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What is behind the dramatic increase in dementia in Japan over recent decades? Maybe it’s rising obesity rates or the “increases in cholesterol, saturated fat, and iron from increases in [meat and other] animal products.” Overall, calories went up just about 10% in Japan, whereas animal fat and meat consumption rose 500%, about 10 times the rise in sugary junk. Now, during this timespan, rice consumption went down, but the thinking is that rather than white rice somehow being protective, maybe they were eating something worse instead. It’s like when you find fish consumption is correlated with less disease, you wonder if it’s because they’re eating that rather than some worse meat.

If you look across multiple countries, you see a similar pattern, with “[t]he most important dietary link to [Alzheimer’s appearing] to be meat consumption, with eggs and high-fat dairy also [maybe] contributing.” There appears to be a really tight correlation between Alzheimer’s and per capita meat supply. And, then, studies within countries uncover similar findings, with Alzheimer’s and cognitive decline associated with meaty, sweety, fatty diets, whereas most plant foods are associated with risk reduction.

This could be for a variety of reasons. Animal products tend to have more copper, mercury, lead, and cadmium, and no folate but contain saturated fat and cholesterol, and pro-inflammatory advanced glycation end products, so many mechanisms that dietary modification may be our best bet for reducing risk of Alzheimer’s disease. But, how do we know it’s cause and effect? The evidence that meat consumption is causally linked to Alzheimer’s disease, well, there’s the strength of the association, the consistency across different types of studies, the fact that the dietary changes preceded the risk of dementia, the dose response—more meat linked to more risk—a bunch of plausible mechanisms. We know that “[m]eat is…a risk factor for other chronic diseases,” but there’s never been randomized controlled trials to put it to the test.

When you read reviews of the damaging effects of high-fat diets to the brain and cognition, “a number of factors are proposed to [account for the] high-fat diet-induced damage to the brain…[—] oxidative stress, insulin resistance, inflammation, and changes to [blood vessels and the integrity of the blood-brain barrier].” But, these are based mostly on studies of rodents. Yes, high fat diets can cause energy dysfunction in the brain, based on fancy MRI techniques, but if you’re looking at that and thinking that’s a weird looking brain, that’s because those are rat brains.

But, let me show you two sets of human cerebral arteries, the arteries deep inside your skull. These are the brain arteries on autopsy of non-demented elderly individuals. Here are the arteries from Alzheimer’s patients, clogged nearly completely shut with atherosclerotic plaque packed with fat and cholesterol. With CT scans, you can follow this “intracranial artery stenosis”—this brain-artery clogging—over time, and follow the “progression from mild cognitive impairment to Alzheimer’s disease.” Those who only had low-grade stenosis were pretty stable over time in terms of their cognitive function and ability to dress themselves and other activities of daily living, whereas those with more clogging started slipping over the years, and those who started out with the most brain atherosclerosis rapidly went downhill, and were twice as likely to progress to full-blown Alzheimer’s.

“Chronic consumption of standard Western diets [rich in saturated fat] and cholesterol [may] compromise [our] cerebrovascular integrity” and compromise the blood vessels in our brain. So, of course, drugs are recommended—“pharmacological modulation” of diet-induced dysfunction—but why not just try to eat healthier in the first place?

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