Dr. Michael Greger noted that the relation between diet and cholesterol levels could be studied in three ways: with controlled feeding experiments, with “free-living dietary change experiments,” and through cross-sectional observational studies of large populations. He wrote that there is…
[…] a clear and strong relationship between change in diet and change in serum cholesterol in the interventional designs, but because of that interindividual variability, in cross-sectional designs, you can get zero correlation…
[A] cross-sectional study doesn’t have the power for detecting such a relationship. Thus because of that variability, these kinds of observational studies would seem an inappropriate method to study this particular relationship.
A layperson-oriented article by Sharon Begley, published by Scientific American, succinctly explains the diet-heart hypothesis:
The hypothesis holds that vegetable oils rich in linoleic acid, like safflower and corn, are good for heart health; that saturated fats, such as those in red meat and dairy products, clog arteries and are very bad; and that replacing the latter with the former reduces deaths from heart attacks, heart disease, and strokes by lowering blood cholesterol levels.
This remained the received wisdom for a long time, but a handful of critics urged professionals and laypeople alike to challenge it. Among other reasons, it was suspected that data had been tinkered with in order to make saturated fat look worse and the polyunsaturated kind look better. After 1970, a prominent study influenced the machinery of the U.S. government to deprecate saturated fat, and advocated for polyunsaturated fats.
This was the Seven Countries Study, whose subjects had originally included many more nations:
But in only seven did populations consuming lots of saturated fats have high levels of heart disease, prompting recent accusations of cherry-picking data.
Also, a fellow named Christopher E. Ramsden and several co-authors upset the applecart. Begley describes Ramsden as a specialist in “excavating lost studies, particularly those with the potential to challenge mainstream, government-sanctioned health advice.” He prevailed on an earlier researcher’s son to dig out the original records from a study conducted in Minnesota from 1968-73.
Ramsden and his colleagues discovered what had been hidden for nearly half a century: records on 9,423 study participants, ages 20 to 97, all living in state mental hospitals or a nursing home. It was the largest experiment of its kind.
This 40-year-old data was from research that Begley says is “more than just another entry in the long-running nutrition wars — it is more rigorous than the vast majority of research on the topic.” She elaborates,
It’s possible, Bob Frantz said, that his father’s team was discouraged by the failure to find a heart benefit from replacing saturated fats with vegetable oils. “My feeling is, when the overall objective of decreasing deaths by decreasing cholesterol wasn’t met, everything else became less compelling,” he said. “I suspect there was a lot of consternation about why” they couldn’t find a benefit.
(To be continued…)
Your responses and feedback are welcome!
Source: “The Saturated Fat Studies: Set Up to Fail,” NutritionFacts.org, 2015
Source: “Records Found in Dusty Basement Undermine Decades of Dietary Advice,” ScientificAmerican.com, 04/19/17
Image by Internet Archive Book Images/Public Domain