Background: Diet and lifestyle are the primary channels in prevention of weight gain and type 2 diabetes, as well as being implicitly involved with body mass index (BMI). The literature on dietary factors related to obesity and type 2 diabetes has continued to expand, but little research has focused on Asian populations. Furthermore, debate over the optimal BMI range in Asians has become an important public health question in need of more thorough investigation. The objective of this dissertation is to investigate the associations between dietary patterns, weight gain and risk of obesity, dietary patterns and risk of type 2 diabetes, and BMI and all-cause mortality in 61,000+ middle aged Chinese men and women in the Singapore Chinese Health Study (SCHS). Methods: This dissertation includes three separate research projects aiming to investigate how dietary patterns associate with weight gain and risk of obesity (1), type 2 diabetes incidence (2), and how BMI is associated with all-cause mortality (3). In the first and second projects dietary patterns were derived using principal components analysis. The first project examined how these patterns along with a western fast food index associate with weight gain and risk of future obesity. The second project examined how the dietary patterns were associated with incident type 2 diabetes. Proportional hazards regression was used to characterize the prospective associations with incident obese status and type 2 diabetes. The last project also utilized proportional hazards regression along with a non-parametric trend graph analysis to investigate the association between BMI and all-cause mortality.
Results: Results for the three projects were as follows: (1 and 2) two main dietary patterns were identified. A pattern characterized by high consumption of vegetables, fruit, and soy foods with some fish and seafood was termed vegetable, fruit and soy rich (VFS). The other dietary pattern was characterized by high consumption of dim sum, fresh and processed meats, higher relative intake of noodles and rice dishes, and some sweetened and deep fried foods and was termed dim sum and meat rich (DSM). 1) An increasing VFS dietary pattern score was associated with lower levels of weight gain and an increasing DSM pattern score was associated with increasing weight gain and risk of future obesity, relative risk (RR) of obesity for 4th and 5th vs. 1st quintile of DSM pattern score (1.59 and 1.62). Additionally, each increase in frequency of western fast food consumption was associated with a mean increase in weight gain. 2) Compared to the lowest quintile of VFS dietary pattern score an inverse association with type 2 diabetes was observed in quintiles 2-5, (RR= 0.80, 0.83, 0.75, 0.81). In the main models for the DSM pattern the RR increased similarly in quintiles 2-4 and was further heightened in quintile 5 compared to the 1st quintile (RR= 1.21, 1.17, 1.27, 1.55). The associations persisted after adjustment for all potential confounders including BMI and were limited to non-smokers. 3) In an optimal model of disease-free non-smokers excluding early deaths (< 5 years follow up time) there was a U-shaped association between BMI and all-cause mortality. Compared to the BMI referent group with the lowest mortality rate (18.5-20 kg/m2) persons with a BMI < 18.5 were at increased risk of premature death (RR=1.41; 95% CI 1.12-1.76), as well as persons with a BMI 26.0-27.4 (RR=1.31; 95% CI 1.05-1.63) and BMI 27.5, (RR=1.49; 95% CI=1.22-1.83). Further analyses suggest that the association observed at the low end of the BMI spectrum was driven by persons > 65 years of age with BMI < 17.0.
Conclusions: These results indicate that higher intake of a dietary pattern rich in vegetables, fruits, soy and some fish and seafood is beneficial for weight maintenance and a decreased risk of future type 2 diabetes. On the other hand, higher intake of a dietary pattern rich in consumption of dim sum, meat, sweetened and deep fried foods was associated with increased weight gain, along with increased risks of future obesity and type 2 diabetes. Consideration of the association of BMI with all-cause mortality found a U-shaped association, with BMI from the normal range through the middle range of overweight status (18.5-26) not associated with risk of premature all-cause mortality. As obesity and diabetes become more prevalent in Asia, it is important that future research continues to address and provide data with which Asian populations can identify, in regards to diet and lifestyle. Continued and further sound methodological research is needed that assesses how direct and indirect measures of adiposity associate with chronic disease, mortality, and cause-specific mortality in order to make appropriate public health recommendations in relation to what an optimal weight range may be in Asians.
University of Minnesota Ph.D. dissertation. July 2009. Major: Epidemiology. Advisor: Dr. Mark A. Pereira. 1 computer file (PDF); x, 183 pages. Ill. (some col.)
Etiology of weight change, Type 2 diabetes, and mortality in adult Chinese Singaporeans: the Singapore Chinese health study..
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