BackgroundFoods with a low glycemic index (GI) may provide a variety of health benefits. The objective of the present study was to measure the GI and insulin index (II) of select soy foods.MethodsThe study was conducted in two parts with low-carbohydrate products being tested separately. In Experiment 1, subjects averaged 23.2 years of age with BMI = 22.0 kg/m2, while subjects in Experiment 2 averaged 23.9 years of age with BMI = 21.6 kg/m2. The reference (glucose) and test foods were served in portions containing 10 g of carbohydrates in Experiment 1 (two test foods) and 25 g of carbohydrates in Experiment 2 (four test foods). Subjects consumed the reference food twice and each test food once. For each test, subjects were instructed to consume a fixed portion of the reference food or test food together with 250 g of water within 12 min. Blood samples were collected before each test and at 15, 30, 45, 60, 90, and 120 min after consumption of reference or test foods to quantify glucose and insulin. Two-hour blood glucose and plasma insulin curves were constructed and areas under the curves were calculated. GI and II values for each subject and test food were calculated.ResultsIn Experiment 1, both low-carbohydrate soy foods were shown to have significantly (P < 0.05) lower GI and II values than the reference food. In Experiment 2, three of the four test foods had significantly (P < 0.05) lower GI and II values than the reference food.ConclusionAll but one of the soy foods tested had a low GI, suggesting that soy foods may be an appropriate part of diets intended to improve control of blood glucose and insulin levels.
Human intervention trials aimed at reducing weight gain and body fat using soy protein and isoflavones are few in number and show equivocal results. The objective of this study was to compare the effects of a daily isoflavone‐rich soy‐based meal replacement versus a casein‐based control on body weight and fat gain over 16 weeks in 18–19 year old female college freshmen (N = 120). Participants were randomized to treatment group (soy or casein) in this double‐blind, placebo‐controlled trial. Fat mass (FM), fat‐free soft tissue mass (FFST) and % body fat (%BF) were measured using dual energy X‐ray absorptiometry (Delphi 4500). A 2 x 3 RM‐ANOVA was used to measure the response of the dependent variables (body weight, FM, FFST, %BF, and waist circumference) to the intervention. No significant group by time interactions were observed. Body weight, FM, FFST, and %BF increased significantly in both groups over time (i.e., time effects; p < 0.05). Average weight gain was 50–75% less than reported in previous studies of college freshmen. Both soy and milk‐based meal replacements may be beneficial with respect to slowing weight gain in healthy premenopausal women; however, further study is needed to determine the effects of soy and casein meal replacements using a non‐intervention control group.
Funded by The University of Georgia Research Foundation.
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