As we gain more knowledge around the complicated ecosystem of the gut, studies are supporting a link between gut health and weight. We asked dietitian Emer Delaney to explain the science, plus give us her top tips to improve gut health along with her opinion on home microbiome testing kits.

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Discover more digestive health recipes and tips on everything from probiotics and the health benefits of fermenting to how a low-FODMAP diet may help ease IBS symptoms.

What is the gut microbiome and why is it important?

The gut microbiota is a complex system made up of the community of bacteria, viruses and other microbes that have colonised the gastrointestinal tract. The terms ‘microbiota’ and ‘microbiome’ are often used to mean the same thing – however, the microbiome refers to the microbes plus their combined genetic material.

Given the global obesity pandemic, scientists are starting to look at the possible relationship between our gut microbiota and our weight. Although our knowledge has advanced at pace, we are still only just beginning to understand the role the gut microbes play in our health, including the influence they have on our waist lines.

How does gut health affect my weight?

The link between the microbiome and weight is a developing field.

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Recent studies found significant differences in the gut bacteria of lean and obese individuals and twins. Those who were obese had different gut bacteria than their non-obese twin, and obesity was associated with lower microbial diversity. However, the reason for this is still not fully understood.

There have also been animal studies that found transplanting the gut bacteria of obese mice into lean ones caused the lean mice to gain fat rapidly.

Plant foods in a shopping bag

How might gut health help with weight?

Scientists are currently determining whether our gut microbes influence our appetite and if so, whether by controlling our gut microbes we might find an effective tool to aid weight management.

One research team concluded that gut bacteria may play a part in controlling when and how much we eat. They found that gut microbes produce the hormones needed for appetite regulation 20 minutes after being given nutrients.

Other research highlights the importance of probiotics and prebiotics in their ability to influence our food consumption. However, more clinical studies are needed to determine what is the optimal amount required for long-term weight management.

What can I do to improve my gut health?

Getting your five-a-day of fruit and veg is important but recent studies suggest increasing the variety of the plant foods you eat may deliver even more benefits. Those who eat a greater variety, with the optimal thought to be 30 plants per week, appear to enjoy an increase in the diversity of bacterial strains in the gut.

These strains are likely to be the beneficial varieties. Their presence in the gut increases the production of healthy chemicals, including short chain fatty acids, which may support our brain and nervous system, immune function and protect us from metabolic disease that can lead to weight gain.

Eating a diet rich in fibre from fruit, vegetables, wholegrains, beans and pulses supports gut health because bacteria in the gut break it down and this stimulates their growth and numbers.

One study found a diet high in fruit and vegetables prevented the growth of strains of bacteria that have been linked to cardiovascular disease. Other studies concluded that apples, Jerusalem artichokes, almonds and pistachios increased the beneficial bifidobacteria, which help prevent intestinal inflammation and improve gut health.

Do home microbiome test kits work?

Home microbiome test kits that require you to send a stool sample to be analysed in a laboratory, claim to help you understand the makeup of your unique gut microbiome.

There is an increasing interest in this form of testing and how the results may influence your health, however there is no standard testing method and no quality control. Furthermore, scientists don’t yet know what actually constitutes a ‘healthy’ gut microbiome.

It is important to appreciate that your gut microbes change regularly in response to diet, sleep, stress, travel and exercise and, as a result, you might achieve different test results on different days. Testing kits claim to provide a snapshot of your “core” microbes however, these may still change due to the factors mentioned above.

Still interested? Check out our review of the best personalised nutrition test kits.

When should you see a specialist?

If you are concerned about your gut health, I would recommend speaking to your GP – especially if you have been feeling unwell for a prolonged period of time. Certain conditions are referred to as ‘red flags’ and require immediate action to be sought.

These include:

  • blood in the stool or urine,
  • stools that are lighter or darker than normal
  • unintentional weight loss
  • persistent vomiting
  • or iron deficient anaemia

Check out our health and nutrition page for more recipe inspiration, health benefits guides and advice on special diets.

Find out more...

How does diet affect gut health?
What are probiotics and what do they do?
What is a plant-based diet?
Gut health: what does it really mean?


This article was last reviewed on 16 April 2024 by Kerry Torrens.

Emer Delaney BSc (Hons), RD has an honours degree in Human Nutrition and Dietetics from the University of Ulster. She has worked as a dietitian in some of London's top teaching hospitals and is currently based in Chelsea.

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