A recent issue of the Swiss popular science magazine "Beobachter Natur" contains an article about microbes in which the following claims are made:

  • 75% of the cells in our body are non-human, however
  • The total weight of these microbial cells is only 1.25kg (in the body of an adult)

Is there any reference for these claims?

  • Good first question! Welcome to Skeptics.
    – Flimzy
    May 18, 2014 at 12:17
  • Regarding the second claim, the linked duplicate has a value of "up to five pounds" near the end of the accepted answer. If this claim is for an average weight and the other is for the maximum weight, they are probably consistent with each other.
    – Ladadadada
    May 19, 2014 at 11:14

1 Answer 1


Yes, and actually the percentage is estimated to be even higher than that. An article in "Scientific American" says:

All the bacteria living inside you would fill a half-gallon jug; there are 10 times more bacterial cells in your body than human cells, according to Carolyn Bohach, a microbiologist at the University of Idaho (U.I.), along with other estimates from scientific studies. (Despite their vast numbers, bacteria don't take up that much space because bacteria are far smaller than human cells.)

Wikipedia provides some references:

It is estimated that 500 to 1,000 species of bacteria live in the human gut[5][6] Bacterial cells are much smaller than human cells, and there are at least ten times as many bacteria as human cells in the body (approximately 10^14 versus 10^13).[7][8] The mass of microorganisms are estimated to account for 1-3% total body mass.[9]

[5] Science, 324: 1190 - 1192. doi:10.1126/science.1171700

[6] Pappas S. (2009). Your Body Is a habitat ... for Bacteria. Science Now Daily News

[7] Savage, D. C. (1977). "Microbial Ecology of the Gastrointestinal Tract". Annual Review of Microbiology 31: 107–33. doi:10.1146/annurev.mi.31.100177.000543. PMID 334036.

[8] Berg, R. (1996). "The indigenous gastrointestinal microflora". Trends in Microbiology 4 (11): 430–5. doi:10.1016/0966-842X(96)10057-3. PMID 8950812.

[9] MacDougall, Raymond (13 June 2012). "NIH Human Microbiome Project defines normal bacterial makeup of the body". NIH. Retrieved 2012-09-20.

  • never mind...... Feb 1, 2019 at 19:46

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