It’s not just you. Diet science on basics like fat, sugar, and salt is confusing by design.
Nutritionists say they can hardly leave the house without someone asking them why dietary advice is so confusing.
How is it that scientists can edit human DNA but can’t say for certain whether basic foods like nuts and eggs are good for us?
Nuts, once considered too fatty to justify eating in any significant amount, were rehabilitated by findings from a large, long-term study that found people who ate nuts lived longer and were no fatter than those who didn’t.
And eggs, once scorned for containing too much cholesterol, are back on the thumbs-up list in the proposed 2015 U.S. dietary guidelinesTrusted Source introduced in January. The public comment period on the guidelines closes next week.
These aren’t the only foods whose health value is being reconsidered in the new guidelines. The new recommendations reverse previous views about fat by taking aim just at saturated fats. They also put coffee back on the menu for the health-conscious set.
Better hold the sugar, though. Nutrition science has been painting a darker picture of added sugars. The 2015 guidelines introduce, for the first time, a cap on how much of our total caloric intake we can safely get from added sugar. They put that number at 10 percent, which is still double what the American Heart Association suggests.
“Everybody’s got an opinion on nutrition,” said Sylvia Rowe, an adjunct professor at the Friedman School of Nutrition Science and Policy at Tufts University and the former president of the International Food Information Council. “We all eat. We all have not only an understanding of it, but in many cases we have values.”
There are a few things that make nutrition a tough nut to crack, scientifically speaking. For example, because we all eat a variety of foods, it’s hard for researchers to parse the body’s response to one specific food the way they could with a medication.
And researchers can only rarely justify bringing people into an in-patient setting to control everything else they eat. Generally, they rely on asking people what they ate the day before — and people often don’t remember.
What about animal studies?
“Animals are not miniature people — they have different lifestyles and dietary habits,” said Marion Nestle, Ph.D., author of Food Politicsand a professor of nutrition and sociology at New York University. “Coprophagia [some animals’ habit of eating one another’s poop], for example, is highly confounding.”
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How Industry Influences Nutrition Studies
The main problem with nutrition science seems to be that food is big business, and food conglomerates influence the questions that are asked and the answers that are provided — or not.
The food industry leaves its fingerprints on research, critics say, starting with the way research agendas are set, through funding studies likely to swing their way and poking holes in the research behind unfavorable findings. The industry also pushes the government to rejigger the way it presents those findings as guidelines and drowns out health messages with advertising.
Right now, the sugar lobby and the National Cattleman’s Beef Association are hard at work lobbying the U.S. Department of Agriculture to demand a change in the proposed dietary guidelines’ verbiage on their products before they finalize them.
It can be hard to pin down exactly what effect industry has on the shape of scientific consensus when it comes to hot topics like sugar and meat. But Kimber Stanhope, Ph.D., a nutritional biologist at the University of California, Davis, has a good vantage point.
Stanhope, a sugar researcher, published a study last week in the American Journal of Clinical Nutrition with dramatic, and potentially controversial, findings. The study showed that consuming even a half a soda’s worth of high-fructose corn syrup (HFCS) with each meal was enough to substantially increase cardiovascular risk factors in young adults. More HFCS led to more trouble signs for heart disease.
Stanhope’s findings met with some confusion. Haven’t other studies shown that HFCS isn’t any worse than table sugar? And what about the studies that specifically show HFCS has no effect on cardiovascular risk factors?
Stanhope dug up a pair of recent studies that found just the opposite of hers. In those studies, even a higher daily dose of HFCS showed no significant effects.
These studies were funded with an unrestricted grant from the Corn Refiners Association, the industry group that makes high-fructose corn syrup. The major author on both of those studies was Dr. James Rippe, whose work has also been funded by ConAgra Foods, PepsiCo International, and Kraft. Stanhope’s study was funded by the National Institutes of Health (NIH).
Both studies gave participants three sweet beverages a day, but were, other than that, quite different. Stanhope and her colleagues provided sweet Kool-Aid drinks that contained a biomarker that allowed them to verify that the participants were regularly drinking the sweet drinks by testing their urine. The control group got drinks sweetened with aspartame.
Participants in the industry-funded study got their HFCS in low-fat milk. Stanhope said it was an odd choice given that as much as two-thirds of the population can’t tolerate lactose. The study didn’t verify that participants who said they were drinking the milk really were.
Low-fat milk has also been shown to improve the very same cardiovascular markers the study was testing. And there was no control group to weed out those effects.
In addition, while separating results for men and women is a baseline requirement for most medical journals, Rippe’s study didn’t sort them out. And Stanhope pointed to one set of line graphs that was made to look the same — showing no effect of HFCS — by using a different scale of values.
Rippe did not respond to a request for comment.
“If you hear frustration in my voice, it’s due to thinking of what I could have done with that money, the public health questions I could help answer,” Stanhope said. “Why are we arguing about such basic things?”
These dueling studies illustrate a larger problem. A 2013 analysis published in the journal PLoS Medicine showed that studies funded by industry were five times as likely to find that there wasn’t enough evidence to conclude sugar-sweetened beverages like soda are linked to weight gain and obesity.
Stanhope worries things may get worse rather than better. She wonders if she’ll ever have the chance to bring patients into a hospital setting, as she did at the beginning and end of the HFCS study.
The NIH has stopped covering the added costs of in-patient studies as a way to cut expenses. It hopes industry will foot the bill, which may make sense for pharmaceutical research where the industry peddles potential cures, but not for the food industry, where the product is often the problem.
