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.

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

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The schematic illustration of the set of scales with Firmicutes to Bacteroidetes (F/B) ratio is shown for a third time, this time in individuals who are obese. There is an increase in the Firmicutes load on the left and a decrease in the blue Bacteroidetes, with the extra red circles of the Firmicutes causing the balance down to tip down on the left.

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

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.

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.