Development and validation of a photographic food atlas for portion size assessment in the southern plains of Nepal

Abstract

Objective: To develop and validate a photographic food atlas of common foods for dietary assessment in southern Nepal.

Design: We created a life-sized photographic atlas of forty locally prepared foods. Between March and June 2014, data collectors weighed portion sizes that respondents consumed during one mealtime and then a different data collector revisited the household the next day to record respondents' estimations of their previous day's intakes using the atlas. Validity was assessed by percentage error, Cohen's weighted kappa (κ w) and Bland-Altman limits of agreement.

Setting: Dhanusha and Mahottari districts in southern Nepal.

Subjects: A random sample of ninety-five adults in forty-eight rural households with a pregnant woman.

Results: Overall, respondents underestimated their intakes (mean error =-4·5 %). Rice and dal (spiced lentil soup) intakes were underestimated (-14·1 % and -34·5 %, respectively), but vegetable curry intake was overestimated (+20·8 %). Rice and vegetable curry portion size images were significantly reliably selected (Cohen's κ w (se): rice=0·391 (0·105); vegetable curry=0·430 (0·139)), whereas dal images were not. Energy intake over one mealtime was under-reported by an average of 569 kJ (136 kcal; 4·5 % error) using recall compared with the weighing method.

Conclusions: The photographic atlas is a useful tool for field estimation of dietary intake. Average errors were low, and there was 'modest' agreement between weighed and recalled portion size image selection of rice and vegetable curry food items. Error in energy estimation was low but with wide limits of agreement, suggesting that there is scope for future work to reduce error further.

Keywords: Dietary intake; Food atlas; Portion size; Validation.

Fig. 1

Examples of portion size images (not to scale), their sizes (g) and the cut-offs (g) within which a selected image would correctly represent a given portion

Fig. 2

Response rate of households that were randomly sampled in their homes

Fig. 3

Bland–Altman plots assessing the validity of a photographic food atlas of common foods for assessing energy intake among a random sample of ninety-five adults (, pregnant woman; ●, household head; , mother-in-law) in forty-eight rural households with a pregnant woman in southern Nepal, March–June 2014. The difference in energy intake (in kilocalories; 1 kcal=4·184 kJ) between the weighed method and the recall method is plotted v. the mean energy intake from the two methods. ——— represents the mean difference; — · — · — represent the upper and lower limits of agreement (LOA) and – – – – – represent the 95 % confidence interval of the mean difference/LOA. Upper LOA=3456 (95 % CI 2944, 3967) kJ (825·9 (703·6, 948·2) kcal); mean difference =576 (95 % CI 280, 871) kJ (137·6 (95 % CI 67·0, 208·2) kcal); lower LOA=–2304 (95 % CI –2815, –1792) kJ (–550·6 (95 % CI –672·9, –428·3) kcal)

Fig. 4

Bland–Altman plots assessing the validity of a photographic food atlas of common foods for assessing protein intake among a random sample of ninety-five adults (, pregnant woman; ●, household head; , mother-in-law) in forty-eight rural households with a pregnant woman in southern Nepal, March–June 2014. The difference in protein intake (in grams) between the weighed method and the recall method is plotted v. the mean protein intake from the two methods. ——— represents the mean difference; — · — · — represent the upper and lower limits of agreement (LOA) and – – – – – represent the 95 % confidence interval of the mean difference/LOA. Upper LOA=22·7 (95 % CI 19·3, 26·1) g; mean difference =3·7 (95 % CI 1·7, 5·6) g; lower LOA=–15·3 (95 % CI –18·7, –12·0) g

Fig. 5

Bland–Altman plots assessing the validity of a photographic food atlas of common foods for assessing iron intake among a random sample of ninety-five adults (, pregnant woman; ●, household head; , mother-in-law) in forty-eight rural households with a pregnant woman in southern Nepal, March–June 2014. The difference in iron intake (in milligrams) between the weighed method and the recall method is plotted v. the mean iron intake from the two methods. ——— represents the mean difference; — · — · — represent the upper and lower limits of agreement (LOA) and – – – – – represent the 95 % confidence interval of the mean difference/LOA. Upper LOA=4·8 (95 % CI 4·1, 5·6) mg; mean difference = 0·5 (95 % CI 0·1, 0·9) mg; lower LOA = –3·8 (95 % CI –4·6, –3·0) mg