Arms, belly or thighs? Where you store fat really matters
Psoriasis is just the latest illness that researchers have found to be linked to body shape, the experts tell Peta Bee.
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The distribution of fat in the body has been shown to affect our risk of everything from brain ageing to type-2 diabetes.
The belly is renowned for being the most damaging area to store it, with countless studies showing an association with inflammation and metabolic disease.
In fact, the wider your waistline, the greater your risk of general disease: a review of 72 studies in the BMJ suggests that those with “apple shapes” are at higher risk of early death from all causes than those whose fat is distributed elsewhere.
In a new study, researchers at King’s College London (KCL) also found a relationship between fat and psoriasis, a chronic inflammatory skin condition that affects about 1.8 million people in the UK and is characterised by flaky, scaly red patches known as plaques.
Drawing on data from the UK Biobank, Catherine Smith, a professor of dermatology, and a research team from KCL’s St John’s Institute of Dermatology, examined 25 measures of body fat, using body measurements and advanced imaging techniques.
Their findings, published in the Journal of Investigative Dermatology, identified belly fat as an independent risk factor for psoriasis, and the association is stronger in women.
The link remained consistent regardless of any genetic predisposition to psoriasis.
“As rates of obesity continue to rise globally, understanding how different patterns of body fat influence chronic inflammatory conditions such as psoriasis is important,” Smith says.
“The total amount of body fat is one key determinant of health, but the distribution of fat is also important,” says Javier Gonzalez, professor at the centre for nutrition, exercise and metabolism at the University of Bath, concurs.
“Relatively high amounts of fat on the abdomen are associated with increased risk of cardiometabolic diseases such as heart disease and type-2 diabetes.”
Upper body fat, including that around the waistline, “is more easily stimulated by your own stress hormones to release the fat to the rest of the body compared with lower body fat,” says Fredrik Karpe, a professor of metabolic medicine at the University of Oxford.
Once in the bloodstream, these fatty acids can wreak havoc.
“When subcutaneous or visible fat has reached its storage capacity, any excess fat spills over to organs including the liver and pancreas,” Gonzalez says. “When there is too much fat in these organs, they stop working effectively.”
Here’s how to tell if your body shape could be harming your health.
– Can I tell much about my body fat by looking in the mirror?
“It is actually a reasonable start to assessing body fat,” Gonzalez says.
“The apple-shape body tends to represent more fat in the abdomen, which is higher risk, whereas a pear shape tends to represent the more protective type of fat storage in the thighs, and is a lower risk.”
Karpe and Gonzalez recommend the waist-to-hip ratio as a measure of whether you are carrying too much weight around your middle.
Using a tape measure, record your waist circumference in centimetres at the widest point and your hip circumference at the hip bones.
Divide the waist measurement by that for the hips to find the ratio. For example, if a person’s waist measurement were 50cm and their hip one 60cm, their ratio would be 0.83.
A ratio of more than 0.85 for women and more than 0.90 for men places a person at increased risk of some conditions.
To assess how much fat you store centrally relative to the rest of your body, the National Institute for Clinical Excellence recommends using the waist-to-height ratio. Measure your height using a piece of string, cut it, then cut this length in half and wrap that section around your waist. If the half-length of string doesn’t reach around your middle, it is a sign you are carrying too much abdominal fat.
– Should I have a Dexa scan?
Dual-energy X-ray absorptiometry scans measure “internal visceral fat but also tell you much more accurately about your upper and lower body fat,” Karpe says. “The results tell you about your bone mineral density as well as lean to fatty tissue. So there’s lots of health-related information from having them.”
I am slim but am I storing fat?
You could be, Karpe says, especially if you drink more than the recommended limit of 14 units of alcohol a week. “Alcohol is the big villain here and it can specifically increase dangerous internal visceral fat that settles around the organs – even in slim people,” Karpe says. “We are preparing to publish a study of 5,000 people and there is a clear dose response between alcohol consumed and an increase in visceral fat.” Only a Dexa scan will be able to determine clearly your levels of hidden fat.
– Do I need to worry about having a meno-belly?
Men and women naturally store fat differently during their reproductive years. “Men tend to store fat around their middle, and it links back to our ancestors who responded well to the stress hormones it releases as it kept them running and able to hunt for food,” Karpe says.
