We studied 3,462 subjects from three independent American cohorts (FOS, GOLDN and Boston-Puerto Rican studies). shows demographic, anthropometric, clinical, biochemical, dietary and lifestyle characteristics of participants according to the APOA2
−265T>C SNP for each population. Prevalence of CC subjects did not differ between FOS (15%) and GOLDN (15%). A statistically significant lower prevalence (10.5%) was found in the Boston-Puerto Rican study. Demographic characteristics and physical activity did not differ between CC and T-allele carriers in either of the three populations (). Among White populations, prevalence of obesity was higher in GOLDN. Likewise, mean fat intake, mainly SATFAT was higher in GOLDN than in FOS. No significant association of the APOA2
−265T>C SNP with HDL-C was found in either of the three populations. APOA2 and APOA1 concentrations were only determined in FOS. In FOS, plasma APOA2 concentrations (Supplemental Table 1
) were significantly lower in CC subjects, whereas no effects were observed for APOA1, supporting the functionality and specificity of this SNP.
General characteristics of the studied populations depending on the APOA2 −265T>C polymorphism
We next examined in FOS our previously described association between the APOA2
SNP, food intake and body-weight. In FOS we also found that CC subjects had higher energy intake than T-allele carriers (P=0.017) (). These results were consistent with our previous finding in GOLDN showing that daily energy intake was ~200 Kcal/d higher in CC subjects than in T-allele carriers (P=0.005). However, the magnitude of the genotype effect was lower in Framingham (~100 Kcal/d), and differences in total fat intake, SATFAT, and monounsaturated fatty acids (MUFA) did not reach the statistical significance as they did in GOLDN. This difference could be due to the higher prevalence of obesity, total fat and SATFAT intake in the GOLDN population (). Therefore, we hypothesized that the APOA2
SNP would have a greater influence in determining food intake in obese subjects. Consistent with this notion, we found that obese CC subjects from FOS had statistically higher intakes of energy, total fat, SATFAT, MUFA, protein, carbohydrates and fructose than T-allele carriers (Supplemental Table 2
). The greater carbohydrate and fructose intake in obese CC subjects from Framingham compared to those of GOLDN, could reflect a greater intake of fruit and cereals in those Framingham subjects to satisfy their higher appetite, possible due to the CC genotype, at the same time as following a healthy diet. Further adjustment for physical activity did not affect the statistical significance of results.
Moreover, in the Framingham population as a whole, the CC genotype was not associated with higher BMI or obesity as previously observed in GOLDN (). In view of the different dietary fat intakes between these populations, we focused on gene-dietary fat interactions. We found a statistically significant interaction between total fat and the APOA2 SNP (P<0.05). However, on analyzing the different fat types, the interaction was stronger and more significant for SATFAT, indicating a more specific effect of this variable, and then we focused on SATFAT. When we considered SATFAT as continuous in FOS (), CC subjects exhibited a higher association (B=0.108 Kg/m2; P=0.006) than carriers of the T-allele (B=0.033 Kg/m2; P=0.026) between SATFAT intake and BMI (P for interaction=0.021). Thus, the impact of increased SATFAT intake on BMI increase was most noticeable for CC individuals, with the crossing point between the two regression lines at 22g/d of SATFAT, which was approximately the population mean. We next assessed the relationship of the APOA2 SNP with BMI, stratified according to these levels of SATFAT (). We also detected a statistically significant interaction term (P=0.013) between the APOA2 SNP and SATFAT intake as categorical. Among those within the lower SATFAT strata (<22g/d), the APOA2 SNP was not significantly associated with BMI (P=0.224). In contrast, the CC genotype was associated with greater BMI (~4.3%; P=0.025) in the higher SATFAT strata. Further adjustment of this interaction for physical activity did not alter the statistical significance of results (P<0.05). Furthermore, in FOS we examined whether the APOA2-SATFAT interaction is influenced by plasma APOA2 concentrations. Thus, the basic model was adjusted for APOA2 and we found that the significance of the interaction term remained practically unchanged (P=0.012).
