Examining the interaction of fast-food outlet exposure and income on diet and obesity: evidence from 51,361 UK Biobank participants

Table 5 Additive interaction between quartiles of fast-food outlet proportion and household income on the odds of frequent processed meat consumption^a (more than once per week), modelled using a binomial logistic regression model in the Greater London UK Biobank sample, UK (n = 51,090)

	Quartiles of fast-food outlet proportion^b								Fast-food outlet exposure (Q4) within household income strata
	Q1 (0–13%)		Q2 (13–17%)		Q3 (17–24%)		Q4 (24–45%)
Household Income (£/year)	More than once/once or less (n)	OR (95% CI)	More than once/once or less (n)	OR (95% CI)	More than once/once or less (n)	OR (95% CI)	More than once/once or less (n)	OR (95% CI)
> 100,000	653/1756	ref ^c	401/1103	0.95 (0.82, 1.10); P = 0.495^d	253/623	1.06 (0.89, 1.27); P = 0.502^d	177/414	1.11 (0.90, 1.37); P = 0.335^d	1.19 (0.93, 1.54) P = 0.158^e
52,000–100,000	782/2274	0.98 (0.86, 1.11); P = 0.742^d	860/2172	1.13 (1.00, 1.29); P = 0.047^d	788/1769	1.22 (1.07, 1.39); P = 0.003^d	790/1622	1.34 (1.17, 1.54); P < 0.001^d	1.39 (1.20, 1.62) P < 0.001^e
31,000–51,999	593/1798	1.06 (0.92, 1.21); P = 0.418^d	695/1960	1.12 (0.99, 1.28); P = 0.079^d	785/1963	1.25 (1.10, 1.42); P = 0.001^d	902/1975	1.41 (1.24, 1.61); P < 0.001^d	1.31 (1.12, 1.54) P = 0.001^e
< 31,000	842/2526	1.17 (1.03, 1.33); P = 0.015^d	1036/2799	1.29 (1.14, 1.46); P < 0.001^d	1277/3253	1.38 (1.22, 1.55); P < 0.001^d	1423/3350	1.46 (1.29, 1.65); P < 0.001^d	1.29 (1.13, 1.46) P < 0.001^e
Household income (< £31,000/year) within takeaway exposure strata		1.11 (0.97, 1.28) P = 0.117^f		1.27 (1.09, 1.48) P = 0.002^f		1.30 (1.09, 1.56) P = 0.003^f		1.45 (1.18, 1.78) P < 0.001^f

Measure of interaction (fast-food exposure*household income with odds of processed meat consumption) on a multiplicative scale based on a likelihood ratio test, P = 0.725 | Measure of interaction on an additive scale for Q4 fast-food exposure and household income < £31,000 (RERI) = 0.18. RERI scores > 0 suggest positive interaction and departure from additivity | ORs are adjusted for age, sex, ethnicity smoking status, number in household, highest education attainment, UK Biobank assessment centre attended, and the sum of counts of Supermarkets, Restaurants, Convenience stores, Cafes and Specialist Stores within 1 mile Euclidean (straight line) radius buffers of home address | ^a Includes bacon, ham, sausages, meat pies, kebabs, burgers, chicken nuggets | ^b Q1 = quartile with lowest fast-food outlet proportion in home neighbourhood (min – max %) – Q4 = quartile with greatest fast-food outlet proportion in home neighbourhood (% range) | ^c Single reference group; those exposed to the highest proportion of fast-food outlets and with the highest household income | ^d ORs and p values relative to single reference group (ref) | ^e ORs and P values relative to those who were least exposed to fast-food outlets within strata of household income | ^f ORs and P values relative to those with the highest household incomes within strata of fast-food outlet exposure