Metabolic effects of soy in post menopausal women.
Cardiovascular disease increases with advancing age and with the menopause transition in women. Specifically menopause is associated with changes in several metabolic cardiovascular risk factors including increased abdominal fat, decreased insulin sensitivity, decreased adiponectin and increased circulating inflammatory markers such as tumour necrosis factor (TNF)-[alpha].
This study investigated whether a daily soy supplement would reduce abdominal fat and improve measures of glucose and insulin metabolism when compared with a casein placebo in a population of obese non diabetic Caucasian and African American menopausal women.
Thirty nine postmenopausal women (age 45-60 years) were recruited and randomised to either soy or placebo arms: 16 randomised to placebo (8 African American, 8 Caucasian) and 17 randomised to soy (8 African American, 9 Caucasian). Participants were excluded if they had diabetes mellitus, consumed a strict vegetarian or low fat diet, consumed a diet high in fibre or soy, or if there was a weight change of >10 pounds (4.5 kg) within the previous 12 months.
Intervention was administered as a shake taken twice daily. The shakes contained 120 calories, 2.5 g fat, 7 g carbohydrates, 600 mg calcium, 500 mg phosphorus, 320 mg sodium, 560 mg potassium and 3 mg iron. The treatment group had shakes with an additional 20 g soy protein and 160 mg isoflavones (96 mg as aglycones). The placebo contained 20 g casein protein and no isoflavones.
Compliance with the supplements was established by measuring serum isoflavone levels at baseline, 4 weeks, 8 weeks and 12 weeks. As expected isoflavone levels increased significantly for the treatment group compared with placebo, with increases of 265% in serum genistein and 10 044% in serum daidzein compared with no changes with placebo (P<0.02).
Three days prior to testing volunteers were given a standardised diet to follow in which meals contained 55% carbohydrates, 30% fat and 15% protein. On the subsequent morning following a 12 hour fast researchers performed a hyperglycaemic clamp. Plasma glucose was also measured. There were no significant differences in first or second phase insulin secretion between treatment groups over time. However second phase decreased in the soy group (-2188 [-11 000 to 5540] pmoL/min).
A four day food record was collected for each participant at the beginning and end of the intervention period and analysed by registered dieticians. Participants' weights were checked twp weeks post enrolment, at 1 month and 2 months. Neither self reported physical activity nor macronutrient intake changed significantly between groups during this short term study.
Inflammatory markers and adipokines were measured using a multiplexing xMAP technology with a Luminex 100 Analyzer. Soy supplementation decreased interleukin (IL)-6 by 2.5% compared witho an increase of 7.1% with placebo (P<0.03). Other markers including CRP and TNF-[alpha] were not significantly different suggesting the supplement may not exert a generalised effect on inflammation.
Regional and total fat mass, percent fat and lean mass was determined using dual energy x-ray absorptiometry. The treatment group significantly reduced total abdominal fat by 7.5% (-58.8 [+ or -] 162.6 [cm.sup.2]) and subcutaneous abdominal fat by 9.1% (-46.9 [+ or -] 136.7 crtf) (P<0.0167), while the placebo showed an increase of 8.8% (56.5 [+ or -] 70.0 [cm.sup.2]) in total abdominal fat and 10% (50.8 [+ or -] 65.2 [cm.sup.2]) in subcutaneous abdominal fat (P<0.0088). African American women in this study lost more weight than Caucasian women who had a great incidence of reduced visceral fat. Serum lipids (total cholesterol, HDL, LDL and triglycerides) were measured at baseline and at three months. These showed no significant change.
This study showed that a daily soy supplement reduced subcutaneous and total abdominal fat and decreased second phase insulin secretion when compared with an isocaloric casein placebo. However the sample size was small and duration short so further investigation is warranted.
Kathleen Murphy MNHAA