Science Round-Up Seconds: Stevia, Cancer & Fertility. What is the Verdict? Exercise, Hunger & GLP-1. Can a Workout Fill You Up? Postactivation Potentiation & Personal Bests. 8% More Maximal Power After 5s Max. Voluntary Contraction?

Other news: Classic cardio ramps up GLP-1 and “posing” increases your maxes by up to 8%.

If you have already downloaded and listened to yesterday’s installment of the SuppVersity Science Round-Up, you will probably be aware that the first thing I am going to do in today’s Seconds is to (re-)address the stevia issue (read up on previous stories about Stevia here at the SuppVersity).

If I recall that correctly, I did in fact forget to mention something that’s actually important if you want to get the whole picture – the gut microbiome! But before we tackle this one, let’s not forget that there are a couple of other news stories which did not make it into the 60min show, news on the effects of LISS on GLP-1 and the potentiation of the post-activation potentiation effect. Sounds interesting, then let”s go for it!

Is stevia toxic, does it cause cancer and infertility? 

Let me start with the bottom line first. The currently available scientific evidence clearly suggest that stevia is safe to consume. Or, as “real” scientists (not that I would not consider myself a scientist, but without a single published paper in this domain of science, I am certainly not an authority 😉 write in their papers:

What was that about the microbiome? I forgot to mention that the “bad” aglycol aka “steviol” is also produced from the benign and usually not even absorbed pure steviosides and is thus not something you’ll find only in “natural” stevia products. That being said, Wingard et al. observed in 1980 already that steviol is readily excreted via the billary pathway in the feces (Wingard. 1980; confirmed by Nakayama. 1986). You may thus be exposed to small amounts of steviol no matter what, but that’s nothing your body cannot dispose of.
“The recent suggestions that steviol glycosides present a muta-genic – and therefore carcinogenic – risk to consumers are not sup-ported by actual test results. The paper making this claim by Matsui et al. (1996a) was published prior to most of the papers assessing the genotoxic risk of steviol glycosides as well as several expert panel reports and a review by Brusick in 2008. The database of genotoxicity studies for steviol glycosides and steviol as it currently stands, combined with a lack of evidence for neoplasm development in rat bioassays (Aze et al., 1991; Xili et al., 1992; Toyoda et al., 1997; reviewed by Carakostas et al., 2008, 2012; EFSA, 2010), is adequate to establish the safety of these food ingredients with respect to their genetic/carcinogenic potential.” (Urban. 2013)

And with respect to the infertility claim, Geuns et al. write in their very detailed review from 2003:

The results of a decrease of live birth rate in rats (Planas and Kuæ, 1968) by Stevia decoctions were refuted by Shiotsu (1996) who did more reliable experiments with many more animals using methods as similar as possible to the methods used by Planas and Kuc. No effect on general condition, body weight, water consumption, live birth rate or litter size was found. No effects of stevioside were found on fertility or reproduction in mice (Akashi and Yokoyama, 1975), rats ( Mori et al., 1981, Xili et al., 1992 and Sinchomi and Marcorities, 1989) or hamsters (Yodyingyuad and Bunyawong, 1991).

No significant effect was found on spermatogenesis, nor on the interstitial cell proliferation and tumor formation in the testes of F344 rats fed a ration containing up to 1% stevioside (95.2% purity) for 22 months (Yamada et al., 1985).

If you are either a newcomer to the SuppVersity or simply cannot remember the summary of selected stevia research from September last year, I suggest you go back in the archives and read up on “More Than Super Sweet: More Scientific Evidence, More Potential Implications for Weight Loss & -Maintenance, Anti-Diabetic & -Autoimmune and Even Pro-Anabolic Effects” (learn more) Some of the benefits are btw. mediated by the same stuff that’s toxic in in-vitro studies…hormesis, you know 😉

Whereas Melis (1999) suggested a possible decrease of the fertility of male rats by a very high dose of Stevia extract, Oliveira-Filho et al. (1989) who administered extracts with similar stevioside content stated that there is certainly not an effect on male fertility. It is not sure that the observed effects were due to the stevioside present in the extract. It should also be mentioned that the used extract concentrations were extremely high, at the start of the experiments even 5.34% of the body weight (or around 5.3 g stevioside/kg bw). For an adult person of 65 kg this means 3.47 kg of dry Stevia leaves or about 34.7 kg fresh leaves/day, i.e. more than 50% of the body weight! The significance of such experiments where only one extremely high concentration was tested, should be questioned. Melis’ results are also in contradiction with the above and below cited studies that could not reveal any effect on fertility of male or female animals.” (Geuns. 2003; my emphases)

Much ado about nothing? Well, in the end it may seem so and the preponderance about freakin’ out over every potential and 0.5% marginal possibility that something you do or eat could be wrong or toxic certainly ain’t healthy. On the other hand, it’s always good to exhibit a certain degree  of suspiciousness – just do me favor: Do that towards both the good and the bad news!

