What To Eat
Navigating Nutritional Advice
Eat your vegetables and avoid fat and cholesterol. Wait — fat and cholesterol are OK. Fine, get plenty of protein. But not animal protein. Well, maybe, but just in small quantities. The basic concepts of healthy eating are little-changed from your great-grandmother’s time: Consume a variety of foods, maintain ideal weight and avoid too much salt, sugar and alcohol. Nutrition wars rage over the details, however, and scientists keep changing their advice. In a 2012 U.S. poll, half of those surveyed said it was easier to do their taxes than to figure out how to eat healthily. Why isn’t it simpler? For one thing, nutrition science is relatively young and inherently unreliable. For another, there’s lots of money at stake, leading businesses to argue that what they offer is good for consumers, even if it isn’t.
In twice-a-decade dietary guidelines issued in early 2016, the U.S. government made two notable reversals, dropping its previous advice to restrict dietary cholesterol and total fat consumption. The panel of scientists that drafted the guidelines wrote that a healthy diet is “lower in red and processed meat,” which have been associated with elevated death rates from cancer and heart disease. After strong objections from the meat industry, that caution was dropped. In the final document, men and teenage boys were advised to eat less protein by decreasing consumption of meat, poultry and eggs.
High levels of cholesterol in blood have long been linked to heart disease. But the body produces the substance on its own, and researchers increasingly have concluded that in healthy people, consuming cholesterol-laden foods like eggs and shellfish doesn’t affect blood levels very much. Guidance on fats has changed as nutritionists have begun to distinguish among what they think are really bad transfats (in margarine and vegetable shortening), bad saturated fats (in red meat and whole milk) and good unsaturated fats (in olive oil and nuts). The new U.S. guidelines recommend eschewing transfats and limiting saturated fats to 10 percent of a day’s calories. Fat science is far from settled, however. A 2013 review of 72 studies found no significant association between saturated fat and heart disease. This disconnect underscores a weakness in nutrition science. It relies not so much on controlled experiments but on observational studies, in which researchers collect data on a group of people and try to connect something about them with a certain outcome. Because so many other factors can affect the outcome, such studies have a limited ability to determine causality. Their results often cannot be replicated. Also, nutrition studies rely on volunteers to self-report what they ate, producing unreliable data.
Critics of the complicated U.S. guidelines — the 2016 edition is 204 pages long — argue that they have at times contributed to worsening health. For instance, warnings that the fat in butter and cream produced heart attacks prompted many consumers to switch to margarine and non-dairy creamer, which contain the transfat scientists now think is more hazardous. Admonitions to avoid fat altogether led Americans to eat significantly more carbohydrates — many promoted as “fat-free” — which helped drive the country’s current obesity and type 2 diabetes epidemics. The 2016 guidelines won praise for focusing less on individual nutrients than on dietary patterns, better reflecting how people actually eat and accounting for the fact that foods interact with each other. Still, detractors note that while the text mentions specific foods that are recommended (a variety of vegetables, whole fruits, grains), when it comes to things to avoid, it reverts to referencing nutrients (added sugars, saturated fats, sodium) rather than items that contain these things (soda, meat and junk food). The critics blame intense lobbying by the food industry. Government officials have said the guidelines are based on a rigorous review of current nutrition science and consideration of comments from the public and input from federal agencies. To make its recommendations more useful and credible, some nutritionists think the U.S. should simplify them to the basics (from great-grandmother’s time, perhaps), which would put them more in line with the eating advice given by the World Health Organization.
The Reference Shelf
- The U.S. government’s “Dietary Guidelines for Americans 2015-2020″ and the scientific report on which it was based.
- In his book “Nutritional Epidemiology,” researcher Walter Willett explores the limits and benefits of applying observational science to nutrition and disease.
- An article in the Guardian lays out the evidence that sugar rather than fat is the biggest threat to our health.
- A New Yorker article examines the gluten-free trend.
- Related QuickTakes on organic food and genetically engineered food.
First published March 30, 2016
To contact the writer of this QuickTake:
Alan Bjerga in Washington at firstname.lastname@example.org
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