To reduce the burden of cardiovascular disease (CVD), the leading killer of post-menopausal women in the US, dietary programs like the AHAD have focused on lowering the fat content of the blood (hyperlipidemia), but a low-fat, high-carbohydrate diet can increase the glycemic load, which has been argued to adversely affect heart health.
The new study, published in the February issue of the journal Nutrition (Vol. 22, pp. 104-113), looked at comparing the AHA step-1 diet with a low glycemic index diet (LGID) supplemented with 30 grams of soy protein (containing 34 mg isoflavones) and 4 grams of phytosterols, delivered as a beverage that was also rich in vitamins and minerals.
The soy isoflavones were genistein, daidzein and glycetein, while the phytosterols present were betasitosterol, campsterol, stigmasterol and brassicasterol.
The scientists from the Functional Medicine Research Center of Mutagenics Inc., the company that also produced the fortified beverage, randomly assigned 30 women to the LGID group, and 29 women to the AHAD group.
The participants had an average age of 55, and a body mass index of 32.5 kg per square meter, meaning that they were all clinically obese and at higher risk of CVD. Both groups started with high levels of total cholesterol (tChol), low-density lipoprotein (bad) cholesterol (LDL-C), and triacylglycerols (TG).
By collecting three-day diet records at week 2, 4, 8 and 12, it was found that 73 per cent of the LGID group had adhered to the dietary guidelines, and 69 per cent of the AHAD group had been compliant.
"After 12 weeks on the program, the LGID group showed significant decreases in tChol (15.8 per cent), LDL-C (14.8 per cent), and TG (44.8 per cent), whereas the AHAD group showed no significant decrease in tChol or LDL-C," reported lead author Dan Lukaczer.
High-density lipoprotein (good) cholesterol (HDL-C) rose significantly in the LGID group, but not the AHAD group.
"In our study, the LGID program resulted in a 5.6 per cent increase in HDL-C over 12 weeks, which corresponds to a 11 to 17 per cent decrease in risk [of death or myocardial infarction]," wrote Lukaczer.
"Recent discussion suggest the addition of specific foods such as phytosterols and soy protein in addition to dietary changes for successful non-pharmacological intervention of hyperlipidemia.
The differing mechanisms of action of phytosterols and soy proteins suggest they may be additive or even synergistic," reported the researchers.
Phytosterols have been shown to reduce cholesterol absorption while soy isoflavones can decrease hepatic cholesterol synthesis.
To suggest that the beneficial effects of the beverage supplement is due to the soy proteins and/or the phytosterols alone, appears somewhat premature, however, given the presence of all the vitamins and minerals in the beverage.
The indication that the effect may be synergistic appears valid, but synergy with certain vitamins and minerals cannot be discounted on the basis of this study.
Indeed, Jeffery Bland, president and chief science officer of Metagenics Inc. said: "The results of this study should open the door for more focus on specific nutrients in the development of successful insulin and lipid management programs, and not just the number of calories as fat, protein, or carbohydrate in the program."
According to the American Heart Association, some form of heart disease affects 38.2 m women, equal to 33.9 per cent of the adult female population.
The direct costs of CVD from hospital, doctors, home care, and medication in the US is a staggering $258 bn, with a further $145 bn as indirect costs from lost productivity.