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Get Started 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.
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.
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
For Women
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).
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:
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.
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:
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.
If you’re a fitness professional who wants to give clients more than just training plans, the Nutrition for Weight Management & Athletic Performance course is a must. With over 75% of gym-goers using nutritional supplements without any expert guidance (Nagy et al., 2025), there’s a clear need for qualified professionals who can offer evidence-based advice. This Level 4 course gives you the knowledge and credibility to help clients achieve their goals safely and effectively, whether they’re aiming to lose fat, build muscle or improve performance. You’ll explore everything from macronutrient balance to supplement protocols and behavioural strategies, making you an invaluable asset to your clients’ results.
Nutrition Coach Course – Distance Study
If you’re a qualified personal trainer working with women in midlife, the Exercise & Nutrition for Menopause course gives you the expertise to make a real difference. In a recent study, only 9.1% of male gym-goers followed a vegetarian diet compared to 17.4% of women, yet many women still struggle to meet their protein needs. This is even more prevalent during menopause when maintaining muscle mass becomes more difficult (Nagy et al., 2025). This course covers the unique hormonal, nutritional and training needs of women in this life stage, so you can design programmes that address common issues like muscle loss, energy dips and unwanted weight gain. Give your clients the support they deserve based on science, not guesswork.
Exercise & Nutrition for Menopause Course – Distance Study
