As Obesity Soars, Microbes Get a Closer Look

Guest BloggerClinical Corner, Microbiome Environment

Americans are getting fatter.

New data from the National Health and Nutrition Examination Survey (tens of thousands surveyed) revealed stark numbers: Nearly 40% of adults are obese, up significantly from previous years. Hispanic and blacks–both adults and children– counted more obesity than whites and Asians.

One other group fared especially poorly: toddlers ages 2 to 5 saw obesity rates rise, from 10% in 2007 and 2008 to nearly 14 percent in 2015 and 2016.

What’s going on?

The researchers didn’t give reasons but several are in play. For one, fast foods are more popular than ever with sales soaring 23% from 2012 according to Euromonitor. A yogurt or a kefir drink is fast but the obvious choices are the fried foods and sweets which are big sellers. Also, with so many people working, home-cooked meals with vegetables are less likely to happen, especially for the youngest who shoulder no responsibility for their weight excess.

But obesity has many bedfellows: inactivity, genetics, pollution, stress, medications and sleep deficits are a few.

Albeit confusing, our microbes are another suspect in the obesity epidemic.

The evidence linking microbes and obesity:

  • Obese and normal weight individuals harbor different sets of gut microbes with some obese subjects showing an increase in the Firmicutes/Bacteroidetes ratio over lean ones.
  • After gastric bypass surgery, bacterial populations in obese people change to increased Proteobacteria and Bacteroidetes and a decrease in Firmicutes and Actinobacteria.
  • Infant microbiota is affected by mode of delivery and type of feeding. Both have shown impact on obesity later in life.
  • Microbes produce metabolites such as short chain fatty acids (SCFA) which are considered in lipid metabolism along with energy harvest.
  • Lactobacilli and bifidobacteria are two primary probiotics under intense study with mostly positive results in reducing weight in either rodents or humans.
  • Our microbes don’t like fast food. Prebiotics or indigestible complex carbohydrates are fermented into short-chain fatty acids; acetate, propionate and butyrate enhance gut function and appear to reduce risk of obesity.

Gut microbes may direct fat build-up in several ways:

  • by harvesting and storing energy
  • producing short chain fatty acids which act as energy sources
  • regulating gastrointestinal hormone and enzyme activity to promote fat mass accumulation triggering inflammation via lipopolysaccharides

Herein lies the rub:

A microbe’s ability to squeeze calories from indigestible fibers is an enviable talent in times of famine. Not so these days when high fat and sugary foods tempt us 24/7. For certain people with genetic predisposition to harvest more calories from food (thrifty genes), microbes could be part of the problem.

Indeed, one recent study conducted at University of Southern California found that probiotic supplements increased obesity in obese Hispanic adolescents. In a random controlled trial with 19 participants, compared with placebo, adolescents who received probiotics had significant increases in total adiposity and trunk adiposity.

But other investigations reported the opposite.

A 2018 meta-analysis of RCTs looked at effects of probiotics on body weight, body mass index, fat mass and fat percentage in subjects with overweight or obesity. Fifteen studies of 800 reviewed showed that in the 957 subjects, probiotics resulted in a significantly larger reduction in body weight and fat compared with placebo; however, the effect sizes were small. The effect of probiotics on fat mass was non-significant.

And in another relavent meta-analysis, also published in 2018, researchers scoured 4721 articles for a final group of 21 studies. Conclusions?  “Overall, when the utilization of gut microbiome-modulating dietary agents (prebiotic/probiotic/synbiotic) was compared to placebo, there were significant decreases in BMI, weight and fat mass.”

Of course, probiotics are probably not the elephant in the obesity room. That honor belongs to a whole herd of culprits, not least of which is an unhealthy processed food diet.