The 24hR-MP camera method, which also used the manual [2] during interviews with participants, was found to be feasible for estimating the intake of foodstuffs and nutrients at a degree similar to that of the WFR method. The correlation coefficient for salt intake was low between the 24hR-camera and WFR methods because intake is difficult to estimate for invisible ingredients such as oils, fats, condiments, and spices. The intake of vegetables was underestimated with the 24hR-camera method compared to the WFR method because in Japan vegetables are frequently consumed after being cooked, which reduces their volume. This was likely a reason why the correlation coefficient for salt was low between the 24hR-camera and WFR methods.
Studies have been conducted that compared 24-hour dietary recall and WFRs. In a 2-day survey of 41 people in China aged 18 to 65 years, no significant differences were observed except for total fat, saturated fatty acid, thiamine, potassium, and magnesium [5]. A 1-day survey of 65 university students in Malaysia aged 18 to 29 years found no significant differences between the methods for measuring energy and nutrients [6]. In a 1-day survey of 58 rural Ethiopian women aged 15 to 49 years, the medians for energy and almost all nutrients were significantly lower in 24-hour dietary recall than in WFR [7]. The correlation coefficients for energy and the three major nutrients (protein, lipid, carbohydrate) between the 24-hour dietary recall and WFR measurements were almost the same as those reported by Marjan et al. [6] but higher than those reported by Xue et al. [5], who adjusted energy.
The 24-hour dietary recall method relies on the memory of a participant, and studies have been conducted using a camera to supplement that memory. In a survey of 45 women aged 20 to 52 years in a rural area of Bolivia, the medians of almost all food groups, except drinks and vegetables, were smaller for the 24-hour dietary recall using camera method compared to the WFR method. The intake values were lower for 24-hour dietary recall using camera than for WFR for almost all nutrients, but Pearson correlation coefficients of nutrition intakes between the methods were high (0.96 or higher) [8]. A 2-day study conducted in England on 10 subjects compared 24-hour dietary recall that used a camera that automatically took photographs in response to movement, heat, and light, with 24-hour dietary recall that did not use a camera [9]. Results demonstrated that “healthy” foods were not over-reported and “unhealthy” foods were not consistently under-reported. Another study showed the effectiveness of dietary assessment using a camera-equipped personal digital assistant and a cell phone card by comparing it with a weighing method. The study subjects were 75 Japanese volunteers consisting of 27 men and 48 women. The study clearly showed that the method was a useful new dietary assessment method [10].
In terms of energy and the three major nutrients (proteins, lipids, carbohydrates), correlation coefficients between our 24hR-camera method and the WFR method were at least 0.80; the correlation was low for salt and potassium, but the coefficients for almost all other nutrients were 0.7 or higher. In a study reported by Lazarte et al. [8], the correlation coefficients of energy and the three major nutrients were 0.96 or higher (at least 0.97 for other nutrients), which showed high correlation, but salt and potassium were not calculated. The difference in correlation coefficients between our study and that by Lazarte et al. was likely attributed to differences in dietary diversity. Furthermore, Lazarte et al. recognized that a limitation of their study was that differences in dietary pattern by individuals were small because the survey was conducted in a low-income nation, which led to easy estimation from the perspective of a nutrition survey. This likely led to the exceedingly high correlation coefficients. In a study with Japanese people, the effectiveness of dietary assessment using a camera-equipped personal digital assistant and a cell phone card was examined by comparing that with WFR, and the correlation coefficients between values obtained by both methods were 0.615 for energy intake, 0.658 for protein intake, 0.773 for fat intake, 0.708 for carbohydrate intake, and 0.408 for salt intake in men, which were lower than those obtained in our study [10]. The authors mentioned that lack of a unified way to take photographs and low quality of digital photographs might cause the decrease in the correlation coefficient. It is considered that we could obtain a high correlation rate because we improved this point. A study comparing 24-hour meal recall and WFR for two days in 41 Chinese people reported a correlation coefficient of 0.76 for energy intake, which was lower than that obtained by us [11].
We compared the 24hR-camera method with the WFR protocol. Using absolute values, the 24hR-camera method produced significantly lower results in the vegetable food group, but there were no significant differences in the other food groups when compared with the WFRs. We also compared intake of the three major nutrients using absolute values. Protein and carbohydrate contents were lower in the 24hR-camera method compared with WFRs. The low protein intake estimation by the 24hR-camera method may have been due to shrinkage in the fish, shellfish and meat groups when cooked. The reduced carbohydrate estimate may be due to a low estimation in the amount of rice consumed. The intake of micronutrients, such as zinc and copper, was also lower with the 24 h R-camera method compared to the WFR method; this may be due to the fact that the absolute intake amounts of these nutrients were small. In addition, there were large differences in the intake of these nutrients in the study population which led to high correlation coefficients but difficulty in obtaining absolute values.
