( CNN ) -- Your saliva is doing all kinds of useful things for you all the time -- for instance , helping you chew and taste food . It 's also home to more than 600 species of bacteria , which are harmlessly enjoying the moisture of your mouth . There 's a slew of bacteria floating around in your mouth , but it 's generally harmless . Since people have different eating habits in different places , you might think an American 's saliva might look a lot different from , say , a South African 's . But a new study published in the journal Genome Research finds that bacteria in saliva may not be as related to environment and diet as you might think . In fact , researchers found that the human salivary microbiome -- that is , the community of bacteria in saliva -- does not vary greatly between different geographic locations . That means your saliva is just as different from your neighbor 's as someone 's on the other side of the planet . `` It was somewhat surprising to us , because in our sampling we did n't control for diet , or environment , or anything like that , '' said Mark Stoneking of the Max Planck Institute for Evolutionary Anthropology in Leipzig , Germany , and co-author of the study . Now , Stoneking and colleagues are trying to figure out why . One theory is that since the researchers looked only at the genus of the bacteria in question , they might find more differences at the level of individual species . They are investigating this in a follow-up study . Stoneking became interested in surveying the bacteria of saliva when he learned that saliva contains more DNA than blood , if you include DNA of bacteria and other organisms . Human blood , as you might guess , still contains more human DNA than saliva . Researchers took saliva samples from a total of 120 healthy subjects . The countries represented in this sample were Germany , Poland , Turkey , Georgia , China , Philippines , South Africa , Republic of the Congo , Argentina , Bolivia and the United States . This was the first global survey of bacteria diversity in human saliva . The most common type of bacteria found in the survey of saliva was Streptococcus , Stoneking said . People typically have Streptococcus in their mouths living benignly , although certain species are responsible for diseases such as strep throat , meningitis and bacterial pneumonia . Why do you need hundreds of bacteria species in your mouth ? It turns out they 're mostly not helping you at all -- you 're just giving them a warm , moist home . `` Having those bacteria -- that 's the price we have to pay for having a lot of saliva in the mouth to begin with , '' said Nate Dominy , anthropologist at the University of California , Santa Cruz . Dominy , who has studied enzymes in saliva , found the results surprising , and said no one had previously surveyed the variety of bacteria in saliva . What else is inside saliva ? One component of saliva that has been shown to vary according to diet is amylase , the only digestive enzyme that converts starch into sugar , Dominy said . Amylase is also found in the pancreas and the small intestine . The human body evolved to start the digestive process early , in the mouth , so we can maximize the amount of sugar that we take in , Dominy said . `` Given that we have such large brains , and our brains are metabolically very demanding tissues , they 're extremely costly and expensive to maintain , so we need a lot of sugar , '' he said . Americans in particular have a lot of amylase in their saliva because their diets are full of starch : chips , rice and baked potatoes . But the Pygmies of central Africa , for example , eat mostly game animals , honey and fruit . They have relatively little amylase in their saliva . Dominy and colleagues found these differences at the genetic level , meaning natural selection has favored large quantities of amylase in populations with starchy diets . But there is also evidence that amylase levels can rise and fall within an individual 's lifetime . A study on college students in Ghana , who typically eat a lot of meat at the university , found that students who had grown up eating traditional starchy Ghanaian home-cooked meals had lower levels of amylase after attending the school . Humans have had starch as an important part of their diet for at least 12,000 years , since the advent of agriculture , he said . So what else is spit good for ? Saliva spreads molecules to the taste receptors on the tongue so you can tell whether something is salty , sour , sweet or spicy , Dominy said . It also helps soften food and spread it to your teeth so that you do n't have to chew as hard . Compared with other animals , humans are not very good at detecting toxins , he said . As a result , humans vomit much more than other species , and saliva buffers the acid that results from throwing up -- meaning you 'll likely salivate immediately beforehand to limit the damage . `` A lot of the value of saliva is attributable to the fact that , in human evolution , we 've had to eat marginal plant foods , things that are marginal in quality and full of toxins , and we need these particular salivary adaptations to help cope with those types of food , '' he said .
Saliva has more bacteria than blood because of all of the oral bacteria . Most common type of bacteria in blood is bacteria , in a mostly harmless form . Saliva spreads molecules to the taste receptors on the tongue .