Testing Animal Pak STAK Testosterone Booster
Effective testosterone support or anecdotal snake oil?
A lot of “testosterone boosting” supplements are bogus. Is STAK by Animal Pak one of them? I tested it for 37 days and statistically analyzed the results in R to see how it independently compares to sleep quality, magnesium, and Vitamin D.
TL;DR:
Most supplements that claim to boost testosterone don’t work (ref.).
In my testing STAK had a statistically significant, negative correlation with Low-T symptoms.
Magnesium, Vitamin D, and sleep quality also all had statistically significant, negative correlations with Low-T symptoms.
STAK’s correlation with Low-T symptoms was independent of time/accumulation, magnesium, Vitamin D, and sleep quality.
It’s well known that Vitamin D (VitD) and Magnesium (Mg) are extremely important for testosterone production (ref.). These appear to be the primary mechanism through which STAK works; though there are several other herbal ingredients added.
Animal Pak makes several other testosterone-supporting products, but my interest in STAK was primarily because of my prior research on VitD and Mg as they relate to testosterone and the corresponding decision to supplement with both of those already.
Note on Titanium Dioxide: This is still listed as an ingredient on the packaging and website; however, the tub shipped with a note indicating that the ingredient has been removed. Titanium Dioxide has been banned in the EU. (ref., ref., ref).
I’m not a pill-and-potion-pusher. I do want to give myself every chance for success, and I want that success to be data-driven. In other words, yes, I do get a kickback for the links on this page. No, I will not continue to endorse or use a product that doesn’t work.
The procedure I followed was to log a daily inventory of:
Vitamin D (supplemental and sun)
Magnesium (supplemental only)
Animal STAK (supplement)
Creatine (supplemental only)
Move-Minutes (per Google Fit)
Overnight Heart Rate (per LetsFit watch)
AWQ Variables
Low-T Variables
I assumed that my dietary intakes of VitD, Creatine, and Mg were approximately consistent day-to-day so therefore only supplement / exogenous sources were considered in logged data.
Dietary sources would look something like:
VitD: ~ 600 IU/day
Mg: ~200 mg/day
Creatine: ~4g/day (2 lbs of beef)
Definitions:
“Low-T” = Sum of mood, fatigue, erectile function, and sex drive, subtracted from the maximum score of 20. That is, a higher “Low-T” score is worse (i.e. more symptoms) and lower is better (i.e. fewer symptoms, higher testosterone).
“AWQ” = Athletic Wellness Questionnaire: sum of sleep (quality), mood, soreness, stress, and fatigue. Some variables are inverted so that a higher AWQ score is better (e.g. less fatigued, less sore, less stressed, better mood, better sleep).
Results:
The data were analyzed with R to evaluate correlation (r) after being screened for statistical significance (p < 0.05) — that is, less than a 5% chance of random occurrence.
Several variables were correlated with “Date.” This is because as the “study” went on, I titrated off STAK and then creatine. STAK was correlated with Mg (obviously), but not significantly with VitD. This is because the vast amount of VitD I was getting came from the sun (as it should be).
In contrast, most of my Mg was coming from supplement form (i.e. 400mg supplemental vs. 200mg dietary) which explains the strength of that correlation with STAK.
Regarding creatine, the overlap is because STAK and creatine were being used at the same time, but we’ll separate these factors later.
We can see that the strongest correlations STAK produced were with AWQ (r = +0.60, p = < 0.0001) and Low-T (r = -0.56, p < 0.001); both of which were moderate in strength (ref.).
Looking at the relationship between Mg and each of those factors we can see the relationship is very similar to STAK, which may indicate that Mg is STAK’s primary operating mechanism — below we’ll look at if these variables are independent of each other.
The specific purpose of this study was to look at what effects Low-T symptoms (or rather improved testosterone as indicated by negative correlation with Low-T symptoms).
VitD, Mg, Sleep (quality), and STAK all had statistically significant negative relationships with Low-T — in other words, they improve testosterone. VitD, Sleep, and Mg all had weak correlations; while STAK’s correlation to Low-T symptoms was moderate in strength.
ANCOVA and Confounding Variables:
ANCOVA is a regression that’s used to tell if variables operate independently of each other. For example, I was able to tell that:
STAK improves Low-T symptoms independent of date (loading/accumulation), creatine, Mg, VitD, and sleep quality.
STAK improves AWQ independent of creatine and date (loading/accumulation).
Mg improves Low-T symptoms independent of sleep quality and VitD.
Mg improves AWQ independent of creatine.
I could also tell that:
Mg’s effect on Low-T symptoms is not independent of creatine supplementation, though this doesn’t necessarily indicate dependence.
VitD’s effect on Low-T symptoms is not independent of date — meaning accumulation in the blood may be more important than day-to-day dosage (and variance therein).
VitD’s effect on Low-T symptoms is not independent of Mg (which is also congruent with the literature, ref.).
Other Conclusions:
“Move minutes” were used as an indicator of activity level, but that’s not necessarily helpful as it does not indicate the intensity of the activity or the corresponding recovery need.
Likewise, “overnight heart rate” was not significantly related to AWQ which may mean that such metrics require triangulation/cross-validation. For example, the aggregate of overnight heart rate, soreness, and sleep quality may be a more helpful indicator than either variable individually.
Sleep quality and soreness were significantly correlated to overall AWQ more than the variables: fatigue, mood, and stress. However, it should be noted that my prior research indicated that mood (independent of total AWQ) had a significant relationship with performance (ref.).
Limitations:
I didn’t extract data or account for Zinc or Vitamin B6 which have notable roles in testosterone production (ref., ref., ref., ref.). Other ingredients included in STAK like tribulus (ref.), nettle root (ref.), fenugreek seed (ref.), maca extract (ref., ref.), and longjack extract (ref.) have some literature support as well.
During the latter half of the study, I had a rib/diaphragm injury. For consistency, I tried to evaluate “soreness” independent of the injury. However, at this time I was also not training at my regular intensity or volume.
However, the later weeks of the study were the “control” or where creatine and STAK were removed. If the removal or decrease in training volume and intensity were to have skewed the results, then the corrected results would only be more supportive of STAK’s benefits.
Summary:
Vitamin D, magnesium, sleep quality, and Animal STAK all had statistically significant, negative correlations with Low-T symptoms. Logically this implies that they improve testosterone levels.
STAK’s effect on Low-T symptoms was the strongest of the above variables, as well as independent of each of them. Vitamin D’s benefit was not independent of time (accumulation) or Magnesium.
I would like to do another 30-day trial that will produce even more robust results and hopefully more accurate ones as well with a consistent training program.
The follow-up will likely include more detailed sleep data as that was shown to be an important factor here — Animal Pak’s PM product, a sleep aid, will also be included for testing.
Data Sources:
Raw data is publicly available on GitLab
Annotated results are available on Google Drive