Can Your Gut Bacteria Determine Your Weight?


There is more and more evidence emerging every day to show that your gut bacteria can improve many aspects of your health, from energy levels, to immunity, to clear skin. But can they also affect your waistline? Yes!

Firstly, what are gut bacteria? And what are probiotics and prebiotics?

If you haven’t already seen my IGTV, take a look at it there or here below! I answer this question and it should clear your confusion! Then, this blog will re-iterate and elaborate on these points further and how a healthy gut can affect your weight.

And, are you following me on instagram yet? You may want to go to my page (@health_with_bec) and follow me to receive daily health and weight loss motivation, education and behind the scenes footage into my services and clients journeys!

Ok, back to it.

Your body contains trillions of bacteria, with the majority of these bacteria being located in your intestines (gut). These bacteria can affect how different foods are digested and they can also produce chemicals that support you to feel full. As a result, certain species of gut bacteria can definitely affect your weight!

I am going to explain how your gut bacteria affect your weight and what foods promote healthy gut bacteria growth.


Firstly, how do they affect how your food is digested?

Since your bacteria line your intestines, the food that you eat comes into direct contact with them. This may affect what nutrients you absorb and how energy is stored in your body.

One study examined the gut bacteria in 77 pairs of twins, one of whom was obese and one of whom was not.

The study found that those who were obese had different gut bacteria than their non-obese twins.

In particular, obesity was associated with lower gut bacteria diversity, meaning there were fewer types of bacteria in the gut (1).

Other studies have shown that if the gut bacteria from obese people are put into mice, the mice gain weight. This suggests that gut bacteria could affect weight (2)3). This may be due to the effect of bacteria on the digestion of different foods.

For example, humans can’t digest fiber, so it’s not absorbed into your blood, but instead travels to your intestines where certain gut bacteria do the digesting. By digesting fiber, these gut bacteria produce a number of chemicals that benefit gut health and possibly promote weight loss (4).

Finally, your gut bacteria can influence how dietary fats are absorbed in the intestines, which may affect how fat is stored in the body! (5).


How do they affect your appetite?

Your body produces a number of different hormones that affect your appetite, including leptin, ghrelin and peptide YY (PYY).

Studies have shown that different species of bacteria in your gut can affect how much of these hormones are released and whether you feel hungry or full (6), (7).

How does this happen? When certain species of gut bacteria break down fibre, short chain fatty acids are produced. One of these fatty acids is called propionate and shows promising effects in studies.

One study in 60 overweight adults found that taking propionate for 24 weeks significantly increased levels of the hormones PYY and GLP-1, both of which influence hunger. People who took propionate also had reduced food intake and reduced weight gain (8).

Other studies have shown that prebiotics (compounds that are fermented by gut bacteria) can have a similar effect on appetite (9). People who ate 16 grams of prebiotics per day for two weeks had higher levels of hydrogen in their breath. This correlates with gut bacterial fermentation, less hunger and higher levels of the hormones GLP-1 and PYY, which make you feel full (10).

So, what foods optimise the amount of good gut bacteria in your gut?

You really want to aim for a large number of probiotics (healthy gut bacteria) and a diverse range of them too, there are so many different types!

Try to include probiotic rich foods into your daily diet.

Foods that are rich in probiotics are:

  • Yogurt (with active or live cultures)

  • Kefir

  • Natto

  • Sauerkraut (unpasteurised and containing live cultures)

  • Tempeh

  • Kimchi

  • Miso

  • Kombucha

  • Pickles (pickled in salty water, not vinegar)

Like I spoke about in the video and above, you need to also consume prebiotic rich foods! These foods will feed the healthy bacteria and keep them alive and thriving!

Prebiotic rich foods to include regularly are:

  • Whole grains*

  • Fruits*

  • Vegetables (and a wide variety of them)

  • Nuts

  • Seeds

  • Green tea, red wine (1 glass per day) and dark chocolate (in moderation!)

* If you have IBS concerns and/or you follow a low carb lifestyle like me (see my dietary approach and the low carb 101 page) you would want to exclude whole grains and watch your fruit intake.


You also want to avoid foods that can harm your healthy bacteria!

The most dangerous one is sugar! A diet high in sugar can stimulate the growth of certain unhealthy bacteria in the gut, which may contribute to weight gain and other chronic health disorders.

Aswell as sugar, avoid artificial sweeteners such as aspartame and saccharin, as they reduce beneficial bacteria in the intestines. Foods containing too many saturated fats may contribute to the growth of disease causing bacteria, so you want to avoid them and aim for healthy fats such as omega 3’s. 

What else (aside from food) affects the balance of your gut bacteria?

This calls for another blog post, otherwise this one will become too long!

But… please remember that these factors can all poorly affect it…

  • Poor sleep

  • Stress

  • Antibiotic consumption

  • Certain medications (especially inflammatory meds and the pill)

  • Excess alcohol consumption


To wrap it up?

Your gut bacteria can affect how your food is digested, how fat is stored and whether you feel hungry or full. So, a healthy gut microbiome may be important for maintaining a healthy weight!

You really want to aim to consume a diet that is varied and rich in foods that are high in fibre. These can all promote a healthy gut bacteria environment as they feed the good guys in your gut. And, the inclusion of probiotic rich foods should also be included your diet.

Adding a good quality probiotic supplement to you day can also boost things along! I recommend consulting with a health care professional and getting appropriate tests to see exactly what’s going on in your gut so that you can correct the imbalance if there is one and specifically improve what may be lacking!

Bec x

PS - have you seen my 3 Week Body Reset? I keep gut health at the forefront of my focus, aswell as weight loss to help you slim down without the hunger and simultaneously keep your gut thriving.


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