Skip to content

What things in our environment have an effect on the microbes living within us? We now know that gut microbes are important for our health in many ways, and that thousands of species of bacteria, as well as viruses, fungi, and other microbes normally live in a healthy person's gut. We refer to these microbes as the human microbiota or human microbiome. When the community of gut microbes is thrown out of whack (dysbiosis) there can be a number of negative health effects, including diseases. Researchers are just learning about all the microbes within us and their importance in health and disease. [See all posts on the human microbiome.]

Past posts have discussed such things as antibiotics, emulsifiers, different foods and diets, heartburn drugs, etc. having an effect on the human microbiome, but what else? A recent study from China reviewed some environmental pollutants and their effects on gut microbiota - as shown in both human and animal studies. They reviewed studies on antibiotics, heavy metals (arsenic, cadmium, lead), persistant organic pollutants or POPs (organochlorine pesticides, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers, and polycyclic aromatic hydrocarbons or PAHs), pesticides (permethrin, chlorpyrifos, pentachlorophenol, epoxiconazole and carbendazim, imazalil), emulsifiers, nanoparticles (e.g., silver nanoparticles), and artificial sweeteners. They found that all these environmental pollutants had effects on gut microbes - with some effects lasting for years. Their conclusion: gut microbes are very sensitive to drugs, diet, and environmental pollutants. By the way, notice that popular food ingredients such as emulsifiers and artificial sweeteners were considered "environmental pollutants" by the researchers.

Excerpts from Environmental Pollution: Effects of environmental pollutants on gut microbiota

Environmental pollutants have become an increasingly common health hazard in the last several decades. Recently, a number of studies have demonstrated the profound relationship between gut microbiota and our health. Gut microbiota are very sensitive to drugs, diet, and even environmental pollutants. In this review, we discuss the possible effects of environmental pollutants including antibiotics, heavy metals, persistent organic pollutants, pesticides, nanomaterials, and food additives on gut microbiota and their subsequent effects on health. We emphasize that gut microbiota are also essential for the toxicity evaluation of environmental pollution. In the future, more studies should focus on the relationship between environmental pollution, gut microbiota, and human health.

Thousands of species are found in the gut microbiome, and the majority of these species belong to six bacterial phyla: Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria, Fusobacteria, and Verrucomicrobia (Eckburg et al., 2005). Gut microbiota are highly dynamic and have substantial interindividual and intraindividual variation....The gut microbiota are very essential for host health. They participate in the regulation of many physiological functions. The gut microbiota reside in our intestinal mucus layer and even participate in shaping the mucus layer (Jakobsson et al., 2015). They help us to digest food (such as fiber); synthesize vitamins and amino acids (Spanogiannopoulos et al., 2016); play very important roles in energy metabolism and storage, immune system modulation, growth, and neurodevelopment; and can even regulate our behavior.... The occurrence of many diseases is correlated with altered gut microbiome composition (Lange et al., 2016). Gut microbiota dysbiosis is considered to be a potential cause of obesity (Cani et al., 2007; Fei and Zhao, 2013). However, gut microbiota are very sensitive to drugs, diet, and environmental pollutants.

Although most environmental pollutants do not directly target gut microbiota, some pollutants can enter the body and interact with the gut microbiota through different pathways. A number of previous studies have shown that exposure to environmental pollutants can alter the composition of the gut microbiome, leading to disorders of energy metabolism, nutrient absorption, and immune system function or the production of other toxic symptoms (Jin et al., 2015c; Zhang et al., 2015b). In the present review, we conclude that different kinds of environmental pollutants can induce gut microbiota dysbiosis and have multiple potential adverse effects on animal health

Heavy metals in the environment have become a severe health risk in recent years (Liu et al., 2016a). As a common form of environmental pollution, heavy metals are associated with a wide range of toxic effects, including carcinogenesis, oxidative stress, and DNA damage, and effects on the immune system..... Recently, several studies have stated that heavy metal exposure could also lead to gut microbiota dysbiosis, indicating that study of gut microbiota provides a new approach to analyze the mechanisms of heavy metal toxicity

Immune system function is tightly coupled to our gut microbiome. Gut microbiota and their metabolites can interact with both the innate immune system and the adaptive immune system (Honda and Littman, 2016; Thaiss et al., 2016).... Alterations in the gut microbiome can disrupt the balance between the host immune system and gut microbiota, induce immune responses, and even trigger some immunological diseases. Furthermore, immune system imbalance may influence the microbiota metabolites. For example, trimethylamine, which is absorbed from food by gut microbiota, can induce atherosclerosis (Chistiakov et al., 2015).

