Objective: To examine the effect of Seventh-day Adventist (SDA) membership on ‘immunity’ to the secular effects of changes in BMI.

Design: Three independent, cross-sectional, screening surveys conducted by Sydney Adventist Hospital in 1976, 1986 and 1988 and a survey conducted among residents of Melbourne in 2006.

Subjects: Two hundred and fifty-two SDA and 464 non-SDA in 1976; 166 SDA and 291 non-SDA in 1986; 120 SDA and 300-non SDA in 1988; and 251 SDA and 294 non-SDA in 2006.

Measurements: Height and weight measured by hospital staff in 1976, 1986 and 1988; self-reported by respondents in 2006.

Results: The mean BMI of non-SDA men increased between 1986 and 2006 (P

Conclusion: The ‘prudent’ dietary and lifestyle prescriptions of SDA men appear to have ‘immunised’ them to the secular effects of changes that occurred among non-SDA men’s BMI. The dietary and lifestyle trends of SDA women did not reflect the increase in their BMI observed in 2006.