This transcript has been edited for clarity.
Hello. I'm Dr David Johnson, professor of medicine and chief of gastroenterology at Eastern Virginia Medical School in Norfolk, Virginia. Welcome back to another GI Common Concerns.
All of us routinely see diet recommendations on the Internet like TikTok or in new books. Every possible diet seems to receive this promotional push, although the evidence behind them is often lacking.
So what do we mean when we talk about a "healthy diet"?
Today, I'd like to spend a few minutes updating you on the current evidence and how I discuss it with my patients so that you can perhaps do the same in your own patient discussions.
The Western diet has really cannibalized the health of the United States and Western civilizations.
This diet is typically characterized by high intakes of processed and prepacked food items, red meat, dairy, and grains, consisting of high-fat, high-protein, and low-fiber components. These food items have become diets of convenience as opposed to diets potentially promoting health.
They've led to an associated increase in so-called "diseases of civilization," including cardiovascular disease, obesity, and a variety of metabolic diseases and cancers.
Western diets have been also associated with a variety of microbial and gut integrity changes, which in turn, are associated with an assortment of bad outcomes. Specifically, they're associated with decreases in microbial diversity in the gut; upregulation of proinflammatory mediators, cytokines, and chemokines; and several changes to gut integrity, immunity, and pathways that are derivatives toward diseases and even promoting translocation of gut bacteria.
In contradistinction, we have the Mediterranean diet, which is often proffered as the good or healthy diet for most patients. This comprises a diet that's high in fiber and low in animal protein and saturated fat, and is characterized by a higher ingestion of vegetables, fruits, and healthy fat and a lower intake of red meat and dairy. The Dietary Guidelines for Americans recommend a Mediterranean diet for promoting health and minimizing disease.
The high fiber content of Mediterranean diets is a key reason behind that recommendation. Fiber comes in soluble and insoluble forms. Soluble fiber gets digested, whereas insoluble fiber moves through the gastrointestinal tract, bringing components of water absorption and promoting gut motility, particularly in the colon.
Insoluble fiber has a variety of ascribed benefits, particularly related to the changes in the gut production of short-chain fatty acids, which are incredibly important for optimizing intestinal function.
We know that short-chain fatty acids increase secretion of immunoglobulins, induce regulatory T-cell tissue repair, promote antimicrobial peptides and mucus production, and basically optimize intestinal function and the intestinal barrier integrity. This is all critically important in promoting health.
There are also some data on short-chain fatty acid production as it relates to crossing the blood-brain barrier. This association with the brain-gut axis potentially changes gut-related derivatives, driving mood and behavioral activities in the brain. Therefore, we can say that the short-chain fatty acid derivative from the intestinal microbiome does have central nervous systemrelated effects.
There are also some very interesting data in this area related to the progression of COVID to severe disease or long-haul COVID, or even the development of COVID. Enhanced microbial diversity seems to be somewhat protective and, if infected with COVID, predictive of a rapid response and resolution. Short-chain fatty acids also serve as a marker, particularly when they're reduced. Branch-chain shorty acid called L-isoleucine has been shown to be predictive of longer-term consequences and more-severe COVID. So diet may have a significant role in even in the COVID world.
There are other elements in the diet that may contribute to disease.
Some things commonly added to diets have been shown in animal models to have a significant impact in changing gut integrity. In particular, this is observed in prepacked foods that are often found in the Western diet, which incorporate things such as emulsifiers and food additives with a goal toward enhanced aesthetics and taste.
Some that we see routinely in popular food items are carboxymethyl cellulose and polysorbate-80. These are derivatives in a variety of dairy products. Interestingly, they decelerate the melting of ice cream. That may be good for your kids eating an ice cream cone in the backseat in the summer, but not so good potentially for the intestine.
The same is true as it relates to maltodextrin, which is a very common thickener and sweetener, but again decreases the mucosal layer thickness and increases gut permeability.
Carrageenan, which is made from red seaweed, is added to increase texture, primarily in dairy products and sauces. It also decreases gut integrity and permeability changes and antigenic translocation.
Another common food additive is high-fructose corn syrup, something we're seeing more and more data about. Its use in sugary beverages was once implied to have, and now clearly is associated with, an increased risk for nonalcoholic fatty liver disease, early colon cancer, and a variety of other cancer pathways. Recent animal model data have shown mechanistically how it contributes to colon cancer. It was also most recently associated with liver cancer in postmenopausal women ingesting one sugary beverage a day.
Almost all sugary beverages have shifted from using cane sugar to high-fructose corn syrup because it's cheaper and sweeter. Interestingly, as data have become more onerous regarding its disease associations, in 2012 the corn industry went to the US Food and Drug Administration and petitioned to change the name from high-fructose corn syrup to corn sugar. That term sounds a lot easier and maybe even sweeter when it comes to possible health implications, but the FDA said no.
Since then, the widespread use of high-fructose corn syrup has been described as a food public health crisis. High-fructose corn syrup is something that is very easy to avoid when you talk about sugary beverages.
When it comes to artificial sweeteners, the top three that have been studied to date are aspartame, saccharin, and sucralose (Splenda). They are not absorbed but rather are fermentable sugars that get to the gut and change the gut microbiome. In animal models, they have been shown to promote obesity and diabetes, which is very much paradoxical to what their advertised intent is. Again, this has only been studied for these three agents, and we also don't have data in lower-threshold exposures.
I think it's common sense to minimize the use of these things and instead ask patients to use natural sugars, consume water, and incorporate other strategies; that's what I discuss with my own patients.
We can go the wrong way and make our patients too rigid about reading nutritional labels. I want to caution you about emerging food restrictive disorders that very much can become an eating disorder. So we don't want to go the opposite way.
I tell my patients to be a good, conscientious thinker, look at your food, minimize the processed foods, and build your meals. The Western diet needs to go. The more we can use the Mediterranean diet, the better off we are. You can still have your occasional cheeseburger and French fries but use common sense.
The Mediterranean diet really is simple. I routinely recommend this to my patients with inflammatory bowel disease, obesity, nonalcoholic fatty liver disease, along with other inflammatory disease conditions. But I do think we can make this a general recommendation across all patients in our attempt to promote health and thereby prevent disease.
I hope this has been helpful.
I'm Dr David Johnson. Thanks for listening.
David A. Johnson, MD, a regular contributor to Medscape, is professor of medicine and chief of gastroenterology at Eastern Virginia Medical School in Norfolk, Virginia, and a past president of the American College of Gastroenterology. His primary focus is the clinical practice of gastroenterology. He has published extensively in the internal medicine/gastroenterology literature, with principal research interests in esophageal and colon disease, and more recently in sleep and microbiome effects on gastrointestinal health and disease.
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