Is Self-Reported Diet Data Good Enough for Nutrition Science?

By Colby Vorland

Southwest Airlines is consistently rated as serving good food on their flights, yet they don’t serve food at all. Can we trust diet data if people don’t know if they even ate? This amusing anecdote was offered by Dr. David Allison at the following session during ASN’s Scientific Sessions in San Diego in April: “Not Everything That Counts Can be Counted and Not Everything That Can Be Counted Counts: How Should We Collect Dietary Data for Research?” chaired by Drs. Regan Bailey and Claire Zizza. The session was organized by ASN’s Nutritional Epidemiology, Aging/Chronic Disease, and Community/Public Health RISs. The panel took a critical perspective but also emphasized the value in using self-reported diet intake data.

Dr. Allison was the first presenter, taking a hard position on self-reported energy intake in nutritional research: it just isn’t good enough. Not only that, it often flat-out misleads obesity research. Allison highlighted a recent paper by Archer and colleagues that looked at energy intake of respondents in NHANES from 1971-2012, finding that 67.3% of women and 58.7% of men were not physiologically plausible – i.e. the number of calories is “incompatible with life.” Correlations with the IOM’s gold standard equation for estimating total energy expenditure were 0.163 for women and 0.225 for men, effectively yielding no meaningful relationship. This “doesn’t seem like science anymore,” Allison stated. This problem has been known for a long time: in 1991, Goldberg and others looked at 37 studies across 10 countries and found that over 65% of the mean ratio between reported energy intake and basal metabolic rate measures were implausible. Forrestal also published a review in 2010 of 28 papers looking specifically at children and adolescents, finding that about half misreport energy intake.

It is time to abandon self-reported energy intakes in favor of less misleading paths in obesity research, Allison said. It is not worthy of scientific use because the measurement errors are not random and modest, estimates are often not in the correct direction, and errors will not lead to the detection of false effects under plausible circumstances. He told a story of how originally, self-report intake data suggested that the overweight consumed less energy than they expended, but using more rigorous methods proved exactly the opposite to be true (here is a 1990 review by Schoeller). Allison said that we currently have no economic and social incentive to make a complete transition to incorporating doubly labeled water, as the cost has been flat since the 1980s. It will be painful initially, but clearly we need to make the transition.

Dr. Amy Subar argued that energy intake is not the only important aspect of diet data, and improvements are being made to collection methods, and therefore we shouldn’t throw the baby out with the bathwater. Even if total energy intake isn’t accurate, we still can track food patterns, diet quality, nutrient intakes, and social and physical environments. Subar emphasized the utility of self-reported data- it can yield more comprehensive data with much less of an investigator burden compared to biomarkers or observation, but there is the issue with error. Within-person variation and memory are 2 potential errors, but adjustments are possible. New technologies, such as keeping food records with mobile phones or wearable sensors to reduce reactivity to monitoring and burden, are being developed to improve self-report data. In addition, Subar has been involved in the development of self-administered 24-hour recalls – ASA24 – to be able to gather a lot more data from participants without investigator burden. They have validated the accuracy of this method against interviewer-administered recalls. Dr. Subar noted that food frequency questionnaires have more bias than short-term methods but combining multiple recalls with food frequency questionnaires could reduce this.

Dr. Elizabeth Yetley expanded on how self-reported diet data is currently relied on in national policy. For example, fortification strategies would not be possible without such data. Many considerations go into fortification, and modeling specific foods and evaluating the outcomes of such programs are important. The IOM uses diet data to track added sugars and salt disappearance. Nutrient safety can also be tracked. For example, data from the Total Diet Study in 1981 was able to quickly identify unexpected iodine sources in the food supply that were resulting in extremely high intakes. Diet data is also used for food additive/GRAS reviewing, to examine what has been added vs naturally occurring. Yetley states that there would be a significant adverse effect on policy if intake data wasn’t available. However, intake data can fail to accurately predict nutrient status, as Pfeiffer et al. (2012) have demonstrated. In 1988, Lewis and colleagues showed that cola intake could be underestimated by about 50%, though Yetley notes that surveys have been improved since then. Iron fortified cereals also virtually always underestimate the actual intake when using the amount listed on the label. Self-reported intake using label data is therefore not accurate. Infrequently consumed foods such as alcohol beverages also cause problems in nutritional epidemiology. However, Dr. Yetley reiterated that it is still crucial for many uses and we can work to improve precision while using caution when interpreting.

