As research on the microbiome explodes, manipulation of the gut flora to ef- fect changes in weight may be a possibility in the near future. One pivotal study used fecal transplantation of intestinal microbiota from lean donors to overweight male recipients with metabolic syndrome—a condi- tion characterized by weight gain and central obesity stemming from insulin resistance (more about this in Chapter 2). Six weeks after the fecal transplant, the insulin sensitivity of the male recipients improved (as measured through blood tests).⁴ These studies are opening up the possibility of developing in- testinal flora as therapeutic agents for metabolic syndrome and obesity. Ultimately, understanding how the bacteria in our guts interact with one an- other will help us devise the types of therapies that create astonishing results by manipulating this previously underappreciated variable.
Gut-Associated Inflammation and Systemic Disease
As the gut-associated immune system becomes activated, it leads to a body-wide increased level of alertness, much like the U.S. terror alert. Messenger molecules secreted by our own immune cells result in inflammation, fat deposition in our bel- lies, weight gain, and systemic diseases. People who suffer from gut-associated in- flammation will present with different symptoms. In one person, this inflammation can lead to migraines, asthma, or allergies; in another person, it can lead to an au- toimmune disease. The individual expression is controlled by genes. However, underlying each of these potential outcomes is the same root cause: a gut system that was knocked out of balance and became inflamed. Anyone with an inflam- matory chronic disease will benefit from an approach that takes into account the health of the gut.
Gut-Associated Inflammation and Cancer
Although cancer is a multifactorial disease, chronic inflammation and chronic acti- vation of the immune system by certain infections are increasingly being recog- nized as important contributing factors.⁵, ⁶ Here are some common associations:
•H. pylori infection and stomach MALT (mucosa-associated lymphoid tissue) lymphoma •Schistosomiasis (a parasitic infection of the bladder) and bladder cancer •Hepatitis B and C viruses and liver cancer Among the top five most deadly cancers in the world, two are gastrointestinal. Stomach cancer is the third most common cause of cancer deaths worldwide, and the fourth most common is colon cancer.⁷ Cancer of the esophagus affects a minority of people in comparison but is also associated with chronic inflammation. Although smoking is a major risk factor, an- other important risk factor for esophageal cancer is acid reflux.⁸ The reflux causes constant irritation and inflammation of the lower esophagus, leading to the changes in the cells that eventually become cancerous. A major risk factor for colon cancer is inflammatory bowel disease, especially ulcerative colitis.⁹ However, studies have also linked inflammation unrelated to IBD to colon cancer.¹⁰
Some studies have suggested a possible association between gut inflammation and cancers outside of the gastrointestinal tract. One study looked at a pos- sible link between prolonged gut inflammation and breast cancer.¹¹ The re- searchers discovered that mammary carcinoma developed within four to six weeks in mice that acquired an infection with Helicobacter hepaticus, a gut- associated pathogen. Perhaps gut bacteria should be on our radar when look- ing for the underlying causes of cancer.