J Gerontol A Biol Sci Med Sci. 2002 Dec; 57(12): M797-802.

Differential relations between cognition and 15N isotopic content of hair in elderly people with dementia and controls.

Williams JH, O'Connell TC.

OPTIMA, Radcliffe Infirmary, Oxford, United Kingdom. jonathan.williams@pharmacology.ox.ac.uk

BACKGROUND: Previous researchers have suggested that a vegetarian diet or one rich in fish may protect against Alzheimer's disease (AD). However, assessing diet is difficult in AD patients. (15)N:(14)N isotopic ratios (delta(15)N) of body proteins can estimate long-term dietary habits in a way that does not depend on memory. delta(15)N is high in people who eat a lot of fish and low in vegetarians. METHODS: To choose between the vegetarian and fish hypotheses of AD, we compared dietary questionnaire reports and delta(15)N of hair samples from AD patients and controls. RESULTS: Patients' cognitive scores related directly to reported frequency of eating fish and to hair delta(15)N(AIR), but inversely to reported frequency of eating beans. Homocysteine levels related inversely to hair delta(15)N(AIR) in controls, but not in patients. Dietary questionnaire reports accounted for slightly more variance in delta(15)N(AIR) in patients than controls. Therefore, our questionnaire assessed dietary habits as reliably for individuals with AD as for cognitively unimpaired controls. CONCLUSIONS: A diet rich in fish may ameliorate AD, possibly by lowering homocysteine, but more vegetarian diets do not. In fact, eating beans correlated with worse cognition in AD patients. Further studies should test if restricting the intake of beans slows the progression of AD.