Evidence supporting the use of: L-leucine
For the health condition: Weight Loss

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Synopsis

Source of validity: Scientific
Rating (out of 5): 2

L-leucine is an essential branched-chain amino acid (BCAA) that has gained attention for its possible role in supporting weight loss, primarily due to its involvement in muscle protein synthesis and metabolic regulation. Several scientific studies have explored L-leucine’s effect on body composition and metabolism. Animal and limited human research suggest that L-leucine supplementation may help preserve lean muscle mass during calorie restriction, which is crucial for maintaining a higher metabolic rate and supporting fat loss. Some evidence also points to L-leucine’s ability to increase satiety and influence metabolic signaling pathways, including the activation of mTOR (mammalian target of rapamycin), which plays a role in muscle growth and energy expenditure.

However, while these mechanisms are promising, the evidence from clinical trials in humans remains limited and mixed. Some small studies have reported modest improvements in body composition or reductions in body fat when L-leucine is supplemented, especially in combination with calorie restriction or exercise. Yet, other studies have found minimal or no effect on weight loss outcomes when compared to control groups. Overall, the current scientific support for L-leucine as a weight loss aid is preliminary and not robust, meriting a moderate-low rating (2 out of 5). More large-scale, well-controlled human studies are needed to determine its efficacy. At this time, L-leucine may have a supportive role in weight management, especially for muscle preservation, but should not be considered a standalone weight loss solution.

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