by Marion Nestle

Currently browsing posts about: Fats-and-oils

Jul 12 2018

Food Navigator’s collection of articles on “healthy fats”

Fat remains in the news.  Which ones are health, and which not?  FoodNavigator-USA collects its articles on the topic.  My thoughts:  Beyond that, food fats are mixtures of monounsaturated, polyunsaturated, and saturated fatty acids, of the omega-3, -6, and -9 varieties.  And then there are the hydrogenated trans-fats.  These variations make fats complicated.

One attribute of fats is not complicated: fat has 9 calories/gram compared to 4 for protein and carbohydrate.  A tablespoon of oil, butter, lard, or tallow has about 100 calories.  If you are concerned about energy balance, watch out for fat calories (and the other ones count too).

FoodNavigator’s Special Edition: Healthy fats
Fat – we are told – is back. But what kind of fat, and can you have too much of a good thing? Is the science changing on saturated fats? Is whole milk a better choice, or should we stick to low fat dairy? Is coconut oil as healthy as some marketers make out, and is the pressure off to reduce fat now all eyes are on added sugar?  Get the lowdown on fat in this special edition…

May 14 2018

WHO seeks comments on saturated fat and trans fat

The World Health Organization (WHO) is collecting comments until June 4 on its recent “consultation” (committee report) on saturated fat and trans fat.

The consultation recommends:

  • Saturated fat: no more than 10% of calories
  • Trans fat: no more than 1% of calories

These recommendations are consistent with

I wish that dietary recommendations would refer to foods, not nutrients.

We don’t eat specific fatty acids.  We eat foods containing mixtures of saturated, unsaturated, and polyunsaturated fatty acids; some foods have more than one kind than another.

Trans fats appear in highly processed foods.  Therefore, they are a euphemism for snack and other foods containing them.

As for saturated fats: the Dietary Guidelines give their main sources:

The guidelines use two layers of euphemisms.

  • Saturated fat is a euphemism for meat and dairy foods; these have higher proportions of saturated fatty acids.
  • “Mixed dishes” and “protein foods” are also euphemisms for meat and dairy foods.

But saying so is politically impossible.

Do comment on the WHO guidelines.  It may help clarify the recommendations.

Dec 12 2017

Oops. Fat replacing sugar in US diets.

In the late 1980s, nutrition scientists identified fat and saturated fat as key nutrients that needed to be reduced in US diets.

One result was the Snackwell’s phenomenon in the early 1990s—“no-fat” cookies with just as many calories as the ones with fat.  They flew off the shelves.

Image result for snackwell's no fat cookies

Now the push is to get rid of carbs, especially sugars.  The result?  Fat is back, along with its calories (fat has more than twice the calories per gram as carbohydrates, 9 as opposed to 4).

A tweet from Kevin Bass tells the story:

The USDA tells the same story, but with respect to specific products:

These products may be more satiating, but watch the calories!

Also watch out for the saturated fat:

 

Sep 5 2017

The PURE study warrants some skepticism

I love getting notes like this one from a reader:

Why aren’t you saying anything about the PURE study.  Doesn’t it prove that everything you’ve been saying about eating more fruits and vegetables and about saturated fat is wrong, wrong, wrong.  Admit it.

Not this time.  Whenever I hear the claim that “everything you thought about nutrition is wrong,” I know that skepticism is in order.  Science rarely works that way; it usually progresses incrementally.

What the PURE study is about: The PURE (Prospective Urban Rural Epidemiology) study was designed to examine, among other things, the effects of lifestyle behaviors on the health of about 135,000 people in 18 countries over up to 10 years.  Its results have just been published in Lancet journals.

What the headlines say: “Study challenges conventional wisdom on fats, fruits and vegetables.”

What the studies say:  Three papers report results: 

1,  Fruit, vegetable, and legumes vs. cardiovascular disease and death

Higher fruit, vegetable, and legume consumption was associated with a lower risk of non-cardiovascular, and total mortality. Benefits appear to be maximum for both non-cardiovascular mortality and total mortality at three to four servings per day (equivalent to 375–500 g/day).

2.  Fat and carbohydrate vs. cardiovascular disease and death

High carbohydrate intake was associated with higher risk of total mortality, whereas total fat and individual types of fat were related to lower total mortality. Total fat and types of fat were not associated with cardiovascular disease, myocardial infarction, or cardiovascular disease mortality, whereas saturated fat had an inverse association with stroke. Global dietary guidelines should be reconsidered in light of these findings.  [Note: the data do not distinguish types of carbohydrate.]

