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Nutritionist: Probiotics – The Germs We Eat

Nutritionist: Probiotics – The Germs We Eat

Dietitian Dialogues

September 24, 2014

by Tiffanie Stewart, MSc

Probiotics are a hot topic in the world of nutrition, but what does the term probiotic mean? Let’s start by explaining that we are covered in germs. Bacteria reside from our head to our toes and even in our gut. We call this our microflora (you may also hear microbiome), and we need these germs to be healthy. They are very different from pathogenic bacteria – the germs that cause disease. Our gut microflora – that is, all the bacteria living in our intestinal tract – play an important role in human health. In fact, we can have up to 500 different species of bacteria in our gut, and the more diverse our bacterial profile, the healthier we tend to be. Since the size of bacteria is incredibly small, we have 100 trillion bacteria living in our gut. That’s 10 times the amount of bacteria cells living in our gut than all the cells that make up our body. Bacteria are considered “probiotics” when we consume them for health benefits. 

Where do these bacteria come from? 

The gut of a newborn is sterile, so colonization of bacteria occurs immediately after birth. The types of bacteria that take hold depend on the type of birth (cesarian or vaginal) and the diet after birth (formula or breast-fed). Research shows that a vaginal birth and breast-feeding lead to better bacterial colonization. This initial colonization sets us up for life, because the bacteria tend to remain permanently in adult microflora, unless we actively try to change our microbial profile.  

What is a microbial profile?

The type of microbial profile we have in our gut depends on the variety and number of bacterial species. In general, bacteria are classified as pathogenic (causing disease), beneficial (healthy bacteria), and non-beneficial (not causing disease, but also not healthy). An overgrowth of non-beneficial bacteria has been linked to conditions like gas, bloating, inflammatory bowel diseases, weight gain, and even depression. Since 60%-70% of our immune system is in our gut, non-beneficial bacteria can wreak havoc, even causing “leaky gut” where bacterial products cross into our blood stream leading to negative systemic effects. Recent research has investigated systemic effects of this type of bacteria. In an interesting twin study, scientists transplanted gut bacteria from an obese twin into a lean mouse, which made the mouse fat. But the gut bacteria from the thin twin did not change the weight of the lean mouse, suggesting that microbial profiles play a role in weight. Studies also show that there is a difference in microbial profiles between people: healthier people tend to have more bacterial diversity (more types of different species), whereas obese people and diabetics have less diversity. It is also hypothesized from animal studies that inflammatory bowel diseases (like Crohn’s disease and ulcerative colitis) are caused by sensitivity in our gut to certain types of bacterial families. On the other hand, beneficial types of bacteria have been suggested to treat inflammatory bowel disease.

Beneficial bacteria (consumed as probiotics) are soldiers against non-beneficial and even pathogenic bacteria, preventing them from growing in our gut. They produce metabolites that strengthen our immune system and improve the health of our intestinal cells (like B vitamins, vitamin K, and short-chain fatty acids). Short-chain fatty acids, like those generated by beneficial bacteria, were attributed to preventing colon cancer in cell model studies. On the other hand, non-beneficial bacteria that thrive on diets consisting of meat and high in saturated fat actually make carcinogenic by-products that may increase cancer risk. Probiotics may even reverse the effect of environmental toxins: one study in Kenya showed that introducing specific species of beneficial bacteria flushed toxins such as lead, mercury and Afloxin from the intestinal tract of the participants. Administering probiotics can also resolve antibiotic-induced diarrhea. They can help digest lactose, the sugar found in milk that causes lactose intolerance. A Canadian study even found that the probiotic Lactobacillus rhamnosus helped overweight women on a weight-loss diet lose an average of 10 pounds more than a similar group taking a placebo. While there is more research that needs to be conducted into the health benefits of specific probiotics, we can use the current research to take action now.

What changes our microbial profile? 

It turns out that people today have a different microbial profile than generations before us. Unfortunately, we are exposed to agents responsible for loss of microbial diversity. Overuse of antibiotics plays a role in this change. Antibiotics are beneficial in killing off pathogenic bacteria, however, they also kill our beneficial bacteria, significantly reducing our microbial diversity. Eating animals that are treated with antibiotics to promote growth are linked to a lack of diversity in gut microflora. Environmental toxins, such as pesticides, also reduce the amount of beneficial bacteria present in our gut. Stress is another culprit. A study found that when mice experienced consistent stressors, they developed a less diverse bacterial profile. Non-beneficial bacteria feed on specific kinds of foods. A diet high in processed foods with refined sugars, red meat, and high saturated fats will increase the number of those bacteria. Over time, this may cause a less favorable shift in your microbial profile.

The good news is you may be able to improve your microbial profile by eating foods that feed the good bacteria. Prebiotics are the food for probiotics. They include foods like bananas, onions, garlic, leeks, asparagus, artichokes, soybeans, and whole-wheat. Foods that actually contain probiotics are fermented foods such as yogurt, kimchi, miso, tempeh, and kombucha drinks.  We know that specific species of bacteria commonly found in fermented foods are particularly beneficial including: Lactobacillus bulgaricus, Streptococcus thermophiles, Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacteria. You can usually find them on nutrition labels as active cultures.

The term probiotics literally means “for life”. While research is continuing to grow in the area of probiotics, these beneficial bacteria clearly play an important role in our health. 

Tiffanie Stewart, MSc, Doctoral Candidate, Florida International University, received an MS in Dietetics and Nutrition from Florida International University in 2010. Her doctoral dissertation studies nutrition in HIV. She has experience in laboratory-based and clinical research in nutrition and is a student blogger for the American Society for Nutrition. Her professional plans include running nutrition-based research projects to improve community health.