 An earlier post discussed how emulsifiers (which are added to most processed foods to aid texture and extend shelf life) can alter the the community of microbes that live in our gut (gut microbiota) in such a way as to cause intestinal inflammation. Now the same researchers found that regular consumption of emulsifiers alter intestinal bacteria in a manner that promotes low-grade intestinal inflammation and possibly colorectal cancer.

The emulsifiers used in the study were the commonly used carboxymethylcellulose and polysorbate-80, but some others are soy lecithin, carrageenan, and polyglycerol ester. Processed foods often contain several emulsifiers, and while food regulations limit the amount of each emulsifier present in a particular food product to 1% to 2%, they don’t restrict the number of emulsifiers allowed. The study was done in mice, but the researchers tried to model the level of exposure of humans who eat a lot of processed food. From Science Daily:

Common food additive promotes colon cancer in mice

Emulsifiers, which are added to most processed foods to aid texture and extend shelf life, can alter intestinal bacteria in a manner that promotes intestinal inflammation and colorectal cancer, according to a new study. The findings, published in the journal Cancer Research, show regular consumption of dietary emulsifiers in mice exacerbated tumor development....There is increasing awareness that the intestinal microbiota, the vast, diverse population of microorganisms that inhabits the human intestines, play a role in driving colorectal cancer.

The microbiota is also a key factor in driving Crohn's disease and ulcerative colitis, the two most common forms of inflammatory bowel disease (IBD). IBD is known to promote colon tumorigenesis and gave rise to the term "colitis-associated cancer." Low-grade inflammation, a condition more prevalent than IBD, was shown to be associated with altered gut microbiota composition and metabolic disease and is observed in many cases of colorectal cancer. These recent findings suggest dietary emulsifiers might be partially responsible for this association.

Previous reports by the Georgia State research team suggested that low-grade inflammation in the intestine is promoted by consumption of dietary emulsifiers, which are detergent-like molecules incorporated into most processed foods that alter the composition of gut microbiota. The addition of emulsifiers to food seems to fit the time frame and had been shown to promote bacterial translocation across epithelial cells. Viennois and Chassaing hypothesized that emulsifiers might affect the gut microbiota in a way that promotes colorectal cancer. They designed experiments in mice to test this possibility.

In this study, the team fed mice with two very commonly used emulsifiers, polysorbate 80 and carboxymethylcellulose, at doses seeking to model the broad consumption of the numerous emulsifiers that are incorporated into the majority of processed foods. Researchers observed that consuming emulsifiers drastically changed the species composition of the gut microbiota in a manner that made it more pro-inflammatory, creating a niche favoring cancer induction and development. Alterations in bacterial species resulted in bacteria expressing more flagellin and lipopolysaccharide, which activate pro-inflammatory gene expression by the immune system.

Image result for farm, wikipedia A thought-provoking article by Heiman and Greenway was just published in the journal Molecular Metabolism making the case that changes in farming practices over the last 50 years have resulted in decreased agricultural diversity which, in turn, has resulted in decreased dietary diversity, and that the reduction in dietary diversity has changed and decreased the richness of the human gut microbiota (microbes living in the gut). And meanwhile, during the past 50 years, the rates of obesity, type 2 diabetes, and inflammatory bowel diseases sharply increased - and in each of these conditions there is a reduction of the gut microbial diversity. Similar views have also been stated by others in the field of microbiology.

The thinking is that the more diverse the diet, the more diverse the gut microbiome (and healthier), and the more it can adapt to disturbances. Heiman and Greenway state: "Unfortunately, dietary diversity has been lost during the past 50 years because of economic pressures for greater food production to support a growing world population.... Of the 250,000 to 300,000 known edible plant species, humans use only 150 to 200...Today, 75 percent of the world's food is generated from only 12 plants and five animal species."

