By Rachel Johnson, Ph.D, M.P.H., R.D.
One reality of life as a university dean is a never-ending schedule of receptions with generous amounts of tempting food and drink. While standing near a sumptuous hors d’oeuvres table recently, I overheard a fellow faculty member being grilled by his spouse about what he had eaten so far that day. This colleague struggles with his weight, and his wife has clearly assumed a policing role. He dutifully reported fruit and yogurt for breakfast and a turkey wrap with water for lunch.
As his placated wife walked away, he whispered to me that he hadn’t mentioned three after-lunch cookies. Moments later, I saw him down four bacon-wrapped pastries, and I mentally calculated the 300 calories he had just added while his wife wasn’t looking. I figured he would also “forget” to include these snacks in his next report.
This common behavior vexes nutritionists as we try to establish the links between diet and health. We know that many people, even highly intelligent and articulate professionals, don’t accurately report what they eat and drink. Some people list food intakes so low that even if they spent all their time sleeping, they would be losing weight or even emaciated. For example, a 5-foot 9-inch 30-year-old woman who weighs 143 pounds and has an active lifestyle needs about 2,550 calories a day to maintain her weight. If she reports eating only 2,000 calories a day, she should be losing about a pound a week. If she’s not losing weight, there’s a good chance she is what nutritionists label an “underreporter.”
I suspect that most of us have been guilty of this at one time or another, and it’s likely that most underreporting comes from a desire to say what seems acceptable to the person asking. We know that overweight people are worse reporters than lean people, women are worse than men, and as children age they get worse too. Women tend to say they weigh less, while men tend to make themselves taller. People especially underreport the “sin” foods that they “don’t remember” eating: cakes and pies, salty snack foods, soft drinks and fatty spreads. On the other hand, they are quite good at describing their intakes of vegetables and fruits.
Why does this matter?
It can dramatically distort what we think we know about the diet-health connection. A few years ago, a widely publicized study using self-reported food intakes of more than 80,000 women found no link between total fat intake and the development of heart disease. But if the overweight women were more likely than the lean to underreport their intakes of high-fat foods, diet researchers could miss a valid association.
To help with this conundrum in my own research, we speculated that participants might be put off by the size 2, 100-pound graduate students interviewing them. Who would want to fess up about the eight cookies or pint of ice cream in one sitting to such questioners? So we tried phone interviews with an unfamiliar interviewer. People still underreported. We tried an empathetic interviewer of similar size and age to the interviewees. Underreporting remained the same. We’re now in the midst of a study in which our volunteers are using PDAs (personal digital assistants) to record their food intake. We’ll see if this technology helps.
The one question I hear constantly is: “Why can’t I lose weight?” What I say is: “Perhaps you’re not really counting everything you eat. One of the most powerful tools you can use is a food diary. I promise—if you keep an honest diary, it will help!”
We know that people who weigh themselves regularly and record what they eat are more successful at losing weight and maintaining the loss compared with those who don’t perform these tasks. But honesty and awareness count: don’t forget the handful of nuts you grabbed on the run, the milkshake you shared with a friend, the last few bites of dinner you savored while cleaning up the dishes. Most people are surprised at how much unconscious eating they do. At the end of the day, look up the calorie content of everything in your diary (see box). Even if you don’t get it exactly right, you’ll be way ahead of the game. I’m thrilled when people are honest with their dietitian, because they have reached the crucial point of just being honest with themselves.
—Rachel Johnson, Ph.D., M.P.H., R.D.