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Marc Brazeau | Editor | Food and Farm Discussion Lab | @eatcookwrite
What constitutes good nutrition advice? Reasonable and well informed people can disagree.
One day not that long ago, I stumbled on two bits of diet related reporting and analysis which I found clarifying, both for what they agreed on and where they departed in emphasis and narrative. Though written months apart and about different large and significant studies, I came across a piece by Jane Brody in The New York Times and one in the Atlantic by James Hamblin, both ruminating on the gap between the stability and continuity of what we know about diet and nutrition and the mania for “contrarian man-bites-dog stories” in Brody’s formulation and narratives that supposedly upend conventional wisdom in Hamblin’s.
The differences expose something I’ve come to see as an invisible fault line that makes our running dialogue on nutrition more confusing than it needs to be. Both author make the case that conventional wisdom is more stable than it feels and that there is less controversy than the media would have you believe. On the other hand, they seem to end up opposite sides of the contentious issue of how saturated fat relates to cardiovascular disease (CVD).
I would suggest that they are on two sides of a divide that nobody has made plain … UNTIL NOW!!!!! (insert dramatic crescendo here)
The basics of what constitutes a healthy diet: There’s nothing new under the Sun
What is made clear, explicitly in Hamblin’s story and more implicitly in Brody’s, is that the agreed upon elements of an optimal diet are well understood and have been for a long time. High fiber content, whole intact grains, beans, nuts, seeds, fruits and vegetables, and fish. There is little to no controversy to eating any of those foods to your heart’s content.
Where we tend to lurch around and around is on what to avoid. And there is no nutrient that has caused more whiplash in the public dialogue than saturated fat. The way these two pieces deal with the noisy data around saturated fat’s role in CVD says more about how they differ in approaching noisy data and weak evidence than it does about what we actually know.
Agreement on “What to Eat” – Diverging views on “What Not to Eat
Brody’s story is about the seemingly bottomless desire for permission from science to stop worrying about saturated fat. She anchors it with last year’s Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association, a 26 page report put together by a team of experts led by Dr. Frank M. Sacks, professor of cardiovascular disease prevention at the Harvard T.H. Chan School of Public Health, looking at “the effects of dietary saturated fat intake and its replacement by other types of fats and carbohydrates on cardiovascular disease”. She writes:
The report helps to explain why the decades-long campaign to curb cardiovascular disease by steering the American diet away from animal fats has been less successful than it might have been and how it inadvertently promoted expanding waistlines and an epidemic of Type 2 diabetes.
When people cut back on a particular nutrient, they usually replace it with something else to maintain their needed caloric input. Unfortunately, in too many cases, saturated fats — and fats in general — gave way to refined carbohydrates and sugars, the so-called SnackWell phenomenon that prompted fat-wary eaters to overindulge in high-calorie, low-nutrient foods.
Still, people do miss their unhealthy fats and, in the latest rage, many have latched onto coconut oil in the mistaken belief that its main highly saturated fat, lauric acid, and other nutrients can enhance health rather than undermine it.
As documented in the new advisory, misleading conclusions that saturated fats do not affect the risk of developing and dying from cardiovascular diseases have largely resulted from studies that were done in good faith but failed to take into account what people who avoided saturated fats ate in their place.
The point of Brody’s story is clear: The evidence doesn’t support letting saturated fat off the hook.
Hamblin starts his piece, titled “New Nutrition Study Changes Nothing”, with a new big study that confirms what we already know and why the media can’t take Yes for an answer.
This week, the world learned the results of an enormous study of food and health. The study included 135,335 people from 18 different countries across five continents who were followed for seven years. It’s known as the Prospective Urban Rural Epidemiology study, or PURE, and the results were presented at the European Society of Cardiology meeting in Barcelona and published in The Lancet.
The practically important findings were that the healthiest people in the world had diets that are full of fruits, beans, seeds, vegetables, and whole grains, and low in refined carbohydrates and sugar.
As a writer and a reader, though, this is very boring. If I pitched that to my editor, he would laugh at me. What is new here? Why is this interesting? You know what would be novel? You getting fired! Now get out there and find me a story, dammit!
Let’s look at the internet. The coverage of the study was mostly fine, but the headlines alone promise novelty. Stat ran “Huge New Study Casts Doubt on Conventional Wisdom About Fat and Carbs.” Reuters ran “Study Challenges Conventional Wisdom on Fats, Fruits, and Vegetables.” Medscape ran “PURE Shakes Up Nutritional Field: Finds High Fat Intake Beneficial.” Even the editors at The Lancet used the headline “PURE Study Challenges the Definition of a Healthy Diet.”
