Athletes and fitness enthusiasts constantly seek strategies to enhance performance. While a proper diet and exercise regimen form the foundation, certain supplements may provide additional advantages. Beta-hydroxy beta-methylbutyrate (HMB), a metabolite of the amino acid leucine, has garnered attention in the health and fitness community for its potential to support muscle growth and exercise performance. This article delves into the existing research on HMB, particularly focusing on its potential role in weight loss and body composition.
What is HMB?
HMB, short for beta-hydroxy beta-methylbutyrate, is naturally produced in the body when it breaks down leucine, a branched-chain amino acid (BCAA) crucial for protein synthesis and muscle repair. It is also known as beta-hydroxy beta-methylbutyric acid or hydroxymethylbutyrate. Since the body only produces HMB in small quantities, many individuals opt to take it as a dietary supplement to elevate their HMB levels. HMB supplements are readily available in various forms, including capsules, tablets, and powders, in supplement stores, health food stores, and online retailers.
Potential Benefits of HMB
Studies suggest that HMB supplementation may offer several benefits, including:
- Increased muscle growth, particularly in untrained individuals and older adults
- Reduced muscle breakdown
- Improved exercise performance
- Quicker muscle recovery and reduced muscle damage
- Improved cognitive function with aging (primarily observed in animal studies)
- Reduced inflammatory markers
However, it's crucial to note that research findings have been mixed and sometimes inconclusive, necessitating further investigation to fully comprehend HMB's effects across diverse populations.
HMB and Muscle Growth
HMB is frequently marketed as a supplement that promotes muscle growth. While research results are varied, some studies indicate that HMB may benefit muscle growth and strength, especially in specific populations. For instance, a 2024 study suggested that HMB supplementation might assist individuals with sarcopenia, an age-related muscle loss condition, although the evidence was limited. Similarly, a 2022 meta-analysis of nine studies indicated benefits for older adults. Another 2022 study provided limited evidence that HMB could improve muscle mass in cancer patients.
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Conversely, other studies have not found a significant impact of HMB on muscle growth. A 2019 review of 10 studies involving 384 adults aged 50 and over revealed that combining HMB supplements with physical exercise had minimal to no effect on altering body composition, strength, or exercise performance compared to exercise alone. Likewise, a 2018 analysis of six studies involving 193 participants concluded that HMB might not improve these factors in trained and competitive athletes, even when taking 3 to 6 grams of HMB daily for 3 days to 12 weeks.
HMB and Muscle Breakdown
Research suggests that HMB may play a role in reducing muscle breakdown. Test-tube studies propose that HMB may help prevent muscle breakdown through various intracellular mechanisms, such as suppressing genes and enzymes that promote muscle protein breakdown.
An analysis of 15 studies involving 2,137 participants with health conditions predisposing them to muscle loss (e.g., cancer, HIV, kidney failure, and malnutrition) found that taking 3 to 4 grams of HMB daily for 7 days to 6 months was significantly more effective than a placebo in preventing muscle loss. Similarly, studies in older adults have demonstrated that HMB supplementation can help preserve muscle mass, especially during periods of bed rest. However, further research is warranted to confirm HMB's protective effects against muscle breakdown in a broader range of individuals, including young and healthy adults.
HMB and Exercise Adaptations
Some research suggests that HMB may enhance exercise adaptations, referring to longer-term changes rather than immediate effects. A 2015 study involving 16 elite rowers found that taking 3 grams of HMB daily for 12 weeks significantly increased aerobic exercise capacity and peak anaerobic power, while also reducing body fat compared to a placebo. Anaerobic power represents the maximum power output during high-intensity exercise. Similarly, another 12-week study involving 42 combat sports athletes revealed that taking 3 grams of HMB daily significantly increased both aerobic and anaerobic exercise capacity compared to a placebo.
Additional Potential Benefits
HMB may offer other potential benefits, including:
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- Quicker muscle recovery and reduced muscle damage
- Improved cognitive function with aging (though primarily in animal studies)
- Reduced inflammatory markers, such as after cancer surgery
Studies have explored other potential benefits, such as improvements in cardiovascular health, but the results have been inconsistent or inconclusive.
HMB and Weight Loss: Examining the Evidence
While HMB is not directly marketed as a weight loss supplement, its potential to influence body composition (muscle mass and fat mass) has sparked interest in its role in weight management.