Finally, Dr. Laurence Freedman discussed some studies that are being done to improve self-reported intake measurement. Freedman began by emphasizing that we can do validation for some nutrients by comparing to recovery of biological products; for example, using doubly-labeled water for energy expenditure, nitrogen for protein, potassium and sodium for themselves. The error is indicative of true intake. However, for many we don’t have accurate recovery products. Freedman described a project he is involved in – the Validation Studies Pooling Project – that aims to better understand measurement errors of food frequency questionnaires and 24-hour recalls using recovery biomarkers. For example, in the AMPM study, energy intake is underreported on 24-hour recalls by about 10%, but underreporting of intake differs by nutrient. Measurement error effects diet-health outcomes by attenuating relative risks and statistical power. This attenuation is expressed as an “attenuation factor” – the ratio of attenuation to the actual value. Preliminary data shows that attenuation factors are more extreme for energy intake compared to protein, and protein density is less so than both. Adjusting datasets from energy intake alleviates attenuation factors somewhat but does not solve it, and increasing samples size does not itself solve it because of unknown confounding. Freedman went into more detail about the ASA24 (multiple 24-hour recalls) – emphasizing that they have a high response and low attrition. With 3 or more recalls, the attenuation factor for protein improves. Relative risks increase with additional recalls compared to 1 food frequency questionnaire, and combining both methods yields even better data according to Carroll and colleagues (2012). Combining biomarkers with self-report data improves statistical power because measurement error is reduced, as Freedman and others (2011) have shown. Dr. Freedman reiterated that self-report data is extremely useful for surveillance, education, dietary guidance apart from the difficulties of using it to measure energy intake.

It is clear that self-reported diet data has many important uses, but caution must be accepted when interpreting it. Hopefully improvements that are currently being validated will be adopted quickly, and for some measures such as energy intake, it seems necessary that current methods be abandoned because we know they are unacceptable.

EB 2014: The Underappreciated Role of Intestinal Fat Storage

By Colby Vorland, Student Blogger

Could a “fatty intestine” be related to insulin resistance and energy balance? These and other provocative questions were addressed by Dr. Elizabeth Parks during ASN’s Scientific Sessions in San Diego. Organized by the Energy and Macronutrient Metabolism Research Interest Section, Dr. Parks gave a seminar titled, “Going with your gut: Individual responses in dietary fat absorption.”

Dr. Parks’ research often focuses on the cephalic phase of digestion – or the early physiological response before food is even ingested. She presented a story that led her to her current path: Teff and Engelman demonstrated in 1996 with a sham feeding model that taste has an important effect on glucose metabolism and, in 2002, Robertson and colleagues published data showing that, compared to a high fat meal, consuming a high carbohydrate meal at night resulted in better glucose tolerance in the morning. Concurrently, they demonstrated a high fat meal at night yields a better fat tolerance the following day. These data suggest that there is some adaptive priming occurring and that, as Dr. Parks put it, “you best metabolize what you’ve just eaten.” She noted that we need to better match the challenge test with the eating pattern of interest.

In 2003, Robertson and colleagues published the results of an experiment in 10 healthy participants scheduled for an endoscopy who were fed a high fat meal, then 5 hours later were fed 50 grams of fat with either 38 grams of glucose or water. The participants who consumed the glucose along with the fat in the second meal showed less lipid in the jejunum. In other words, some dietary fat was stored in the intestine from a meal and its release was accelerated when glucose in combination with fat was consumed. Since then, Dr. Parks and others have shown that simply tasting fat without ingesting it, or just consuming carbohydrate, can cause an early rise in chylomicron secretion and blood triglyceride levels. This means that the intestine stores some of the fat from previous meals; in fact, Parks estimates that ⅕ to ¼ of the fat in your meal is stored in the intestine for at least 16 hours, and it is released in response to taste. Their data also suggests that body fat is negatively correlated with the amount of fat coming from the intestine and entering the blood at a subsequent meal. If intestinal fat stores serve a regulatory function to control energy balance (by releasing in response to taste), this raises the possibility that the mechanism that controls how much is release is perturbed.

Parks then discussed research supporting that we can taste fat. As further evidence, they have scoured literature for kinetic data and devised a mathematical model to show that rate of release of fat from the gut is consistent with the idea that this physiological response is due to our ability to taste fat. She also noted that chylomicrons may be supported in the absence of dietary fat by fatty acids in circulation entering the enterocyte, being packaged into chylomicrons, and secreted. Some data suggest that high free fatty acids increase the contribution from plasma to chylomicrons.

Dr. Parks has also been asking: does the rate of fat absorption impact health? Dr. Jennifer Lambert and Parks have unpublished data showing that the time-course of triglyceride absorption between people can vary substantially – about 1 to 4 hours. She showed graphs of the fat absorption curves of individual participants, and the patterns were often variable, emphasizing that much remains to be understood about why this occurs. Finally, she showed that stratifying by an early or late absorption peak revealed differences in participants in each group. For example, participants with an early peak tended to be more insulin resistant than those with a later peak.

