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# 4.3 Obesity and Type 2 diabetes

The World Health Organisation (2022) defines obesity as abnormal or excessive fat accumulation that presents a risk to health. Obesity is a complex, multifactorial condition linked to a wide range of genetic and non-genetic factors, including environmental, lifestyle, socioeconomic and psychological factors. The primary cause of obesity is an imbalance between the energy consumed by an individual and the energy they expend.

The gut microbiome is involved in energy usage and digestion of carbohydrates for the human host, so the gut microbiome is thought to play a key role in energy balance. Dysbiosis is a frequent finding in obesity, which may affect how those individuals extract and use energy from food (Boccuto, 2023).

You may recall that the ratio of Firmicutes to Bacteroidetes (F/B ratio) is important for a healthy microbiome and human host.

- Question 19

  In inflammatory bowel disease (IBS – Crohn’s and UC) there is an imbalance in the F/B ratio. Is there a shift towards more Bacteroidetes or more Firmicutes?

Bacteroidetes
Firmicutes

In contrast, in obesity there is again a loss of the healthy F/B ratio, but this time with a shift towards more Firmicutes and less Bacteroidetes (Figure 27).

Figure 27 The F/B ratio in obese individuals typically shows an increase in Firmicutes and reduction in Bacteroidetes

## Fun fact: complex interactions

Research has shown that specific types of bacteria are linked to obesity. However, perhaps unsurprisingly, research suggests this is highly complex! For example:

- Christensenellaceae – associated with weight loss
- Akkermansia muciniphila – associated with weight loss
- Lactobacillus paracasei – associated with a reduction in obesity
- Lactobacillus reuteri and Lactobacillus gasseri – increase in obesity
- Bifidobacterium – increase in obesity

As you can probably tell, unpicking the role of the different bacterial species in obesity is challenging as there are an estimated 500-1000 different types of bacteria in the gut microbiome! As the bacterial species also influence each other, trying to identify the role of a single bacterial species in obesity may not give true understanding of what happens when you combine all the influences of the entire gut microbiota, microbiome and human host. However, this is still a promising area of research into obesity and understanding some of challenges that individuals may face in losing weight. Finding a way to improve the gut microbiome may also help some individuals with their weight loss goals.

One of the conditions commonly linked with obesity is Type 2 diabetes (T2D). In T2D, the body has poor sensitivity to insulin, the hormone which helps to reduce blood glucose (sugar) levels.

- Question 20

  In T2D, are blood glucose levels likely to be higher than normal or lower than normal?

Higher than normal
Lower than normal

- Higher than normal.

  In T2D the prolonged unregulated blood glucose sugar levels can result in damage to multiple parts of the body.

Dysbiosis is a common finding in diabetics and is related to poor sensitivity to insulin and poor control of blood glucose levels (Sadagopan, 2023).

Obesity and Type 2 diabetes are rising at a rapid rate, with both being among the ten most common health conditions globally. So, addressing gut dysbiosis to improve the health of the gut microbiome raises the possibility of providing a fairly cheap and easy mechanism to reduce the impact of these conditions, both for the individual and globally.

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OpenLearn - The gut microbiome – balancing the body
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