How your microbiome controls your weight

Calories in versus calories out, right?
And whoever is overweight and not losing fat is just not trying hard enough!?

In the 80s, students from Canada enrolled into a study in which they were isolated from the rest of the world for 120 days and where they were only allowed to eat, sleep, watch tv, or to read [1].
Sounds like a dream for most students. But here is the caveat:
The students were over-fed. 1000 calories extra and no sports allowed.
After that time period, the students gained on average 8.1kg of body weight. Which is not very surprising.
What was the surprising, was the range of weight gain:
While some students only gained 4.3kg, other gained up to three times more.

                                          Modified after [1]

                                          Modified after [1]


Does this mean that it is after all just the genetics making the difference here?

Well, again, I wouldn’t say so. What I am getting at is that there is actually a third factor, who seems to play a much bigger role. A factor that was easily overlooked and never put into consideration very much.
I am talking about the inhabitants of your gut. Your Microbiome!
With 100 trillion microbes in your gut, there are about 10 times as many microbial cells in the body as there are human cells.
And with an estimate of more than 10,000 different species of microbes, they provide a metabolic capacity which exceeds the liver with a factor of 100.

The obese microbiome

Researchers found that what actually differs more than genes is the composition of microbes in your gut. While we share on average 99.9% of genes among people, the microbiome can be so different that only 20% are identical between individuals.
Often, the microbiome of overweight people is so different that scientist invented the special name for it  “the obese microbiome”.
And the composition of microbes is not only different between people of different backgrounds and origin, but can be very different between relatives as well.
Researchers analyzed the microbiome of twins. And twins, especially, monozygotic twins offer researchers the perfect opportunity to the exclude the factor of genes.
These twins were quite different from each other when it comes down to their looks, as one twin was lean while the other one was obese.
When the scientist had a closer look at their microbes they concluded that:
obesity was associated with phylum-level changes and a reduced diversity in the microbiota.”[2]

So, another group of researchers looked into these phylums (certain groups of microbes) in lean and obese twins. They found that the obese twins had 20% more of the group of Firmicutes and nearly 90% less of the group of Bacteroidetes [3].

          Obese volunteers increased their of abundance                Bacteroidetes by losing weight [3].

          Obese volunteers increased their of abundance                Bacteroidetes by losing weight [3].

These are the two largest bacterial groups of our microbiome and make up to 90% of our microbiome.
By now researchers use the ratio of these two groups as a kind of biomarker for obesity. The higher the ratio of Firmicutes to Bacteroidetes the higher is the risk to become overweight.
And indeed, while the obese co-twin had a much greater ratio, to begin with, it was something that was reversible. The obese volunteers were set on a diet for one year and their percentage of bacteroidetes nicely increased while they were losing weight!

Microbiome in Africans

Not just between obese and lean people there are huge differences, but it also matters where people live and of course - what they eat.
Researchers from Italy went to a very rural village in Burkina Faso and compared their microbiomes with the ones of average European people [4].
They found that the African people have a much higher percentage of bacteroidetes and less Firmicutes.

                            Microbiome of African villagers differs extremely from European people [4]

                            Microbiome of African villagers differs extremely from European people [4]

They further found that the African villagers had much higher levels of Short-Chain fatty acids [4].
Short-chain fatty acids are produced when dietary fiber is fermented in the gut by the microbes.
Studies showed us that SCFAs can increase satiety, reduce triglyceride and LDL cholesterol levels in the blood, suppress inflammation and even have anti-carcinogenic properties.

        Higher levels of Short-Chain Fatty Acids in African Villagers (BF) [4]

        Higher levels of Short-Chain Fatty Acids in African Villagers (BF) [4]


Transfer of obese mice microbes

The next study is a great example of how reversible your health and also your waistline is.
Researchers sucked microbes from the guts of either lean mice or the obese ones [5]. Then they injected the microbes into the intestines of animals whose own microbes were deleted due to sterile caging.

The mice injected with the 'obese' microbes gained roughly double the quantity of fat than those that received the 'lean' microbes.

Another paper published in the journal Science went one step further and took the microbiome of human twins where one twin was obese and the other one lean and transferred the microbes into sterile mice. The outcome was the same: the mice who received the obese microbiome gained more body mass, especially fat [6].

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Mice harboring the microbiome of obese people gained 10% body fat [6]

Mice harboring the microbiome of obese people gained 10% body fat [6]

As Helen Pearson, chief editor of the Nature journal nicely formulated:

“Fat people harbor fat microbes.”
“The obese are often blamed for their own corpulence. But perhaps, just perhaps, some of the blame should be placed on another type of organism entirely: bacteria.”

Here is another example of how easy you can improve your odds:
In 2015, scientist gave a group of volunteers 21 grams of fiber extra per day or just a placebo. After just 21 days the abundance of bacteroidetes increase by 13% in the group that received the fiber [7].

With this knowledge, one might consider that the first step of a diet should be to reset our microbiome!
To start with, it would be the best to focus on less processed food as they contain naturally more fiber. Maybe even include some probiotic food like kimchi or sauerkraut - or even take some probiotic supplements to get a fast start.

For my last diet, it certainly helped me a lot to focus on a high fiber intake  - and I never lost fat so easily while staying mentally sharp.





  1. Bouchard et al., The response to long-term overfeeding in indentical twins, N Engl J Med, 1990
  2. Turnbaugh et al., A core gut microbiome in obese and lean twins, Nature, 2009
  3. Ley et al., Human gut microbes associated with obesity, Nature, 2006
  4. De Filippo et al., Impact of diet in shaping gut microbiota revealed by a comparative study in children from Europe and rural Africa, PNAS, 2010
  5. Turnbaugh et al.. An obesity-associated gut microbiome with increased capacity for energy harvest, Nature, 2006
  6. Ridaura et al., Gut Microbiota from Twins Discordant for Obesity Modulate Metabolism
    in Mice, Science, 2013
  7. Holscher et al., Fiber supplementation influences phylogenetic structure and functional capacity of the human intestinal microbiome: follow-up of a randomized controlled trial, Am J Clin Nutr 2015