What evidence is there that our meat-sweet diets play a cause-and-effect role in dementia?
What is behind the dramatic increase in dementia in Japan over recent decades? As you can see at the start of my video How to Prevent Alzheimer’s with Diet, rates have climbed significantly. Is it due to rising obesity rates or “increases in cholesterol, saturated fat, and iron from increases in animal products and meat supply for Japan”? Overall in Japan, calories only went up about 10 percent, but animal fat and meat consumption rose 500 percent, which was about ten times the rise in sugary junk. During this time span, rice consumption went down. Was white rice protective in some way so the decrease in intake is to blame? Instead, the thinking is that they were eating something worse: “it seems that the association between rice supply and AD [Alzheimer’s disease] in Japan is more likely due to replacement of rice by animal products.” It’s like when fish consumption is found to be correlated with less disease, so you have to wonder if the decrease is actually because of something protective in fish or, instead, because fish just isn’t as bad as other kinds of meat.
If you look across multiple countries, you see a similar pattern: “The most important dietary link to AD appears to be meat consumption, with eggs and high-fat dairy also contributing.” As you can see at 1:02 in my video, there appears to be a really tight correlation between Alzheimer’s and per capita meat supply. Studies within countries have uncovered similar findings, with Alzheimer’s and cognitive decline associated with meaty, sweet, and 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, and also contain saturated fat, cholesterol, and pro-inflammatory advanced glycation end products. In fact, “there are many mechanisms linking meat in particular and diet in general to risk of AD” so dietary modification may be our best bet for reducing risk of Alzheimer’s. How do we know that it’s cause and effect, though? What is the evidence that meat consumption is linked causally to Alzheimer’s disease? Well, as you can see at 1:49 in my video, there are a number of plausible mechanisms: the “strength of association,” “consistency of findings” across different types of studies, the fact that the dietary changes preceded the risk of dementia, and the dose response of more meat linked to more risk. We know that meat is a risk factor for other chronic diseases, but there have never been randomized controlled trials to put it to the test for brain dysfunction.
When you read reviews of the “damaging effects of a high-fat diet to the brain and cognition,” “a number of factors have been proposed to cause high-fat diet-induced damage to the brain, especially with aging, including oxidative stress, insulin resistance, inflammation, and changes to vascularization/BBB integrity,” that is, the blood vessels and the integrity of the blood-brain barrier—but these are based mostly on studies of rodents. Yes, based on MRI techniques, high-fat diets have been shown to cause energy dysfunction in the brains…of rats.
What about human brains? At 2:46 in my video, you can see two sets of human cerebral arteries, the arteries deep inside the skull, on autopsy of non-demented elderly individuals compared to Alzheimer’s patients. As you can see, the cerebral arteries of people with Alzheimer’s are so clogged with atherosclerotic plaque packed with fat and cholesterol that they’re nearly completely shut. With CT scans, you can follow the intracranial artery stenosis—that is, the clogging of the brain arteries—over time and observe the progression from mild cognitive impairment to Alzheimer’s disease. As you can see at 3:17 in my video, those who had only low-grade stenosis were fairly stable over time in terms of their cognitive function and ability to dress themselves and execute other activities of daily living, whereas those with more arterial clogging started to slip over the years. In contrast, 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 Western-style diets enriched in SFA [saturated fat] and cholesterol compromise cerebrovascular integrity”—the integrity of the blood vessels in our brain. So, of course, “pharmacological modulation” of diet-induced dysfunction is recommended, but, rather than taking drugs, why not just try to eat more healthfully in the first place?
- The dramatic increase in dementia in Japan over recent decades has been associated with an increase in animal products, including meat, and a decrease in rice consumption.
- Animal fat and meat consumption has gone up by 500 percent in Japan, while calories only increased by approximately 10 percent.
- Across countries, intake of meat, especially, as well as eggs and high-fat dairy, appears to be the “most important dietary link” to Alzheimer’s disease.
- Alzheimer’s and cognitive decline have been associated with diets heavy in meat, sweets, and fat, while most plant foods are associated with reduced risk.
- Many factors have been proposed as the cause of high-fat, diet-induced damage to the brain, particularly with aging, including inflammation and changes to blood vessels and the integrity of the blood-brain barrier.
- On autopsy, the cerebral arteries of Alzheimer’s patients are so clogged with atherosclerotic plaque packed with cholesterol and fat that they are nearly closed.
- The standard American diet, rich in saturated fat, cholesterol, and animal products, has been shown to compromise the integrity of blood vessels in the brain.
For those familiar with the scientific record, none of this comes as a surprise. In fact, I’ve covered similar studies in the past. Check out:
In fact, I even debated whether or not to make this video. When a new broccoli-is-good-for-you study comes out, for instance, I just think: Been there, done that. But, so many people seem confused about the role of diet and lifestyle in dementia that I figured I’d just cover the latest study even though not much new ground has been broken.
Michael Greger, M.D.
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