Does constipation cause weight gain?

Yes, it's true – constipation can play a significant role in weight gain. In our clinic, we've observed countless cases where resolving constipation leads people to return to more normal weight management, often without making drastic changes to their diet. It's a remarkable phenomenon that underscores the intricate relationship between our digestive system and body weight.

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How does this work?

There is so much we don't yet know about the gut microbiome, and despite the hugely useful tool of microbiome testing, and the usual tools available for a nutritional therapist, I'm still in awe over how much we don't yet know which has become clear by the results produced by some nutritional interventions.

Some bacteria are known to influence metabolism, but there's much more to discover...


Three potential causes of weight gain in constipation 

1. Water retention

Many of my clients complain of water retention when they're particularly constipated, which eases when constipation lessons. Perhaps this is the body's way of trying to hold on to water to ease constipation - or it could be related to gut bacteria, we just don't know. Either way, it can create rapid and uncomfortable weight gain. 

2. The thyroid and constipation

In some cases of persistent constipation, an underachieving thyroid gland may be involved, which could promote weight gain.

Chronic constipation alters the microbiome, which can become unbalanced and unfavourable. 

If the thyroid function is found to be a little low, we want to think about specific nutrients the thyroid needs to function well. Sufficient protein and iron are the two main nutrients I would assess, followed by iodine and selenium. Many vegetarians think they consume enough protein, but I'd recommend you use software to calculate this for a couple of weeks to assess if your thyroid is struggling. If you have gut problems, you may struggle a little bit to absorb plant sources of protein.

3. Small intestine bacterial overgrowth (SIBO)

Persistent constipation will almost always cause SIBO to some level, and SIBO often tends to be associated with weight gain, likely due to the bacterial action in the small intestine directly.

It also tends to be associated with food intolerances or worsening of symptoms with certain foods (but you may be struggling to identify which exactly). SIBO is also associated with inflammation. This can manifest as skin eruptions, rashes and joint pain to mention some.  


Gut molecules - serotonin and short-chain fatty acids (SCFA)

Our gut bacteria are responsible for producing a number of molecules that are responsible for gut motility (movement), namely SCFAs and serotonin. It's quite common to discover that people have very low, or even undetected levels of particular bacteria responsible for producing some very beneficial SCFAs, which can stem from not eating enough fibre, or possibly past antibiotic courses (interestingly, serotonin is involved in appetite regulation, and SCFAs are key players in our metabolism and how we use our stored energy!).

These bacteria are restored by using probiotics and fibre, however, if you have SIBO, be careful with what you introduce as you may not tolerate these well.

Establishing whether you have troublesome gut bacteria is the first thing to do. Simply guessing will lead you around the houses and lead to a loss of valuable time and life quality.

Want to know if constipation is causing your weight gain? Complete our free two-minute constipation review to receive your personalised assessment and recommendations or contact me via my profile

The views expressed in this article are those of the author. All articles published on Nutritionist Resource are reviewed by our editorial team.

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London W1H & NW6
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Written by Linda Albinsson, Advanced Gut Health Nutrition Clinic
London W1H & NW6

Linda Albinsson is a highly experienced and qualified nutritionist specialising in areas of the microbiome, gut health, inflammatory conditions (skin, cardiovascular, pain and joint) and others

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