A recent study conducted in Sweden investigated the association between dietary fat intake and the incidence of Parkinson's Disease (PD) in over 41,000 individuals for an average of 17.6 years. The researchers found a potential link between saturated fat intake and a higher risk of PD, but they did not observe any association with total fat, monounsaturated fat or polyunsaturated fat.
However, the study's conclusion that saturated fat intake might be associated with a higher risk of PD has a logical flaw as saturated fats form a significant constituent of total fat and they are always found in the same foods as both unsaturated fats. Hence finding associations with one fat and not the others, or total fat, raises concern. The saturated fat finding might implicate dairy foods (as this is the only food group with more saturated than unsaturated fat). However, the study barely mentioned dairy products and did not investigate this further.
I did investigate dairy further and found interesting, but inconsistent results - the suggestion that milk consumption is associated with a higher risk of PD, but only in men. Another finding that low-fat dairy products have an association with PD, while high-fat dairy products do not. No plausible mechanisms were offered for any of these findings.
We also have all the usual flaws of population studies - the inaccuracy of the food frequency questionnaire, association not causation, the relative risk seems high/the absolute risk is tiny and a healthy person thing going on. The relative vs absolute risk issue was a big one in this study - the incident rates of Parkinson's Disease in the Swedish study were approximately 100 in 200,000 person-years.
My research did find some factors that seemed protective against PD (coffee, exercise and smoking) and some factors that were far greater risks than anything to do with fat (pesticides, chemical exposure and general anaesthetics).
In conclusion, it would be impossible to avoid saturated fat, as it is ubiquitous in foods. Similarly, dairy foods are valuable sources of essential nutrients, and people should not be deterred from consuming them.