What the Science Says About Supplement Choices for Men & Women
Walk into any gym and it won’t take long before you overhear someone chatting about supplements. And it’s usually over a shaker full of something vaguely chalky. Whey protein, creatine and L-carnitine are the holy trinity of gym-floor chat. But how effective are they, really? Do they actually help your clients get stronger or leaner? And more importantly, do they work the same way for everyone?
A new study published in Sports (Nagy et al., 2025) gives us one of the most detailed looks yet at how these supplements perform in real-world gym-goers over eight weeks of structured resistance training. And the results? Let’s just say it’s not a one-size-fits-all situation.
The Big Three: What They Do and Who They Might Help
Before we get into the details, here’s a quick refresher:
Whey Protein
Whey’s the go-to for anyone looking to build muscle and speed up recovery. It’s rich in essential amino acids, including BCAAs, and it’s digested quickly. This makes it perfect for post-workout shakes. But in this study, whey protein on its own didn’t perform as well as you might expect. Those taking only whey saw less improvement in 1RM strength tests than those on creatine, L-carnitine or the combination of all three.
That doesn’t mean it’s useless. In fact, far from it. Whey still plays a key role in supporting muscle protein synthesis, particularly when total daily protein intake is low or meals are lacking in quality protein sources (Devries & Phillips, 2015). But in this trial, it was more of a solid baseline than a performance booster.
Creatine
Creatine monohydrate is the most studied and consistently effective ergogenic aid for strength, power and high-intensity performance (Hespel & Derave, 2007). In the Nagy study, it showed strong results, particularly in young men aged 18–30. This group saw big jumps in exercises like deadlifts, bench press and biceps curls.
Interestingly for women, creatine’s effects were far more hit-or-miss. While some improvements were noted, they weren’t statistically consistent. Other studies have shown that women may experience smaller absolute gains from creatine compared to men, potentially due to lower baseline muscle creatine stores and differences in muscle mass and hormonal profiles (Wang et al., 2024).
L-Carnitine
Often sold as a fat-burning supplement, L-carnitine is a bit misunderstood. It plays a key role in transporting fatty acids into the mitochondria to be used for energy, which has led to its popularity for weight loss. But it also appears to reduce muscle damage, support recovery and improve endurance (Spiering et al., 2007; Gnoni et al., 2020).
In this study, L-carnitine users saw a unique benefit in that they were the only group that lost weight over the eight weeks. Everyone else gained, mostly muscle, but carnitine seemed to support those looking for leaner outcomes. This was particularly the case among women and older adults. Female participants aged 50–60 leaned heavily towards carnitine use and showed strength gains despite a general trend of lower baseline performance.
Men vs. Women: It’s Not Just About the Supplement
The Sports study’s authors made a point of splitting results by gender and age. And this is where things get really interesting.
For Men
- 83% of men in the study took supplements and they were most likely to go for the triple combo of whey + creatine + L-carnitine.
- Creatine led to the best gains in upper body lifts like bench press and curls.
- Men consuming the combo consistently outperformed those taking any single supplement.
- Diet made a difference as gains were highest in men consuming over 150g protein/day and >2500 kcal.
For Women
- Only 64% of women took supplements and whey protein and L-carnitine were the most popular choices.
- L-carnitine stood out as the most effective for strength gains and body composition improvements.
- Creatine had a mixed record as some gains were seen in triceps and pull-ups, but not as reliably as in men.
- Women’s improvements were more sensitive to dietary intake. Those eating less than 100g protein/day didn’t see much benefit, regardless of supplement.
This supports previous findings suggesting women may require higher relative protein intake to stimulate comparable muscle protein synthesis (MPS), especially around menopause or in older age (Phillips & van Loon, 2011).
When Supplements Might Be a Waste of Money
As always, context matters. Not every client needs a tub of powder and a direct debit to a supplement site. In fact, the control group, that is those that didn’t take any supplements, still improved across all exercises, just not as much.
Here’s when supplements might not be worth it:
- Low daily protein intake: Those eating <100g/day saw limited benefit.
- Very low calories (<1500 kcal/day): Even the best supplements won’t work if the body’s underfed.
- Infrequent training: This study had participants doing 3 RT sessions/week. Without that baseline, gains will be minimal.
- Older adults with no diet support: Over-50s showed the lowest response to supplements unless they also had a solid diet.
And it’s worth noting here that in exercises like pull-ups, results didn’t align neatly with supplement use. Gains there seemed more related to gender, body weight and training history than what was in the shaker bottle.
So, What Should We Take From This?
If you’ve got clients asking whether they should spend their money on whey, creatine or carnitine, this study provides a solid foundation for making recommendations:
- Younger men looking to gain strength and size? Creatine or the triple combo could give them the biggest return.
- Women looking to improve tone and performance, especially with fat loss goals? L-carnitine may be the most useful, especially when combined with a higher protein intake.
- Older adults? Focus on overall diet quality first. Supplements may help, but only if the basics are covered.
- Everyone else? Training consistency and a decent protein intake (1.6–2.2 g/kg/day) remain the real game changers.
Always start by assessing diet, training volume and recovery before diving into supplement advice. And most importantly, don’t assume what works for one client will work for another.
Supplements can be useful tools but they’re not shortcuts. As this study shows, whey, creatine and carnitine each have their place, but their effectiveness varies by age, sex, training status and diet.
When we understand these nuances, we’re better placed to guide clients in a way that’s actually based on evidence, not just gym-floor myth.
References
- Nagy, S.-R. et al. (2025). The Impact of Protein and Amino Acid Supplementation on Muscular Strength and Endurance in Recreational Gym-Goers During 8-Week Resistance Training. Sports, 13(182). Click here to review the full research article.
- Hespel, P., & Derave, W. (2007). Ergogenic effects of creatine in sports and rehabilitation. In Creatine and Creatine Kinase in Health and Disease. Click here to review the full research article.
- Wang, Z. et al. (2024). Effects of Creatine Supplementation and Resistance Training on Muscle Strength Gains in Adults <50 Years of Age: A Systematic Review and Meta-Analysis. Nutrients, 16, 3665. Click here to review the full research article.
- Devries, M. C., & Phillips, S. M. (2015). Supplemental protein in support of muscle mass and health: advantage whey. Journal of Food Science, 80, A8–A15. Click here to review the full research article.
- Spiering, B. A. et al. (2007). Responses of criterion variables to different supplemental doses of L-carnitine L-tartrate. J Strength Cond Res, 21, 259–264. Click here to review the full research article.
- Gnoni, A. et al. (2020). Carnitine in human muscle bioenergetics: Can carnitine supplementation improve physical exercise? Molecules, 25, 182. Click here to review the full research article.
- Phillips, S. M., & van Loon, L. J. C. (2011). Dietary protein for athletes: from requirements to optimum adaptation. J Sports Sci, 29, S29–S38. Click here to review the full research article.
75% of Gym-Goers Use Supplements. Are You Qualified to Guide Them?
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