Milk may be a risk factor for depression, yogurt and kefir are not
A high intake of dairy may increase the risk of depression. At least, when it comes to non-fermented forms of dairy. Fermented dairy varieties such as yogurt, buttermilk and kefir actually lower the risk of depression.
The men with the highest intake of fermented dairy were 30 percent less likely to be diagnosed with depression than the men in the tertile with the lowest intake. You can see this above. The differences between the groups were not statistically significant.
When the researchers omitted cheese and only looked at other fermented dairy products, the protective effect of a high intake increased to 38 percent and was statistically significant.
Mechanism
The researchers propose a number of possible explanations for the associations they found. One is that non-fermented dairy contains lactose. Galactose is a disaccharide, and one of them is galactose. In animal experiments, sugar accelerates aging processes. In addition, it damages brain cells. Fermented dairy contains little galactose because bacteria have converted it.
Another suspect is the protein in dairy. Many cows produce the protein A1 beta casein. That protein changes in the body into the peptide beta-casomorphin-7 [BCM-7; structural formula below].
Some nutrition scientists suspect that BCM-7 may damage the brain. If they are right, then that problem hardly arises, if at all, with fermented dairy. The fermentation process cuts beta casein proteins into smaller pieces that can no longer act as a BCM-7 precursor.
Conclusion
"If corroborated by future research, including moderate amounts of fermented dairy products (e.g., sour milk, kefir, yogurt) while limiting intake of nonfermented dairy products (e.g., milk) could form part of dietary recommendations for the prevention of depression", summarize the researchers.
"To confirm findings observed in this study, prospective studies that include repeated measures of diet and are conducted in different populations and sexes are required."
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