3.  Association of nutrients with blood lipids and blood pressure

Our data are at odds with current recommendations to reduce total fat and saturated fats. Reducing saturated fatty acid intake and replacing it with carbohydrate has an adverse effect on blood lipids. Substituting saturated fatty acids with unsaturated fats might improve some risk markers, but might worsen others.

Why the need for skepticism:

I like the way James Hamblin explains the problem in The Atlantic:

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!

Why did they do this study?  

I looked immediately to see who paid for it.  The list of funders is very long (it must have been extremely expensive).  The list begins:

The PURE Study is an investigator initiated study funded by the Population Health Research Institute, the Canadian Institutes of Health Research (CIHR), Heart and Stroke Foundation of Ontario, support from CIHR’s Strategy for Patient Oriented Research (SPOR) through the Ontario SPOR Support Unit, as well as the Ontario Ministry of Health and Long­Term Care and through unrestricted grants from several pharmaceutical companies, with major contributions from AstraZeneca (Canada), Sanofi­Aventis (France and Canada), Boehringer Ingelheim (Germany and Canada), Servier, and GlaxoSmithkline, and additional contributions from Novartis and King Pharma and from various national or local organisations in participating countries [the funders that follow are mainly government and private research bodies along with a sugar trade association and more drug companies—the list takes up more than half a column].

Drug companies have a big interest in this topic, especially if dietary approaches to heart disease prevention aren’t proven.

What the PURE study really tells us: For this, I am going to quote from David Katz’s lengthy analysis:

On the basis of all of the details in these published papers, the conclusion, and attendant headlines, might have been: “very poor people with barely anything to eat get sick and die more often than affluent people with access to both ample diets, and hospitals.” One certainly understands why the media did NOT choose that! It is, however, true- and entirely consistent with the data.

Also, by way of reminder: the HIGHEST levels of both total fat, and saturated fat intake observed in the PURE data were still LOWER then prevailing levels in the U.S. and much of Europe, providing no basis whatsoever for headlines encouraging people already exceeding these levels to add yet more meat, butter, and cheese to their diets. Absolutely none.

My translation: This study confirms that the single most important risk factor for poor health is poverty.  The study results are consistent with the idea that largely plant-based diets are good for health.  No single study can settle the fat vs. carbohydrate debate because people eat complicated combinations of foods and diets containing those nutrients.  What we really need are well designed studies of dietary patterns—the ones done to date suggest that largely plant-based diets are associated with excellent health and longevity.  

Aug 30 2017

Another ongoing saga: the legacy of Ancel Keys

I cannot understand the revisionist attack on the work of Ancel Keys, who died at the age of 100 in 2004.  Most scientists are lucky to have made important contributions in one area.  Keys produced outstanding work in several:

  • High altitude physiology
  • The physiology of starvation (for this alone, he should be honored)
  • Mediterranean diet benefits
  • Heart disease epidemiology

The fuss, of course, is over this last one, particularly his role in the Seven Countries Study.  The arguments falls right into today’s absurd debate about sugar vs. fat as a cause of disease (absurd, because we don’t eat sugar or fat; we eat foods and diets that provide energy measured as calories).

What started off this most recent fuss is Ian Leslie’s The Sugar Conspiracy, which begins with the question “How did the world’s top nutrition scientists get it so wrong for so long?”  This alone is a red flag.  “Everything you thought you knew about nutrition is wrong” is a sure signal for caution; that’s not how science works.

The attack on Keys’ work induced the True Health Initiative to develop a ​White Paper in defense (here’s its press release).  Its authors: Katherine Pett (who had written a blog post in defense), Joel Kahn (who also wrote a blog post) Walter Willet (long a champion of Mediterranean diets), and David Katz (who wrote about it in his own blog post).

In response, Michael Joyner pointed out that R.A. Stallones (a professor of mine at the School of Public Health at Berkeley) had made the same arguments years ago.

Another defense of Keys’ work comes from Kevin Klatt, a nutrition biochemistry PhD student at Cornell.

Sarah Tracy, a science historian at the University of Oklahoma, has been working on a biography of Ancel Keys for years.  I can’t wait for it to come out.  We need to have Keys’ life and work put in reasonable perspective.

While waiting for the fat v. sugar debate to resolve (I’m predicting it won’t), eat a healthy diet, enjoy what you eat, and be skeptical when writers write about nutrients, not food.

Sep 12 2016

Sugar industry funding of research, 1967 style (with many lessons for today)

I wrote a commentary for a study published this morning in JAMA Internal Medicine: “Food industry funding of nutrition research: The relevance of history for current debates.”

