The Microbiome, Insulin Balance and Healthy Brain Function: A Nutritionist’s View

Alana Kessler MS RD avatar

by Alana Kessler MS RD |

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diet and Alzheimer's

My grandfather was diagnosed with Alzheimer’s disease 15 years ago and passed away in 2013. I remember his final years well — the confusion, the despair, and the devastation on my father and uncle’s face as he would call them “sonny,” because he couldn’t remember their names.

I could feel his frustration, too. He was an artist. A man with a spirit and a voice that would fill up a room, and eyes that were kind and inviting, always available to listen and nurture. 

Those years would prove to be a challenge for the whole family, as the disease progressed and his vibrancy, enthusiasm and effervescence slowly began to fade.

Patience and understanding were the only “treatments” available. Alzheimer’s was seen as a hereditary and, exclusively, neurological affliction, and those factors alone ruled determinations of its likely prevalence and progression.

But as the medical community has begun to explore the concept of “gut integrity” — the idea of a connection, even a conversation, between the brain and the gut — new holistic insights into how lifestyle, including diet and mindfulness, may affect disease development, its management and prevention are coming to the fore.

The microbiome is a word being used often and is defined as this. The microbiota is a community of microorganisms, for example, fungi, bacteria and viruses, that live inside the human body. Their collective genomes comprise the microbiome. 

These microorganisms, the gut and its unique enteric nervous system, and the brain all communicate through a brain-gut axis that comprises and involves the autonomic nervous system — the part of the nervous system in charge of bodily functions that include breathing, heartbeats and digestive processes. This system is also in charge of “flight or fight” reactivity, which is the sympathetic nervous system, and “rest and digest” response, which is the parasympathetic nervous system. 

The vagus nerve, the principal component of the parasympathetic nervous system, runs from the brainstem to the gut, and is able to sense the metabolites of the microbiota. It transfers that information to the central nervous system, where it is integrated and, in turn, creates a response via the autonomic nervous system.

The vagus nerve has an inherent anti-inflammatory pathway within its fibers, regulating the innate immune response by decreasing intestinal permeability — defined as the ability of foreign substances to enter into the bloodstream and create inflammation. Stress and poor diet inhibit the vagus nerve and create a dysbiosis, or instability, of the microbiota. This dysbiosis creates a pathway where potentially harmful substances can enter the blood-brain barrier, altering the integrity of the cells and their functionality.

Attention to the microbiomes of people with Alzheimer’s disease (AD) is increasing, and changes in the intestinal flora caused by inflammatory responses to fat- and sugar-rich Western diets, pathogens, chemicals, and stress are becoming more significant. We are beginning to learn more about how the vagus nerve, which connects the gut to the brain, can impact the initiation of AD as well as its progression.

One theory is that of increased intestinal permeability, or the idea that microbes and harmful antigens that are normally unable to cross the epithelial (cellular) barrier that surrounds the gut, and ideally works only to let nutrients through, are able to gain access to the bloodstream and enter system-wide circulation. Their very presence creates oxidative stress (an excess of reactive oxygen molecules) that leads to chronic inflammation and — because of the gut-brain connection — damages nerve cells in the brain.

In the study “Gut microbiome alterations in Alzheimer’s disease published in Scientific Reports in 2017, vast differences were found in the gut microbiome of Alzheimer’s patients and healthy age- and sex-matched individuals, with patients showing a marked decrease in bacterial “richness and diversity” that may “play important roles in disease progression and maintenance, potentially through immune activation and systemic inflammation,” its authors wrote. The significance of the findings in what is said to be the first study of the gut microbiome in Alzheimer’s patients isn’t yet clear and more research needs to be done.

But similar, broad-scale dysbiosis has also been reported in people with Parkinson’s, diabetes, and obesity, among other chronic ills.

How do standard Western diets and sugar contribute to the pathogenesis of AD? To answer this question we must take a look at how sugar is digested and processed in the body, and explore the important and precarious role of insulin.

Insulin is a hormone produced by the pancreas. Its main function is to uptake glucose from the blood that we get from food, and transport it to muscles, fat, and the liver for energy. A Western diet is the most common and convenient choice for most of us, but its focus on fast and pre-packaged food has put a strain on our overall health via its impact on the microbiota and hormone balance — specifically, insulin. 

In “Insulin resistance and Alzheimer’s disease pathogenesis: potential mechanisms and implications for treatment,” published more than a decade ago in Current Alzheimer Research, the authors reported on insulin resistance and its effect on cognition and brain function.

They noted “insulin resistance increases the risk of age-related memory impairment and Alzheimer’s disease. Possible mechanisms through which these risks are increased include the effects of peripheral hyperinsulinemia on memory, CNS [central nervous system] inflammation, and regulation of the beta-amyloid peptide.”

How does resistance to insulin begin?

Resistance ensues when highly processed and refined sugar diets stimulate the pancreas to produce insulin at such an excessive rate that cells become desensitized. As a result, insulin circulates in the blood and signals the body to eat more sugar, which signals more resistance, and so on and so forth.

Obesity, type 2 diabetes, hypertension, high cholesterol, and inflammation are also correlated strongly with insulin resistance. What such findings clearly point to is the growing importance of food and lifestyle choices as a factor — and possibly a crucial factor — in AD onset and perhaps even its prevention throughout all the stages of life.

Because the brain is formed over time and over different developmental stages, conscientious attention to diet may provide protective and beneficial long-term outcomes when it comes to health.

