Having a pot belly is long-established as a warning sign that your diet and lifestyle might be endangering your health. Even in otherwise slim people, an accumulation of fat around the abdomen is known to be harmful.
This is because a paunch can indicate high levels of visceral fat – or deep layers of fatty tissue surrounding vital organs such as the liver and even the heart.
Visceral fat is made up of cells that secrete chemicals and hormones that are toxic to the body, triggering widespread inflammation, which in turn raises the risk of heart disease, stroke and type 2 diabetes. But now scientists are discovering this type of belly fat can affect our health more widely, from hearing and eyesight, to mental well-being and whether we can taste food properly.
In the latest finding, scientists discovered that adults with excess tummy fat are much more at risk of depression.
When researchers at Xiangya School of Medicine in China tracked 7,258 middle-aged men and women, those with the highest body roundness index (a measure of waist circumference compared to height) were almost 40 per cent more likely to have depression than those with the lowest.
The scientists said this might be because fat cells drive the production of free radicals – harmful molecules that are known to reduce levels of the feel-good brain chemical serotonin (they oxidise serotonin, similar to how rust rots steel).
In a report on their findings, recently published in the journal PLOS One, they said: ‘This suggests that body roundness index could serve as a simple and readily accessible indicator for predicting depression risk.’
It’s not just mood that is influenced by waist size. It can affect your memory and risk of dementia, according to a 2023 study in the journal Ageing and Disease.
Researchers at Washington University analysed data from 10,000 healthy adults aged 20 to 80, who underwent MRI scans to measure the volume of their brains, and found that in those with the most tummy fat, areas of the brain associated with memory, concentration, planning and decision-making were smaller.
While the researchers said they couldn’t be certain belly fat causes these brain changes, previous studies have found it raises levels of inflammatory chemicals, called cytokines, in brain tissue, which may cause lasting damage.
Scientists are discovering this type of belly fat can affect our health more widely, from hearing and eyesight, to mental well-being and whether we can taste food properly
Researchers in China found people with the highest body roundness index were almost 40 per cent more likely to have depression than those with the lowest
‘People with obesity are often found to have smaller brain volumes,’ explains Alex Miras, a professor of endocrinology at Ulster University.
‘They have elements of cognitive dysfunction which are known to improve when they lose weight.
‘Visceral fat is a toxic fat mass that triggers generalised inflammation [all over the body].
‘It can be anywhere – for example, if you have fat around the heart, you get inflammation there that leads to narrowing of the arteries [which can increase the risk of a heart attack].
‘And in the brain, this inflammation is in the brain tissue itself, where it affects memory and executive function [the ability to focus, remember instructions and juggle several tasks at once].’
How much visceral fat you have is partly genetic, but it starts to form when calorie intake consistently outweighs calories burned.
Other studies show pot bellies can heighten the risk of age-related macular degeneration (AMD), a leading cause of blindness which affects an estimated 700,000 people in the UK.
The condition usually develops after the age of 50. The most common form, dry AMD, accounts for 90 per cent of cases and develops when light-sensitive cells in the macula (the central part of the retina) break down and are not renewed. Inflammation in dry AMD has been linked with ageing, genetics, smoking and sunlight exposure.
When researchers in Austria compared people with AMD against a group without vision problems, they found that the AMD patients were much more likely to have large deposits of visceral fat in their abdomen, reported the journal Acta Ophthalmologica in 2015.
Blood tests showed AMD patients also had significantly higher levels of inflammatory chemicals – secreted by fat cells.
Meanwhile, scientists from the University of Valencia in Spain have found carrying extra pounds around the waist could affect your sense of taste and smell. This is due to the fact that adipokines, chemicals that visceral fat pumps out, can alter the perception of specific odours and flavours.
The team tracked 179 women, varying from very slim to obese, and measured their levels of visceral fat before giving them smell and taste tests. The results, published in PLOS One in 2017, showed that those with the highest proportion of abdominal fat found it the hardest to identify common smells and tastes.
Even your hearing could be at risk: at least three studies have found that adults with the biggest fat deposits around the waist are more likely to have poorer hearing.
One theory is that inflammation triggered by chemicals stored in fat narrows the tiny blood vessels in the ear, depriving the inner ear of the oxygen it needs to stay healthy.
But visceral fat may not be entirely bad. A 2020 study by the University of Edinburgh found it also contains vital immune system cells that can combat dangerous bugs such as those that cause peritonitis, an infection of the abdominal lining that’s a leading cause of sepsis.
The researchers stressed that these cells occur naturally in the fatty wall of tissue we all have (even those with flat tummies), called the omentum, which helps protect our internal organs.
So how can you tell if your health is at risk from tummy fat? ‘The simplest way is by comparing your waist circumference with your height,’ says Professor Miras. ‘If your waist is less than half of your height, then you should be fine.’
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