“In contrast, the natural female fat depot in the lower body is sluggish to respond and, in evolutionary terms, sits there until needed to mobilise energy when they need to breastfeed.”
After the menopause, when oestrogen levels drop, women undergo a rapid transition.
“They don’t tend to lose lower body fat but they gain quite a lot of visceral fat and fat around the middle,” he says.
“Around the menopausal age you also lose muscle – the part of the body that burns fat – so if you continue eating the same, you will put on weight often around the middle.”
This shift in fat storage raises the risk of metabolic disease for many women. The good news is that if you lose weight – whether through diet and exercise or weight-loss drugs – the fat will disappear more rapidly from your middle than from elsewhere. “Fat around the middle is normally the fat with the highest turnover,” Karpe says.
– Are bigger arms bad news?
In isolation, they are not a significant risk factor for metabolic disease. “But when the fatness of arms is part of a very substantial overall obesity, it is an added indication,” Karpe says.
A 2024 study published in the journal Neurology tracking people from middle age found that those with arm fat were 18 per cent more likely to develop neurodegenerative diseases including Alzheimer’s, other forms of dementia and Parkinson’s disease than those with higher levels of leg fat.
High amounts of belly fat raised the risk by 13 per cent. However, having strong muscles – including in the arms – reduced the risk by 26 per cent, suggesting that working on your biceps and triceps is worth the effort.
Last year researchers from the National and Kapodistrian University of Athens looked at the distribution of fat beneath the skin in 83 men and women aged over 50, none of whom had been diagnosed with the bone-thinning disease osteoporosis. At the European Congress of Endocrinology they reported that those with fatter upper arms were more likely to have lower bone quality and were most at risk of spinal fracture later in life. “Surprisingly we identified, for the first time, that the body composition of the arms – in particular the fat mass of the arms – is negatively associated with the bone quality and strength of the vertebrae,” said Professor Eva Kassi, a senior author of the report.
– What about thighs?
A pear shape is a sign that you are to some extent protected against disease: fat around the thighs is metabolically superior to belly fat.
“Whereas fat around the abdomen is strongly associated with fat in the liver and pancreas, leg fat stores behave differently,” Gonzalez says. “Leg fat seems better able to ‘hold on to’ and store fat, whereas centrally located fat is more sensitive to hormones such as adrenaline and will release the fat more readily into the bloodstream.”
Scientists at Rutgers University found that adults with fatter legs were less likely to have high blood pressure than those with a lower percentage of fat tissue in the thighs. They considered hypertension rates in relation to the percentage of fat tissue in the legs of people mostly in their thirties and forties, and discovered that those who had higher proportions of leg fat were 49 per cent less likely to have high blood pressure where both numbers were elevated. And men and postmenopausal women with higher leg-fat levels were found to be at lower risk of osteoporosis in another study at the First Affiliated Hospital of Wenzhou Medical University in China.
– Can slim legs be a bad sign?
“Slim legs on a slim body are not risky,” says Karpe, who is researching the composition of lower body fat.
“But if you have too much weight around the waistline and a distinct absence of fat in the hips and legs, it is a potentially risky situation.”
The thighs are key a site for storing fat that comes directly from the liver, Karpe says.
“When it is not possible to store fat in the thighs effectively, the liver may need to retain an excess of fat. That comes with substantial health risks including fatty liver disease, type 2 diabetes and liver cirrhosis.”
– What can neck fat indicate?
Research suggests that men with a neck circumference of more than 17in and women with a measurement of 14in or more are at increased risk of various health concerns.
Neck fat, says Karpe, carries “a very high risk” for metabolic disease. It stores a significant amount of free fatty acids that are released into the bloodstream where, according to a 2024 study in the Science journal, they are implicated in the onset of inflammation and metabolic disease.
A study of 4,093 midlifers by researchers at the University of Boston School of Medicine showed that high levels of fat in the neck were associated with atrial fibrillation, which causes erratic heart beats.
“The larger your neck circumference, the more likely you are to have sleep problems, partly because the pressure of fat stored there obstructs breathing and leads to issues such as sleep apnoea,” Karpe adds.