3.2 Estimating Energy Intake

As discussed previously, a bomb calorimeter can be used to measure the number of calories or heat energy found in food. However, this is not practical for everyday use. Tracking what you eat through for a period of time is the most common method of estimating energy intake. There are several methods of tracking nutrient and energy intake (1), but all require recording what has been eaten so that it can be entered into a nutrient analysis program.

• A 24 hour recall is a method of recording food intake that requires the individual to remember all foods and beverages consumed during the past 24 hour period (or the last day). Though not the most accurate way to collect information, it can provide a general idea of an individual’s eating habits and a rough estimate of caloric intake for this snapshot in time. Multiple 24 hour recalls would be necessary to get an accurate picture of energy intake over a longer period.
• The most useful and common method of obtaining information on caloric intake is a 3, 5, or 7 day food record. This requires the individual to keep a record of all foods and beverages for a more extended period of time. Foods and beverages should be logged as soon as possible after consumption and condiments, snacks, and bites from a friend’s plate should all be recorded to obtain the most accurate information. If a 3 day record is used, it should include 2 weekdays and 1 weekend day. If a 5 day record is used then 3 weekdays and 2 weekend days are preferred. Many people eat differently on the weekends than on the weekdays so including both give a more accurate and comprehensive view of energy and nutrient intake.

Once a food log has been kept, the foods can then be entered into a nutrient analysis program. Nutrient analysis programs average the intake of kcals and other nutrients over the total time frame. Some apps can serve as both a food record and nutrient analysis program. MyFitnessPal is a popular app and website that individuals can use to track the foods they eat and see how many calories and macronutrients they consume over time. Cronometer is another app and website where users can enter foods they eat and see how their diet over time compares to the nutrition recommendations that were discussed in chapter 2. Using an app like these can be beneficial because most people have their smartphone with them at all times and can enter foods into the program immediately.

The accuracy of a food record or 24 hour recall is highly dependent on the accuracy and detail provided by the individual keeping the record. The most accurate information would come from weighing and measuring all foods and beverages consumed. For most people this is an unrealistic expectation. Therefore, we have to expect a rather large margin of error when people are “guesstimating” portions. For example, many people don’t know what 3 oz of chicken looks like compared to 6 oz of chicken. When filling out a food record, these people are likely to choose the default serving size regardless of what they actually ate. If the individual is not recording the food as they eat it, it is likely the estimated serving will be even less accurate and foods are more likely to be omitted. Other factors that will reduce the accuracy of a food record or 24 hour recall are the omission of condiments, beverages, snacks, and licks of the spoon or tastes when cooking. It is estimated that when keeping food records, most people underestimate their caloric intake by 10-20%.