Is Your Nutrition Tank Full? Dietary Assessment vs Biomarkers
Imagine this scene. You are going out the door to drive to see family or friends during the holidays. Other people drive the same vehicle. As you approach it, you wonder: do I need to buy gas? What would you do? 1) Go back inside to ask available drivers when they last purchased gas and how much they spent. 2) Check the fuel gauge in the car. My reason for asking is to force you to contemplate nutrition assessment.
Because of convenience and cost, dietary assessment is the most frequent approach. Kilpatrick and colleagues conducted a systematic review of studies measuring food environments and at least one functional outcome. Fifty-one papers were identified. In 2/3 of them, only 1-2 questions were used to assess intake. Unbelievably, most studies asked only 1 question. About 10% used 24 hour recalls. Tow percent used food diaries.
Food surveys, especially brief ones, lead to errors in estimating food intake and nutritional status. Archer and associates reported that food energy intakes reported by most men and women are not physiologically plausible. They attributed this to bias among individuals when reporting food intake and inaccuracies in nutrient databases. We know from experience that the amount of gas currently in a shared vehicle depends upon the number of gallons of gas added to the car and the miles driven afterwards. And like EPA fuel economy values for a vehicle, the caloric impact of a diet depends upon conditions of use.
By looking at a fuel gauge, you know if gas needs to be purchased. Similarly, biochemical measurements are a more accurate assessment of nutritional status. Fortunately, there is one nationally representative biochemical assessments for 58 indicators (CDC’s Second Nutrition Report). Having biochemical indicators elevates science from opinions on the effects of lifestyle factors, the characteristics of people who volunteer for nutrition randomized controlled trials (RCTs) and their compliance to fact-based assessment of individual nutritional status.
In nutrition we need fewer pharmaceutical-like RCTs (comparing placebo against treatment) and more studies applying biochemical indicators to assess nutritional status. Because everyone eats and has some level of nutritional status, researchers shouldn’t be testing whether randomization to a nutrition intervention, eg vitamin E or placebo (Miller et al, 2005), affects outcome. Rather, they should be trying to understand why people with serum α-tocopherol concentrations of 30 µmol/L have the lowest risk of mortality (Wright et al. 2006) and how many people (what proportion) have this vitamin E status.
Kirkpatrick SI, Reedy J, Butler EN, Dodd KW, Subar AM, Thompson FE, McKinnon RA. Dietary assessment in food environment research: A systematic review. 2013 Am J Prev Med doi: 10.1016/j.amepre.2013.08.015
Archer E, Hand GA, Blair SN. Validity of US nutritional surveillance: National Health and Nutrition Examination Survey caloric energy intake data, 1971-2010. 2013 PLoSONE doi: 10.1371/journal.pone.0076632
Guallar E, Stranges S, Mulrow C, Appel LJ, Miller ER. Enough is enough: Stop wasting money on vitamin D and mineral supplements. 2013 Ann Intern Med doi: 10.7326/0003-4819-159-12-201312170-00011
Miller ER, Pastor-Barriuso R, Dalal D, Riemersma RA, Appel LJ, Guallar E. Meta-analysis: High-dosage vitamin E supplementation may increase all-cause mortality. 2005 Ann Intern Med doi: 10.7326/0003-4819-142-1-200501040-00110
Wright ME, Lawson KA, Weinstein SJ, Pietinen P, Taylor PR, Virtamo J, Albanes D. Higher baseline serum concentrations of vitamin E are associated with lower total and cause-specific mortality in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study. 2006 Am J Clin Nutr 84:1200-1207