Protein sources that have the most essential amino acids (EAAs) are derived from cow’s milk. Milk has two types of protein: 80% of its total proteins comes from casein, and 20% of its total proteins comes from whey. Whey protein is typically found in two forms: concentrate and isolate. Whey protein concentrate typically contains 80% protein, but when you remove the lactose and fat from whey concentrate, it creates whey protein isolate, which is 90%t protein. 

What is alpha-lactalbumin?

Alpha-lactalbumin is the protein found in the second-highest amount in whey protein isolate at about 17%. It has all the benefits of whey protein; i.e., it is a complete source of protein that is high in EAAs, rich in branched-chain amino acids (BCAAs), has high digestibility, and is lactose- and fat-free.* 

It is the unique amino acid composition that makes alpha-lactalbumin a perfect protein option for individuals seeking a variety of benefits.

1. Alpha-lactalbumin is naturally high in tryptophan

Tryptophan is one of the most limited amino acids in food proteins. However, alpha-lactalbumin provides 48 mg of tryptophan per gram of protein, its highest content in all food protein sources.1

Alpha-lactalbumin as a protein source increases blood tryptophan levels, which promotes the synthesis and availability of serotonin in the brain.* In turn, serotonin supports the production of melatonin, the hormone that helps regulate sleep patterns.*

Newer research suggests that alpha-lactalbumin promotes restful sleep in adults who experience inconsistent sleep due to shift work or who restrict food or fast for periods of time.*

Tryptophan content is one reason why alpha-lactalbumin consumption is recommended prior to sleeping.

Although the amino acid tryptophan is also recognized for its neurological benefits.* Research has shown that tryptophan from alpha-lactalbumin whey isolate, via its conversion to serotonin, can improve abstract visual memory,2 cognitive performance,3 and mood4 in individuals vulnerable to stress.*

Furthermore, the body uses tryptophan to synthesize niacin (vitamin B3), which is involved in functions of the digestive system, cardiovascular system, skin, and nervous system.*

2. Alpha-lactalbumin is high in cysteine

Alpha-lactalbumin provides 48 mg of cysteine per gram of protein. Cysteine is the direct precursor to the antioxidant glutathione, which is involved in body processes that support the immune system, build and repair tissues, and protect against oxidative damage.*

However, the bioavailability of cysteine is rate limiting to produce glutathione, and research suggests typical diets are limited in cysteine availability.1

In the latest position stand on protein by the International Society of Sports Nutrition, alpha-lactalbumin is also promoted for its capacity to speed wound healing,5 which is vital for recovery from combat and contact sports.*6

3. Alpha-lactalbumin is a rich source of sulfur-containing amino acids

Alpha-lactalbumin whey protein contains a highly unique 5:1 ratio of cysteine to methionine – a ratio that is physiologically favorable. Methionine is central to the methylation cycle, a crucial process that requires folate, vitamin B12, and choline, and is essential for the synthesis of nucleotides, the building blocks of DNA.*

However, in excess, too much methionine can prevent re-methylation of homocysteine, resulting in build-up of homocysteine in the blood. High levels of homocysteine have been linked to cardiovascular disease, osteoporosis, and other chronic health conditions. 

The diet and supplementation together need to provide adequate cysteine to support glutathione production and sufficient methionine.*

Whey protein provides a rich source of cysteine with lower levels of methionine, and the source of cysteine from alpha-lactalbumin, specifically, supports digestion, absorption, and utilization of this important amino acid.*1

4. Whey protein (including alpha-lactalbumin) is a rich source of essential amino acids.

Whey protein is high in EAAs, the nine of 20 amino acids that must come from the diet because the body can't synthesize them. Furthermore, BCAAs, specifically leucine, plays a direct role in initiating muscle protein synthesis.*

EAAs support rebuilding, repair, and synthesis of muscle proteins even in the presence of lower protein or lower caloric intake.*

Therefore, alpha-lactalbumin whey protein supports athletes or individuals seeking to maintain or build muscle mass during periods of catabolic conditions, such as overnight fasting, weight loss, bed rest, aging, intense exercise/stress, or illness* – another reason to consume alpha-lactalbumin during the pre-sleep window.

5. Alpha-lactalbumin whey protein contains bioactive peptides

Bioactive peptides possess prebiotic properties and have a unique potential application for human health. Research suggests the specific effects of alpha-lactalbumin on the gut are in part from the bioactive peptides from the unique tryptophan and cysteine combination and other post-translational modifications of these amino acids.

These two amino acids can have regulatory effects on the gut; together, they support intestinal motility, immune health, the functioning of the gastrointestinal, endocrine, cardiovascular, and pulmonary systems, and play a role in regulating food intake and energy (caloric) balance.*7

While much of the research in this area supports infant development, the theory of the ability of bioactive peptides to promote gastrointestinal function might also translate to supporting immune function in adults.*1 


1. Layman D, Lönnerdal B, Fernstrom J. Applications for α-lactalbumin in human nutrition. Nutr Rev 2018;76(6):444-460.

2. Booij L, Merens W, Markus C, Van der Does A. Diet rich in alpha-lactalbumin improves memory in unmedicated recovered depressed patients and matched controls. J Psychopharmacol 2006;20(4):526-535.

3. Markus C, Olivier B, de Haan E. Whey protein rich in alpha-lactalbumin increases the ratio of plasma tryptophan to the sum of the other large neutral amino acids and improves cognitive performance in stress-vulnerable subjects. Am J Clin Nutr 2002;75(6):1051-1056.

4. Markus C, Olivier B, Panhuysen G, et al. The bovine protein alpha-lactalbumin increases the plasma ratio of tryptophan to the other large neutral amino acids, and in vulnerable subjects raises brain serotonin activity, reduces cortisol concentration, and improves mood under stress. Am J Clin Nutr 2000;71(6):1536-1544.

5. Minet-Ringuet J, Le Ruyet P, Tomé D, Even P. A tryptophan-rich protein diet efficiently restores sleep after food deprivation in the rat. Behav Brain Res 2004;152(2):335-340.

6. Jäger R, Kerksick C, Campbell B, et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr 2017;14:20.

7. Berger M, Gray J, Roth B. The expanded biology of serotonin. Annu Rev Med 2009;60:355-366.