Fast Food and Obesity

foodies welcome

Research at Washington University showed that fat lab mice have in their intestines more Firmicutes, which are a type of bacteria. Thin mice have more Bacteroidetes. When both groups of mice are given the identical amount and type of food, the Firmicutes mice extract more calories from the food and grow fatter. Extrapolating from this, it is possible that patients who insist that they are eating sensibly, yet remain obese, are not lying.

Dr. Tim Spector teaches genetic epidemiology at King’s College, London. His new book, The Diet Myth: The Real Science Behind What We Eat, is all about how our chosen diet affects our inner colonies of bacteria, for better or worse. His particular interest is fast food, an interest shared by another family member. A report from tells how…

…his 23-year-old son put himself on a strict diet of fast food for 10 days as part of his dissertation project. It stripped his gut microbiome of about a third of its 3,500 bacterial species. Bacteria that have been linked obesity flourished.

The story goes on to recall a 2014 study that recruited 20 subjects in rural South Africa and 20 African Americans in the U.S. to swap diets. In other words, the South Africans switched to meats and fried foods, while the Americans switched to root vegetables and cornmeal porridge. The report says:

After only two weeks of diet “Westernization,” the microbiomes of Africans were producing about half the levels of a molecule called butyrate, which has been linked to lower inflammation, as before their diet intervention. In contrast, the microbiomes of Americans started churning out about twice as much butyrate after they went on the healthier African diet. The Africans also acquired more bacteroidetes, the same group of obesity-associated bacteria that took over Spector’s son’s microbiome.

The astute reader will have noticed an apparent contradiction regarding the role of bacteroidetes, which is not within the scope of this post to explore. Study of the gut microbiome is in its infancy, and the mysteries greatly outnumber the certainties. Any reader who wishes to grasp the full, bewildering spectrum of possibilities being explored can glean a notion of the complexity from “Firmicutes and Bacteroidetes,” which includes a further list of recommended reading.

Sugar Strikes Again

A book called How to Quit Drinking Without AA by Jerry Dorsman, reminds us that…

…your body converts alcohol to sugar, and physical addiction to this sugar contributes to dependence on alcohol. Consuming foods high in refined sugars may sustain this physical addiction, making it more difficult to give up alcohol or stay on a sobriety plan.

Fast food, of course, is mentioned as an obesity villain because of its abundance of refined flour, which the body also converts into sugars. It also contains a massive amount of saturated fats, which certain species of gut bacteria are known to like. When laboratory mice received transplants of lean bacteria, they could stay at a normal weight as long as saturated fats were absent. But as soon as special food pellets laced with saturated fats were introduced to their diets, they lost the ability to fight off weight gain.

This points to two conclusions. One, it is unlikely that junk food manufacturers, even with the intention of turning the spotlight away from their culpability in causing childhood obesity, would want to sponsor research on the gut microbiome. They would be reluctant to back such research because of the many indications that their products are the very ones that the useful bugs shun.

The other conclusion is that even if lean bacteria transplants work on humans, manipulation of the microbiome is no magic bullet. People can mess up that fix, just like they mess up their expensive and traumatic bariatric surgery. Anyone who wants to retain the title of “formerly obese” will still need to work very hard, with the help of such programs as W8Loss2Go, and extensively re-train themselves to become followers of a very different lifestyle.

Bonus Fact:

From Gut: The Inside Story of Our Body’s Most Underrated Organ, by Giulia Enders, here is a little contribution to the re-education of children and teens who are fighting obesity. When the stomach “growls” or “grumbles,” it’s not a sign of hunger.

The small intestine loves to clean and it’s very busy all the time, moving things forward. When we haven’t eaten for a while, the small intestine is like, ‘Okay, no need to digest. Everything that’s still here, I’m going to wipe it out,’ so it creates this muscular wave.

Your responses and feedback are welcome!

Source: “Microbes: The Trillions of Creatures Governing Your Health
,”, May 2013
Source: “How fast food could wreak havoc on your gut microbiome,”, 05/27/15
Source: “Foods to Avoid for Alcoholics,”, 11/03/10
Source: “Say hello to your little friends: Making sense of gut bacteria,”, 06/07/15
Image by Dr. Pretlow


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OVERWEIGHT: What Kids Say explores the obesity problem from the often-overlooked perspective of children struggling with being overweight.

About Dr. Robert A. Pretlow

Dr. Robert A. Pretlow is a pediatrician and childhood obesity specialist. He has been researching and spreading awareness on the childhood obesity epidemic in the US for more than a decade.
You can contact Dr. Pretlow at:


Dr. Pretlow’s invited presentation at the American Society of Animal Science 2020 Conference
What’s Causing Obesity in Companion Animals and What Can We Do About It

Dr. Pretlow’s invited presentation at the World Obesity Federation 2019 Conference:
Food/Eating Addiction and the Displacement Mechanism

Dr. Pretlow’s Multi-Center Clinical Trial Kick-off Speech 2018:
Obesity: Tackling the Root Cause

Dr. Pretlow’s 2017 Workshop on
Treatment of Obesity Using the Addiction Model

Dr. Pretlow’s invited presentation for
TEC and UNC 2016

Dr. Pretlow’s invited presentation at the 2015 Obesity Summit in London, UK.

Dr. Pretlow’s invited keynote at the 2014 European Childhood Obesity Group Congress in Salzburg, Austria.

Dr. Pretlow’s presentation at the 2013 European Congress on Obesity in Liverpool, UK.

Dr. Pretlow’s presentation at the 2011 International Conference on Childhood Obesity in Lisbon, Portugal.

Dr. Pretlow’s presentation at the 2010 Uniting Against Childhood Obesity Conference in Houston, TX.

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