Clearly the development of antibiotics in the 1940s and 50s has had a huge impact on human health as many of the previously serious and/or fatal infectious diseases were now cured. However, it has taken almost 50 years for us to realize that all these health benefits come with a cost. The gut bacterial pool, called the microbiome, is now well recognized to be a vital part of long term good health. There are over 2000 species and well over 100 trillion bacteria in the colon. Almost all bacteria will have destructive effects on this health organ. It may take over 2 months for the bacterial make up to reach its previous normal level. This article gives a general overview of the problem.
This article makes the case for obesity being tied to the low dose of antibiotics that have been fed to food animals to increase their weight. These low levels of antibiotics then flow through the food chain, finally reaching the customer who is then exposed to these small doses of residual antibiotics. The effect on colon bacteria which can lead to a bacterial make up that inadvertently increases calories in the consumer is a potential problem.
Even liver disease can be tied to abnormalities in the gut bacterial make up. Here is a situation where an antibiotic is clearly tied to abnormal liver and bile abnormalities as well as to insulin resistance in the type 2 diabetic.
Finally, this is another overview that shows how antibiotics can indiscriminately and adversely affect the colonic health organ.
The bottom line is to be sure that a course of antibiotics is clearly needed. Remember that your colon bacterial makeup is a health organ and antibiotics are not its friend. Use them only when clearly needed. Further, it might be appropriate to purchase meats and poultry from producers who do not use antibiotics in their feed so as to fatten their animals prior to sale.