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Casein is a high quality dairy protein with an excellent amino acid profile. It is rich in essential amino acids, including BCAAs, and contains other ingredients, like calcium, that stimulate muscle growth. Casein is most commonly used in its long acting micellar form, where it can provide the body with amino acids for up to eight hours. It is a great night-time protein, and a lot of bodybuilders and athletes rely on casein to keep their nitrogen balance positive so they can build muscle while they sleep. In their groundbreaking 1997 research, Yves Boirie and his team declared Casein to be the only known anti-catabolic protein (4). Casein is packed full of benefits, but some people also have side effects.

Casein & Acne

Casein is known to stimulate the release Insulin-Like Growth Factor-1 (IGF-1). IGF-1 is a hormone which is produced in the liver in response to Human Growth Hormone (HGH), and it is responsible for the bulk of HGH's anabolic effects (1).

IGF-1 is associated with increased growth of all cells in the body, including the skin. Studies have correlated the level of IGF-1 in the bloodstream with higher production of oils in the skin, greater skin cell turnover, and larger pore size (2). While these are all factors that can encourage acne, this evidence may be circumstantial. When a later study looked at the prevalence and severity of acne and levels of circulating IGF-1, they couldn't find a significant correlation between these two factors in men, although they did in women (3).

There are a lot of arguments debating whether or not casein causes acne – arguments which may never be solved one way or another. The best thing to remember is that not every supplement is going to do the same thing for everyone. Casein is a very safe product with a huge number of benefits, so there's really no harm in giving it a go.

Casein & Indigestion

Casein has been reported by some people to cause symptoms of indigestion.

Micellar casein is taken for its long-acting properties. The reason casein is able to release amino acids into the body over such a long time period is due to the fact that it forms a bolus, or large clot, when it comes into contact with stomach acid. This bolus is then slowly dissolved by stomach acid and enzymes over the course of many hours.

The stomach, when empty, is a very small organ, with a capacity of less than 100mL. The distension of the stomach is known to stimulate the production of gastric juices, which are rich in hydrochloric acid – This is an important part of digestion. It is possible that the prolonged distension of the stomach may produce a feeling of bloating, along with excess acid production, which may cause symptoms of indigestion, like heartburn and acid reflux in people who are susceptible to such conditions. Casein allergies or intolerances may also cause symptoms of indigestion.

Casein & Allergies

As is the case with almost every protein, people can be allergic to Casein. Casein makes up 80% of the protein in milk, and casein allergy is likely something that the sufferer would have a prior awareness of (5).

That said, milk is made up of a number of different proteins and sugars, including whey protein and lactose, the milk sugar which is one of the most common causes of food intolerence in adults.

Casein allergy can cause effects similar to other food allergies such as swollen lips, hives and eczema, difficulty breathing, or in extreme cases, anaphylactic shock.

Casein intolerances are also common. An intolerance is not the same as an allergy, and may cause gastrointestinal symptoms, such as diarrhoea, bloating and vomiting, or less commonly, people report fatigue and joint pain.

If an allergy is suspected, the first thing to do is to stop taking supplements and see a doctor, who can test you for allergies. If the tests do not show an allergic reaction, try a casein free diet for a month and see if symptoms improve.

(1) Michelle D. Holmes, Michael N. Pollak, Walter C. Willett, Susan E. Hankinson. Dietary Correlates of Plasma Insulin-like Growth Factor I and Insulin-like Growth Factor Binding Protein 3 Concentrations. Cancer Epidemiol Biomarkers PrevSeptember 2002 11; 852
(2) Sugiyama-Nakagiri Y, Naoe A, Ohuchi A, Kitahara T. Serum levels of IGF-1 are related to human skin characteristics including the conspicuousness of facial pores. Int J Cosmet Sci. 2011 Apr;33(2):144-9.
(3) Cappel M, Mauger D, Thiboutot D. Correlation between serum levels of insulin-like growth factor 1, dehydroepiandrosterone sulfate, and dihydrotestosterone and acne lesion counts in adult women. Arch Dermatol. 2005 Mar;141(3):333-8.
(4) Boirie Y, Dangin M, Gachon P, Vasson MP, Maubois JL, Beaufrère B. Slow and fast dietary proteins differently modulate postprandial protein accretion. Proc Natl Acad Sci U S A. 1997 Dec 23;94(26):14930-5.
(5) G. H. Docena, R. Fernandez, F. G. Chirdo, C. A. Fossati. Identification of casein as the major allergenic and antigenic protein of cow's milk AllergyVolume 51, Issue 6, pages 412–416, June 1996

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