The past few weeks and months have seen the publication of a raft of studies on the complex interplay of diet, obesity and dementia.

We learned that the very common “heavier” allele of the obesity-related FTO gene is associated with brain atrophy in older adults.¹ A prospective study of 2,148 healthy elderly New Yorkers found that foods considered good for heart health were also associated with lower rates of Alzheimer’s diagnosis: salad dressing, nuts, fish, tomatoes, poultry, cruciferous vegetables, fruits, and dark, green leafy vegetables. Those who ate more high-fat dairy products and butter, red meat and organ meat, conversely, had higher rates of AD diagnosis.²

Another recent study found that a high-fat diet was associated with cognitive impairment in mice, and with higher levels of brain inflammation markers.³

Bigger waist = smaller brain?

These add to a growing literature on the association between cardiovascular risk factors and dementia. Recent observational studies from Sweden⁴ and California⁵ found an association between obesity or adipose fat at age 40, and cognitive decline decades later. Meanwhile, the 30,000-subject ongoing REGARDS trial, though mainly designed to find stroke risk factors, has shown that a 10% increase in diastolic BP in people over 45 correlates to a 7% increased risk of cognitive impairment.⁶

We have plenty of observational (hypothesis-generating) data that being overweight, or having diabetes and hypercholesterolemia leads to more dementing illnesses. We have few good-quality randomized controlled trials to prove that hypothesis — that controlling risk factors prevents cognitive decline. And the role of the FTO gene certainly needs more investigation.

Weighing the evidence

But the evidence all leans in the same direction. Even dementia that isn’t classified as vascular dementia is likely to have a vascular component. And even if the link between diet and Alzheimer’s risk is disproved, a good diet should still help protect against dementia by preventing strokes. The same is certainly true of exercise, where the evidence of a cognitive protective effect is stronger.

In my clinical practice, I tell patients that to live to 100 outside the nursing home requires for most a lot of hard work as well as good genes. I personally believe — but can’t prove — that controlling risk factors will reduce vascular events in a period of 2-5 years, not least, of course, by preventing cerebrovascular accidents. Like most healthcare providers, I’m saddened and frustrated that over 75% of my patients are overweight and, despite good medications to control risk factors, are suffering from the epidemic of obesity. Unfortunately, keeping one’s weight down is the hardest risk factor to treat.