In the Gut: The Mix of Bacteria Can Affect Weight


There has been an explosion of research into how bacteria affect human health, and body weight is one of the most intriguing areas.  There is growing speculation that rising rates of obesity may be due in part to increased use of antibiotics, which may be wiping out bacteria that help humans efficiently convert food into energy.


Babies are born without any bacteria and eventually play host to approximately 100 trillion of the tiny micro-organisms, which outnumber human cells by about tenfold.  Bacteria coat every inch of skin, the mouth, nose, ears, genitals and particular the gastrointestinal tract.  They not only digest foods and help fight off invaders, but also produce vitamins and chemicals that help regulate the immune system, metabolism, even mood.


In the past, the main bacteria you knew about were the nasty guys, the ones that kill you.  We haven’t been looking at the thousands of nice guys that help us and keep us trim.  This microbiome, as it’s called, has evolved along with humans, and even small disruptions have been implicated in a long list of health problems, including obesity, diabetes, high blood pressure, abnormal cholesterol, belly fat, cancer, and atherosclerosis, or plaque build-up in the arteries.


The field is booming in part because scientists are now able to use gene analysis to identify and count bacteria more easily in stool, saliva, and other samples.  The collections can provide a wealth of information about how complex and different human bacteria communities can be.


It has been known for decades that gut bacteria affect weight in animals.  Farmers have been giving antibiotics to livestock and poultry since the 1950s because it makes them grow fatter.  Mice receiving penicillin every four weeks early in life became obese in later life, even when their gut bacteria appeared to be normal.  The proliferation of antibiotics, antibacterial soaps, and other products isn’t just creating some resistant strains, but decimating the bacterial population with which humans evolved.  Of particular concern: the type of bacteria that helps regulate appetite is disappearing from human GI tracts.  The Helicobacter pylori is notorious for causing peptic ulcers, but studies show that it also helps regulate ghrelin, the hormone that increases appetite.  Without H. pylori to keep ghrelin in check, humans may miss the natural signals that tell them to stop eating.  Other animal studies have shown that altering bacteria alone can change body weight, regardless of diet and exercise levels.  Little-known Christensenellaceae bacteria affect human metabolism, but not much is known about how they are inherited.  The speculation is that human genes affect which bacteria flourish and which dwindle: much like seeds fare better or worse in different soil.


We’re finding that the microbiome is affected not just by age and antibiotics, but how many plants you eat, how much alcohol you drink, how much you exercise and how much sleep you get on average.  More research into the role bacteria play in health is under way.  Most microbiologists say the legions of yogurts, smoothies, supplements and other products on the market packed with “probiotics” are probably harmless but largely untested and unregulated with little evidence to back up the claims.  Watch for more information in the coming months as we update you with the latest information available on this fascinating topic!

Melinda Beck; Edited from The Wall Street Journal


Getting to Know Your Gut Microbiome

Among the most common bacteria:

  • Bifidobacteria are transferred in breast milk
  • Christensenella guard against obesity, and run in families
  • Helicobacterer pylori cause peptic ulcers but help regulate appetite.
  • Escherichia coli produce vitamin K, but can cause severe illness.
  • Clostridium difficile causes colitis and diarrhea, and can be deadly
  • Staphylococcus aureus causes boils and MRSA, and is drug-resistant.
  • Pseudomonas aeruginosa cause ear, eye infections and can spread in hospitals