Purpose: It is unclear whether habitual intake of soy or isoflavones induces long-term changes in the concentrations of blood lipids and glycaemia. We examined the associations of soy food and isoflavone consumption with changes in blood lipids and HbA1c concentrations over 5 years among Japanese adults.
Methods: This cohort study included 7252 subjects with no known history of major chronic disease at baseline. Soy intake was measured using a food frequency questionnaire; while the concentrations of serum lipids and HbA1c were measured using standard laboratory methods. We used multivariable linear mixed-effects models to examine the associations of changes in lipids and HbA1c concentrations with intakes of soy food and isoflavones.
Results: Among the participants, mean age was 61 years, 67% were females and median intakes of soy and isoflavones were 95.3 g/day and 47.4 mg/day, respectively. Soy food and isoflavone intakes were not associated with 5-year changes in blood lipids or HbA1c concentrations. However, stratified analyses showed inverse associations between fermented soy intake and serum lipids among obese/overweight subjects. In particular, intake of 20 g/day of natto was associated with a reduction of 1.4 (95% CI 0.3, 2.5) mg/dL in TC, 1.5 (95% CI 0.4, 2.6) mg/dL in non-high-density lipoprotein cholesterol, 1.0 (95% CI - 0.0, 2.0) mg/dL in low-density lipoprotein cholesterol and 4.0 (95% CI 0.6, 7.5) mg/dL in triglycerides.
Conclusions: Overall, habitual consumption of soy or isoflavones was not associated with changes in serum lipids or HbA1c concentrations. The negative associations between intake of natto and changes in serum lipids among overweight/obese subjects deserve further investigation.
Keywords: Cardiovascular disease; Cholesterol; Diabetes; Dyslipidemia; Isoflavones; Soy.