Grab any newspaper and you’re almost certain to read that “according to the latest study…” you’re going to die from something — everything — you enjoy eating. But let the buyer beware: these headlines are rarely justified. Supposedly “conclusive” science can flip so dramatically that we’re frightened silly about a food item on one day, and then encouraged to eat plenty of it on the next. Yet many honest scientists warn against overreaction to the usual food scares. When faced with studies attempting to tie a particular food with disease, they tell us to ask: “Where’s the beef?” Harvard Medical School’s Marcia Angell, the former editor-in-chief of the New England Journal of Medicine, argues: “Science has hardly begun to touch the big mysteries about diet and other habits. We simply do not know much about what is risky and what isn’t, and what we do know is often distorted or misinterpreted.”
An article published in the American Journal of Clinical Nutrition (AJCN) offers a giant grain of salt for the next over-hyped food scare study. Its strongly worded conclusion warns: “In the future epidemiologists should not feel compelled to make too many recommendations or to state them with more certainty than they deserve.”
Consider just a few ways the AJCN says these frightening studies can be fatally flawed:
It’s the dose that makes the poison
“[M]any dietary factors are weak and do not show linear dose-response relations with disease risk within the range of exposures common in the population.” Newspaper readers are treated to a steady diet of articles fretting over minute concentrations of substances found in fish. For example, one recent headline warned: “More chemicals found in farmed salmon than wild.” That may be enough to spook the average reader into a fish-free diet. You would have had to get several paragraphs into the story to know a top health official advised that we don’t consume nearly enough fish-borne chemicals to warrant concern, saying: “There’s no reason to change eating patterns, whether it’s wild or farmed salmon, as far as we’re concerned based on all of the data we’ve collected, they’re both safe to consume.”
“Several controversies are fed by imprecision and bias in nutritional assessment methods, uncertainty about the ability of statistical methods to identify meaningful independent effects of nutrients, and difficulty in choosing among the many hypotheses that could be tested.” Of the many notorious food scares over the last few years, the Center for Science in the Public Interest’s (CSPI’s) attempt to worry consumers about the chemical acrylamide stands out for its unbelievably shoddy methodology. CSPI made the ridiculous claim — since rebuffed by a top panel of National Institutes of Health experts — that dietary acrylamide causes 8,900 U.S. cancers a year. To arrive at that number, CSPI acknowledged that it arbitrarily “adjusted [USDA] consumption data” on Americans’ intake of nine categories of foods. CSPI also quietly conceded that its chosen method of estimating cancer risk is outdated. And it knowingly underestimated the average American body weight by more than 7 percent, which resulted in an overestimation of dietary acrylamide’s theoretical carcinogenic effects. CSPI was too busy fiddling with figures to simply mention that no evidence has ever shown a negative health effect of acrylamide in humans.
Consider the source
“Firmly held opinions can create ethical belief systems that can cloud our interpretations.” “Firmly held opinions” drive anti-fat warriors who see sin where the rest of us see soda. Those with possibly clouded interpretations include obesity researcher and fat-tax advocate David Ludwig, who publishes anti-soda and anti-fast-food studies that lead to outrageous and unfounded headlines. Ludwig has complained of an “invasion of our diet by soft drinks, fast foods and high calorie, poor quality snack food.” His ilk may not be able to generate compelling evidence, but they manage to alarm millions of consumers.