Most dishes in Japan are not made of a single foodstuff but instead contain various ingredients in addition to salt, pepper, oil, and other condiments, as exemplified by stew, stir-fried meat, and vegetables. Therefore, it is difficult for a participant to estimate what he or she has eaten, and this likely explains our study’s lower correlation coefficients compared to the study by Lazarte et al. Despite the difficulty doing the survey of complexed diet, the correlation coefficients of 0.8 or higher for energy and the three major nutrients imply sufficiently high correlation, and suggest that the 24hR-MP camera method is useful for dietary assessment. Additionally, our study was novel because the participants were males, who do not cook on a daily basis, while participants in the Lazarte et al. study were females. Compared to women, men have difficulty evaluating the kind and amount of foodstuff. Therefore, the high correlation, even with male participants, indicated a significant result and implies that this dietary assessment method is also applicable to women.
Regarding the intake of each food group, it is difficult to directly compare our study with that of Lazarte et al., which used a different approach. Our results demonstrated correlation coefficients of 0.7 or higher in almost all food groups except oils, fats, condiments, and spices, which had low correlations of 0.3 to 0.5. The correlation coefficient between the two methods for salt was also low. It is likely the correlation coefficients were low for these ingredients because they are not visible and have to be evaluated by the taste.
Lazarte et al. investigated fewer food groups than our study and did not evaluate oils, fats, condiments, or spices. Their participants consumed much fewer vegetables (a median of 52 g) than did the Japanese (372.0 g on average) who participated in our study. Japanese also eat vegetables but are generally accustomed to eating them cooked. Considering that cooking reduces the volume of vegetables, our participants probably underestimated the total intake, which was likely to have resulted in underestimation of potassium intake. The study by Lazarte et al. did not assess potassium.
Taking photographs of actual meals before and after eating is likely to help individuals estimate the correct intake (including leftovers) and prevent them from forgetting to record what they ate or drank [12–20]. One advantage of the camera for a surveyor is that it enables correct assessment of nutrient intake. The amount (in weight base) of foods taken is estimated by the following procedures in 24-hour dietary recall method and 24hR-camera method: 1) Make a distinction between breakfast, lunch, supper, snack, and late-night snack; 2) name each dish; 3) presume food components that make up the dish; 4) classify the food components into the component listed in the Standard Tables of Food Composition in Japan, in principle; 5) presume seasonings and condiments used; and 6) estimate wet weight of foods taken. Because the 24hR-camera, it has the following advantages in the above-mentioned steps: 1) Distinction between breakfast, lunch, dinner, snack, and late-night snack becomes clear; 2) the name of dishes can be objectively determined by an investigator; 3) the food components that make up a dish can be objectively determined by an investigator ; 4) the food can be more accurately classified into the food listed in the standard tables of food composition; 5) the type and usage of seasonings and condiments can be confirmed; and 6) weight or wet weight of foods can be more accurately estimated as compared with the 24-hour dietary recall method. Therefore, the 24hR-camera method is expected to estimate the intakes of food, energy and nutrients more accurately than 24-hour dietary recall method. Since it is customary for many people to take photographs easily with a mobile camera nowadays, taking photographs before and after eating is not that big of a deal.
There have been studies to validate a method that combined 24-hour dietary recall and use of photo atlas during participant interviews by comparison to the WFR method [21–23]. These studies confirmed that the combination method was useful for participants. Similarly, we were able to obtain high correlations in food groups as well as nutrients because we used the manual [2] during interviews and implemented a method of taking photographs before and after each meal.
One limitation of our study was that it had a relatively small sample size. However, the number of patients (n = 30) had a statistical power of 80% with a significance level of 5% to detect a true correlation coefficient of 0.5 and most of the correlation coefficients in this study were larger than it. It is significant that we were able to assess salt and potassium, which are crucial to the prevention and treatment of lifestyle-related diseases, such as stroke and coronary heart diseases, but it is also a limitation of this survey method that correlations of these nutrients were lower compared to other nutrients. We did not confirm the reproducibility of the test methods in this study, and it is future subjects.
The strength of this study was that we developed a dietary assessment method to evaluate male participants who eat Japanese-style meals that commonly have diverse foodstuffs cooked in diverse ways (boiled, stir-fried, deep-fried, etc.), but who also regularly eat Western-style foods such as hamburger steak and stew, as well as Chinese, Spanish, and French cuisines. There is a large variety of food and food preparation in Japan, and thus it is difficult to accurately assess meal intake. The methodology imposed a relatively small burden on participants, as evidenced by 100% participation in the survey. Finally, because the results from this study pertain to meals consumed under regular life conditions, the method is likely to be feasible for the assessment of daily diet and the results would be internationally comparable.