That’s where calcium HMB (Ca-HMB) comes in. It’s one of the most well-researched ingredients in sports nutrition, backed by decades of peer-reviewed studies on muscle health. And newer research shows it works even better when paired with vitamin D and creatine.
Here’s what the evidence says.
HMB is a naturally occurring compound produced in the body as a metabolite of leucine, the essential amino acid that signals muscles to grow and repair. When you eat protein-rich foods, your body converts a small fraction (roughly 5%) of that leucine into HMB. The catch: that conversion rate is low. To get even 1.5 grams of HMB from diet alone, you’d need far more leucine than most eating patterns can realistically deliver.1
Ca-HMB is HMB bound to calcium. On its own, HMB is unstable and difficult to work with, so it is paired with calcium to create a stable, shelf-friendly powder that can be formulated into capsules or powders.2 This is also the form of HMB used in the original research nearly 30 years ago1, and which is used in AG1 Pro.
HMB supports muscle health through two interlocking pathways:
In other words, these mechanisms work at both ends of the muscle protein equation: helping your body build more muscle while slowing the rate at which it breaks down.
One of the more exciting developments in muscle nutrition research is the growing body of evidence suggesting that Ca-HMB and vitamin D work better together than either does alone.*
Vitamin D receptors are found directly on skeletal muscle cells. When activated, vitamin D supports gene expression involved in muscle protein synthesis, calcium handling within muscle fibers, and the activation of stem cell-like precursors that help repair and regenerate muscle tissue after stress.5 Maintaining an optimal vitamin D status can support muscle strength, physical function, and muscle health.6
Here’s where the synergy with HMB becomes meaningful: HMB balances protein turnover pathways, while vitamin D supports the structural and genomic machinery that muscle cells need to respond to anabolic signals. In short, vitamin D helps prime the muscle cell environment, and HMB helps tip the protein balance in favor of growth and maintenance.*
Creatine monohydrate is one of the best-studied performance supplements, supporting the rapid regeneration of ATP during high-intensity exercise. HMB works primarily on the protein side of the equation, managing synthesis and breakdown over time. These are fundamentally different mechanisms, which is exactly why they stack well.
One controlled study directly tested this combination — comparing HMB alone, creatine alone, and the two together in men undergoing resistance training. The group taking both saw greater gains in lean body mass and strength than either supplement produced on its own, without any additional side effects.8 The proposed explanation is that creatine amplifies the training stimulus by fueling harder, more productive workouts, while HMB supports the muscle recovery and adaptation process that follows. Creatine helps you do quick, powerful work; HMB helps your muscle tissue adapt to that work more effectively.*
For anyone already consuming creatine, whether for athletic performance or muscle maintenance as they age, Ca-HMB is a logical companion.*
GLP-1s (like semaglutide and tirzepatide) have reshaped weight management, helping people lose significant body weight. But there’s a catch: research shows that anywhere from 25% to nearly 40% of the weight lost during GLP-1s may come from lean muscle mass, not just fat. For long-term health, independence, and quality of life, supporting muscle preservation matters.9 Supporting muscle mass during weight loss may be an important consideration for overall health, physical function, and quality of life.
HMB may be a useful consideration for individuals on GLP-1. By supporting normal muscle protein metabolism, HMB may help support lean tissue as part of a comprehensive nutrition and exercise program.*
Combining calcium HMB with adequate protein intake and resistance training can be one component of a broader approach to supporting body composition goals during weight management efforts.* For individuals seeking nutritional support while pursuing weight loss goals, 1.5 grams of HMB per day may serve as a practical starting point within an overall healthy lifestyle plan.*
Early research tested both 1.5 g per day and 3 g per day, with both doses producing meaningful benefits over placebo in lean mass and muscle biomarkers.1 Research since then has landed on 1.5 g per day as a practical and effective amount — especially when paired with adequate protein, vitamin D, and regular exercise. Combined with creatine (typically 5 g per day), you get complementary support for both performance and long-term muscle health.*
Ca-HMB isn’t a trendy supplement — it’s one of the most thoroughly researched ingredients in muscle health, backed by 30+ years of peer-reviewed science across a wide range of people. It works on two fronts: helping your body build muscle while helping to slow the rate at which it breaks down. That makes it relevant whether you’re an athlete pushing through heavy training, someone over 40 looking to stay strong, or a person navigating weight loss on a GLP-1.*
By providing 1.5 grams of calcium HMB alongside 5 grams of creatine monohydrate, zinc carnosine, probiotics, prebiotics, superfoods, and adaptogens, AG1 Pro offers an advanced daily foundational formula. The combination of research-backed ingredients is designed to support muscle performance while promoting energy, immune, gut, and metabolic health.* AG1 Pro is NSF Certified for Sport®.
For athletes, HMB’s value lies primarily in its ability to reduce exercise-induced muscle protein breakdown, which is especially relevant during heavy training blocks, when training volume spikes, or when athletes are competing across back-to-back events with limited recovery time.*
In a clinical study, researchers tested whether a 1.5-gram Ca-HMB supplement per day for two weeks could support muscle function recovery after a demanding bout of eccentric exercise4 (the kind of hard, muscle-lengthening effort). Subjects taking HMB retained significantly more muscle strength immediately after exercise and through day 5 of recovery compared to the placebo group. At three days post-exercise, the HMB group had lost roughly half the strength of the placebo group (-25.5% vs. -48.7%).
For athletes pairing HMB with creatine, as many strength and power athletes logically would, the combination of performance support (creatine) and structural preservation (HMB) addresses two distinct training demands simultaneously.