Dr. Parks has been innovative in her use of stable isotopes for exploring lipid metabolism in health and disease. Clearly the intestine is an underappreciated tissue in fat storage and we are just on the cusp of understanding the role in which it mediates health and energy balance.

YPIG Asks: What’s the Winning Formula to Careers?

By Debbie Fetter, Guest Blogger

It was an early start to the “Successful Scientist: What’s the Winning Formula” session hosted by ASN’s Young Professional Interest Group (YPIG) on April 29, but it was well worth it. The five panel members were pleased with the great turnout of young professionals at the early hour. Regan Bailey, PhD, RD, a Nutritional Epidemiologist from the National Institutes of Health, set the relaxed tone for the session by exclaiming, “If you are able to make it to an 8:00 a.m. session as a student, then you’re already more successful than I was!” The attendees laughed and knew they were about to get the rare opportunity to interact with and receive priceless advice about varying career paths with the well-established panel.

Dr. Bailey proceeded to give the audience instrumental information; such as apparently there really isn’t a set way to land a government job. She reiterated the importance of networking, especially with those who could teach you. The best-kept secrets to finding a career path are serendipity and an open-mind. Also, bars in Copenhagen are a great place to hang out. That’s where Dr. Bailey ran into a prior contact and he ended up helping her get a job. You never know who may become a vital connection and help you discover your calling. This is why people are the best resource in the entire world and you should “be yourself; unless you are mean, then be nice.” It’s also important to get involved and to stay involved (i.e., professional organizations: hint, hint, ASN). Finding your balance is key, and Dr. Bailey reassured us with, “If ‘Plan A’ didn’t work. The alphabet has 25 more letters! Stay cool.”

Marion B. Sewer, PhD from the University of California, San Diego was the next panel member to speak. Dr. Sewer told the attendees to embrace failure, since many will criticize–if the bottle of scotch hidden in your drawer is not sufficient, this may not be the career for you. Surround yourself with personal cheerleaders that understand how difficult this field is. Be a team player, but learn to say “no” to protect your time to be successful. To all the perfectionists in the crowd, Dr. Sewer said, “Sometimes, 70% is good enough.”

After, Michael L. McBurney, PhD, FACN from DSM Nutritional Products, put in his two cents. Trust and reputation are earned, not given. Accumulate knowledge and expertise–know your science. It also probably takes about 10,000 hours to become an expert, so might as well start now. Work well with others and do what you do with intent. Most importantly, when you go on sabbatical, go somewhere warm.

Connie M. Weaver, PhD from Purdue University, followed with an eye-opening thought, “Aiming for success is the wrong aim point, it’s not your goal. Your goal is to be of value and to like what you’re doing.” She also emphasized the significance of interdisciplinary interfaces and to explore unfamiliar areas. This is the pathway to discovery.

The last panel member, Brian Wansink, PhD from Cornell University, told us to think of your career as chapters and each chapter could offer something different. He shared his observation that the single best predictor of success is “the number of papers you co-author and submit with a productive professor while you are in residence.” Dr. Wansink let us all in on the secret that the fourth times actually the charm. He ended with, “If my Dean knew how much I loved this job, he wouldn’t pay me.” We can all hope to find a career we are passionate and excited about; that’s definitely something to strive for.

An open panel followed and more advice was given. Finding a way to turn negative energy into something positive was a common theme. Dr. Bailey suggests exercise for stress release. “There’s nothing a good run can’t cure,” she offers. Moving forward is important for success, Dr. McBurney told attendees. If the study didn’t work, find out why and try again. It’s also critical to set some “me” time. Dr. Weavers suggests budgeting it in, like an appointment. Dr. Sewer spends her “me” time doing home improvement. “Stress equals a new bathroom,” she shares and the audience laughed.

In terms of figuring out your passion, Dr. Sewer said to pay attention to how you feel when you’re doing different activities to discover what you value in a career. Dr. Wansink recommends getting involved in as many projects as possible while in graduate school to explore different areas and to build your skill set. Dr. Sewer feels the winning formula to success is what works for you and keeps you motivated and excited. Never be afraid to change if you’re unsatisfied. Dr. Weaver told the attendees to find a way to be of value, and with that you will be happy. Dr. McBurney shared that life is a series of choices, some good, some bad, and no job is perfect. It’s far better to work for a great boss at a mediocre company than a mediocre boss at a great company. Dr. Wansink identified people in academics, who had a huge impact and attempted to find a commonality. He found they all not only dedicated a lot of time to their work and worked hard, but they took a seemingly strange risk that magnified their impact. Don’t be afraid of what others may think of you, if you want to take on a project that interests and entices you, do it. The real secret is there are many paths to success, you just have to find your own.