Gut Bacteria and Alzheimer’s: The Hidden Molecule Revealed

Have you ever walked into a room and completely forgotten why you went there? Most of us have. After 50, that little moment can bring a quiet worry: Is my memory slipping?

Most people picture the brain as the whole story of memory. But one of the most exciting areas of research I follow points somewhere you might never expect: your gut. A study recently published in Nature Communications adds a surprising new chapter to the story of gut bacteria and Alzheimer’s.

Researchers at the University of Wisconsin-Madison found that a molecule called imidazole propionate, or ImP, which is made by certain gut bacteria, was linked to Alzheimer’s-type changes and faster decline in thinking skills. You can read the summary in the ScienceDaily story. In this article, I want to walk you through what the researchers found, what it does and does not mean, and the practical steps I share with my own patients.

🔬 What the Study on Gut Bacteria and Alzheimer’s Found

This was not one simple experiment. It was a mixed study that looked at the question from three angles: people, mice and cells. That matters, because each kind of evidence tells us something different.

The human side: almost 1,200 people

The team analyzed blood samples from almost 1,200 people enrolled in the Wisconsin Registry for Alzheimer’s Prevention and the Wisconsin Alzheimer’s Disease Research Center. According to the earlier preprint version of the paper, these were cognitively unimpaired adults, meaning their memory and thinking tested as normal, with an average age of about 61.

People with higher blood levels of ImP were much more likely to show biological markers of abnormal brain proteins and impaired nerve cell function. Those with the very highest ImP levels also showed much faster cognitive decline when their memory and thinking were tested again over time.

The researchers also looked at stool samples from 294 people in a separate gut microbiome group to see which bacteria carry the genes for making ImP. The preprint reports that two other large groups, one in Britain and one in the Netherlands, showed matching results linking ImP and cognition.

The animal and cell side

In mice, ImP that reached the brain increased the buildup of beta-amyloid and tau. These are two proteins that form clumps and tangles in the brains of people with Alzheimer’s. The preprint also found that giving ImP to mice made the blood-brain barrier leakier.

In lab dishes, human brain blood vessel cells exposed to ImP at levels seen in people showed weaker barrier integrity. That is a cell finding, not a human trial, but it gives us a clue about how this molecule might act.

A genetic twist

About 43 percent of the people in the study carried a genetic variant tied to substantially higher blood ImP. The researchers suspect this variant affects how well the kidneys clear ImP from the body. Interestingly, that same variant had already been linked to Alzheimer’s risk in earlier large genetic studies.

The honest limitations

I always want you to know the strengths and the weak spots of any study. Here, the human data show an association, not proof of cause. In other words, higher ImP traveled together with worse brain markers, but that does not prove ImP caused the decline in people.

The cause-and-effect evidence comes from mice and cells. The mice received ImP in their drinking water, which may not work the same way as bacteria producing it inside the gut. The main human group came from a single site, was mostly White and mostly female, and had limited information on diet and lifestyle. And importantly, no study has shown that lowering ImP through diet, probiotics or supplements protects the brain. One study is never the final word.

🧠 Why the Gut-Brain Connection Matters

For years I have taught that the gut and the brain are in constant conversation. Your gut is home to trillions of microbes, together called the microbiome. These tiny residents digest food, train your immune system and produce a wide range of compounds that travel through your bloodstream.

ImP is one of those compounds. Gut bacteria make it from histidine, an essential amino acid. “Essential” means your body cannot make it on its own, so you must get it from food. Histidine is found in many protein foods, which is exactly why this story is more complicated than it first appears.

According to the University of Wisconsin-Madison news release, bacteria in most people’s digestive tracts produce ImP. Senior author Federico Rey explained that production varies a great deal from person to person, and that the bacteria able to make it are present in many people but usually not abundant.

Here is the picture that emerges. Certain gut bacteria turn histidine into ImP. ImP enters the blood. In animals, it appears to weaken the brain’s protective barrier and worsen the protein buildup seen in Alzheimer’s. And if your kidneys clear it more slowly because of your genes, levels may run higher.

This same team noticed nearly 10 years ago that the gut microbe communities of people with Alzheimer’s look different from those of healthy people. Now they may have found one molecule that helps explain why. That is how good science works: one careful step at a time.

Other research is pointing in a similar direction. A separate UCLA study of nearly 1,500 adults found that brains that looked older than their actual age on scans were linked with specific gut bacteria and metabolites, along with poorer working memory. That study was also a snapshot in time, but its senior author said it opens the door to exploring whether gut health could one day support healthier brain aging. And an abstract in Alzheimer’s & Dementia describes ImP as a gut-derived histidine byproduct that may cross the blood-brain barrier, framing the microbiome as a possible target for early action.

Please do not throw out your eggs

When patients hear “a protein building block feeds this molecule,” their first instinct is often to cut out eggs, meat or fish. Please do not do that. Senior author Barbara Bendlin said that improving your diet in general would probably help, but it is not as simple as “stop eating eggs” or “don’t eat so much red meat,” because histidine is in so many foods and your body needs it.