Also, agricultural practices of using antibiotics as growth promoters for poultry, swine, and cattle further harm the human gut microbiome when the meat is ingested by humans, and pesticide residues on crops ingested by humans may have gut microbiome effects. Even emulsifiers, used in processed foods, reduce microbial richness. Every time a person goes on a certain diet (vegan, Paleo, etc) or makes dietary choices in which some foods are eliminated, it makes it easier for some microbial species, and gives them a competitive advantage over other gut microbes. From Science Daily:

Reduction in dietary diversity impacts richness of human gut microbiota

Changes in farming practices over the last 50 years have resulted in decreased agro-diversity which, in turn, has resulted in decreased dietary diversity. The significant impact of this change in dietary richness on human health is an emerging topic for discussion

Heiman and Greenway describe how the reduction in dietary diversity has changed the richness of human gut microbiota, the community of microorganisms living in the gut. The researchers point out that healthy individuals have diverse gut microbiota and many of the common pathologies of the 21st century, including type 2 diabetes, obesity and inflammatory bowel disease, are associated with reduced microbiotic richness.

Gut microbiota function as an endocrine organ, metabolizing specific nutrients from the diet and producing specific substances that act as metabolic signals in the host. It follows then that highly specialized diets will change the landscape of the gut microbiome over time. In fact, it takes only a few days of changing diet to alter the microbiotic makeup of the human gut. And if the dietary change involves elimination of one or more macronutrients (think Atkins or Paleo or vegan), humans are essentially selecting for some microbiotic species over others.

The importance of microbiota diversity cannot be overstated. They produce an abundance of important molecules for the host and with increased variation comes increased adaptability and an increased range of physiological responses. "The greater the repertoire of signals, the more likely is the ability to maintain homeostasis when dietary intake is perturbed," explain Heiman and Greenway. "Furthermore, because each particular macronutrient has the potential to be metabolized by microbiota into unique metabolic signals, the greater the variety in signals, the greater the variety of responses possible."

    Artificial trans fats in foods are bad for health in so many ways: linked to increased risk of coronary heart disease, atherosclerosis, inflammation, and risk of early death. And even though the FDA is finally phasing out partially hydrogenated oils (because they have high levels of artificial trans fats) within the next 3 years, trans fats will still be found in foods (processed foods). How can this be? Well, trans fats are still allowed to be in foods that are labeled as 0 trans fats if it is less than .5 grams trans fats per serving (a loophole allows them to round downward to zero ). And according to research by Environmental Working Group (EWG), trans fats are being used by the food industry in undisclosed ways in amounts low enough to exploit the trans fat loophole. Besides partially hydrogenated oils, they are found in other types of refined oils, monoglycerides, diglycerides and other emulsifiers, and even in flavors and colors. So when you see ZERO trans fats on the label, it doesn't actually mean that it is zero trans fats. The problem is that over the course of a day, eating a number of foods and servings that have under .5 grams of trans fats adds up to levels that research now says has negative health effects!

Artificial trans fats are found in a lot of processed foods. A EWG analysis found that harmful artificial trans fatty acids lurk in more than 27 percent of more than 84,000 processed foods common in American supermarkets.  Another 10 percent contain ingredients likely to contain trans fat. Foods most likely to have hidden trans fats are: breakfast bars, granola and trail mix bars, pretzels, peanut butter, crackers, breads, kids fruit snacks, kids cereal, graham crackers, whipped topping, non-dairy creamers, pudding mixes, cupcakes, and ice cream cones.

So what can you do? Read ingredient lists on labels and try to avoid foods with the above mentioned ingredients: partially hydrogenated oils, emulsifiers, monoglycerides, diglycerides and other emulsifiers, artificial flavors, artificial flavors, and colors. Try to cut back or avoid foods that have ingredients that are not real foods - tough to do, but it can be done.

And the amazing part, saturated fats (such as butter) are NOT linked to early death and heart disease, but trans fat in foods is. Latest research, from Science Daily:

Trans fats, but not saturated fats like butter, linked to greater risk of early death and heart disease

A study led by researchers at McMaster University has found that that trans fats are associated with greater risk of death and coronary heart disease, but saturated fats are not associated with an increased risk of death, heart disease, stroke, or Type 2 diabetes. The findings were published today by the British Medical Journal (BMJ)...."For years everyone has been advised to cut out fats. Trans fats have no health benefits and pose a significant risk for heart disease, but the case for saturated fat is less clear," said de Souza.

