Research shows that people with neuropsychiatric diseases – including schizophrenia, bipolar disorder, depression, anxiety, and autism – often have significantly elevated immune reactions to casein in milk, which corresponds with the severity of their mental symptoms. And their symptoms can be “improved substantially or even been cured completely” on a dairy-free diet (82-83, 85-91).
Interestingly, casein has been shown to reduce the absorption of cysteine by 64% (92).
Cysteine is an important amino acid for mental health. I previously discussed it here.
It plays a role in the production of glutathione, your body’s master antioxidant, which protects your body from oxidative stress. And people with mental health problems often have high levels of oxidative stress (93-94).
Therefore, milk may indirectly reduce glutathione levels and increase oxidative stress by preventing the amino acid cysteine from entering cells (92).
Perhaps this is why so many people find benefit from supplementing with n-acetyl-cysteine.
Folate is another critical nutrient for mental health, and milk has been shown to decrease the transport of folate into the brain (95).
This makes sense considering that folate plays a key role in methylation, and other research has found that casein also reduces DNA methylation by 43% (96).
Lastly, researchers have also discovered that high levels of lactose in the intestines can interfere with tryptophan metabolism and serotonin levels. They concluded that lactose malabsorption may play a role in the development of depression (84).
All this being said, it seems that dairy affects everyone differently.
So you should try eliminating all conventional milk-based foods including ice cream, cheese and yogurt for 30 days. Then try adding it back in and examine how you feel.
It’s important to note that the milk in the grocery store is usually processed, homogenized, and pasteurized with distorted fats and denatured proteins. It’s not considered a whole food and I think everyone should avoid it.
My free food guide still includes grass-fed, full-fat, organic dairy because it’s a healthy whole food and plenty of people can tolerate it just fine.
I personally choose not to eat any milk or dairy though because I still feel better without it.
In conclusion, here is Dr. Daniel Kalish’s take on dairy. He is the author of The Kalish Method: Healing the Body, Mapping the Mind: