Why is self-reported data so unreliable? Do people just have bad memories or lie about how much they eat?
We can’t tell whether or not people are deliberately misreporting. We are a body image-conscious society and people might tend to not report as much intake of high energy, fatty foods and desserts, without even being consciously aware of it.
But it’s not a matter of finding who to blame. The research issue concerns the whole set of tools that are used for dietary assessment. We can’t just rely on what’s been done; there are well-documented problems with current approaches. It’s time to try additional approaches, along with what’s already being done.
What would you do differently?
We sometimes have the ability to assess short-term dietary intake reliably through the use of objective measures in urine or blood or other body fluids. Established biological measures, or biomarkers, can assess the intake of total proteins, mostly expressed as nitrogen in the urine. Similarly, sodium and potassium can be recovered in the urine, although it might take a few days of urine collection for precise estimation. There is also an excellent, but rather expensive, biomarker of the short-term consumption of total energy (calories).
Some studies use self-reported diet with an objective measure that correlates with the dietary factor under evaluation but does not actually assess intake. These measures can be useful, but they usually do not provide a reliable assessment of actual intake.
Intake biomarkers would be a more accurate way to determine what a person really ate so you could more accurately measure dietary impact on their health?
Biomarkers, if they’re actually reflecting intake, could be used for reliable disease association studies by themselves, if you have stored specimens for deriving these measures.
Drs. Johanna Lampe, Marian Neuhouser, other Hutch colleagues and I published a paper last year that did just that for some vitamin A and vitamin E-related micronutrients. We conducted a feeding study that used intake biomarkers, derived from blood micronutrient concentrations and study participant characteristics obtained routinely in a subset of more than 5,000 women in the Women’s Health Initiative study to accurately estimate short-term micronutrient consumption.
We then examined these biological assessments of intake to subsequent chronic disease risk.
The micronutrients we studied in the research, published in the American Journal of Clinical Nutrition, included alpha-carotene [found in yellow-orange and dark-green veggies like carrots, sweet potatoes, squash, broccoli, spinach, green beans and collards]; beta-carotene [found in yellow-orange fruits like cantaloupe, mangoes, papayas and dark-green veggies like kale and spinach]; carotenoids such as lutein plus zeaxanthin, or L+Z, [plant chemicals found in bright red, yellow and orange fruits and veggies like squash, carrots, grapefruit, oranges and apricots] and alpha-tocopherol or vitamin E [commonly found in seeds, nuts, leafy green veggies and vegetable oils].
What did you find?
We found that somewhat lower risks of specific cardiovascular outcomes, breast cancer and diabetes were associated with a higher intake of alpha- and beta-carotene; that a lower risk of diabetes was associated with higher L+Z intake; and that elevated risks of certain cardiovascular outcomes were associated with a higher intake of alpha-tocopherol, or vitamin E. Additionally, we showed that suitable biomarkers can be calculated from blood specimens obtained in large cohorts and applied directly in disease-association analyses.
That’s pretty cool. Are you doing more of this biomarker-driven nutritional research?
Our research group is also studying small molecules that circulate in body fluids, seeking novel dietary markers. We’re working in collaboration with Dr. Dan Raftery, a metabolomics expert from the Hutch and the University of Washington Medical School.
And we’re strongly advocating for a much larger research enterprise to identify intake biomarkers for other components of diet. We still have a very short list, but this approach could be a big part of the answer.
So it’s not that our nutritional guidelines are wrong. We absolutely know that eating lots of processed foods and sugar is unhealthy. It’s just the data we have leaves too much “wiggle room." Do we need to do more? Ban junk food from advertising on TV like they did with cigarettes in the '60s?
There’s a lot of improvement needed in the American diet. Poor quality diets are likely a big part of the reason we have such high risks for various chronic diseases. Yes, there might be a need to ban bad food ads.
Even though we may need to continue to depend substantially on observational studies to answer the many diet and chronic disease questions of importance, we can learn from research on cigarette smoking and its impact on the risk of lung cancer and various other chronic diseases, which also relied on observational data.
But cigarette smoking epidemiology is much simpler since there are many nonsmokers, never-smokers and smokers. With diet, you don’t have never-eaters. Everybody has to consume calories. Furthermore, the human diet is such a complex mixture of nutrients, foods and practices that it becomes a difficult challenge to identify what might be bad and what might be beneficial. A lot of the notions about what’s good and bad in the dietary guidelines are reasonable, but it just can’t be said to be based on a convincing body of evidence.
In summary, there’s a great need for the development of additional intake biomarkers, perhaps using metabolomics [the study of small molecules, metabolites, and how they interact with cells and tissues], microbiomics [the study of microorganisms found in, say, the human gut or mouth] or other high-dimensional platforms. Doing so may be able to help us avoid another 50 years of uncertainty concerning the impact of diet on the risk of various cancers and other chronic diseases.
