Devlin Brown at the Water Cooler | Studies link gut microbiome to weight gain

I saw a social media post that suggested the gut microbiome in rats is related to whether they are obese or not. If this is the case, does it mean that whether I gain or lose weight is already determined by what’s in my gut?

Well, yes. On a number of levels. What you put in your gut matters, what your genetics say about your gut matters and the microbiome in your gut matters, though, surprisingly, we are far more complex — and even nuanced — than lab rats. You learn something new every day.

Here we go again, the poor old rats really do take one for the team. When I was much younger I did some part-time work for a charity in London that was raising money for animal research to advance medicine. I copped immense abuse while walking up and down pedestrian walkways with a notepad, umbrella and a request to set up a “five quid direct debit”.

What do all these studies about rats and the gut microbiome say about weight gain? In a nutshell, more diverse gut bacteria are shown to be correlated with better resistance to obesity and less aggressive energy extraction from food. The opposite is also shown to be true. Rats prone to being obese tend to show lower gut bacteria diversity.

Apparently, lower diversity in obesity-prone rats often stems from diet-driven shifts, especially from high-fat or specific carbohydrates, which causes unbalanced fermentation, in addition to genetic and physiological traits that make the gut less hospitable to a wide range of bacteria. What came first, the chicken or the egg? Ultimately, based on various studies, higher gut bacteria diversity tends to correlate to better metabolic outcomes such as less fat gain.

In humans the picture is similar but more complex. A low-fibre, high-processed food diet, for example, is known to significantly reduce the diversity of gut bacteria, but in addition to this we must factor genetics, antibiotics, stress and age. If we want to create an environment with a broader range of bacteria, this usually comes from eating a variety of plants and fibre to feed a broad range of bacteria, rather than letting one group dominate.

Some interesting studies on rats focus on transferring gut bacteria through faecal microbiota transplantation (FMT) from lean rats to obese ones and the findings show that the bacteria themselves can influence weight in the rodents.

The experiments show that “obese-type” gut bacteria are associated with weight gain while the “lean-type” may protect against it through better energy use, reduced gut inflammation and effects on actual appetite signals.

Again, the picture is more complex in humans because if we are to become adherents of something, we need causation, and this has not been proven. Human trials with FMT show some promise, but results vary across subjects and actual weight loss is often modest or inconsistent.

So, what then can we learn from all of this? As usual, your gut microbiome matters. What you eat matters hugely to what is happening in your gut and what is happening in your gut matters to a whole host of physiological outcomes.

We have seen the association and rather than wait for something like FMT to become a miracle cure for weight loss we can shift our lifestyles to build a healthy gut microbiome through everyday choices.

We know we should eat plenty of fibre from vegetables, fruits, whole grains, beans and nuts. We know that this feeds good bacteria and increases variety in our guts. I’ve seen someone radically change their bloated feeling and a host of other uncomfortable symptoms by adding fermented foods to her diet. Things such as yoghurt, kefir and sauerkraut.

We are far more likely to benefit from proven, simple changes in what we eat, a focus on exercise and good sleep and a concerted effort to manage stress. Don’t let the social media fitfluencers distract you from doing what you know is right.