Join us!

If you enjoy writing about science, then join our team of student writers to get your work published on our site!


Obesity - Could The Key Be In Your Gut?

By James Lee

Photo credit: Pixabay


Those of you who watch the Channel 4 series ‘Food Unwrapped’ may be aware of a recent episode, aired on June the 13th, in which numerous weight loss strategies were trialled. One of the more interesting and effective strategies that the show looked into was the effect of gut bacteria on our weight. One species in particular was shown to halt weight gain, and could prevent and even treat obesity. But how is this possible?

Well, this discovery was one of many found through investigations into the ‘microbiome’ of the body, but as you can imagine, with such significant discoveries, there has also been plenty of misinterpretation from the media. So hopefully I can help break down the facts we know so far. But first, what is the microbiome?

The Microbiome

The microbiome is the name given to the community of microorganisms that literally share our body space [1]. They can be pathogenic (cause infectious diseases), but in general most are either commensal (they benefit from us without damaging us) or symbiotic (we both benefit from each other).

The microbiome in humans is vast, some estimates suggest you have as many bacterial cells as human cells, and others suggest nearly 100 trillion bacterial cells can be found in an adult human body. Compare this to the number of cells we have, and you begin to understand just quite how many bacterial cells live inside our body. Because bacteria are small, this huge number of cells only accounts for about 2% of our body weight, yet the role of the microbiome in maintaining our health means it is often termed 'the forgotten organ' [2].

The term microbiome technically covers all of the bacteria found on or in our body, from our skin to our airways, mouth, and the rest of our digestive system. About 70% of the bacteria found in humans are thought to be in the intestines, and it is these bacteria that have the potential to influence the development of obesity.

Photo credit: Pixabay

First Evidence

Some of the first research into the gut microbiome and obesity was published in 2005, with obesity being shown to change our body environment to favour the Firmicute groups of bacteria [3]. A year later, these results were confirmed in dieting humans [4]. Further research showed that when the same group of bacteria were transplanted into mice, they started to gain weight [5].

What can have caused this? Subsequent studies have since discovered that the Firmicute group of bacteria are responsible for an increased digestion of food, specifically the polysaccharides (large sugars) [6]. In mice with more of the Firmicute bacteria, fewer of these sugars, and hence less energy overall, was found in the faeces of these mice. The mice therefore extracted more calories from their food as a result of the bacteria, contributing to their weight gain and obesity.

Antibiotics and Obesity

Antibiotics are drugs, such as penicillin, which are used to treat bacterial infections, by inhibiting or reducing bacterial growth. However, unfortunately antibiotics also have the same effects on the important bacteria in your gut, meaning many of the useful bacteria can be killed along with the harmful ones when a course of antibiotics is taken.

What effect does this have on us? A 2014 study has shown that children who take several courses of antibiotics during their childhood have around a 10% higher risk of being obese in later life [7]. This is likely to be because some gut bacteria are more prone to being killed by antibiotics, and hence the balance of different bacteria is disrupted, and this can affect how we absorb food. Unsurprisingly, broad-spectrum antibiotics, which effect most bacteria, were found to have the largest effect.

This doesn’t mean we should stop taking antibiotics, or stop our children taking them. This could, in many cases, make their illnesses last longer or become more dangerous. It also doesn’t mean you should take antibiotics for a shorter time either, this can increase the risk of developing antibiotic-resistant strains of bacteria.

The Biggest Breakthrough?

An important species of bacteria in our microbiome is a species called Christensinella minuta, or C. minuta. A 2014 study investigating how much of our gut microbiome is inherited, found that this species of bacteria were inherited more than other bacteria. Interestingly, the lower the patients BMI, the more of this species of bacteria they had, suggesting Christensinella minuta could be involved in reducing our body weight [8].

