Can the bacteria in our digestive system influence body weight issues?

On Thursday I went to the Nutrition Society Summer meeting at the University of Surrey.  The five day conference had concentrated on various aspects of over- and undernutrition.  The symposia that I attended were exceptionally interesting and thought provoking.  One of the presentations(1) was given by Dr Paul Kelly of Barts and London School of Medicine and Dentistry.  He was speaking about the microorganisms in the digestive system and links to diarrhoea in individuals in developing countries.  However, he briefly mentioned an animal study that linked the makeup of the bacteria in the digestive system and a propensity to obesity.  This got me thinking about whether that link was present in humans.  Upon returning home I had a search through the medical databases to see if there was any literature to support these thoughts.

Can bacteria in the gut have anything to do with developing excess body weight or obesity?

There seems to be a fair amount of recently published interest in the topic of digestive bacterial balance and the links to obesity and overweight (e.g. 2,3,4,5,6).  For many years the large intestine was thought only to be important for water absorption and storage of waste.  However, the adult human gut contains up to 100 trillion microbial organisms (including bacteria and yeasts) collectively known as the microbiota or microbiome.  These gut bacteria seem to have an effect on the entire body and not just the health of the digestive system.

Obesity is a complex disease involving many factors with no miracle cure and no easy solutions – I am not about to disillusion anyone by inferring that bacterial balance is a major factor and probiotics (supplemental good gut bacteria) are the cure.  However, gut bacteria may well be having some kind of impact on the development of excess body weight in some people.  What we eat does affect the composition of the microorganisms that are present in our digestive systems and in turn these microorganisms can have an effect on the health of our body.  A review published in French this year (2) looked at the evidence which suggests that the gut microorganisms are linked with metabolism and inflammation, and could be involved in type 2 diabetes, metabolic syndrome and obesity.

An extensive review published in America last year (3) looked at a wide range of evidence in order to investigate the potential role of the gut bacteria in the development of obesity. The authors of the paper found that interactions among the microorganisms in the gut appear to have complex effects in the human body and that the gut organisms may have an important role in regulating weight and may also be partly responsible for the development of obesity in some people.  Evidence suggests that our gut microorganism environment is established within the first year of life and then remains fairly constant through adulthood.  However dietary factors, infections and antibiotic use may lead to long-term changes.

The gut bacteria may be acting on weight via effects on: calorie utilisation from food, metabolism, inflammatory responses, hormone regulation or other means and evidence does suggest that obese and lean individuals seem to have different composition of gut bacteria (3).  A study published last year (4) followed children from birth to age 7 years.  Children of normal weight and those who were overweight had significant differences in their gut bacterial composition suggesting that an important link between bacterial balance and obesity development possibly via inflammatory pathways.  The authors conclude that their findings may offer “new possibilities for preventive and therapeutic applications in weight management”.

Can modifying the gut bacteria through diet and/or probiotic or prebiotic (such as FOS, fructooligoosaccharides) supplements have an impact on body weight?

The review paper (3) emphasises that the best, nonsurgical, strategy for reversing obesity in the population seems to be to promote small but long-term changes in diet and physical activity.  The authors go on to say that further evidence with regards bacterial gut balance is needed but that microorganisms may well be influencing obesity.  They suggest that probiotic and prebiotic supplements may be useful in order to positively change the gut bacterial balance and help prevent and treat overweight but that these manipulations should clearly not be viewed as a substitute for a healthy diet and exercise.

Prebiotics act as food for the good ‘friendly’ bacteria in the digestive system and studies (3) suggest that prebiotics in the diet may reduce our energy and food intake, increase satiety, reduce hunger and appetite and reduce total daily calorie intakes.  FOS may also have effects on blood sugar balance in the body.

Probiotics, live ‘friendly’ bacterial supplements, may also change the bacterial balance of the digestive system and have an effect on overall health in the body, but studies in humans and the links to weight control are lacking.  An interesting study presented at a conference this year (6,7) found that probiotics during and after pregnancy may help prevent the development of obesity after birth.  The study found that at 1 year after giving birth, 25% of women given probiotics along with dietary counseling had central obesity based on that definition, compared with 43% of women given diet advice alone. In a press release the author stated that “This is the first study showing that probiotics-supplemented diet during pregnancy and breastfeeding influences the adiposity [fat mass]of women over the 12-month postpartum period,” Further evidence is needed but the author said that modification of bacterial balance in the intestines with probiotic supplements “together with a balanced diet may offer a reasonably economic, practical, safe and potentially successful method to be used with other lifestyle-related factors in controlling obesity” (7).

Further conclusive evidence needed, however prebiotics (such as FOS) and probiotics do seem to positively change the composition of bacteria in our digestive systems and affect overall health.  Supplements are readily available but should not be seem as a quick-weight loss fix.  A healthy diet and lifestyle is of paramount importance for weight control and overweight prevention and treatment.

(1)Dr Paul Kelly.  2009.  Symposium 4: Gut function: effects on over and under-nutrition.  Nutrition, intestinal defence and the microbiome.  The Nutrition Society Summer Meeting.  University of Surrey.  Thursday 2nd July 2009.
(2) Pataky Z et al.  2009.  Gut microbiota, responsible for our body weight?  Rev Med Suisse.  5:662-664 [Article in French]
(3) DoBaise JK et al.  2008.  Gut microbiota and its possible relationship with obesity.  Mayo Clinical Processings.  83:460-469
(4) Kalliomaki M et al.  2008.  Early differences in fecal microbiota composition in children may predict overweight.  Am J Clin Nutr.  87:534-538
(5) Tennyson CA &Friedman G.  2008.  Microecology, obesity and probiotics.  Curr Opin Endocrinol Diabetes Obes.  15:442-447
(6) Kirsi Laitinen, nutritionist and senior lecturer at the University of Turku in Finland.  Study findings presented at 17th European Congress on Obesity 6-9 May 2009 held in Amsterdam
(7)  Anthony J. Brown, MD.  2009.  Probiotics may help ward off postpartum obesity.  2009-05-08 15:24:34 -0400 (Reuters Health).

Written by Ani Kowal