Dr Jeffrey Horowitz is professor of movement science at the University of Michigan school of kinesiology. “Our study found that people who exercised regularly and over long periods showed positive effects on their adipose (fat) tissue in overweight or obesity,” he says. “As well as being a means to expend calories, exercising regularly seems to modify your fat tissue in a way that allows you to store your body more healthfully if and when you do experience some weight gain – and nearly everyone does as they get older.”
The study examined and compared belly fat samples from two groups of adults who – to the naked eye – looked similarly overweight, especially in the central area. But one group exercised four times a week and the other did not. “The exercisers had more ‘good fat’,” says Horowitz. “It seems that their efforts increased the capacity to store fat under the skin – or subcutaneously – as opposed to around their organs.”
So, can you tell how much visceral fat you have? And does this encouraging new study mean we can stuff ourselves with fancy crisps, as long as we then go crazy at the gym? Here’s what the experts say.
What is bad belly fat?
Visceral fat is stored in the omentum, an apron-like flap of tissue that lies under our belly muscles and covers our intestines. The omentum gets harder and thicker as it fills with fat. “We used to think this fat was just ‘empty storage’, but newer studies have shown that this type of fat is a biologically active organ that secretes harmful hormones,” says King.
A growing body of research has linked visceral fat to a surprisingly wide variety of diseases. “Visceral fat interferes with the functions of the kidney and liver,” says King. “It contributes to diabetes and circulatory diseases, as well as high cholesterol.” Visceral fat makes proteins called cytokines, which can trigger inflammation, a risk factor for heart disease and other chronic conditions.
A study reported in Harvard Health that looked at women between the age of 45 and 79 concluded that those with the biggest waists (and those with the largest waists in relation to their hip size) had more than double the risk of developing heart disease. Abdominal fat also raises the risk of asthma, dementia, breast and bowel cancer.
What is ‘good’ belly fat?
“We need to reframe the way we look at all fat,” says Horowitz. “Some subcutaneous fat is good for you. It protects your body and serves as an energy source. Only 20 per cent of healthy fat tissue is actually made of fat cells, the rest is made of collagen that has a lower inflammatory profile. This tissue is also full of capillaries that remove waste from the body.”
However, Horowitz makes clear this is only the case with subcutaneous fat that develops under the skin, rather than around the organs.
How can you tell which type of fat you have?
“You can’t tell where your fat is by looking in the mirror,” says Horowitz. “It’s even pretty hard to decipher this in an imaging study.” Despite this, a quick Google will bring up a raft of adverts for easily-available scans that promise to show how much visceral fat you have.
Dexa scans, for example, were created to measure bone density, but some practitioners now market them as a pricey private way of looking at fat composition. “It’s not that easy to use a Dexa scan to give you the real nitty gritty of where your fat lies,” says King. “The most accurate way of doing this is via a CT scan or full-body MRI, but these are expensive and most doctors won’t agree to perform them for this purpose.”
The best way to monitor your belly fat, says King, is to keep an eye on your waist circumference. “If you feel your jeans are getting tight, this suggests you are putting on weight in the central area,” he says. For a more detailed analysis, measure your waist circumference by wrapping a tape measure around your waist just above your hip bones. For women, 35 inches or more means you’re at risk for health problems stemming from visceral fat. For men, the number is 40 inches or more.
Then, divide your waist circumference by your height measurement. A ratio over 0.5 to 0.59 suggests that you have excess fat around your belly. And if your ratio is 0.6 or above, your risk is even higher.
““For a layperson, this is a pretty good way of telling whether you are at risk,” says King. “It won’t necessarily tell you if the fat is subcutaneous or visceral, but it’s pretty likely that a large waist circumference is an indication that you have some harmful abdominal fat.”
The role of exercise in reducing belly fat
“It’s clear that living a physically active lifestyle can equate to a more healthy fat tissue,” says Jeffrey Horowitz. The good news is that while we tend to put on visceral fat more quickly than subcutaneous fat, research suggests we also start to lose it rapidly when we address our lifestyles – particularly through exercise.
So are there specific exercises that can help? Spot exercises, such as sit-ups, can tighten abdominal muscles but won’t get at visceral fat (and liposuction for cosmetic fat removal doesn’t reach inside the abdominal wall). “It’s unfortunately not possible to target one area or type of fat,” says King. “To lose weight, you simply need to have an energy deficit, i.e. expend more calories than you take on board.”
Both King and Horowitz suggest that endurance exercise – such as brisk walking, jogging, cycling or rowing – is probably more effective than resistance training such as weights, which burns fewer calories. A 2021 meta-study published in the journal Obesity indicated there was no significant difference between regular exercise and high impact exercise, so there’s no need to go crazy.
However, an important point to note: exercise alone will not be sufficient in a programme of global weight loss. The 2021 Obesity study also notes that exercise is capped at an overall weight loss of between 1.5 to 3.5 kg. Hence, a healthy diet remains important in the overall maintenance of a healthy weight and fat composition.
Ultimately, James King welcomes Horowitz’s Michigan study and while he points to some limitations – that the study was “cross-sectional”, rather than “cause and effect”, meaning that it didn’t show visceral fat turning into subcutaneous fat in real time – he feels it’s encouraging news. “Anything that adds to the story of ‘exercise is medicine’ has to be a good thing,” says King. “It shows yet another benefit to being active.”