The study, by UCSF investigators Cristin Kearns, Laura Schmidt and Stanton Glantz, is based on their archival research.  They found documentary evidence of shocking manipulation by the sugar industry of a Harvard review of studies on dietary factors and heart disease published in the New England Journal of Medicine in 1967.

Kearns et al. discovered that the sugar industry trade association paid investigators at Harvard an impressive amount of money ($48,000 in today’s dollars) to produce research demonstrating that saturated fat—not sugar—raises the risk of heart disease.

In my commentary, I reproduced a figure from the sugar-funded 1967 reviews.  This summarizes the epidemiology showing that both sugar and saturated fat intake were then indistinguishably associated with increased mortality in 14 countries.

Nevertheless, the reviews exonerated sugars and blamed saturated fat.

Yes, I know that association does not necessarily mean causation, but I’m guessing that the epidemiology still shows that both sugars and saturated fats are associated with increased heart disease risk.

My interpretation: We would all be healthier eating less of sugary foods and fatty meats.

Here are the relevant documents for your reading pleasure:

The Sugar Association issued a response to today’s article by Kearns et al.:

We acknowledge that the Sugar Research Foundation should have exercised greater transparency in all of its research activities…Generally speaking, it is not only unfortunate but a disservice that industry-funded research is branded as tainted…We question this author’s continued attempts to reframe historical occurrences to conveniently align with the currently trending anti-sugar narrative, particularly when the last several decades of research have concluded that sugar does not have a unique role in heart disease.  Most concerning is the growing use of headline-baiting articles to trump quality scientific research—we’re disappointed to see a journal of JAMA’s stature being drawn into this trend.

I will post press accounts as they appear (I’m quoted in most of these):

Jul 6 2016

No, butter is not back (eat in moderation, please)

I like butter as much as you do—and definitely more than margarine—but Time Magazine took it to an extreme with its cover story last year on how scientists (they are so dumb) got it wrong.

Hype alert: any time you read that science got it wrong, be skeptical.  Maybe they did, but it’s more likely that the science is still incomplete.

Time Magazine is really dug in on the butter issue.  It continues to insist that scientists were wrong about saturated fats.  Indeed, Time says, its case against saturated fats has just gotten even stronger.

On what basis?  A new study with the provocative title, “Is butter back?”   The study concludes:

This systematic review and meta-analysis suggests relatively small or neutral overall associations of butter with mortality, CVD, and diabetes.

It comes as no surprise that a single food like butter is not linked to a higher risk of heart disease. The highly respected Cochrane Collaboration’s meta-analysis of 15 randomized clinical trials concluded that replacing saturated fat (from all sources) with polyunsaturated fats lowers the risk of heart attacks and other cardiovascular events. (That finding is consistent with clinical studies on blood cholesterol levels and well-designed analyses of observational studies). One would not expect any single food to matter, since people who eat butter don’t necessarily eat an overall diet that is high in saturated fat.

No, butter is not back says the Harvard School of Public Health:

What the headlines miss is that in a meta-analysis such as this, there is no specific comparison (i.e. butter vs. olive oil), so the default comparison becomes butter vs. the rest of the diet. That means butter is being compared to a largely unhealthy mix of refined grains, soda, other sources of sugar, potatoes, and red meat…Here is the most important takeaway from this study not making headlines: Butter, a concentrated source of saturated fat, is still a worse choice than sources of healthy unsaturated fats such as extra virgin olive, soybean, or canola oils.

And just published is the Harvard group’s latest report on the diet and health of tens of thousands of nurses:

Different types of dietary fats have divergent associations with total and cause-specific mortality. These findings support current dietary recommendations to replace saturated fat and trans-fat with unsaturated fats.

Even the “Is butter back?” investigators temper their conclusions:

These findings do not support a need for major emphasis in dietary guidelines on either increasing or decreasing butter consumption, in comparison to other better established dietary priorities; while also highlighting the need for additional investigation of health and metabolic effects of butter and dairy fat.

Time Magazine:  Your science writers need to do a better job of reading the literature and putting new studies in context.

Readers: consider “scientists are wrong” (and, by implication, “we are right”) to be a red flag.  Saturated fat is one nutrient in diets that contain many, and studies that examine the effects of one nutrient without considering the total diet—and calorie balance—are highly likely to require further research.   In the meantime, enjoy butter—in moderation, of course.

