Dietary data in the Southampton Women’s Survey

Learn more about the Southampton Women’s Survey (SWS) and its dietary measurements

Summary of cohort
Dietary data collection
Estimation of nutrient intake
Response
Key findings

Summary of cohort

The Southampton Women’s Survey (SWS) is a prospective cohort study of mothers and their children. The cohort began as a study of non-pregnant women aged 20-34 years registered with a general practitioner in Southampton between 1998 and 2002 [114]. A total of 12,583 women (75% of all women contacted) were interviewed. A sub-group of women who did not become pregnant were followed-up two years after their initial interview (n=94) [115]. Women who became pregnant after the initial interview were invited to take part in the pregnancy phase of the survey at Southampton Princess Anne Hospital at 11, 19 and 34 weeks gestation. By the end of 2007, 3,158 singleton live babies had been born to these women [116]. To date, these babies have been followed up with home visits at 6 months, 1, 2, and 3 years. Due to the study design, the data from the children are collected over a range of years. A sub-sample of children were examined at 4 years, 6-7 years, 8-9 years and 11-13 years.

The initial aim of the study was to examine maternal factors affecting fetal growth. This goal has widened to include the effects on post-natal and early childhood growth. Diet and body composition have been the main focus of this study with additional information such as physical activity, lifestyle and social circumstances also being collected [114].

Dietary data collection

The SWS collected dietary information from both women and their children using three methods: FFQ, prospective food diaries and 24-hour recalls. The most commonly used DATs were FFQs. All questionnaires outlining the dietary assessments can be found at: https://www.mrc.soton.ac.uk/sws/for-researchers. The table below outlines the methods and timing of these DATs.

Women’s diets

During the initial home visit and at 11 and 34 weeks’ gestation, research nurses assessed dietary intake during the preceding three months using a 100-item FFQ. The foods or food groups included in the FFQ were based on their ability to contribute at least 90% of the macronutrients, iron and vitamin C in the diet based on published data [117].

Women reported their average frequency of consumption of each food group using the following responses: (1) never, (2) once every 2-3 months, (3) once per month, (4) once per fortnight, (5) 1-2 time per week, (6) 3-6 times per week, (7) once a day or (8) more than once per day (with the option to specify the number of times per day). Prompt cards with lists of foods included in food groups were used to ensure standardised responses. The amount of milk and sugar consumed daily over the last three months as well as the average portion size of bread and potatoes were also recorded. The frequencies of consumption of foods not listed on the FFQ were recorded if they were consumed ≥1x/week.

The 100-item FFQ was used during a home visit to record the dietary intake of the sub-group of non-pregnant women two years after the initial interview to assess stability of dietary patterns over time. In addition to the FFQ, participants were asked ‘Have there been any major changes to your diet since we saw you two years ago?’ and if ‘yes’, details of the changes were recorded.

Children’s diets: 6 to 12 months

At approximately 6 and 12 months, an FFQ and details of the child’s milk-feeding history over the prior 6 months as reported by their main caregiver (usually the mother) were recorded by research nurses. Breast milk intake was estimated from the reported duration of breast-feeding at each feed [118] and the age of introduction to solid foods was recorded.

Two infant FFQs were developed using a variety of dietary information sources. The list of foods to be included was compiled using information from a nationally representative sample of children aged 18 months [97], the weighed food diaries of preterm infants aged 6 and 12 months [119], infant-feeding literature and dietary data from women in Southampton [120]. This food list was refined after a 24-hour recall of a sample of infants and through piloting [121].

At 6 months, a 34-item FFQ was administered to capture average frequency and amount of listed foods consumed over the 7 days preceding the interview. Responses included the number of times the food/food group was consumed over the past week, the brand and amount consumed in household measured.

At 12 months, a 78-item FFQ was administered to capture the listed foods over the month preceding the interview. Responses included: never, 1-3 times per month, 1 to 7 times per week, more than once a day (with the option to specify the amount of times per day).

