As widely reported last month, including in the New York Times, the Dietary Guidelines Advisory Committee has eased some of its previous restrictions on fat and cholesterol, and recommended that Americans significantly reduce how much sugar we eat.
In a follow-up editorial in The Times, Nina Teicholz, author of “The Big Fat Surprise: Why Butter, Meat and Cheese Belong in a Healthy Diet,” addressed what seems to be “experts” advising on nutritional habits one day, only to change their minds the next. If these recommendations are based on scientific studies, why do they so often seem more like fashion than long-term healthful behavior?
As Teicholz recounted, for years American have been advised to eat fewer eggs and other animal products because their fat and cholesterol content was unhealthful. Now, it seems, that’s a big old “never mind.”
In the autumn, the committee acknowledged dropping the low-fat approach to diet. But the new guidelines are an even bigger step back in lifting limits on dietary cholesterol. The experts said there was “no appreciable relationship” between dietary cholesterol and blood cholesterol. As Teicholz wrote, “Americans, it seems, had needlessly been avoiding egg yolks, liver and shellfish for decades.
“… How did experts get it so wrong? Certainly, the food industry has muddied the waters through its lobbying. But the primary problem is that nutrition policy has long relied on a very weak kind of science: epidemiological, or ‘observational,’ studies in which researchers follow large groups of people over many years. But even the most rigorous epidemiological studies suffer from a fundamental limitation. At best they can show only association, not causation.
Epidemiological data can be used to suggest hypotheses but not to prove them.”
We’ve written often about how media expand the idea of “association” into “causation,” mostly to garner attention for “breakthrough” studies that, on closer inspection, fail to live up to that description. But as Teicholz explained, even the “expert” scientists fall prey to those conclusions.
She reported that a lot of the observational data that was the foundation of the government’s dietary advice were from Harvard school of public health studies. But in 2011, the National Institute of Statistical Sciences examined many of its significant conclusions, and discovered that they weren’t able to be reproduced in clinical trials. Any status quo-changing science should be reproducible in subsequent studies.
In 2013, Teicholz recalled, the government advised people to reduce their salt intake, and although this advice remains in the current report, the Institute of Medicine (IOM) disputed its scientific foundation as a health guide. And several recent significant studies have called into question whether saturated fats really are linked to heart disease, but the guidelines still contend they do. (See Patrick’s newsletter, “Saturated Fat: The Good, the Bad, the In-Between.”)
“Uncertain science should no longer guide our nutrition policy,” Teicholz stated. “Indeed, cutting fat and cholesterol, as Americans have conscientiously done, may have even worsened our health. In clearing our plates of meat, eggs and cheese (fat and protein), we ate more grains, pasta and starchy vegetables (carbohydrates). Over the past 50 years, we cut fat intake by 25 percent and increased carbohydrates by more than 30 percent, according to a new analysis of government data. Yet recent science has increasingly shown that a high-carb diet rich in sugar and refined grains increases the risk of obesity, diabetes and heart disease — much more so than a diet high in fat and cholesterol.”
This reality, Teicholz said, should not have come as a surprise to health authorities because it wasn’t based on evidence, but on a reasonable idea that wasn’t fully tested. And the new guidelines maintain this short-sighted analysis, she said. The committee also advises eliminating “lean meat” from the list of recommended healthy foods, and cutting back on red and processed meats.
That means that a lot of people trying to eat less meat (protein) will eat more carbs. And it means official policies could change, such as limiting meat in school lunches and other federal food programs.
“It’s possible that a mostly meatless diet could be healthy for all Americans,” Teicholz pondered, “but then again, it might not be. We simply do not know. There are no rigorous clinical trials on such a diet, and although epidemiological data exists for adult vegetarians, there is none for children.”
The first nutritional guidelines restricting saturated fat and cholesterol were devised in 1961 by the American Heart Association, and ever since, Americans basically have been subjects in a huge, uncontrolled diet experiment with, as Teicholz said, “disastrous consequences. We have to start looking more skeptically at epidemiological studies and rethinking nutrition policy from the ground up.”
She supports the diet that worked for previous generations, which included fewer grains, less sugar and more animal foods like meat, full-fat dairy and eggs. We’re not totally on the same page here, because the lifestyles of previous generations were much different from ours; they worked harder physically.
We lean more toward what’s emerging scientifically as the best overall diet for health, which is known as the Mediterranean diet. (See the Mediterranean diet section of Patrick’s newsletter on healthful living. But Teicholz’s main point is well taken — association isn’t causation, and that relationship has been driving government nutritional policy for too long with possibly negative results. Consumers feel whip-sawed, and that makes them less likely to pay attention when scientifically sound recommendations are given.
When you keep changing your mind, people stop listening.