Abstract: High protein diets exert beneficial effects on appetite, anthropometry, and body composition; however, the effects of protein preloads depend upon the amount, type, and time of consumption. Therefore, we hypothesized that long term supplemental preloads of whey protein concentrate (WPC) and soy protein isolate (SPI) consumed 30 min before the largest meal, would decrease appetite, caloric intake (CI), anthropometry, and improve body composition in overweight and obese men in free living conditions. The subjects included forty-five men with a BMI between 25 to 40 kg/m2 and who were randomly allocated to either the WPC (n = 26) or SPI (n = 19) groups. For 12 weeks, the subjects consumed 65 gr WPC or 60 gr SPI that was dissolved in 500 ml water 30 min before their ad libitum lunch. Appetite, CI, anthropometry, and body composition were assessed before and after the study and biweekly throughout. After 12 weeks, mean changes between the groups were significant for appetite (p = 0.032), CI (p = 0.045), anthropometry (body weight (BW) (p = 0.008), body mass index (BMI) (p = 0.006), and waist circumference (WC)), and body composition (body fat mass (BFM) and lean muscle (LM) (p < 0.001)). Relative to baseline, within group mean changes from WPC were significant for appetite, CI, anthropometry, and body composition (p < 0.001). In the SPI group, mean changes were significant, relative to baseline, for all variables except LM (p = 0.37). According to this 12-week study, WPC preloads conducted 30 min prior to the ad libitummain meal exerted stronger beneficial effects than SPI preloads on appetite, CI, anthropometry, and body composition of free living overweight and obese men.
Alex’s Notes: I don’t believe the whey and soy proteins need any introduction, so let’s get straight to the study. 52 middle-aged (avg. 39 years) and obese (avg. BMI of 32) men with no history of smoking, alcohol consumption, caffeine consumption (>250mg/day), medication or supplement usage, or history of diseases were recruited to undergo seven visits for completion of 24-hour dietary recalls, appetite, anthropometry, and body composition measurements (baseline, then at the end of every other week for 12 weeks).
The men were randomly divided into two groups that received either a whey protein concentrate (WPC) sachet or a soy protein isolate (SPI) sachet. Both groups were instructed to dissolve one sachet into 500mL of water drink it 30 minutes prior to their afternoon meal, which is traditionally the largest meal in Iran (where the study was conducted). Aside from the biweekly visits, the researchers actually went to the subjects’ workplaces during lunch to directly observe them consuming the supplements. Both WPC and SPI provided 54 grams of protein, although WPC required 262 kcal to do so while SPI was only 216 kcal.
First and foremost, seven SPI group participants (27%) left the study within the first two weeks because of GI distress, while the WPC was well tolerated. At the end of 12 weeks, compared to the SPI, the WPC resulted in a 40% lower appetite rating, 46% reduced caloric intake at lunch, greater weight loss (the SPI group actually gained weight), reduced waist circumference (lost nearly 10 cm while the SPI group gained 0.6 cm), a 3-fold greater increase in lean body mass, and an average 9% reduction in body fat percentage (SPI group gained 1%).
It is sad that there was no control group or women included, but at least the study was a randomized, double-blinded protocol. Overall, this study provides strong evidence for the superiority of whey rather than soy as an adjunct to weight loss therapy in obese middle-aged men.