In my practice, I see the opposite problem far more often in adults over 50: too little protein, which can contribute to muscle loss and frailty. Balance, not elimination, is the wise path.

🌿 How to Protect Your Brain as You Age: 6 Gut-Friendly Habits

Since no diet, probiotic or supplement has been shown to lower ImP or protect memory, what can you do? The answer is reassuring. The same lifestyle habits that support a healthy, diverse microbiome and a healthy brain remain your best foundation. These are the habits I teach in my books and with my patients every week.

If you want to go deeper on the first habit, I explain how fiber shapes your microbiome in my article on a high-fiber diet and gut bacteria. For an eating pattern built specifically around brain health, see my review of the MIND diet and brain aging. And because rest is so often overlooked, I also recommend reading about how sleep loss affects brain health.

A word about probiotics. Many of my patients ask whether a probiotic could “fix” ImP. The honest answer is that no study shows that. In fact, the preprint lists some species of Lactobacillus and Streptococcus among bacteria that carry the gene for making ImP. That does not mean these friendly bacteria are bad. It simply reminds us that the microbiome is complex, and no single capsule replaces a whole-food, whole-person lifestyle.

The researchers do see a possible future in which ImP could be lowered with a targeted approach, perhaps aimed at the bacteria or the enzyme that makes it. They compared that idea to the way statins target cholesterol. That is future speculation, and there is nothing available today. For now, the time-tested foundations are where your power lies.

That is the heart of what I have written about for years in two of my books. In Dr. Colbert’s Healthy Gut Zone, I show readers how to build a healthier gut ecosystem step by step. In Dr. Colbert’s Healthy Brain Zone, I lay out a whole-person plan for protecting memory and mental sharpness as we age. This new research is a fresh reminder of why those two subjects belong together.

✅ Your Gut-Brain Action Plan

Here is a simple plan you can start this week. None of these steps depends on lowering ImP. They are the everyday foundations that support a healthy gut and a healthy brain.

1. Fill half your plate with plants. Make vegetables the main event at lunch and dinner, and add berries, beans, nuts or seeds wherever you can.
2. Trade one processed food for a whole food each day. Swap chips for a handful of walnuts, or a sugary drink for sparkling water with lemon.
3. Keep your protein balanced. Enjoy eggs, fish, poultry and legumes in sensible portions. Do not cut out protein because of this study.
4. Take a daily walk. Start where you are, even 10 minutes after a meal, and build from there.
5. Protect your sleep. Choose a consistent bedtime, dim the lights in the evening and keep your bedroom dark and cool.
6. Make room for peace. Spend a few quiet minutes each morning in prayer, Scripture and gratitude, and reach out to a friend or family member each week.
7. Talk with your doctor. If you notice memory changes or have a family history of dementia, schedule a visit. Keep up with routine checkups for heart, kidney and metabolic health, and never stop or change a prescribed medication without your physician’s guidance.
8. Keep learning. Use Dr. Colbert’s Healthy Gut Zone and Dr. Colbert’s Healthy Brain Zone as your step-by-step guides.

❓ Frequently Asked Questions

Do gut bacteria cause Alzheimer’s?

This study does not show that. In people, higher ImP was associated with brain protein markers and faster cognitive decline, but an association is not proof of cause. The cause-and-effect evidence so far comes from mice and cultured cells, and more human research is needed.

What is imidazole propionate?

Imidazole propionate, or ImP, is a compound some gut bacteria make from histidine, an essential amino acid found in many foods. How much ImP a person makes varies widely. Earlier research had linked ImP to type 2 diabetes and coronary artery disease, and this new study adds brain health to the conversation.

Should I stop eating eggs or red meat to protect my brain?

No. The researchers specifically said it is not as simple as cutting out eggs or red meat, because histidine is essential and found in many foods. A balanced, whole-food diet rich in plants with sensible protein portions is a wiser approach than eliminating protein.

Can probiotics or supplements lower ImP?

No study has shown that diet, probiotics or supplements lower ImP or protect memory. Some common friendly bacteria actually carry the gene for making ImP, which shows how complex the microbiome is. Focus on fiber-rich whole foods, movement, sleep and stress care, and talk with your doctor about any concerns.

If I carry the genetic variant, am I destined to get dementia?

Not at all. About 43 percent of participants carried the variant tied to higher ImP, so it is very common. Risk is not destiny, and your daily habits, along with regular care from your physician, still matter a great deal.

🌅 A Final Word of Hope

When I first started talking about the gut-brain connection decades ago, many people raised an eyebrow. Today, studies like this one from the University of Wisconsin-Madison are filling in the picture in remarkable detail. The science is still early, and I want you to hold it with both curiosity and calm.

Here is what I want you to remember. You do not need to fear your gut or cut out the foods God provided. You need to nourish the whole system: colorful plants, balanced protein, daily movement, restful sleep, loving relationships and a heart at peace with God. Those choices support your gut, your brain and your entire life.

Start with one step this week. Then take another. You are fearfully and wonderfully made, and every step of stewardship is an act of worship.

Dr. Don Colbert, MD