Nutritionists say the lack of government funding for their field is almost as big a problem as the presence of industry research. By way of comparison, the 2014 research and development budget for a single company, PepsiCo, was half as big as the NIH’s entire nutrition budget for the same year.
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Sugar by Another Name Is No Less Sweet
There’s another layer of confusion here, too. In these studies, are we talking about the damaging effects of high-fructose corn syrup or sugar?
This years-long debate is little more than a distraction, it turns out, from the real issue. There’s some debate among nutritionists about whether HFCS, which is usually 42 percent fructose and 53 percent glucose, and table sugar, an even mix of both types of sugar, have different effects on the body.
But the real issue is that both are different from natural carbohydrates. And they’re both awful for you, nutritionists say.
“In the last decade, there’s been kind of a paradigm shift. It’s not just that sugar makes people fat; it’s that sugar makes people sick,” said Laura Schmidt, Ph.D., a professor of medicine at the University of California, San Francisco (UCSF), who helps run the website SugarScience.org.
That theory first emerged in the 1960s, but got lost amid the focus on how red meat made people sick. In recent years, evidence against sugar has accumulated.
Stanhope’s study is part of this new, harsher look at sugar. It wasn’t intended to differentiate HFCS from sugar. It was probing how much added sugar we can safely consume — the very number that remains up for debate in national and international guidelines.
Added sugar is also the focus of proposed new FDA labeling requirements. And food companies are now drumming up scientific controversy about what makes an added sugar “added.”
It’s a familiar story for Schmidt, who was part of a team that recently published an analysis of a cache of industry documents from the 1960s that showed the sugar industry successfully redirected the government’s dental health messaging and research funding away from limiting sugar intake and toward minimizing its damage to teeth.
“They’re saying, ‘What’s really the difference between added and total sugar? Chemically isn’t it the same thing, and if so, why would you want to distinguish them?’” Schmidt said. “It’s an esoteric and bizarre position to take.”
It’s not hard to know when sugar is being added to food after first being laboriously extracted from sugar beets or sugar cane. Physiologically, the difference is also clear. A sugar that’s still inside its cell membrane gets digested more slowly, Schmidt said, and takes longer to hit the digestive tract in the first place — imagine peeling and eating the four oranges it takes to account for the amount of sugar in one can of soda.
“Added sugar slams your liver, it slams your pancreas. But if you put me on the stand and said, ‘Is the fructose in an apple chemically identical to the fructose in high-fructose corn syrup?’, I might have to say yes,” Schmidt said.
These latest protestations from the sugar industry and push-back from scientists may make the public even more likely to throw up their hands in frustration.
“It does little to foster the health of the public to make nutrition science appear more controversial than it really is,” Nestle wrote in Food Politics.
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Where’s the Beef?
Mary Story, Ph.D., RD, the program director for Healthy Eating Research, was a member of the 2015 dietary guidelines committee. She says there was absolutely no industry influence on their recommendations, an assertion Schmidt thinks is likely true.
But some of the ways government recommendations cater to industry and ultimately create confusion may be deeply embedded in the process.“The government has an ‘eat more’ bias,” said Katie Ferraro, MPH, RD, a nutritionist at UCSF.
The government, and especially the USDA, whose mission is to support agriculture, is put in an uncomfortable position if it tells consumers to eat less of any given product, because doing so will hurt the farmers and agribusinesses that produce the product.
You can see this in earlier advice to choose “lean meats” (with no specific reference to what those may be) or to “limit” rather than avoid sugar. In the 2015 guidelines, for instance, there’s a push to eat more “plant-based foods.”
“They’re not going to come right out and say, ‘Eat less cow,’” Ferraro said.
But pushing for plant foods is closer to calling for “less cow” than previous guidelines, which advocated for “lean meats.” The beef lobby has taken aim at the newer language.
Ferraro says she sees the government moving to smarter advice on fats in the new guidelines.
“What they’re not saying this time is, ‘Follow a low-fat diet.’ What that is essentially saying is, ‘We were totally wrong.’ What happened with a low-fat diet was everyone gained a bunch of weight,” she said.
Singling out saturated fatsTrusted Source — fats that are solid at room temperature, usually from animal sources — brings the American recommendations closer in line with the Mediterranean diet that nutritionists say they’ve known for decades is the right way to eat, regardless of dust-ups about eggs and nuts. Both have more unsaturated than saturated fats.
The newer language also loses some of the layers of misdirection that come with talking about nutrients like saturated fats instead of naming the foods — like beef, whole milk, and butter — that we should mostly avoid.
“It’s job security for dieticians,” Ferraro joked. “There is a need for a credible professional to interpret government doublespeak.”
But even clearer language would do more to help Americans select healthier foods. Some continue to justify potato chips as “plant-based foods,” for example.
“People don’t go to the store to buy fiber, salt, and potassium. They go to the store to buy food,” Ferraro said. “I’m glad to see [the government] making more food-based recommendations. That’s helpful.”
So what foods should you eat? Every nutritionist Healthline spoke to said that the Mediterranean diet has been known to be best for at least a decade.
The diet includes vegetables and fruits, legumes and whole grains, some nuts and low-fat dairy, some seafood and chicken, with little added sugar or red meat, “lean” or otherwise.
Adding or subtracting an egg hardly matters. Coffee or no coffee matters even less.
“Basic dietary advice remains the same — constant, but dull,” Nestle wrote in 2002.