Impact on Fat Mass
Several studies have investigated the impact of HMB supplementation on fat mass, with some showing promising results. For instance, the 2015 study on elite rowers mentioned earlier found that HMB supplementation, in addition to increasing aerobic exercise capacity and peak anaerobic power, also helped reduce body fat compared to a placebo. Similarly, Vukovich et al. [29] showed that HMB supplementation in 31 untrained, elderly men and women during an 8 week resistance training program resulted in increased body fat lost (-.66 vs. -.03 %).
A study involving combat sports athletes found that HMB supplementation led to a significant reduction of fat mass compared to a placebo. These findings suggest that HMB may have a role in promoting fat loss, particularly when combined with exercise.
Potential Mechanisms for Fat Loss
The exact mechanisms by which HMB might influence fat loss are not fully understood, but several possibilities have been proposed:
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- Increased Muscle Mass: By promoting muscle growth, HMB may indirectly contribute to fat loss. Muscle tissue is more metabolically active than fat tissue, meaning it burns more calories at rest. Therefore, an increase in muscle mass could lead to a higher resting metabolic rate and increased calorie expenditure, potentially facilitating fat loss.
- Enhanced Exercise Performance: HMB's potential to improve exercise performance could also contribute to fat loss. By enabling individuals to exercise at a higher intensity or for a longer duration, HMB may help increase calorie expenditure during workouts.
- Increased Fat Oxidation: There is also evidence to suggest that HMB increases fat oxidation in muscle cells. This means that the body may be more efficient at using fat as a fuel source, which could contribute to fat loss.
Considerations and Limitations
It's important to acknowledge that the research on HMB and weight loss is still evolving, and several factors need to be considered:
- Inconsistent Results: As mentioned earlier, not all studies have found a significant impact of HMB on body composition. Some studies have shown no effect on fat mass or muscle mass. These inconsistencies may be due to differences in study design, participant characteristics, training protocols, and HMB dosage.
- Need for Exercise: The majority of studies that have shown positive effects of HMB on body composition have involved participants engaged in exercise, particularly resistance training. This suggests that HMB may be most effective when combined with an exercise program.
- Further Research Required: More research is needed to fully understand the mechanisms by which HMB may influence fat loss and to determine the optimal dosage and timing for maximizing its potential benefits.
HMB in Combination with Other Supplements
Some research suggests that combining HMB with other supplements may provide additional benefits. These include:
- Creatine: A 2019 review of studies involving athletes and individuals already engaged in resistance training found that taking 3 grams of HMB with varying doses of creatine improved strength and high-intensity exercise performance, aided muscle growth, and reduced body fat. However, some studies, such as a 2020 study of rugby players, found no improvement.
- Vitamin D: Studies have indicated that older adults taking HMB with vitamin D may experience increased muscle strength, even without an exercise routine.
- Other Amino Acids: Several studies have identified beneficial effects of combining HMB with the amino acids glutamine and arginine, such as increasing body mass in older adults, preventing cancer cachexia (wasting away), and promoting wound healing from bedsores.
While these combinations show promise, it's important to note that some of the research has yielded mixed results.
Safety and Dosage
HMB appears to be generally safe in standard doses of 3 grams daily. In rare cases, individuals may experience stomach pain, constipation, or itching while taking HMB. Although there is no standardized dosage for HMB, most studies have used 3 grams per day. A 2019 review recommends this dosage for 3 to 4 weeks for competitive athletes. The safety of long-term HMB use has not been extensively studied.
As with any dietary supplement, consulting with a healthcare professional before taking HMB is crucial, especially if you are on medications or have pre-existing health conditions.
What Does HMB Do in the Body?
HMB plays a vital role in regulating protein production in the body. Since muscles are primarily composed of protein, HMB can aid in building muscle mass or preventing muscle loss.
HMB Forms: HMB-Ca vs. HMB-FA
Currently, two forms of HMB are available: Calcium HMB (HMB-Ca) and a free acid form of HMB (HMB-FA). HMB-FA may increase plasma absorption and retention of HMB to a greater extent than HMB-CA. However, research with HMB-FA is relatively new, and there is insufficient evidence to definitively conclude whether one form is superior.
Initial studies have shown that HMB-FA supplementation results in approximately double the plasma levels of HMB in about one-quarter the time after administration when compared with HMB-Ca. Additionally, HMB-FA has demonstrated a greater clearance by the body, indicating improved utilization.