Does Alzheimer’s Start in the Gut?

1 in 3 seniors die of Alzheimer's.

Source: Source: Midjourney

A new study from a group of researchers at University College Cork (UCC), in Ireland, has found that symptoms of Alzheimer’s can be transferred by gut microbes. This has major ramifications for the prevention and treatment of this malady.

Alzheimer’s is an intractable disease that afflicts one in nine people over the age of 65. It leads to a progressive decline in cognitive function, memory, and behavior. There are no cures, even after decades of research. It is characterized by the accumulation of amyloid beta, a protein that builds up between nerve cells in the brain and is a common target of drug treatments.

However, some people with amyloid beta do not show symptoms of dementia, and some people with dementia do not have amyloid beta in their brains. Thus, amyloid beta is a less than perfect marker of the disease. In fact, there is some evidence that amyloid beta is part of the brain’s defense against inflammation, and therefore is more like the fireman at the fire than an arsonist.

The hundreds of drugs created to treat amyloid beta have not made much of a dent in the rates of Alzheimer’s and many researchers believe it is time to reevaluate the amyloid theory altogether. That is why this new study is so important: It posits a new way of looking at the disease and potentially offers a hopeful way to prevent or even treat Alzheimer’s.

What they found

The study, by Yvonne Nolan, Stefanie Grabrucker, Sandrine Thuret, Annamaria Cattaneo, John Cryan, and colleagues, transferred fecal matter from people with Alzheimer’s to rats, and found that doing so impaired nerve growth in the rat hippocampus, a part of the brain responsible for memory, cognition, and mood. The more severe the donor’s disease, the greater the cognitive loss in the rats. As they put it, “Our findings reveal for the first time that Alzheimer’s symptoms can be transferred to a healthy young organism via the gut microbiota, confirming a causal role of gut microbiota in Alzheimer’s disease.”

Alzheimer’s research has long suffered from low expectations and failure, so this is a heartening breakthrough. The study used rats, so it awaits clinical confirmation, but it demonstrates causality, and cross-species causality to boot.

It’s a powerful finding. Revealing a microbial root of the disease is especially cheering because we can control our gut microbiota.

How did we get here?

The odds of dementia increase with age. So, as our life expectancy increases, the rates of Alzheimer’s naturally go up. But there may be another contributor to the current high rates of Alzheimer’s: diet.

Over the last 75 years, the consumption of ultra-processed foods has gone from essentially zero to 60 percent of our diet today. Today’s foods are more manufactured than grown.

Fiber can make food coarser and brown, so the first step in most food processing is to eliminate it. In the mid 1900s, fiber seemed like superfluous indigestible roughage. We may not be able to digest fiber, but our gut microbes can and they love it. Eliminating fiber also has a side effect of concentrating the fats and carbs, which may favor pathogenic microbes.

Fiber supports beneficial bacteria like species of Clostridia and Coprococcus that create butyrate, a substance that both heals and nourishes the gut lining. The UCC study found that levels of these bacteria, as well as butyrate, were lower in the rats who got the Alzheimer’s microbiota.

The amino acid taurine was also decreased in the Alzheimer’s rats, and it may play an important role as well. Both butyrate and taurine can easily cross the blood-brain barrier, where they can encourage the growth of new nerve cells in the hippocampus.

The Alzheimer’s microbiotas had high levels of disease-associated bacteria like Desulfovibrio and Dialister that can secrete toxins when unbalanced. Low levels of butyrate could lead to a “leaky gut," allowing those toxins and other bacterial secretions to breach the gut lining and enter the bloodstream. Over time, that bitter cocktail can damage tissue and cause inflammation.

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In a separate experiment, the UCC study found exactly that: Serum from Alzheimer’s patients was able to halt the growth of nerve cells.

What to do

The implication is that reintroducing fiber to our diets may protect us from Alzheimer’s. That’s as easy as rediscovering the veggie department in your local store.

A diverse gut microbiota is healthiest. To support it, you need variety in your diet. So aim for a couple of dozen different veggies a week. Broccoli, Brussels sprouts, cabbage, asparagus, and cauliflower are easy and familiar. But give Jerusalem artichokes, escarole, celeriac, ramps, dragon fruit, and kohlrabi a chance. Fermented foods like yogurt, kimchi, and sauerkraut include both probiotics and prebiotics and promote a healthy microbiota. A recent study found a protective effect of fish, coffee, cocoa, and red wine. That’s a Mediterranean-style diet, and it is not a hardship.

If you can’t manage to include these healthy foods in your diet, a probiotic or prebiotic supplement may help. Just make sure they have a good blend of ingredients to promote diversity.

Exercise also has tons of benefits, and it helps your gut microbes as well.

You may be set in your ways, but give it a try. If it lowers your odds of getting Alzheimer’s, a little novelty in your life is a small price to pay.