|Probiotics act on in the digestive tract, but their effects are still systemic.|
Before we delve deeper into the study design, results and evaluation in the bottom line, I'd yet like you to know that (a) we don't know if the effects will persist for more than 4-weeks, if they will become stronger or weaker and that (b) the study was funded by VSL Pharmaceuticals (Osterberg. 2015) - both additional reasons not to confuse a single study like this with "proof" that probiotics block fat gain.
The objective of Osterberg's latest study was to "determine the effects of the probiotic, VSL#3, on body and fat mass, insulin sensitivity, and skeletal muscle substrate oxidation following 4 weeks of a high-fat diet" - in humans, and even better in 20 non-obese men (18-30 years) who participated in the study.
Subsequently, participants were randomized to receive either VSL#3 (2x450 billion bacteria), a dietary probiotic supplement that contains a motley mix of bacteria, i.e. Streptococcus thermophilus DSM24731, Lactobacillus acidophilus DSM24735, Lactobacillus delbrueckii ssp. bulgaricus DSM24734, Lactobacillus paracasei DSM24733, Lactobacillus plantarum DSM24730, Bifidobacterium longum DSM24736, Bifidobacterium infantis DSM24737, and Bifidobacterium breve DSM24732, or placebo daily during 4 weeks.
"All testing took place at the Human Integrative Physiology Laboratory between the hours of 5:00 and 11:00 am. Participants fasted for 12 h, did not consume caffeine or alcohol, performed no vigorous physical activity for the prior 48 h, and were free from acute illness for the prior 2 weeks.
Learn everything about overfeeding! How do the effects of high vs. low fat, high vs. low protein and high vs. extra-high energy intake differ, what's the effect on thyroid and other important hormones and more
[...]Following a 2-week eucaloric control diet, participants underwent dual X-ray absorptiometry to determine body composition, an intravenous glucose tolerance test to determine insulin sensitivity, and a skeletal muscle biopsy for measurement of in vitro substrate oxidation" (Osterberg. 2015).
|Figure 1: Composition (in g/day) and energy consumption (kcal/day) of the lead in and high fat diet (Osterberg. 2015).|
|Figure 2: Changes in body composition in response to 4-week high fat overfeeding with or without probiotic supplementation (VSL#3, a 900 billion multi-strain probiotic) in 20 normal-weight young men (Osterberg. 2015).|
Since there were neither significant differences in body fat% due to the lower lean mass gains in the probiotic group and considering the fact that there were no additional health effects in form improvements in insulin sensitivity or fat oxidation. Since neither of them was affected by the overfeeding, anyways, the significance of the lack of change is questionable.
- David, Lawrence A., et al. "Diet rapidly and reproducibly alters the human gut microbiome." Nature 505.7484 (2014): 559-563.
- Osterberg, et al. "Probiotic Supplementation Attenuates Increases in Body Mass and Fat Mass During High-Fat Diet in Healthy Young Adults." Obesity (2015): Ahead of print.