Upon Further Review
Could saturated fats be good for us? Scientists seem to understand far less than most people believe about which foods are positive or negative for long-term health, including trade-offs among food groups. This subject is inherently difficult to study in a controlled manner.
“Saturated fat does not cause heart disease” — or so concluded a big study published in March in the journal Annals of Internal Medicine. How could this be? The very cornerstone of dietary advice for generations has been that the saturated fats in butter, cheese and red meat should be avoided because they clog our arteries. For many diet-conscious Americans, it is simply second nature to opt for chicken over sirloin, canola oil over butter. The new study’s conclusion shouldn’t surprise anyone familiar with modern nutritional science, however. The fact is, there has never been solid evidence for the idea that these fats cause disease. We only believe this to be the case because nutrition policy has been derailed over the past half-century by a mixture of personal ambition, bad science, politics and bias.
Our distrust of saturated fat can be traced back to the 1950s, to a man named Ancel Benjamin Keys, a scientist at the University of Minnesota. Dr. Keys was formidably persuasive and, through sheer force of will, rose to the top of the nutrition world — even gracing the cover of Time magazine — for relentlessly championing the idea that saturated fats raise cholesterol and, as a result, cause heart attacks.
Critics have pointed out that Dr. Keys violated several basic scientific norms in his study. For one, he didn’t choose countries randomly but instead selected only those likely to prove his beliefs, including Yugoslavia, Finland and Italy. Excluded were France, land of the famously healthy omelet eater, as well as other countries where people consumed a lot of fat yet didn’t suffer from high rates of heart disease, such as Switzerland, Sweden and West Germany. The study’s star subjects — upon whom much of our current understanding of the Mediterranean diet is based — were peasants from Crete, islanders who tilled their fields well into old age and who appeared to eat very little meat or cheese.
As it turns out, Dr. Keys visited Crete during an unrepresentative period of extreme hardship after World War II. Furthermore, he made the mistake of measuring the islanders’ diet partly during Lent, when they were forgoing meat and cheese. Dr. Keys therefore undercounted their consumption of saturated fat. Also, due to problems with the surveys, he ended up relying on data from just a few dozen men — far from the representative sample of 655 that he had initially selected. These flaws weren’t revealed until much later, in a 2002 paper by scientists investigating the work on Crete — but by then, the misimpression left by his erroneous data had become international dogma.
But there was no turning back: Too much institutional energy and research money had already been spent trying to prove Dr. Keys’ hypothesis. A bias in its favor had grown so strong that the idea just started to seem like common sense. As Harvard nutrition professor Mark Hegsted said in 1977, after successfully persuading the U.S. Senate to recommend Dr. Keys diet for the entire nation, the question wasn’t whether Americans should change their diets, but why not? Important benefits could be expected, he argued. And the risks? “None can be identified,” he said. In fact, even back then, other scientists were warning about the diet’s potential unintended consequences. Today, we are dealing with the reality that these have come to pass.
One consequence is that in cutting back on fats, we are now eating a lot more carbohydrates — at least 25% more since the early 1970s. Consumption of saturated fat, meanwhile, has dropped by 11%, according to the best available government data. Translation: Instead of meat, eggs and cheese, we’re eating more pasta, grains, fruit and starchy vegetables such as potatoes. Even seemingly healthy low-fat foods, such as yogurt, are stealth carb-delivery systems, since removing the fat often requires the addition of fillers to make up for lost texture — and these are usually carbohydrate-based. The problem is that carbohydrates break down into glucose, which causes the body to release insulin — a hormone that is fantastically efficient at storing fat. Meanwhile, fructose, the main sugar in fruit, causes the liver to generate triglycerides and other lipids in the blood that are altogether bad news. Excessive carbohydrates lead not only to obesity but also, over time, to Type 2 diabetes and, very likely, heart disease…
The second big unintended consequence of our shift away from animal fats is that we’re now consuming more vegetable oils. Butter and lard had long been staples of the American pantry until Crisco, introduced in 1911, became the first vegetable-based fat to win wide acceptance in U.S. kitchens. Then came margarines made from vegetable oil and then just plain vegetable oil in bottles… After the AHA advised the public to eat less saturated fat and switch to vegetable oils for a “healthy heart” in 1961, Americans changed their diets. Now these oils represent 7% to 8% of all calories in our diet, up from nearly zero in 1900, the biggest increase in consumption of any type of food over the past century.
This shift seemed like a good idea at the time, but it brought many potential health problems in its wake. In those early clinical trials, people on diets high in vegetable oil were found to suffer higher rates not only of cancer but also of gallstones… We’ve also known since the 1940s that when heated, vegetable oils create oxidation products that, in experiments on animals, lead to cirrhosis of the liver and early death. For these reasons, some midcentury chemists warned against the consumption of these oils, but their concerns were allayed by a chemical fix: Oils could be rendered more stable through a process called hydrogenation, which used a catalyst to turn them from oils into solids. From the 1950s on, these hardened oils became the backbone of the entire food industry, used in cakes, cookies, chips, breads, frostings, fillings, and frozen and fried food. Unfortunately, hydrogenation also produced trans fats, which since the 1970s have been suspected of interfering with basic cellular functioning and were recently condemned by the Food and Drug Administration for their ability to raise our levels of “bad” LDL cholesterol.