School of Social and Community Medicine University of BRISTOL Longitudinal analysis of diet in...

School ofSocial and Community Medicine

University ofBRISTOL

Longitudinal analysis of diet in ALSPAC

Laura D HoweEUCCONET, Bristol, October 2011



Outline

Trajectories of energy intake and macro-nutrients

Planned analysis

Very preliminary results



120

01

400

160

01

800

200

0m

ean

kca

l

3 5 7 9 11 13Age (average age at measurement)

Diet diary FFQ



50

60

70

80

me

an fa

t int

ake


Diet diary FFQ

45

50

55

60

65

70

me

an p

rote

in in

take


Diet diary FFQ

160

180

200

220

240

260

me

an c

arb

ohy

dra

te in

take


Diet diary FFQ

40

50

60

70

80

90

me

an 'u

nhea

lthy'

sug

ar in

take


Diet diary FFQ



Data issues

Different # measures per individual Exact ages of measurement vary FFQ and diary data

Want a full trajectory that is comparable for all individuals

Want to reduce the dimensionality of the data



Multi-level models:Random-slopes model

Effect of time varies between individuals (u1i)

The model estimates:The regression coefficients a and b Individuals intercepts (a + u0i)

Individual slopes (b+u1i)The covariance between the intercept and slope

yij = a + u0i + (b+u1i)tij + eij

yij=weight for individual i at occasion j, time tij



Multi-level models in pictures!

kCal

Age

Average regression line



Multi-level models in pictures!

kCal

Age



But the real world isn’t always linear...

Model the data as a curve?

Model the data as piecewise linear?



What shape?

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01

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01

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200

0m

ean

kca

l


Diet diary FFQ



Raw data1

000

200

03

000

400

0kc

al

3 5 7 9 11 13occ



120

01

400

160

01

800

200

02

200

kCal

3 5 7 9 11 13Age, years

female male



Next steps

Include adjustment for over-reporting

Repeat for fat, protein, carbs, unhealthy sugars

Repeat for energy-adjusted fat, protein, carbs, unhealthy sugars



Using the models: diet as the exposure

Individual-level residuals = how an individual deviates from the normal

Use in standard regression techniques

Obesity NAFLD Cardiovascular risk factors etc



Using the models: diet as the outcome

Include the exposure in the multilevel models

e.g. SEP For each category of SEP, allow:

1. Different intercept

2. Different slope in each period



120

01

400

160

01

800

200

02

200

Kca

l, m

ale

s

3 5 7 9 11 13Age, years

< O-Level O-LevelA-Level Degree



120

01

400

160

01

800

200

0K

cal,

fem

ale

s

3 5 7 9 11 13Age, years

< O-Level O-LevelA-Level Degree



Acknowledgements

Emma Anderson Kate Tilling Debbie Lawlor ALSPAC nutrition team

School of Social and Community Medicine University of BRISTOL Longitudinal analysis of diet in...

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