Some microorganisms initiate chronic low-grade inflammation and weight gain
Chronic disease, weight gain, and obesity are multifactorial problems with no easy solutions. However, there are some conditions, like low-grade inflammation and oxidative stress, that seem to play an especially important role in the development and progression of many health disorders. Contrary to the acute inflammation that occurs when you sprain your ankle or get a wound, low-grade inflammation often goes unnoticed for a long time before symptoms of disease occur. The million dollar question is where this inflammation stems from and how we can prevent or treat disease by managing the inflammatory mileu in the body.
As we’re now starting to unveil secrets of the microbiome and understand the connection between microbes and human health, a lot of researchers are starting to believe that the trillions of microbes in our body could be a key player in driving inflammation and disease. One of the characteristics of chronic low-grade inflammation is elevated levels of proinflammatory compounds in the blood, such as c-reactive protein (CRP) and lipopolysaccharide (LPS). LPS is a toxin found in the outer cell wall of gram negative bacteria, and seems to be especially important in terms of the chronic low-grade inflammation associated with weight gain and obesity.
It’s been shown that the “obese microbiota” has an increased abundance of proinflammatory microorganisms that contain endotoxins like LPS, and that people who are overweight and obese have more lipopolysaccharide circulating in the blood, a state referred to as endotoxemia (29). It’s even been shown that just taking one endotoxin-producing bacterium isolated from a morbidly obese human’s gut induces obesity and insulin resistance in germ-free mice (30).
When gut bacteria ferment prebiotic fiber in the colon, they provide the cells lining the colon – colonocytes – with short-chain fatty acids. The tight junctions lining the intestine depend on these fatty acids, such as butyrate and acetate, to function properly and prevent leakage of bacterial endotoxins such as LPS (31).
So, we have established that obesity is characterized by changes to the bacterial communities in the intestine, and that people who are overweight and obese have elevated levels of proinflammatory compound such as LPS in their blood. These endotoxins immediately prompt an inflammatory response in the body by binding to toll-like receptor 4 at the surface of innate immune cells (32). Since we know that fat tissue in itself can be proinflammatory, it was often believed that the chronic low-grade inflammation associated with obesity was solely a consequence, and not a cause, of weight gain. However, we now know that endotoxemia, and the subsequent inflammation, in itself can initiate weight gain, insulin resistance, obesity, diabetes, and other metabolic disturbances (33,34,35,36,37).
It’s important to note that other mechanisms such as regulation of adipose tissue and liver fatty acid composition, and modulation of gut-derived peptide secretion also are important in terms of gut microbiota and weight regulation. The fact is that there is still a lot we don’t know about the trillions of bugs that inhabit the human body, and although it’s well established that the microbiome plays a role in overweight and obesity, the magnitude of its contribution is still unknown.
Probiotics and prebiotics
As mentioned earlier, prebiotics are non-digestible food ingredients that stimulate the growth of beneficial bacteria in the digestive system. When we eat these types of fermentable substrates, our beneficial gut bugs get a chance to flourish, pathogens are suppressed due to lowering of the pH in the colon, and the production of short-chain fatty acids increases (38). Although only a few types of carbohydrates are officially classified as prebiotics, all of the non-starch polysaccharides found in food are broken down by gut bacteria and could have a prebiotic effect.
Onions, leeks, and jerusalem artichoke are some of the vegetables that are rich in prebiotic inulin-type fructans. Resistant starch is another food ingredient that’s especially effective when it comes to increasing the production of short-chain fatty acids in the colon and enhancing the growth of beneficial bacteria (39). Resistant starch is essentially starch that resists digestion in the small intestine and passes into the colon where most of it’s broken down by gut bacteria. Good sources of resistant starch include green bananas, potato starch, legumes, and potatoes. The resistant starch content of foods like potatoes increase when they are cooked and then allowed to cool for several hours (retrograded starch).
Probiotics are bacteria that have claimed health benefits when consumed. The two most well-studied types of probiotics are bifidobacteria and lactobacillus, which are commonly found in probiotic supplements and fermented foods such as sauerkraut, yogurt, and kefir. Just like with prebiotics, it’s likely that several species of microorganisms have a beneficial effect on human health even if they aren’t officially classified as probiotics. We know that humans have co-evolved for millions of years with the vast bacterial communities in soil, water, and other animals, and one of the costs of modern hygiene seems to be that we are losing touch with these microbial “old friends“ that helped shape our immune system.