He then points out that these headlines all assume that the conventional wisdom is that a low fat diet is the most healthful. That hasn’t really been the case for sometime, and he runs through a bit of history before turning to saturated fats with a seemingly much different take than Brody.
“My hope is that our results will stop the whole population from feeling guilty if they eat fat in moderation,” said Salim Yusuf, another author on the study. “While very high fat intake—when it accounts for 40 percent or more of your dietary intake—may be bad, the average fat intake is about 30 percent, and that’s okay. We’re all afraid of saturated fat, but actually we shouldn’t be.”
Are we all afraid of saturated fat? The evidence on that particular type of lipid has shifted over the past half-century. The story of the public perception of saturated fat is long and embattled, but essentially there was initially an argument over how harmful it was, and as more evidence has come to light, it became clear that saturated fat is like other types of macronutrients—good in moderation, bad in scarcity, and probably bad in overexposure. Some experts argue that it’s impossible to eat too much saturated fat, and a few outliers believe it should be significantly limited, but mostly there is agreement that it’s unwise to either chase or fear it.
The U.S. Dietary Guidelines still recommend that people limit saturated fat intake, and many experts find this inappropriate.
Same evidence, different conclusions regarding saturated fat
What’s going on here? Both Brody and Hamblin are skilled health and science reporters ostensibly looking at more or less the same body of evidence.
A cynic might point to a generational difference. Now 76, Jane Brody started writing for the New York Times in 1965, first on medicine and biology and then starting in 1976 as a health columnist. During that time, and at the height of her prominence as a bestselling diet and cookbook author in the 80s she was one of the foremost public advocates for a low fat diet. Hamblin, an MD, is in his mid-thirties, coming of age as the low fat mantra had been discredited and much more research on the effects of saturated fat had called into question it’s position on list of nutritional villains. While Brody has updated her views as the conventional wisdom on fats has shifted, she still has considerable reputational sunk costs on hanging on to the idea that even if there is little need to reduce fat intake as a percentage of total intake, there is still good reason to at least reduce the dreaded saturated fat.
I’ve read most of the literature on the subject from the last decade or at least the abstracts and it’s hard to come away with the impression that saturated fat is all that problematic. As Brody explains in her piece, one of the reasons that researchers keep finding little correlation between saturated fat and CVD is that the nutrients people tend to replace it with are worse – sugar, refined carbohydrates and, for a long time, transfats (old school margarine). Nor is the evidence that strong for replacing saturated fats with monounsaturated fats. So, the only energy dense nutrients that represent and improvement over saturated fats are polyunsaturated fats and high fiber sources of carbohydrate. I don’t think Brody is correct that the recent literature ignored what people replaced saturated fats with. They just drew different conclusions.
The most logical way to read that, it seems to me, is that saturated fat “contributes” to CVD is by crowding out polyunsatured fats – especially omega 3s – and fiber which are protective, the problem being that left to their own devices people counseled to avoid saturated fat by and large don’t swap in polyunsaturated fats and whole intact grains and starchy root vegetables, they dumb down their diets even more. Of the six types of nutrients that are sources of energy that researchers look at – polyunsatured fats, monounsatured fats, saturated fats, sugar, refined carbohydrate, and high fiber sources of carbohydrate – two – polyunsaturated fat and high fiber carbs – are protective, monosaturated fats seem about the same or maybe a little less healthful than saturated fat, and sugar and refined carbs are less healthy. (See Addendum #2 below for examples of this body of research literature.)
Left to their own devices, admonishments to reduce saturated fat intake tend to lead to more consumption of polyunsaturated fats, refined carbohydrate, and sugar – none of which represent an improvement over saturated fat and are often significantly worse. People have to get their energy from among those six sources of energy under normal conditions and they like their food to taste good. If only two energy dense nutrients are acceptable that’s a pretty limited diet, especially if those sources can generally use at least a little nudge in the flavor department.
Here’s what I suspect actually divides Brody and Hamblin in their approaches. Brody, as a health reporter and author of guides and cookbooks for healthy living is interested in the question of what constitutes an optimal diet. Hamblin, trained as a doctor, is interested in what advice his patients will most likely understand and adhere to. He concludes his piece on the way the desire for novel dietary advice tends to confuse rather than clarify by considering what to do with new research that demonstrates health benefits for eating raw vegetables rather than cooked vegetables.
All that said, I should end with something novel. There’s always something new and interesting in any study, and there were a few things in this one. For instance, eating vegetables in any state was associated with good health, but as compared to cooked vegetables, eating raw vegetables was more strongly linked to a lower risk of death (during the study) compared to cooked vegetable intake.
As researcher Victoria Miller of McMaster University put it, “Our results indicate that recommendations should emphasize raw vegetable intake over cooked.”