For both the 6 and 12 month FFQs, prompt cards listing foods included in each food group were used at both ages to ensure standardised responses and portion sizes were recorded in household measures and with the aid of food models. Participants were also asked to report frequencies of consumption and amounts of any foods that were not listed in FFQ if they were consumed once a week or more.

In addition to these FFQs, a 24-hour diet recall was conducted in the whole sample at 6 months and a 4-day weighed food diary was conducted among fifty mothers of 6 month olds, and fifty mothers of 12 month old babies [122, 123].

Children’s diets: 3 to 11 years

At 3 years diet was assessed using an 80-item FFQ administered by research nurses to the main caregiver (usually the mother [124]). As with the FFQ in infancy, the food list was compiled from a variety of sources including: a review of dietary intake data from a nationally representative sample of children aged 3 years [125], the SWS infants [121], the SWS adults [117], and 3 year old children in the Avon Longitudinal Study of Pregnancy and Childhood [110]. The food list was refined during the piloting stage.

The average frequency of consumption of food and beverage items over the preceding three months was recoded with the following eleven possible responses: (1) never, less than once/month, (2) 1-3 times /month, (3-10) number of times per week, (11) more than once/day (with the option to specify the amount of times per day). Prompt cards with lists of examples of foods included in each food group were used. Portion sizes were recorded in household measures. There was space to record frequency of consumption of foods not listed in the FFQ if they were consumed once a week or more. The amount and type of milk, teaspoons of sugar added to food and drinks and dose and frequency of supplements were also recorded.

At the end of the visit at 3 years, the caregiver was invited to complete a 2 day prospective food diary on behalf of the child which was returned using a prepaid envelope. In this, they recorded all food and drinks consumed by the child from midnight the day following the interview until midnight two days later. Weight, size or household measures were used to quantify the amounts consumed. Details on brand name, meal ingredients and cooking methods were recorded. Dietary supplements during this two day period were also recorded. The relative validity of the FFQ was assessed in comparison to the 2-day food diaries among 892 children in the SWS [124].

The main caregiver also completed an FFQ based on the 3 year FFQ on behalf of the child at 6-7 years. A short FFQ was used to assess diets of children at 8-9 years and 11-13 years.

Overview of dietary assessment in SWS

Time point	Women	Women	Child	Child	Child	Child
	100-item FFQ	24-hour food diary	Milk-feeding history	FFQ	24-hour recall	Food diary
Before pregnancy	✔	✔
Sub-group of 94 non-pregnant women in repeatability study	✔
Early pregnancy (11 weeks gestation)	✔	✔
Late pregnancy (34 weeks gestation)	✔
Child age 6 months			✔	✔ (34-item)	✔	✔ (4-day diary among validation subsample)
Child age 12 months			✔	✔ (78-item)		✔ (4-day diary among validation subsample)
Child age 3 years				✔ (80-item)		✔ (2-day prospective)
Child age 6-7 years				✔ (80-item)
Child age 8-9 years				✔*
Child age 11-13 years				✔*

Notes.
*Short FFQ.

All questionnaires used in collecting the dietary data can be found at: https://www.mrc.soton.ac.uk/sws/for-researchers
Responses to women’s 100-item FFQ based on the preceding three months: never, once every 2-3 months, one per month, once per fortnight, 1-2 times per week, 3-6 times per week, once a day, more than once per day.
At 6 months, the 34-item FFQ was based on the preceding 7 days. Responses were: number of times the food/food group was consumed over the past week, the brand and amount consumed in household measured.
At 12 months, the 78-item FFQ was based on the preceding month. Responses were: never, 1-3 times per month, 1 to 7 times per week, more than once a day.
At 3 years, the 80-item FFQ was based on the preceding three months with the following eleven possible responses: (1) never, less than once/month, (2) 1-3 times /month, (3-10) 1-7 times/week, (11) more than once/day.

Estimation of nutrient intake

Following the process outlined in Estimating nutrient intakes from DATs, where portion sizes were not reported in the FFQs, standard portion sizes were assigned based on children’s portion sizes where appropriate. Nutrient intakes were then calculated by multiplying the weight of the portion by its nutrient content as obtained from McCance and Widdowson’s the composition of foods 5^th edition and its supplements [25, 39, 70, 71].