Interaction between the APOA2 -265T>C polymorphism and SATFAT intake on BMI in the Framingham Study
To verify the internal replication of this gene-diet interaction, we analyzed BMI data from 1,087 subjects who attended Framingham examinations 1 through 5 (20 years of follow-up). When the interaction with SATFAT was not considered, no differences in BMI were observed depending on the APOA2 SNP at any exam (). However, if two strata of SATFAT intake were considered (assuming a similar fat intake strata across the exams), a statistically significant interaction between the APOA2 SNP and SATFAT (P=0.035) on BMI across the 20-year follow-up was noted (). Thus, consistent with the results observed for exam 5, CC subjects present a higher BMI than the other genotypes throughout the 20-year follow-up period, only when they have a high saturated fat consumption.
Due to the relevance and novelty of this gene-diet interaction, we examined its replication in GOLDN. Considering the two categories of SATFAT (below and above 22 g/d) that we considered in Framingham, we consistently found the same statistically significant interaction whether considering the unadjusted model or the multivariate basic model (P=0.009) (). Further adjustment of this basic model for family relationships (P=0.040) or for physical activity (P=0.007) did not alter the statistical significance of results. Given that this GOLDN population consumes a higher SATFAT-diet, the APOA2 SNP was generally associated with higher BMI. However, this observation was not present in GOLDN subjects with a low SATFAT intake (P=0.447). In contrast, the CC genotype was strongly associated with greater BMI in subjects with a high SATFAT intake (~6.4%; P=0.002).
Interaction between the APOA2 − 265T>C polymorphism and SATFAT intake on BMI in the GOLDN Study
Further internal replication of this interaction was obtained from separate analyses of the Minnesota- and Utah-based subjects ().
Furthermore, we investigated the replication of this gene-diet interaction in an ethnically different population of US-Hispanics of Caribbean origin living in Boston. We consistently found a statistically significant interaction between the APOA2
SNP and SATFAT on BMI (basic models) whether SATFAT was considered as continuous (P=0.003) or as categorical (P=0.002) (). After additional adjustment for physical activity, the interaction terms remained statistically significant (P=0.004 and P=0.001, respectively). These results were totally in accordance with our previous findings in Whites. Thus, in the Boston-Puerto Rican study, when SATFAT intake was high, CC subjects also had significantly higher BMI than carriers of the T allele (~7.9%; P=0.021). Moreover, further adjustment of basic models for admixture (27
) did not change the statistical significance of the interaction terms (P=0.006 and P=0.003, for continuous and for categorical SATFAT variables, respectively).
Interaction between the APOA2 -265T>C polymorphism and SATFAT intake on BMI in the Boston-Puerto Rican Study
Considering that in the Boston-Puerto Rican population prevalence of diabetes was high (42%), we analyzed if the APOA2-SATFAT interaction was present in both diabetic and non-diabetic subjects. The internal replication of this interaction was also obtained (P for interaction <0.05 in each group, results not shown).
Finally, we examined the APOA2-SATFAT interaction in determining obesity in the three populations independently and pooled in a meta-analysis (). We found consistent gene-diet interactions across all three populations. The CC genotype was only associated with a higher obesity in subjects in the high-SATFAT stratum. If SATFAT consumption was low, the CC genotype was not associated with obesity. In the meta-analysis, we observed no significant heterogeneity either for the high-SATFAT (I²=0%, P=0.899) or for the low-SATFAT stratum (I²=0%, P=0.548). The overall association meta-analysis in the high-SATFAT group showed a statistically higher OR of obesity for CC homozygotes of OR: 1.84 (95%CI: 1.38, 2.47; P<0.0001), using the fixed effect model. However, in the low-SATFAT group no increased OR for obesity was found for CC homozygotes in comparison with carriers of the T allele (OR =0.81; 95%CI:0.59-1.11; P=0.181).
Interaction between the APOA2 -265T>C polymorphism and SATFAT intake in determining obesity risk in three independent populations (the Framingham Study, the GOLDN Study and the Boston-Puerto Rican Study)