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opinion | Walter Willett and Frank Hu

Resist temptation to oversimplify diet reports

Health research may whipsaw back and forth, but one diet tip always holds true: All things in moderation

dina rudick/heather hopp-bruce/globe staff/Globe Staff

People took notice when scientists from the federal government’s Dietary Guidelines Advisory Committee recently published a 500-page report that seemed to call for the return of eggs to the breakfast menu. The findings — or at least the interpretation of them — seemed at odds with a longstanding message delivered by nutritionists — stay away from consuming too much cholesterol.

The apparent abrupt turn left many wondering: Why listen to these so-called health “experts” when they are always changing their minds about what’s good or bad to eat?

Federal dietary guidelines date to the late 1800s, and have evolved over the years in response to improved scientific research. That’s how it will always be — they’re a work in progress. But as the science has gotten better, the guidance has grown in quantity and quality and — despite the appearance of frequent flip-flopping — has been remarkably consistent over the last decade or more. With the exception of some on the fringes, scientists and medical experts agree in more ways than they disagree about what people should eat — and have for some time.

It may not always seem that way because confirmation of existing knowledge gets scant attention in the media compared with the widespread coverage lavished on “new” nutrition announcements and fads.


Compelling data from a large randomized trial as well as from 30-year-long Harvard cohort studies, for example, have shown a so-called Mediterranean style diet — which emphasizes nuts, olive oil, fruits, vegetables and legumes, and whole grains, and discourages red meat and sugar — cuts cardiovascular disease. These studies provide strong evidence pointing to the benefits of healthy fats (as in nuts and olive oil) and the adverse effects of added sugar (especially sugar-sweetened beverages) and trans fats, a form of fat that thankfully has largely been eliminated from foods in restaurants and grocery stores.


This research formed the basis of a book we published in 2000 called “Eat, Drink, and Be Healthy.” It has helped the US Department of Agriculture realize it was off target in promoting a simplistic low-fat diet. While the government has moved slowly and incrementally in adjusting its recommendations, the recent “eggs are OK” report does acknowledge the accumulation of evidence by dropping any recommendation for a specific limit on the percentage of calories people consume from total fat.

If scientists agree on so much, why is the Dietary Guidelines Advisory Committee’s report generating media coverage and critical opinion pieces suggesting its findings regarding eggs, sugar, fats and other foods are “new” or significantly contradict past findings?

Unfortunately, the way the government guidelines are drawn up is not based solely on research, but also is influenced lobbying by food interests, and the government’s desire to make guidelines easy for the public to understand.

istockphoto/globe staff illustration

The old advice that “fat is bad” was an oversimplified message created in a misguided attempt to translate research on the problems with saturated fat into easy-to-follow guidelines.

Fat’s bad rep over the years kept gaining traction even though scientists knew as early as the 1960s that saturated fats — primarily from meat and dairy — behaved differently than polyunsaturated fats, which are mainly from plant sources and actually reduce blood cholesterol levels.

In the 1990s, mounting evidence indicated trans fats were significantly worse than saturated fats. The food industry responded, but often replaced fats of all types with unhealthy simple sugars and refined starches to make foods taste better. They then labeled those products “low fat,” further promoting the fat-as-evil notion with millions of dollars in annual advertising.


The government has made its message regarding fats clearer in the last few years – especially in this most recent report, which advocates consuming healthy plant-related fats, steering clear of trans fats, and avoiding the replacement of saturated fats with sugar-laden low-fat foods. Trans fats and sugary foods both tend to increase heart disease.

This advice, however, is a bit nuanced, which complicates matters for headline writers and the bullet-point style of many online new reports.

And that is why we must resist the temptation to use this latest report make yet another gross oversimplification by saying “fat is fine, carbs are bad!” Some carbs – sugars and refined carbohydrates – are bad in large amounts, while others (like whole grains) are healthful. There isn’t any science to support adding steak and processed meats to your daily diet, along with full-fat dairy foods.

So what should you do about menu planning? Don’t think of single foods or nutrients, but base your eating habits on a day’s worth of food consumption. Put more fruits and vegetables on your plate. Eat more nuts, beans and soy foods, and substitute whole grains for refined grains and potatoes. Red meat, especially processed products such as bacon and salami, shouldn’t be the centerpiece of your plate, but can be enjoyed in small amounts once in awhile.


As for eggs – research we published in 1999 in the Journal of the American Medical Association showed that consuming up to one a day was not associated with risk of heart disease, despite the cholesterol. That was 16 years before the report that just came out with what has been interpreted as “new” findings that say the same thing. While we still suggest people with diabetes steer clear of eating eggs regularly, others can enjoy them for breakfast, scrambled or otherwise. Eggs are better than a sugary cereal drowned in whole milk — but an even healthier morning meal would include oatmeal, nuts, blueberries, and a bit of yogurt.

The choice is yours.

Walter Willet is chair of the Department of Nutrition at Harvard University’s T.H. Chan School of Public Health. Frank Hu is a professor of nutrition and epidemiology at the school. Meir Stampfer of the school of public health also contributed to this column.


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