There is a novel idea. Dietary guidelines usually don’t encourage people to prioritize raw vegetables over cooked. Maybe they should. That could be a headline. “Cooking Your Vegetables? Welcome to Early Death.”
… Except that raw vegetables often don’t taste as good as cooked vegetables, and cooking is the basis for human social interaction and culture.
People are complex, and the ways we perceive and communicate and relate to one another are complex. But the basic agreement on what to eat for the health of people and the planet is not: diverse, naturally high-fiber, minimally processed foods, mostly plants. Eating based on macronutrient numbers isn’t likely useful and is easily distracting. Sufficient amounts of protein and fats come to most people in wealthy countries without thinking.
There are a couple of principles embedded here. First, recognizing when optimal advice is unlikely to be widely adopted – “raw vegetables often don’t taste as good as cooked vegetable”. Then, don’t get too technical, people understand food, not macronutrients and macronutrients often come bundled in different foods. Consider that monounsaturated fats have long been considered a linchpin of why the Mediterranean diet (really a Greek island diet) results in such good health outcomes. Olive oil, central to that diet, is 75% monosaturated fat, canola oil and cashews are both contain about 58% monounsaturated fat, but tallow (beef fat) is about 50% monounsaturated fat, and lard is about 40% monounsaturated fat. Good nutrition advice should be focusing, not distracting. The evidence on What Foods To Eat is stronger (in most cases) and easier to follow than the advice on What Nutrients Not To Eat (except for too much sugar which is well documented and easy to understand). There is a recognition that most people are not looking for the answer to the question What Is The Optimal Diet? They want to know how to eat better, but that’s balanced against competing values – “cooking is the basis for human social interaction and culture”.
A longstanding pet peeve of mine is that in crafting public health messages, especially where nutrition is concerned, not enough consideration is given to how simple, how idiot proof they need to be. The advice to lower fat intake in the 70s and 80s is a case in point. Public health messages are run through numerous platforms and mediators. They travel through the culture like the children’s game of Telephone, with something lost at each relay until they become gibberish. People will interpret them to as permission to do something they want to do – avoid fat by eating more sugar – rather than admonition to move in less pleasurable, less convenient direction. Food processors and markets will be devilishly clever at exploiting loopholes (Snackwells). Yet ever after the failure of the low fat advice, I see very little care given to idiot-proofing public health messages. It rarely seems that thought leaders and public health officials ever ask themselves the questions, “What’s the dumb version of this advice going to be? Is that still pretty good advice? Are people even likely to follow this advice?”
Before my Registered Dietitian friends register their disagreement, let me clarify that I’m talking about public health messaging from government, health reporting written for a general audience, and boilerplate advice from general practitioner doctors to their patience on shifting their diet to improve health and chronic disease markers. This argument doesn’t apply to treating people with serious diet-related health issues that require specific, substantial diet interventions and are getting intensive, individually tailored counseling and meal planning advice.
Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies (2009)
The associations suggest that replacing SFAs with PUFAs rather than MUFAs or carbohydrates prevents CHD over a wide range of intakes.
Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. (2010)
A meta-analysis of prospective epidemiologic studies showed that there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD or CVD.
The role of reducing intakes of saturated fat in the prevention of cardiovascular disease: where does the evidence stand in 2010? (2010)
This expert panel reviewed the evidence and reached the following conclusions: the evidence from epidemiologic, clinical, and mechanistic studies is consistent in finding that the risk of CHD is reduced when SFAs are replaced with polyunsaturated fatty acids (PUFAs). In populations who consume a Western diet, the replacement of 1% of energy from SFAs with PUFAs lowers LDL cholesterol and is likely to produce a reduction in CHD incidence of ≥2–3%. No clear benefit of substituting carbohydrates for SFAs has been shown, although there might be a benefit if the carbohydrate is unrefined and has a low glycemic index. Insufficient evidence exists to judge the effect on CHD risk of replacing SFAs with MUFAs
The relationship between high-fat dairy consumption and obesity, cardiovascular, and metabolic disease. (2012)
The observational evidence does not support the hypothesis that dairy fat or high-fat dairy foods contribute to obesity or cardiometabolic risk, and suggests that high-fat dairy consumption within typical dietary patterns is inversely associated with obesity risk.
Reduction in saturated fat intake for cardiovascular disease The Cochrane Library of Systematic Reviews (2015)
Subgrouping and meta-regression suggested that the degree of reduction in cardiovascular events was related to the degree of reduction of serum total cholesterol, and there were suggestions of greater protection with greater saturated fat reduction or greater increase in polyunsaturated and monounsaturated fats. There was no evidence of harmful effects of reducing saturated fat intakes on cancer mortality, cancer diagnoses or blood pressure, while there was some evidence of improvements in weight and BMI.
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