Saturated fats come mainly from animal products, such as butter, cows' milk, meat, salmon and egg yolks, and some plant products such as chocolate and palm oils. Trans unsaturated fats (trans fats) are mainly produced industrially from plant oils (a process known as hydrogenation) for use in margarine, snack foods and packaged baked goods.

Contrary to prevailing dietary advice, a recent evidence review found no excess cardiovascular risk associated with intake of saturated fat. In contrast, research suggests that industrial trans fats may increase the risk of coronary heart disease.

To help clarify these controversies, de Souza and colleagues analysed the results of 50 observational studies assessing the association between saturated and/or trans fats and health outcomes in adults....The team found no clear association between higher intake of saturated fats and death for any reason, coronary heart disease (CHD), cardiovascular disease (CVD), ischemic stroke or type 2 diabetes. However, consumption of industrial trans fats was associated with a 34 per cent increase in death for any reason, a 28 per cent increased risk of CHD mortality, and a 21 per cent increase in the risk of CHD.

Inconsistencies in the studies analysed meant that the researchers could not confirm an association between trans fats and type 2 diabetes. And, they found no clear association between trans fats and ischemic stroke. The researchers stress that their results are based on observational studies, so no definitive conclusions can be drawn about cause and effect. 


 This research suggests that emulsifiers (which are added to most processed foods to aid texture and extend shelf life) can alter the gut microbiota (the community of microbes that live in our gut) in such a way as to cause intestinal inflammation. Even though the study was done on mice, it is thought it also applies to humans. From Medical Daily:

You Are What You Eat: Food Additive Emulsifier Inflames Mouse Gut And Causes Obesity

Processed foods have changed the way we eat. Food can sit longer on shelves, but what does that mean for the stomach? In a new study published in the journal Nature, researchers from Georgia State University investigated how the widely used processed food additive emulsifiers played a role in the gut.

Emulsifiers are added to most processed foods in order to extend shelf life and add texture to the foods. The research team decided to feed mice a couple of the most common emulsifiers on the market — polysorbate 80 and carboxymethylcelluloseat doses comparable to a human’s consumption of processed foods. They watched the emulsifier change the mice’s gut microbiota, which is an individual’s personal 100 trillion bacteria inside the intestinal tract. Not only did this increase their chance of developing obesity-related disorders, but also inflammatory bowel disease. It’s no coincidence both conditions have been increasing since the 1950s.

"The dramatic increase in these diseases has occurred despite consistent human genetics, suggesting a pivotal role for an environmental factor," the study’s coauthor Benoit Chassaing, a researcher from GSU’s Institute for Biomedical Sciences, said in a press release. "Food interacts intimately with the microbiota, so we considered what modern additions to the food supply might possibly make gut bacteria more pro-inflammatory."

The emulsifiers, which are groups of oil-and water-friendly molecules, help to hold food together. Mayonnaise without emulsifiers, for example, will separate from an oily top layer to a thicker white layer that rests on the bottom of the jar. Once the emulsifiers were digested by the mice, their blood-glucose levels went awry, inflamed their intestinal mucus layer, which left them with weight gain, specifically concentrated in the abdomen. The bacterial changed triggered chronic colitis from causing intestinal inflammation and metabolic syndrome, which includes obesity, hyperglycemia, and insulin resistance.

Ultimately, microbiologists say you are what you eat. If your diet is smeared with margarine, mayonnaise, creamy sauces, candy, ice cream, and most other packaged and processed baked goods, you and your gut may be at risk.

"We do not disagree with the commonly held assumption that over-eating is a central cause of obesity and metabolic syndrome," the study’s coauthor Andrew T. Gewirtz, a researcher from GSU’s Institute for Biomedical Sciences, said in a press release. "Rather, our findings reinforce the concept suggested by earlier work that low-grade inflammation resulting from an altered microbiota can be an underlying cause of excess eating."