Response

Response to dietary measures in SWS

Phase	Respondent	N interviewed	Response to at least one diet question
Initial Interview	Non-pregnant women	12,583	12,572 FFQ
Initial Interview	Non-pregnant women	12,583	8,089 Food Diary
Early pregnancy	Women	2,867	2,270 FFQ
Late pregnancy	Women	2,649	2,649 FFQ
6 months	Child	2,959	1,869 FFQ
6 months	Child	2,959	2,010 24-hour recall
1 years	Child	2,875	2,206 FFQ
3 years	Child	2,625	2,625 FFQ
3 years	Child	2,625	893 Food Diary
6-7 years	Child	2,034	2,032 FFQ
8-9 years	Child	1,214	1,213 FFQ
11-13 years	Child		1,067 FFQ*

Notes.
*As of April 2019.

Key findings

Dietary patterns of women

The SWS has a unique study design that facilitates the examination of women’s diets both before and during pregnancy as well as their offspring’s dietary intake. An interesting finding from the SWS that takes advantage of the study design, is that women who become pregnant within 3 months of the initial interview were not more likely to comply with recommendations for planning a pregnancy compared to those who did not [126]. Although women who became pregnant reduced smoking, alcohol consumption and caffeinated drinks there was little change in their adherence to fruit and vegetable recommendations [127]. These findings suggest that more work on promoting dietary recommendations for women of childbearing is required.

One of the major pieces of work using these dietary data has been the identification of dietary patterns (DPs). A consistent DP termed the ‘prudent’ DP was identified using principal component analysis (PCA) of the women’s FFQ data. This diet is high in fruit, vegetables, wholemeal bread, pasta, yoghurt and breakfast cereals and low in chips and roast potatoes, sugar, white bread, red and processed meat, full-fat dairy, crisps cakes and biscuits and soft drinks [128]. Higher educational attainment was found to be the most important influence on adherence to the prudent DP [120]. In a subgroup of non-pregnant women, adherence to the prudent DP remained relatively stable over a two year period [115].

Dietary patterns of children

PCA was also applied to the children’s FFQ data at 6 and 12 months. The main DP identified was one that is high in fruit, vegetables and home-prepared foods (the ‘infant-guidelines’ DP). The DPs at 6 and 12 months were correlated and a higher adherence to this DP was associated higher maternal educational attainment, lower maternal BMI, older mothers and those who are non-smokers and watch television less [121]. Children who adhered to this infant-guideline DP were also found to gain weight and skinfold thickness more rapidly from 6 to 12 months [129] and have higher scores for full-scale and verbal IQ at 4 years [130]. Maternal diet was a major influencer on adherence to a prudent DP at 3 years [131].

Validation of DATs

There have been a number of validation studies. In papers comparing dietary data from FFQs among women and children with food diaries, estimated nutrient intakes were slightly higher from FFQs [117, 122, 124]. However, the ranking of individuals in quartiles according to estimated nutrient intakes was similar between FFQ and food diaries [117, 124]. Furthermore when compared to serum vitamin C as a biomarker, the percentage of women classified into the correct quartile for intake was similar for the FFQ and food diaries [117]. The ‘prudent’ dietary pattern identified using PCA from FFQs and food diaries from women in early pregnancy in the Princess Anne Hospital study was similar, providing further evidence for the ability of the FFQs to accurately classify individuals according to their dietary pattern [132]. The FFQ data from the women were used to derive a shorter 20-item FFQ that has the ability to characterise a prudent dietary pattern which could potentially be used in future studies lacking time and resources and because it limits participant burden, making it easy to use among hard to reach groups [133].

Learn about the other studies covered by this guide and their dietary measurements:

Get background detail on this guide:

Learn about harmonisation in the context of dietary data:

Discussion & illustration of dietary data harmonisation

Further information:

This page is part of the CLOSER resource: ‘A guide to the dietary data in eight CLOSER studies’.