|Will the fat-burning magic of 1g/day of yeast hydrolysate dissolve the fat that's still covering the last 2 packs?|
This obviously warrants a heightened degree of suspicion, but it does not mean that the study results could or even must be doctored. I would thus suggest, we take a look at what the Korean scientists from Jeonju University, the University of Seoul, the Korea University and the Neo Cremar Company Ltd. actually did and found before we jump to any premature conclusions about the validity or non-validity of the data.
What exactly is yeast hydrolysate?
I guess, the first thing we have to address is what exactly it was Jung et al. administered to their 24 male and 30 female participants with body mass indices (BMI) of at least 25 kg/m² (the obesity cut off in the Asia-Pacific region is 25 kg/m²). To this end, it's best to look at how this "supplement" was produced (if you want the short version fast forward to the first red box ;-)
You've read about the anti-Crohn's effects of saccharomyces cerv. (bakers yeast) in the SuppVersity Facebook News, recently.
- After incubation, the culture is centrifuged at 10,000g for 20 minutes.
- Immediately after the cells are removed from the centrifuge, they are suspended in 20 mM phosphate buffer (pH 7.0) and hydrolyzed with 1000 units of bromelain at 30 C for 4 h.
"Hold on! So what do I need?" Before you hit the "too complicated button" at the bottom of this page, let me briefly point out that you don't need to understand or memorize the production process. The thing you have to look for, when you are shopping for corresponding products is a yeast hydrolysate with a maximal molecular weight (that's ~ the size of the indiv. peptides) of <10kDa that was produced from Saccharomyces cerevisiae.In the study at hand, the of this 3+1 step process was packed into 500 mg pouches before it was handed over to the subjects in the active arm of the study (the placebo contained dextrin).
|Figure 1: Inter-group baseline differences for weight + body composition for men and women (Young. 2014)|
Speaking of dietary interventions! there was no dietary intervention.
I know, it sounds hilarious, but there was no dietary intervention. All the participants had to do was to consume the 1g of yeast hydrolysate or the 1g of dextrin in 2x500mg servings 30 min before breakfast and dinner. That's at least what they were advised to do.
|Figure 2: Changes in energy intake (% baseline) and body composition (Young. 2014)|
There are no effects on resting metabolic rate! The notion that the reduced energy intake is the main, if not the only driving force of the fat loss Jung et al. observed in the study at hand is supported by observations the researchers made in a previous study from 2011 (Jung. 2011a). In the said study, the 20 obese females (body fat >28%) in the yeast group did experience a non-significantly improved fat loss compared to the control group. They did yet also suffer from a "higher" reduction in resting metabolic race (-9.69kcal/day vs. -4.35kcal/day) - similarly non-significant as the weight loss difference, obviously.This does not mean that the yeast extract doesn't work - quite the contrary, for the average individual who is neither willing nor able to adhere to a caloric deficit without the help of tools like this, it could actually come very handy. For the average physical culturist, it would yet obviously be more interesting if yeast hydrolysates had spot reducing qualities (learn more about spot reduction). And if we take another look at the full text of the study, we could actually argue that this is basically what the authors suggest, when they refer to the results of previous studies and state:
"Yeast hydrolysate increases the reduction of body fat in obese individuals compared with placebo, which supports the hypothesized abdominal fat-lowering effects of yeast hydrolysate" (Young. 2014)If you look at the study at hand, the question we would have to answer should thus read: Are the abdominal and total fat mass disproportionate. Or to say it differently: Did the subjects lose signifcantly more abdominal than total fat? And in view of the previously discussed problem: Did this vary between male and female participants? Unfortunately, the scientists didn't do us (or rather me) the favor of doing this for us, already. Therefore I had to do the calculations and plotting for Figure 3 myself:
|Figure 3: Relative change in body fat mass and abdominal fat thickness (Jung. 2014)|
Is the fat loss really localized?
Furthermore, a previous study by the same researchers clearly refutes the abdominal specific fat loss effects. The corresponding paper was published in 2011 in the Journal of Food and Biochemistry (Jung. 2011a; same paper I referenced in the box above), and despite the fact that the researchers observed a trend for an increase in weight loss within only 4 weeks on the same <10kDa yeast hydrolysate, the fat loss results of the obese women who participated in the study were at best triceps (-2.15 vs. -1.05mm reduction in skinfold thickness in yeast vs. control) and not belly specific (-1.70 vs. -1.08mm reduction in skinfold thickness in yeast vs. control).
Unfortunately, I cannot tell you whether the same can be said of the 2009 paper by Suh et al., because the online archive of the Journal of Food Science and Nutrition, where it was published starts in March 2011. In view of the fact that it was not "ab-specific" in obese women, I really doubt that it will have has particularly pronounced effects on the waistline of female college students - a subject group of whom you would expect that they are at least somewhat closer to the fitness and leanness level of the average SuppVersity reader.
- Jung, E. Y., Kim, S. Y., Bae, S. H., Chang, U. J., Choi, J. W., & Suh, H. J. (2011a). Weight reduction effects of yeast hydrolysate below 10 kDa on obese young women. Journal of Food Biochemistry, 35(2), 337-350.
- Jung, E. Y., Lee, H. S., Choi, J. W., Ra, K. S., Kim, M. R., & Suh, H. J. (2011b). Glucose Tolerance and Antioxidant Activity of Spent Brewer's Yeast Hydrolysate with a High Content of Cyclo‐His‐Pro (CHP). Journal of food science, 76(2), C272-C278.
- Jung, E. Y., Hong, Y. H., Kim, J. H., Park, Y., Bae, S. H., Chang, U. J., & Suh, H. J. (2012). Effects of Yeast Hydrolysate on Hepatic Lipid Metabolism in High-Fat-Diet-Induced Obese Mice: Yeast Hydrolysate Suppresses Body Fat Accumulation by Attenuating Fatty Acid Synthesis. Annals of Nutrition and Metabolism, 61(2), 89-94.
- Jung, E. Y., Cho, M. K., Hong, Y. H., Kim, J. H., Park, Y., Chang, U. J., & Suh, H. J. (2014). Yeast hydrolysate can reduce body weight and abdominal fat accumulation in obese adults. Nutrition, 30(1), 25-32.
- Suh, H. J. (2009). The weight reduction effect of yeast hydrolysate-SR101 on female college students. Journal of Food Science and Nutrition, 14(2), 123-128.