The Good, Bad and Ugly

Wellness Update - - Your Microbes and You -

Mi­cro­scopic crea­tures—in­clud­ing bac­te­ria, fungi and viruses— can make you ill. But what you may not re­al­ize is that tril­lions of mi­crobes are liv­ing in and on your body right now. Most don’t harm you at all. In fact, they help you di­gest food, pro­tect against in­fec­tion and even main­tain your re­pro­duc­tive health. We tend to fo­cus on de­stroy­ing bad mi­crobes. But tak­ing care of good ones may be even more im­por­tant. You might be sur­prised to learn that your mi­crobes ac­tu­ally out­num­ber your own cells by 10 to 1. “The cur­rent es­ti­mate is that hu­mans have 10 tril­lion hu­man cells and about 100 tril­lion bac­te­rial cells,” says Dr. Martin J. Blaser at the New York Univer­sity School of Medicine. New tech­niques al­low sci­en­tists to study th­ese rich mi­cro­bial com­mu­ni­ties and their genes—the “mi­cro­biome.” In 2007, NIH launched the Hu­man Mi­cro­biome Pro­ject to study mi­crobes in and on the body. Ear­lier this year, re­searchers from al­most 80 in­sti­tu­tions pub­lished a land­mark se­ries of re­ports. They found that more than 10,000 dif­fer­ent species oc­cupy the hu­man body. The mi­cro­biome ac­tu­ally pro­vides more genes that con­trib­ute to hu­man sur­vival than the hu­man genome it­self (8 mil­lion vs. 22,000). Hu­mans need bac­te­ria and their genes more than most of us thought. One of the most im­por­tant things mi­crobes do for us is to help with di­ges­tion. The mix of mi­crobes in your gut can af­fect how well you use and store en­ergy from food. In lab­o­ra­tory ex­per­i­ments, trans­fer­ring bac­te­ria from cer­tain obese mice to nor­mal ones led to in­creased fat in the nor­mal mice. Blaser and his col­leagues are con­cerned that changes in our mi­cro­biome early in life may con­trib­ute to weight prob­lems later. “We’re in the mid­dle of an epi­demic of obe­sity that is very se­vere,” Blaser says. “It’s rel­a­tively re­cent, it’s wide­spread across the United States and across the world, and in­creased calo­ries and de­creased ex­er­cise seem in­suf­fi­cient to ex­plain this.” We might be chang­ing our mi­cro­biome for the worse, he says, by us­ing an­tibi­otics too of­ten. In a re­cent NIH-funded study, Blaser’s team found that low­dose an­tibi­otic ther­apy af­fected the gut mi­cro­biomes of young mice. An­tibi­otics also al­tered how the mice used sug­ars and fats. Af­ter 7 weeks, treated mice had up to 15% more fat than un­treated mice. This and other stud­ies sug­gest that gut bac­te­ria can af­fect both ap­petite and how you use en­ergy in food. In re­lated work, Dr. Leonardo Trasande, Blaser and col­leagues an­a­lyzed data from more than 11,000 chil­dren. Al­though the re­sults weren’t con­clu­sive, they sug­gest that in­fants given an­tibi­otics might be at in­creased risk of be­com­ing over­weight. More work will be needed to con­firm this con­nec­tion. “Mi­crobes in our in­testines may play crit­i­cal roles in how we ab­sorb calo­ries,” Trasande says. “Ex­po­sure to an­tibi­otics, es­pe­cially early in life, may kill off healthy bac­te­ria that in­flu­ence how we ab­sorb nu­tri­ents into our bod­ies, and would oth­er­wise keep us lean.” Mi­crobes are also im­por­tant for your skin, one of the body’s first lines of de­fense against ill­ness and in­jury. Skin health de­pends on the del­i­cate bal­ance be­tween your own cells and the mi­crobes that live on its sur­face.

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