended for children age 2 to 3 years.

[...]

Published Evidence. The IOM report Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (IOM, 2002) includes a systematic, extensive review of the scientific literature regarding total fat and carbohydrate intake in relation to weight change, blood lipid concentrations, and metabolic parameters for glucose and insulin. Documentation relevant to the conclusions above is found in the following tables:

• 11-1: Decreased Fat Intake and Body Weight Change in Non- or Moderately-Obese Subjects

• 11-2: Fat and Carbohydrate Intake and Blood Lipid Concentrations in Healthy Individuals

• 11-8: Interventional Studies on the Effect of Dietary Fat on the Metabolic Parameters for Glucose and Insulin in Healthy Subjects

Evidence in Table 11-1 (IOM, 2002), which includes nine short-term and nine long-term intervention studies, reports small losses in body weight with substantial reductions (greater than 4 percentage points) in the percentage of energy consumed as fat. The IOM report concludes that evidence suggests that low-fat diets (diets with a low percentage of calories from fat) tend to be slightly hypocaloric compared to higher fat diets in outpatient intervention trials. Data in Table 11-2 (IOM, 2002), which covers 14 intervention studies, demonstrate that decreasing fat and increasing carbohydrate intake is associated with an increase in serum triacylglycerol concentration and a decrease in plasma HDL cholesterol. Moreover, the reduction in HDL cholesterol that is associated with a low fat intake results in a higher total:HDL cholesterol ratio, which may increase the risk of CHD. Table 11-8 (IOM, 2002), which covers 13 intervention studies, reports a lack of definitive evidence that higher fat intakes impair insulin sensitivity in humans. Collectively, the evidence in these tables provides the rationale for the lower and upper range for fat in the diet.

[...]

Positions Taken by Other Expert Groups. Using an evidence-based approach, the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (2002) published the following evidence statement and recommendation related to total fat:

Evidence Statement

The percentage of total fat in the diet, independent of caloric intake, has not been documented to be related to body weight or risk for cancer in the general population. Short-term studies suggest that very high fat intakes (>35 percent calories from fat) modify metabolism in ways that could promote obesity. On the other hand, very high carbohydrate intakes (>60 percent calories) aggravate some of the lipid and non-lipid risk factors common in metabolic syndrome.

Recommendations

Dietary fat recommendations should emphasize a reduction in saturated fatty acids. Furthermore, in individuals with lipid disorders or metabolic syndrome, extremes of total fat intake – either high or low – should be avoided. In such persons, total fat intakes should range from 25-35 percent of calories. For some persons with the metabolic syndrome, a total fat intake of 30-35 percent may reduce lipid and nonlipid risk factors.

(National Cholesterol Education Program Expert Panel, 2002, p. V-12)

[...]

(Emphasis added.)

My take is: 1) The guidelines are based on observed associations. They don't claim causation. 2) They say that low fat diet, high carb diets can lead to vitamin deficiencies and other problems, so that's not recommended. 3) They say that high fat diets are discouraged because they're associated with excess calories and excess saturated fat. 4) They acknowledge other groups that have slightly different recommendations regarding fats and say that there isn't enough information.

They don't say that if someone has a diet with 35+% fat that they can't be healthy. They don't say that fat causes you to become fat. They apparently don't have enough data to say whether someone weighing 150 pounds can be on a 2000 calorie 40% fat diet and be healthy over the long term by the usual measures.

AFAIK, FDA isn't involved with these dietary guidelines. FDA's mission is:

The FDA is responsible for protecting the public health by assuring the safety, efficacy, and security of human and veterinary drugs, biological products, medical devices, our nation’s food supply, cosmetics, products that emit radiation, and tobacco products.

The FDA is also responsible for advancing the public health by helping to speed innovations that make medicines and foods more effective, safer, and more affordable; and helping the public get the accurate, science-based information they need to use medicines and foods to improve their health.

FWIW. :-)

Cheers,
Scott.