Gut Check!

Hippocrates, the father of modern medicine, once said that all disease begins in the gut. Since 2016, there have been more than 17,000 studies on gut health, and 90% of all diseases can be linked to gut health.¹ Type 2 diabetes, for example, results from improper cortisol response to sugars, and hypertension is heavily influenced by salt intake. Autoimmune disease is correlated to an increase in inflammatory markers. Autism, type 1 diabetes, and some autoimmune disease all have a genetic predisposition that can be triggered by environmental stress, such as diet.

As optometrists, we know that the eyes are one of the best indicators of overall systemic health, because the effects of metabolic diseases are often seen during thorough ocular health evaluations. This puts us in a unique position to influence our patients via discussions about all aspects of disease control and prevention, including diet. If you observe ocular findings associated with metabolic disease, or if you have patients who are at risk for developing metabolic disease, use the information below to advise them on taking steps to improve their health by growing and supporting good gut bacteria.

METABOLIC DISEASE AND SIGNALING PATHWAYS IN THE GUT

You might be wondering how diet and gut health affects one’s chances of developing the diseases mentioned above. The answer is relatively simple. Our gut and brain are connected via the vagus nerve. Basically, our gut acts like our second brain. The bacterial cells harbored within the human gastrointestinal tract outnumber the host’s cells by a factor of 10, and the genes encoded by the bacteria residing within the gastrointestinal tract outnumber their host’s genes by more than 100 times.² This means that the bacteria in our bodies outnumber our cells almost 100 to one, and studies show that the more diverse the population of bacteria, the healthier we are.^3,4

As bacteria break down our food, they generate metabolites that are used in other signaling cascades throughout our body. For example, if the bacteria break down the burger we ate into salt, trimethyl-amine-n-oxide, and bile acids, then our system will absorb those molecules and use them in pathways that promote hypertension, atherosclerotic buildup, and diabetes (respectively). This is known as bottom-up signaling. One of the coolest examples of this occurs with short chain fatty acids (SCFAs). They directly promote the activity of microglia in the brain, resulting in increased neuronal branching. A diet and gut biome that produces large amounts of SCFAs can actually make you smarter.⁵

Hypertension

High blood pressure affects about half of the US population, with a quarter of those individuals considered uncontrolled.⁶ In school, we are taught that hypertension is caused by over action of the angiotensin-renin-aldosterone signaling pathway. This pathway results in the release of inflammatory markers such as TNF-alpha, reactive oxygen species, interleukin-1b, aldosterone, water resorption, and vasopressin, which causes blood vessel constriction. Many of the drugs used in the treatment of high blood pressure (eg, angiotensin-converting enzyme inhibitors) are targeted to block this signaling cascade.

A patient’s diet can increase or decrease the signaling cascade involved in hypertension. For example, increased salt intake can increase the number of inflammatory mediators and the amount of water resorption, which is the same end product as the angiotensin pathway. This results in a higher signal for increasing blood pressure in the body. Although dietary guidelines published by the United States Department of Agriculture recommend a 2,300 mg daily maximum intake of sodium,⁷ only 10% of the population adheres to this recommendation, with most people clocking in around 9,000 mg to 12,000 mg of salt each day.⁸

Another example of how diet affects this signaling cascade involves SCFAs. These intermediaries combat inflammation and directly affect renin and vasodilation, working to lower blood pressure. Fermented foods such as cheese, pickles, and yogurt generate more SCFAs, which helps reduce blood pressure and maintain a disease-free state for our patients.⁹

Diabetes

Diabetes affects 34 million Americans and is the seventh leading cause of death in the United States.¹⁰ An estimated 90% to 95% of all patients with diabetes have type 2,¹⁰ which is commonly treated with a combination of medications, diet, and exercise. Medications such as metformin are often the first line of treatment, and what makes this particular drug such an effective treatment is the fact that it works on the gut. Both metformin and berberine, a supplement sometimes used to aid in lowering blood sugar, inhibit the metabolism of bile acids by gut bacteria and, therefore, reduce bile acid signaling, resulting in hypoglycemic effects.¹¹ Berberine also increases SCFA production, making it an attractive option to recommend to patients or managing physicians, either before starting drug therapies or escalating to insulin management. Bile acid signaling is not a well understood process, but even patients who undergo bariatric surgery show inhibition of bile acid metabolism.¹² Some studies have shown that a gut bacterial transplant generated the same health benefits and end result as bariatric surgery.^11,13

PROMOTING HEALTHY BACTERIA GROWTH

Inflammation in the digestive track can be greatly reduced with dietary changes or fecal transplants. The way that gut or fecal transplants work is simple: Patients typically will undergo antibiotic treatment for 2 weeks, a bowel cleanse, and then have healthy fecal microbiota transplanted into their intestines.¹⁴ The transplant uses standardized human gut microbiota (SHGM) and can be done orally or through a suppository. Because one dose is often not sufficient for long-term change, an extended transplant time is often suggested using a high initial dose of SHGM and a lower oral daily dose with 8 weeks of a stomach-acid suppressant to allow the SHGM to grow.

But what if your patients aren’t interested in fecal transplants? You as a provider can absolutely still make specific recommendations for diets to follow and supplements to use. One diet that is particularly good at reducing gut dysbiosis is the Mediterranean diet, which emphasizes healthy fats, whole grains, fruits, vegetables, beans, nuts, and seeds. A low lectin diet, which keeps the consumption of legumes, whole wheat, and nightshades to a minimum, is also beneficial. Also, we are so used to prescribing and ingesting antibiotics ourselves, but we rarely talk about prebiotics, probiotics, and postbiotics to our patients (see Prebiotics, Probiotics, and Postbiotics Explained).

Prebiotics, probiotics, and postbiotics can be helpful in generating the best possible microbial environment in which to prevent the emergence of certain metabolic disease states. Be sure to educate your patients that these microbial changes take approximately 8 weeks of consistent dietary change, so they cannot simply take probiotics one day and expect their health issues to resolve. One healthy meal will not change a disease state, and one unhealthy meal will not make a patient diabetic—consistency is key!

GOOD HEALTH TAKES EFFORT

Outside of dietary changes and supplementation, recommending low grade, consistent exercise, such as walking 20 minutes every day or avoiding unnecessary antibiotic prescriptions, will help your patients on their journey toward improved gut and overall systemic health, not to mention better eye health.