New Study Shows These Proteins Are Crucial For Building Muscle & Losing Fat*
Protein plays a central role in metabolic health—not only by supporting muscle, but because muscle helps regulate blood sugar, insulin sensitivity, and resting energy expenditure.* Still, questions remain about which protein sources matter most and whether supplementation actually makes a meaningful difference for most folks (not just elite athletes).
In one of the most comprehensive analyses to date, researchers reviewed 150 randomized controlled trials to explore how milk-derived proteins like whey and casein affect body composition in adults. And the results are promising. Here’s what you need to know.
About the study
The goal of this research was to clarify whether supplementing with milk-based proteins (specifically whey and casein) meaningfully improved measures of metabolic health like lean mass, fat mass, body fat percentage, and waist circumference.
To do this, researchers conducted a systematic review and meta-analysis of 150 randomized controlled trials, including nearly 8,000 participants of all ages. The studies ranged from 2 to 96 weeks in length and examined daily intakes of milk protein, whey, or casein.
Milk protein improves body composition
Across studies, milk protein supplementation was consistently linked to improvements in body composition, including:
- Increases in lean body mass and fat-free mass.*
- Reductions in fat mass, body fat percentage, and waist circumference.*
Notably, these benefits occurred without significant changes in body weight or BMI. Meaning? Participants were often losing fat while maintaining (or gaining) muscle, a process known as body recomposition.*
From a metabolic health perspective, this is often more meaningful than weight loss alone, since lean mass supports glucose regulation, metabolic rate, and healthy aging.*
Further analysis revealed:
- Women and adults under 60 experienced modest reductions in body weight and BMI
- Higher whey intakes (above ~30 grams per day) over longer periods (8+ weeks) led to greater reductions in waist circumference.
- Older adults tended to gain weight, likely reflecting lean mass preservation rather than fat gain.
This is why milk protein may be especially helpful when used consistently and strategically.
How to supplement
While both whey and casein contribute to the benefits seen in this analysis, whey protein stands out as the most practical and well-studied option for daily supplementation.
Whey is:
- Rapidly digested, making it efficient for stimulating muscle protein synthesis.
- Naturally rich in leucine, the amino acid most strongly linked to muscle-building signals.*
- Often easier on digestion than casein as it has less lactose (whey protein isolate in particular has less than 1% lactose).
- Well-supported by research for improving body composition and supporting cardiometabolic health.*
For most adults, 20–25 grams of whey protein per day is enough to meaningfully support muscle maintenance and metabolic health, especially when paired with resistance training or consumed as part of a balanced meal.*
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The takeaway
This large analysis shows that protein supplements can support metabolic health by increasing lean mass while reducing fat mass and waist circumference, even when body weight stays the same.* It’s an easy addition to your daily routine that can have a big impact on your health.