Low Dose Silymarin (Milk Thistle) Boosts Reduction in Body Fat % W/ Both, Strength (-9%) & Endurance Training (-11%)

The "classic" user of silymarin supplements is either fat, sick and suffering from NAFLD, or big, buffed and taking oral steroids. Athletic women like the ones in the photos above, on the other hand, have not yet been very likely to buy and use silymarin supplements... well, unless they were (ab-)using oral, hepatoxic steroids, as well, obviously.

When bros talk about Silymarin, the active ingredient in milk thistle, they usually do that in the context of "cycle support", i.e. the use of supplements to buffer the negative effects of (oral pro-)hormones on organ- and, specifically, liver-health. A recent study from the Ahvaz Jundishapur University of Medical Sciences in Iran, however, the "bro-talk" may change that, though.

In the study, which was meant to test, whether silymarin a scientifically proven (Dixit. 2007; Saller. 2009; Surai. 2015) "powerful antioxidant" (Shirali. 2016), will also affect athletic performance, N = 45 (unfortunately) previously untrained men were randomly assigned to one out of the following five groups: (a) endurance training with placebo (ET + P), (b) endurance training with 140 mg of silymarin/day (ET+S), (c) strength training with placebo (ST+P), (d) strength training with 140 mg of silymarin/day (ST + S) and (e) a placebo (C) to identify both, the effects of exercise and supplementation.
Anthropometrical and VO2max measurements and ELISA assay for paraoxonase (PON), leptin and adiponectin levels were performed at the beginning and after the 4-week of the study. Of these, the latter were meant to identify the mechanism behind the effects of exercise + silymarin supplementation.

Figure 1: Changes in body composition and physical fitness over four weeks of exercise training plus/minus 140mg/day of silymarin (ethanol extract from dried Silybum marianum seeds | Shirali. 2016)

Effects such as those I have plotted for you in Figure 1, namely significant improvements in body composition - not only the often falsely overvalued BMI / body weight with its very limited health-significance. Effects that were more (albeit not sign. more) pronounced in the silymarin groups; and effects that also involved a non-significantly more pronounced increase in VO2max in the placebo- vs. silymarin-supplemented endurance training group - a difference of which one could argue that it supports the hormesis hypothesis, i.e. the hypothesis that it's the exposure of your mitochondria to mito-hormetic stress that will have them adapt to the stress with the very cellular growth and functional improvements which drive the adaptational response to exercise.
We have to be careful, though. Neither the additive effect of silymarin on VO2max in the strength training group, in which the subjects did a standardized supervised circuit training workout (3 circuits per workout) involving exercises for all large muscle groups (3 sets of 10-15 reps for each muscle group) thrice a week, nor the disadvantage(s) the subjects in the ET+S group, who participated in three supervised 50 minute running workouts (60% - 80% of maximal heart rate), was statistically significant. It is thus speculative to argue that

• the additive beneficial effect of silymarin on VO2max in the strength training (ST + S) and
• the subtractive negative effect on VO2max in the endurance training (ET) group

are a result of optimized / too low "stress" / oxidation levels - that's speculative, but it appears to be supported by the relative pre-/post-changes in paraoxonase, leptin and adiponectin levels (remember: leptin, just like insulin, is usually increased w/ increasing inflammation, while adiponectin is decreased) I've plotted in Figure 2:

Figure 2: %-changes in plasma PON, adiponectin and leptin levels in resp. to 4 wks of exercise +/- silymarin (Shirali. 2016).

Previous studies by Cakmak et al. (2010), show that PON activity is increased in adolescent athletes, suggesting that the cardioprotective effect of regular exercise might be mediated by increased PON activity. On the other hand, Romani et al. (2009) reported that physical stress, such as acute exercise, by altering membrane composition, may impair PON release from liver membranes and can decrease the level of PON in serum - an effect of which the study at hand appears to show that it is blunted by the provision of small amounts of the 'liver tonic' silymarin.

Addendum: What else do we know?

From previous studies, we also know that silymarin appears to increase the use of fat / trigs during exercise while sparing muscle glycogen (Choi. 2016). The latter may be one, yet certainly not the only reason why the study at hand and a previous study by Barari et al. (2014), both suggest that silymarin can help you lose body fat in the absence of energy systemic restriction... speaking of wich: the lack of dietary control is not necessarily a weakness of the study at hand; after all, a study without dietary control provides evidence that a given supplement will work in the real world, where people often fail to adhere to energy restricted diets - plus: the mood improving effects of silymarin Nazarali et al. (2015) observed in 40 female athletes may be an added bonus I haven't even mentioned yet.

Last question: Do I have to pay extra for "super-bioavailable" silymarin

As Angelo points out in response to the publication of the article at hand, silymarin has a suboptimal bioavailability - meaning: not all the silymarin you ingest will actually make it into your blood. Now, that's correct, but supplement producers abuse the notion of a low bioavailability to make money on allegedly "superior" silymarin products.

Figure 3: Primary reasons for poor oral bioavailability of Silymarin (Javed. 2011)

With a mean bioavailability of 20-50%, regular silymarin is yet far from being as quasi-useless as resveratrol with a 1%-ish absorption rate (note: silybin, the main active substance in silymarin, is not fat soluble, so having it with a fatty meal is not going to increase its bioavailability).
References:

• Barari, A., And A. Eftekhari. "Exercise And Silymarin On Clotting Factors." (2014): 88-88.
• Cakmak, Alpay, et al. "Paraoxonase activity in athletic adolescents." Pediatric exercise science 22.1 (2010): 93.
• Choi, Eun-Ju, et al. "Effect of silymarin on gluconeogenesis and lactate production in exercising rats." Food Science and Biotechnology 25.1 (2016): 119-124.
• Dixit, Nitin, et al. "Silymarin: A review of pharmacological aspects and bioavailability enhancement approaches." Indian journal of pharmacology 39.4 (2007): 172.
• Javed, Shamama, Kanchan Kohli, and Mushir Ali. "Reassessing bioavailability of silymarin." Altern Med Rev 16.3 (2011): 239-49.
• Mackness, Michael I., et al. "Protection of low-density lipoprotein against oxidative modification by high-density lipoprotein associated paraoxonase." Atherosclerosis 104.1 (1993): 129-135.
• Nazarali, Parvaneh, Ahdiyeh Pormphamadi, and Parichehr Hanachi. "Effect of Six Weeks of Resistance Training (RT) and Silymarin Supplement On the Changes in the Inflammation Marker Interleukin 6 and Psychological Profile in Elite Female Taekwondo Players in Alborz Province." International Journal of Sport Studies. Vol., 5 (1), 57-61, 2015
• Romani, Rita, et al. "Modulation of paraoxonase 1 and 3 expression after moderate exercise training in the rat." Journal of lipid research 50.10 (2009): 2036-2045.
• Saller, Reinhard, et al. "An updated systematic review with meta-analysis for the clinical evidence of silymarin." Forschende Komplementärmedizin/Research in Complementary Medicine 15.1 (2009): 9-20.
• Shirali, Saeed, et al. "Effects of Silymarin Supplementation on Leptin, Adiponectin and Paraoxanase Levels and Body Composition During Exercise: A Randomized Double-Blind Placebo Controlled Clinical Trial." (2016).
• Surai, Peter F. "Silymarin as a natural antioxidant: An overview of the current evidence and perspectives." Antioxidants 4.1 (2015): 204-247.
• Wikipedia contributors. "Paraoxonase." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 15 Jul. 2016. Web. 15 Jul. 2016.