Microbiota and obesity

Our gut bacteria can be partially blamed for being overweight or obese. There is a causal link between the microbiota and obesity, driven in combination with overnutrition and drastic lifestyle changes.

The prevalence of obesity is reported to increase worldwide and it is a major challenge in our modern days. There are various attempts to explain the large increase in obesity, mostly due to the last three decades of research. They include calorie intake, changes in dietary composition, decrease in physical activity and changes in the gut microbiome. Is the gut microbiota contributing to the excessive weight accumulation in our body? A piece of evidence was published in 2005, when scientist found that obese mice microbiota composition is different from the healthy lean ones. An increase of Phylum Firmicutes bacteria was noticed in the obese mices, and their microbial diversity was lower than normal. This made them wonder if is obesity causing the changes in the microbiota or is the gut bacteria causing obesity? They got sample from human twins (one fat, one lean) and give them to germ free mice. The ones with bacteria from the slim ones stayed slim, the others quickly gained weight. So the conclusion was that there is a direct causal link between the gut microbiota and the weight gain. The next trials started with gut microbes from lean humans, given to obese individuals, and they improved their metabolic response and experienced weight loss. The effect lasted for few weeks when the study was done, but we do not know if the effect is sustained. Also, fecal transplant is prone to high risk of infection. We will talk later about this.

The gut microbiota is a major contributor to obesity. Our diet is another one, as the Western style diet is an example , characterized by highly processed and refined foods, rich in proteins and fats. It has a high salt, fat and sugar content, with protein mainly from red meat. This diet is the major contributor to the actual crysis of obesity and to a wide range of obesity related diseases. This type of diet leads to a low presence of bacteroidetes and akkermansia, followed by an increase in the firmicutes and proteobacteria groups. These alterations were associated with obesity and the subsecvent related chronic diseases. The high fat content causes an overload in energy leading to obesity, but the change in microbiota can also cause inflammation, which in turn can lead to many obesity related diseases.

Diet can increase obesity and obesity related diseases directly and indirectly. The evidence supporting the link between obesity and lifestyle changes is very strong. Modulation of the microbiota might help to ameliorate metabolic responses and initial weight loss attempts. Adapting the microbiota might be useful to keep a healthy weight or even to lose weight.

Next post: Undernutrition and weight loss.

See you soon.
G.

Microbiota - Man versus mice

There are clear differences between the genomes and diets of different species. Is there some evolutionary relationship of animal microbiota? There is indeed a definite difference between the genomes and diets of different animal species. Choosing the microbiome of the elephant, panda, python and few others for study, the microbiota of different animals will form clusters based of their evolutionary distance and dietary behaviour. We got herbivores, carnivores and omnivores. If we look for similarities based on the types of microbes and their abundance in the gut, then animals who are evolutionary close are also more alike on the microbiome level. But even for a big group like herbivores, there are clusters, based on whether the animal is a foregut or hindgut fermenter. Let me explain. A foregut fermenter has a fermenting chamber called rumen placed before the stomach. A hindgut fermenter has a fermenting chamber called cecum at the end of small intestine. Because they are different evolved digestive organs, they are selective for different microbes, hence the difference in the microbiota. The microbes are different based on the evolutionary relatedness of the host, but this clear separation dissapear when we consider the microbiota gene content. The gut microbial communities all share genes with similar functions, so even if the microbes are different, the functions executed are similar.

There was an experiment done, where zebra microbiota was transplanted to germ free mices. The microbes had to find a previous balance in their overall structure, adapting to the new host in the same time. The new environment forces the macrobiota to reach a new stable state. The new environmental conditions are determined by host genetics and lead to specific immune system and physiology, but they are also determined by the host dietary habits. There was another experiment where microbes where transferred from mices to germ free mice and from fish to germ free fish. The conclusion was that the host genetics is of major importance for the microbiota development. The mouse itself will adapt to the new microbiome using immune and metabolic adjustments.

So, the microbiome will adapt to its specific environment as the genetic make-up of the host and its dietary habits will determine the environmental conditions. Every animal species carry their own specific microbiota.

Next post : Microbiota and obesity. Now this will be an interesting one!

Notes (A blast from the past)

The man was looking mesmerized at the towering monster that just came out of the lake's calm waters, and for a moment froze. It was then when i turned and I could see him. Like every other human until now, stopped for a moment, looked at me and start to run back to his small village.

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Ship Journal Log 21365 - Year 5

The giant lizzards just got extinct when a big meteorite has fallen in the western hemisphere of the planet.

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Ship Journal Log 456365 - Year 61.333.215

I am kind of bored with this exploring mission. But the primates just started to use rudimentary tools. I am thinking to help them evolve a bit by teaching how to start a fire.

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Ship Journal Log 45578- Year 61.333.232

I like to think that i saved the future intelligent life on this planet. Just as i teach them how to make fire, another ice age just started. Most of the giant mammals got extinct.

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Ship Journal Log 1245365 - Year 65.245.235

My new favorite species started to paint the walls of their caves. I see a glorious future.

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Ship Journal Log 1294576 - Year 65.428.520

Humans are petty little creatures, thinking only at war and destruction. But there are few of them that make me hope that the end of the cycle will not come very soon. This Leonardo guy is bringing the art to a new level right now.

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Ship Journal Log 1298254 - Year 65.429.005

Oh, they found the entrance of my underground base, but the shields are still on. I have a name now. Nessie, also known as the Lock Ness monster. How cute!

(This was the last entrance from our explorer from Solar System XFSTF 31337)

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Press Release 15.12.1998 16:45 - After decades of terror and mysterious dissapearings, a serpent-like animal was killed by the Police helicopter near Lock Ness. We want to thanks to Mr. John Major, who promptly reported and confirmed the target location.