In order to confirm the effects of this bacterium, bacterial samples of Christensinella minuta were added to the guts of participants, and the effects were compared with mice that did not have these bacteria added. Monitoring the levels of these bacteria showed a lower bacterial abundance by the end of the first week, but abundance then remained stable until the end of the third week. At this time, mice with C. minuta added to their guts gained less weight, and their fat tissue masss increased by a smaller amount. Again, this may lead us to believe that the Christensinella minuta bacterium contributes to a slower rate of weight gain.

How Can I Take Advantage Of This?

Unfortunately, due to this being a relatively recent discovery, it’s hard to be able to utilise this information. As we further our research into the gut microbiome, we may further understand how this bacterium, among others, can be used to treat obesity and other human diseases.

At the moment, we have two main ways we can modify our gut microbiomes. First, the more unsavoury, difficult and expensive method - faecal transplant. If this sounds disgusting, yes, it is. It involves taking a faecal sample from someone known to have plenty of these bacteria, separating out the bacteria from the sample, and inserting a solution with these bacteria into your own colon via the rectum. This currently isn’t available as an option with the NHS, except for patients with diseases such as Crohn’s disease, where it is used to replace gut bacteria lost in these patients.

The more palatable approach may be in diet modification. Doctors and other microbiome researchers believe that a diet with little to no processed food and rich in leafy green vegetables provides better food for your gut bacteria. The theory is that this leads to levels of all bacteria in your gut increasing, including C.minuta, which could lead to better weight management, and will likely lead to better health overall anyway.

Supporters of such a diet usually recommend a probiotic, a food or supplement which contains lots of bacteria to try and increase the number of bacteria in your gut. There have already been a few newspaper articles suggesting probiotics help you improve your gut bacterial diversity, which can lead obesity prevention. But NO research has yet been done on the effects of probiotics on obesity in humans.

Continually, there is currently mixed evidence on how effective probiotics are for healthy people. Most of the supporting evidence is for probiotic use following illness, with the most current studies suggesting little beneficial effects in healthy adults [9]. Most studies on probiotics highlight the variation in how each of the different studies were carried out, so we will know more once further, better designed studies are produced.

The Take Away Points

A decade ago, studies began to show that obese people had more bacteria from a group known as the Firmicutes. This meant these individuals digested more of the complex sugars from food, and this increased the energy they absorbed. Calorie restricted diets were found to decrease the amount of these bacteria.

Recent studies have suggested Christensinella minuta is a bacterium found in the gut that appears to reduce weight gain. This bacterium could be a new hope in the battle against obesity. We are unsure yet how this bacterium influences our body to reduce levels of obesity. So, currently the only way to utilise its benefits is to increase the amount of the bacterium in our guts.

A diet with processed food removed, and replaced with lots of fruits and vegetables are recommended to help develop your gut bacterial diversity. (Apparently dark chocolate and red wine help too!)

There is mixed evidence on how helpful probiotics actually are, and currently no studies have been performed to investigate whether they can help tackle obesity, so use them cautiously.

Antibiotic use in children has been shown to slightly increase the risk of developing obesity in later life. BUT this doesn’t mean you shouldn’t take them. Doctors will likely change how they prescribe antibiotics in the next few years. After taking antibiotics, consider a few weeks of the suggested diet above to try and increase the levels of the surviving bacteria in your gut.

Useful Links


  1. [1] PJ Turnbaugh et al., Nature,2012,449(7164):804-810
  2. [2] AM O'Hara et al., EMBO reports, 2006,7(7):668-693
  3. [3] RE Ley et al., PNAS2005,102(31):11070-11075
  4. [4] RE Ley et al., Nature2006,444:1022-1023
  5. [5] PJ Turnbaugh et al., Cell Host Microbe2008,3:213-223
  6. [6] PJ Turnbaugh et al., Nature2006,444:1027-1031
  7. [7] LC Bailey et al., JAMA Pediatrics,2014,168(11):1063-1069
  8. [8] JK Goodrich et al., Cell,2014,159(4):789-799
  9. [9] NB Kristensen et al., Genome Medicine,2016,8:52

Copyright © Reaction Science 2019