Something of note is prenatal nutrition. It is advised that pregnant women pay close attention to their own food choices, as nutrition consumed in-utero impacts the cellular composition of the fetus, directly affecting the health trajectory as it matures.

But there is hope to be had! It is possible to choose and prepare foods in such a way that microbiome symbiosis, insulin balance, and healthy brain function can be prioritized.  

Here we go:

Choose foods from sources that are low in trans-fats, like that found in processed baked goods and margarine, and low in saturated fats  

Both trans-fats and saturated fats, as opposed to poly-unsaturated or mono-unsaturated fats, produce a blood-cholesterol profile that has been associated with AD. They both raise the “bad” LDL (Low Density Lipoprotein) cholesterol and lower the “good” HDL ( High density Lipoprotein) cholesterol. For optimal health, we want the LDL < 100 and the HDL > 40.

A Mediterranean-style diet, one high in unsaturated fats and lean protein, is recommended to support a balanced cholesterol profile. Examples of mono-unsaturated and poly-unsaturated fats are olive oil, peanut oil, canola oil, avocados, and most nuts, as well as high-oleic safflower and sunflower oils.

Poultry, lean beef, and fish — like cod, tuna, and mackerel — are great sources of protein. Vegetarians can also find healthy protein in beans, seeds, and lentils. They pack an extra punch of fiber to boot.

Eat a variety of foods with both ‘probiotic’ and ‘prebiotic’ properties

As mentioned, the gut is home for many species of microbiota, and their equilibrium is key for overall health. Probiotics are good bacteria that help digest food, synthesize vitamins, and aid in supporting the immune system. One of their most important roles is acting as a barrier with the vagus nerve to help our bodies filter and properly absorb nutrients from what we eat. It is recommended to consume between 1–25 CFU’s per day (Colony Forming Units) of prebiotics, the fiber-rich and nourishing foods that help the probiotics grow.      

Food sources of probiotics are mostly found in dairy and fermented foods. To ferment is to convert carbohydrates to alcohol, and it is important that they are “active” and “live cultures,” especially when purchased at a store. Examples are miso, kimchi, kombucha, natto, and yogurt.  

Prebiotics are foods that contain a non-digestible food ingredient that probiotics can feed upon, and is found in asparagus, unripe bananas, dandelion greens, sunchokes, leeks, legumes, onions, and peas.

Pre-existing conditions, like lactose intolerance and acid reflux, can make it difficult to get enough probiotics from food sources. In that case, supplementation (vitamin supplements) may be indicated.

Include omega-3 fatty acid sources

In a 2017 study published in the Journal of Alzheimer’s Disease, researchers found that AD patients with high omega-3 levels had better blood flow in specific areas of the brain. Overall, the study showed positive relationships between omega-3 EPA+DHA status, brain perfusion, and cognition.

Its lead author, Daniel G. Amen, MD, of the Amen Clinics wellness centers, added, “This is very important research because it shows a correlation between lower omega-3 fatty acid levels and reduced brain blood flow to regions important for learning, memory, depression and dementia.”

The recommendation for omega-3 fatty acid intake is 1,000 mg/day, and sources can include 3.5 ounces of salmon, tuna, mackerel, or herring. Vegetarians may consider flax seeds, chia seeds, and walnuts. Supplements from marine sources like krill oil and marine algae are excellent alternative options.

It is always important to speak with a health professional when including supplements into a health routine, as interactions may occur with medications.

Cruciferous vegetables include any vegetables that are part of the cabbage family — such as broccoli, cauliflower, kale, bok choy and Brussels sprouts — and they contain the powerful anti-inflammatory vitamins A, C, and folic acid. They are essential to combat the free radicals that may potentially leak into the bloodstream from dysbiosis and travel to the brain. Brussels sprouts, in particular, have the most plant-based omega-3 fatty acids, and broccoli comes in at a close second at 200 mg. Adding olive oil or grapeseed oil to these vegetables enhances the absorption of some of the vitamins, and provides a great taste.

Spices are powerful immunological soldiers, supporting protein synthesis, nervous system equilibrium, gut health, and free radical reduction. Free radicals are the byproduct of oxygen metabolism. These molecules are unstable and can stimulate the body’s inflammatory response. Spices such as oregano, turmeric, cinnamon, and rosemary are great additions to the diet for their culinary as well as nutritive properties.

Adopting a holistic worldview when it comes to nutrition is new and has introduced topics like meditation, positive social engagement, and physical activity as potent medicines for brain health. As we continue to learn more about how the confluence of nature and nurture impact Alzheimer’s onset and progression, the critical role of diet and lifestyle will continue to be an exciting area to explore.


Alana Kessler, MS RDAlana Kessler, MS, RD, CDN, E-RYT, is a registered dietitian, nutritionist, weight management expert, and an accredited member of the CDR (Commission on Dietetic Registration) and the American Dietetic Association. She is also a yoga and meditation teacher, Ayurveda specialist, and the founder of the New York City-based fully integrated mind, body, and spirit urban sanctuary, BE WELL. Alana’s BE WELL ARC System and Method Mapping technique is a holistic multidisciplinary approach to health and wellness that blends Eastern and clinical Western diet and lifestyle support to effect long-lasting behavior change.

A graduate of NYU with a BA and MS in clinical nutrition, Alana is dedicated to helping others learn how to nourish themselves, create balance, and understand their true nature through nutrition, yoga, and inner wellness. She leads Yin Yoga workshops and trainings as well as wellness retreats at international locations. Her health, fitness, and lifestyle expertise has been featured in,,,, Redbook,, and Vogue. For more information, visit her website at