National Academy of Sciences says diet-heart hypothesis is still unproven.
Toward Healthful Diets
Aside from Ahrens’s panel, there was one other group of nutrition experts who did not buy Hegsted’s argument about the science being good enough to justify these guidelines. This was the National Academy of Sciences, a private society created by Congress in 1863 to be a resource for advice on scientific matters. Its Food and Nutrition Board has been the most respected expert group in Washington, DC, on matters of nutrition since it was established in 1940, and it sets the Recommended Dietary Allowances (RDAs) of nutrients every few years. The board had actually been solicited by the USDA to write up a review of the Dietary Goals, but the contract was never signed. Someone canceled it, quite likely, as the magazine Science reported, because USDA officials had caught wind of the board’s lack of sympathy for the Senate’s new low-fat diet.
Unwilling to be silenced, the academy used its own funds to prepare a review. An academy panel went through the now-familiar process of reviewing those same studies that everyone else had been looking at. Its conclusion on the available diet-heart evidence, published in a report called Toward Healthful Diets, was that the studies had “generally unimpressive results.”
One of the more forceful points made by the academy was that Americans had been doing fairly well on their diet to date. The traditional diet was abundant in essential vitamins and high-quality proteins and was, as Gil Leveille, head of the Food and Nutrition Board, described it in 1978, “better than ever before and is one of the best, if not the best in the world.” The average height of the American male—a fairly reliable indicator of lifelong nutrition—had been fast rising throughout the first half of the twentieth century. Compared to countries with comparable statistics, Americans were among the tallest people on earth.XV
"Despite these generally unimpressive results, some organizations (American Heart Association, 1961. 1978; Select Committee on Nutrition and Human Needs, 1977) have recommended that dietary lipids be reduced from 40 percent to about 30 percent of calories and that the ratio of polyunsaturated to saturated fat (P:S ratio) be changed from the present value in the American diet of 0.4 to 0.5 to a ratio of about 1.0, in order to achieve lower serum cholesterol levels in the population generally Unfortunately, the benefit of altering the diet to this extent has not been established. As noted, other studies employing diets containing 35-40 percent of calories from fat and higher P:S ratios have shown equivocal effects on coronary disease and have been accompanied by a somewhat greater incidence of gastrointestinal disease (Ahrens, 1976)."