Scheduled news that did not make it into the live show

The fat burning benefits of hydroxypropyl-distarch phosphate from waxy maize starch  (WMHDP) are – at least in part – also mediated by increases in GLP-1 production (read more)

Short and long-term effects of exercise on appetite and metabolism regulating hormones — (Ueda. 2013) As a SuppVersity reader and SHR listener, you are no stranger to the acronym GLP-1 and the effects the “satiety hormone” it stands for has on your desire to eat and, more importantly, your metabolisms willingness to use not store the energy from the food you consume (learn more).

In a soon to be published paper, Shin-ya Ueda and colleagues report that chronic exercise, in this case 3x/week 60min of light intensit (65% of VO2max) cardio on a treadmill and/or cycle ergometer results in a statistically highly significant increase in GLP-1 in response to exercise.

Usually I don’t like to repeat myself, but I would probably have missed the main important message here, if I were just skimming the above: The 20 healthy middle-aged women who participated in the 12-week experiment did not simply have higher GLP-1 levels after a meal. No, the post-exercise levels of GLP-1 and the other satiety hormone PYY increased hours before the ladies even got their next meal.

Figure 1: GLP-1 (pmol/ml; left) and PYY (pmol/ml; right) response to exercise before and after (0, 30, 60 min) a 80min (60 min effective training + 20min warm-up, cool-down etc.) supervised workout before (untrained) the 12-week exercise intervention and after (trained) the 12-week exercise intervention (Ueda. 2013)

In conjunction with the significant correlation of GLP-1 with the reduction in body weight the study participants achieved over the course of the course of the 12×3 = 36 supervised exercise session, this was reason enough for the scientists to hypothesize that…

“[…] that the ability of exercise training to create a negative energy balance relies not only directly on its impact on energy expenditure, but also indirectly on its potential to modulate energy intake.” (Ueda. 2013)

So, does exercise “just make you hungry”. No, it turns you into a satisfied fat burning machine – and that even if it’s just 3x60min of LISS per week.

Training increases the efficacy of 5-6s maximal contractions to before a maximal voluntary effort (Miyamoto. 2013) I guess you will be aware that Superman usually does a 5-6s maximal voluntary contraction (MVC) while checking out if everybody is watching before he eventually does the deed and lifts the car that has just overrun the beautiful blond bombshell with a “single-armed deadlift”, right? Good, because if you know that, I don’t have to explain why the scientists from the Waseda University in Japan 21 healthy male subjects perform a 5s MVC before they did their maximal voluntary concentric knee extensions 1, 3 and 5 minutes, thereafter.

Figure 2: Voluntary concentric torque on knee extensions after previous peak contractions before (left) and after (right) in the trained and untrained study participants.

What I probably still have to tell you though is that the “after” values you see in figure 2 were taken after 12-weeks of doing 5x 8 reps with 80% of the one-repetition max in a standard knee extension machine. Ok, I have to admit that the actual training effect is not really impressive, but since most of you have it already built in (after all, you probably train for more than 12-weeks already, right?) doing a single 5s maximal voluntary contraction before a max-effort trial is an easy and time-efficient (1 min!) way to increase your performance by superman-like 8%! What this funky technique is called like? Postactivation Potentiation – nice alliteration, isn’t it?

That is it, for the day – at least for the Seconds. If you don’t know what to do before the weekend begins, browse over to the SuppVersity Facebook Wall and check out news on

  • If you have not done so, already, click here and teach yourself “How to Make the Correct Fish choices”? There is luckily way more swimming around in our oceans than farmed salmon with it’s more than 4x elevated n6:n3 ratio (compared to wild salmon, learn more)

    Salmon in the vicious cycle of soy supplementation – Scientists try to come up with a certain bacteria that could protect farmed salmon from the junk, ah… soy it’s fed (read more)

  • Alpha lipoic acid (ALA) helps otherwise healthy schizophrenics on heavy anti-histamine regimen to lose weight – 2x 1gram of regular ALA does the trick (read more
  • People who were breastfed as kids have healthier eating habits in their adulthood – Interestingly, this effect did not depend on social class at birth or later in life and occurred irrespective of smoking status, alcohol intake or reported physical activity.

Once you’ve done that, you first make sure that you did not miss part three of my interview with Sean Casey and then get off the screen and into the night, family or whatever real life, I’d hope you did not give up on after you bought your latest iPhone 😉


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“Science Round-Up Seconds: Stevia, Cancer & Fertility. What is the Verdict? Exercise, Hunger & GLP-1. Can a Workout Fill You Up? Postactivation Potentiation & Personal Bests. 8% More Maximal Power After 5s Max. Voluntary Contraction?” is replublished article from