Apr 27 2016

The fuss over previously unpublished data from the Minnesota Heart Study

A couple of weeks ago, I mentioned several new studies that elicited much media attention.  I am now getting around to them.

Let’s start with the article in the BMJ about newly discovered data from the Minnesota Heart Study purportedly casting doubt on the risks of saturated fat (here’s what the Washington Post said about it).

The BMJ article concluded:

Findings from the Minnesota Coronary Experiment add to growing evidence that incomplete publication has contributed to overestimation of the benefits of replacing saturated fat with vegetable oils rich in linoleic acid.

I’ve been at this game long enough to guess that any statement suggesting that everything you thought you knew about nutrition is wrong ought to raise red flags and call for more than the usual degree of skepticism.

Here are some sensible and, yes, skeptical comments about this study:

From Julia Belluz of Vox

But there were a few major problems with the research. The study involved men and women of an average age of 52 who had been admitted to a nursing home and six state mental health hospitals because they were sick. The researchers who conducted the meta-analysis note the “results are not necessarily generalizable to populations without mental illnesses or living outside nursing homes.”

Another issue: The study followed 9,423 women and men, but only a quarter of the participants followed the diets for more than a year. Altering one’s diet for a short period of time — especially in old age — would not necessarily affect one’s long-term health risks….

…Some of the biggest controversies surround saturated fats. Scientists disagree about the extent to which saturated fats contribute to important health outcomes like heart disease, stroke, and cancer. The available research does suggest, however, that there are health benefits from replacing saturated fats with unsaturated fats in the diet, and that eating lots of nutrient-poor carbs (like sugary cereals, soda, and white bread) instead of fat is a bad idea.

From David Katz, to whom I am often grateful for taking on such things, writes that this study

tested something that nobody expert in nutrition is recommending: an extremely high dose of omega-6, linoleic acid…we already got the memo that this is a dubious proposition.

With all due respect to the BMJ authors, I personally found it a bit odd that they stated the following: “A key component of dietary guidelines has long been to replace saturated fat with oils rich in linoleic acid…” The current Dietary Guidelines for Americans, let alone the far better 2015 Dietary Guidelines Advisory Committee Report, make no such recommendation. Searching for any mention of linoleic acid, I found it only in the appendices in the context of descriptions and definitions, not in any of the actionable guidance. While the current Dietary Guidelines do recommend limiting saturated fat intake, the replacement encouraged is a balance of healthful oils, such as olive, and the fats found natively in, as noted, nuts, seeds, avocado, and fish.

From Martijn Katan, the Dutch lipid biochemist who did the original work demonstrating the cholesterol-raising effects of trans fats, writes in an e-mail:

I have not had time to study the BMJ article on the Minnesota Heart Study in detail. However, some of my colleagues did, and I think that their conclusions are correct:

  1. The randomized trial itself showed no effect on disease or death
  2. This was to be expected because most subjects were on the diet for less than 1 year. This was due to the change in regime for psychiatric patients that took place during that period, which essentially caused the trial to fail. Lowering cholesterol by 14% for one year does not noticably affect CVD risk.
  3. The relation of a larger fall in cholesterol with a larger risk of mortality did not emerge from the randomized study; subjects were not randomized to various levels of cholesterol lowering. It is an observational association. The question than arises which causes which. Various occult diseases, notably cancer, cause cholesterol to fall as the disease progresses. This also explains the association seen in observational studies between low cholesterol and cancer. That observation led me to think up in 1985 the technique now known as ‘Mendelian Randomization’ [1]. Application of that technique showed that the association of low cholesterol and cancer is indeed spurious [2].

The only new thing about the present study is that they revived the long disproved hypothesis that lowering cholesterol causes various diseases. Hundreds of thousands of patients in statin trials have proven this wrong….

[1] Katan, M.B., 1986. Apolipoprotein E isoforms, serum cholesterol, and cancer. Lancet 1, 507–8.

[2] Trompet, S.,et al ., 2009. Apolipoprotein E genotype, plasma cholesterol, and cancer: a Mendelian randomization study. Am J Epidemiol 170, 1415–21.

My bottom line on this one

It confirms the value of basic dietary advice: Eat a variety of relatively unprocessed foods, mostly plants (fruits, vegetables, grains, beans, nuts), balance calories, and enjoy what you eat!

Do this and food fatty acids will balance out too and you won’t need to give them another thought.

The moral

Whenever you read a headline suggesting that everything you know about nutrition is wrong, roll your eyes, eat something delicious, and wait for confirming studies to come along before deciding to ignore that basic advice.

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