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Science & the Public

Janet Raloff
Science & the Public

Pernicious influences on dietary choices

Many economic, sensory and lifestyle factors can subtly influence food consumption

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New data confirm what many of us have secretly known: We don’t eat wisely — either in terms of what menu items we select or how much food we eat. Of course, people are probably not ignoring the food-pyramid recommendations and consumption guidance of federal nutritionists so much as paying rapt attention to the siren calls of foods we have evolved to prize.

There’s plenty of evidence to indicate that because humanity developed during eons of cyclical feasts and famines, we survived by chowing down on energy-dense foods when they became available. Which today is all of the time.

But a number of recent studies point to additional, less obvious influences on what and how much we choose to eat.

For instance, Adam Drewnowski of the University of Washington and his colleagues have for years been linking dietary choices and food costs. On a weight basis, grains and fats tend to be quite affordable. So it should come as no surprise, they’ve noted, that low-income families tend to rely on wheat, corn and fat as dietary staples at home — and the basis of entrees purchased in fast-food restaurants.

In a new paper, Drewnowski now analyzes the market prices for more than 1,375 foods on a per-calorie basis. Again, grains, sugars and fats were about the cheapest; fruits and veggies proved comparatively expensive. His findings appear in the American Journal of Clinical Nutrition, available online ahead of print.

“The fact that healthful foods cost more than less healthy options is a formidable real-world challenge for nutrition interventions,” he points out. “No wonder that many of us would prefer to focus on intricate personal preferences and other psychosocial factors.”

University of North Carolina scientists recently provided some quantification of a growing trend that also threatens to jeopardize healthful eating — snacking. They point to federal survey data showing that a little more than three decades ago, some three-quarters of American adults ate a snack on at least one of the two days during which they had been surveyed. By around 2005, the share who snacked had jumped to 97 percent, Carmen Piernas and Barry Popkin reported in the February 2010 Journal of Nutrition. And 78 percent of those surveyed around 5 years ago snacked on both days that they had been surveyed — almost twice the rate seen in the ‘70s.

Two additional studies have focused on ways a high-fat diet can inadvertently fool us into downing excess calories.

In one, a Dutch study published in the Journal of Nutrition early last year, people ate somewhat more — about 8 to 9 percent more calories throughout the day — if they had been unaware that their lunch had been especially high in fat. In this experiment, people appeared to semi-consciously compensate for a high-fat meal when they knew that they’d over-consumed. Take away the sensory cues to overindulgence and they may not recognize when they’ll need to cut back on calories later, Mirre Viskaal-van Dongen and her colleagues at Wageningen University say.

Researchers in China and at the Harvard School of Public Health in Boston took a different approach and compared hormone-signaling responses by the body to meals rich in carbohydrates — sugars and starches — versus dietary fat. In both cases, the meals had the same number of calories. In the July 2009 Journal of Nutrition, they showed that high-carb meals shut off the hunger signal better and longer than did a high-fat meal. And the study’s obese participants were less likely to get a hormonal signal of satiety than were its lean diners.

Such findings are in line with what I reported five years ago on lifestyle issues that can affect hunger and satiety signals. Back then, I quoted David Cummings of the University of Washington in Seattle as finding evidence in both animals and people “that one of the mechanisms behind weight gain typically associated with high-fat diets is that they don't suppress the hunger hormone as well [as low-fat fare]."

Bottom line: Emerging data show there are many economic, sensory and lifestyle factors (like too little sleep) that can subtly influence food consumption.

Citations

A. Drewnowski. The cost of US foods as related to their nutritive value. American Journal of Clinical Nutrition, in press. doi: 10.3945/ajcn.2010.29300

C. Piernas and B.M. Popkin. Snacking iIncreased among U.S. adults between 1977 and 2006. Journal of Nutrition, Feb 2010; Vol. 140, p. 325. doi:10.3945/jn.109.112763.


M. Viskaal-van Dongen et al. Hidden fat facilitates passive overconsumption, Journal of Nutrition, Vol. 139, February 2009, p. 394. doi:10.3945/jn.108.096123


N. Yang et al. Impaired ghrelin response after high-fat meals is associated with decreased satiety in obese and lean Chinese young adults. Journal of Nutrition, Vol. 139, Jul 2009, p. 1286. doi:10.3945/jn.109.104406

Further Reading

S.M. Krebs-Smith. Americans do not meet federal dietary recommendations. Journal of Nutrition, Vol. 14October 2010, p. 1832. doi:10.3945/jn.110.124826 0,

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