Most of us think we have a good understanding of belly fat. It is the soft pinch at the waistline, the stubborn mound that “spoils” photos, which we often blame on too many takeaways or a sedentary lifestyle.
Yet, there is another type you can’t see, something far more complex and dangerous. Beneath what you grab – the subcutaneous fat – lies visceral fat. It doesn’t just sit under the skin; it wraps itself around your internal organs, releasing harmful inflammatory chemicals and hormones, quietly influencing everything from your metabolism to your cancer risk.
Visceral fat is “a silent killer”, with high levels linked to a greater risk of developing cardiovascular disease, type 2 diabetes, Alzheimer’s and a range of cancers, including endometrial, liver, oesophageal and bowel, warns Dr Sean O’Mara, a leading expert in visceral fat reduction. Formerly a US army colonel and emergency physician, Dr O’Mara has spent the past 13 years helping senior political figures and top business executives to reduce their visceral fat levels in order to optimise their health.
“The danger is that visceral fat is not always visible,” he explains. While overweight and obese people are likely to carry more, those who appear average-sized or even slim may also be hiding unexpectedly high levels.
Traditional methods of weight measurement, such as body mass index (BMI), often fail to detect visceral fat, while imaging methods like MRI scans – the most reliable method of checking – can be expensive. Although not a perfect science, discovering your waist-to-height ratio can help to determine your risk.
Here, Dr O’Mara explains four of the major causes of visceral fat and how to lose yours for good.
1. Being stressed all the time
We are a nation of stressers – in fact, one survey found that almost three-quarters of UK adults were so stressed at some point over the past year that they felt overwhelmed or unable to cope. While we often link chronic stress to adverse mental health effects, Dr O’Mara believes it can be physically destructive, too.
“Stress is a killer,” he says. Some of his patients who were chronically stressed stored excessive amounts of visceral fat and fat around the heart (known as epicardial adipose tissue). “Remarkably, lots of my patients aren’t aware of how stressed they are, but once they start to actively manage their levels, while also eating and sleeping better, their MRI scans show gradual visceral fat reduction,” he says.
When we are stressed, our bodies release cortisol, a hormone that provides energy and focus, acting as part of the fight-or-flight response. This is beneficial in the short term. However, chronic stress and consistently elevated cortisol levels encourage fat to accumulate around the abdominal organs, Dr O’Mara explains.
This process was illustrated in one 2015 study, which found that people under chronic stress were more likely to store metabolically harmful fat around their organs, rather than under the skin. The researchers found that this pattern of fat distribution was associated with a higher risk of cardiovascular disease, heart attacks and early death.
Meanwhile, a randomised control study published in 2022 found that participants who slept less consumed more calories and, consequently, experienced an 11 per cent increase in abdominal visceral fat, compared with a control group. Sleep deprivation can disrupt key hormones including ghrelin (the “hunger hormone”) and leptin (the “satiety hormone”), resulting in increased hunger and cravings. The team noted that inadequate sleep appeared to redirect fat to the more dangerous visceral stores, making it a “previously unrecognised trigger”.
Dr O’Mara advises implementing stress-reduction techniques, whether that is spending time in nature or reading before bed, to help you relax, as well as getting a consistent seven to nine hours of sleep to help regulate hormones and cortisol levels.
2. Extreme endurance workouts
While running and other aerobic exercises are generally beneficial for fat loss, Dr O’Mara notes that extreme endurance training can actually be harmful. “Those who run long distances regularly or competitively are putting their bodies under a great deal of physical stress,” he explains. “This can result in higher levels of inflammation, muscle loss and the elimination of beneficial subcutaneous fat.”
Endurance exercise (like long-distance running, cycling or swimming) can raise cortisol levels, which can lead to increased visceral fat storage. If not done alongside strength training, endurance exercise can also reduce muscle mass, which hinders metabolism, meaning fewer calories are burnt at rest. Plus, those consistently running or cycling long distances are likely to have increased appetite, so may overeat and gain weight over time.
Additionally, extreme training can reduce levels of superficial subcutaneous body fat. This “beneficial” fat is closer to the skin’s surface and can be protective in healthy amounts, as it secretes adiponectin, a molecule that can regulate metabolism, reduce inflammation and increase insulin sensitivity, according to Dr O’Mara.
Dr O’Mara says, “We need to do everything we can to preserve healthy amounts of beneficial subcutaneous fat,” while actively trying to reduce levels of inflammatory harmful fat.
Consistent movement throughout the day, alongside short, maximum-effort sprints or interval training, is the recipe for success, as opposed to lots of endurance exercise. “When you sprint, you engage your fight-or-flight response. Your cortisol goes up and then immediately goes down and it drops lower than it was before,” he says. “This signals the body to burn deep fat stores and may also improve insulin sensitivity.”
3. Neglecting your muscles
When reviewing his patient’s MRI scans, Dr O’Mara refers to the dark areas of muscle as “health”, and the marbled patches of white fat within them as “disease”. If you lose muscle mass due to inactivity or ageing, they become more susceptible to fat accumulating in them, he explains. This has been linked to a higher risk of insulin resistance and conditions like type 2 diabetes, as poor-quality, low-mass muscles are less equipped for glucose uptake and blood sugar regulation.
Therefore, alongside consistent movement and interval training, strength training is key, Dr O’Mara says. This is supported by a 2016 study, which found that a higher muscle-to-visceral-fat ratio was associated with better metabolic markers, including lower glucose and better insulin sensitivity. Essentially, “building muscle isn’t just about looking good, it’s about creating a metabolic shield against visceral fat”, Dr O’Mara explains. Plus, those with high muscle mass are likely to have a better metabolism, which burns more calories at rest, potentially assisting visceral fat reduction.
Dr O’Mara advises implementing three brief but intense strength-training sessions per week, focusing on the large muscle groups like the legs, back and chest, through exercises such as squats and dead lifts.
4. Eating processed foods and refined carbohydrates
It isn’t just how much you eat, it’s what you eat that makes a difference to belly fat. Like many health experts, Dr O’Mara is a firm believer in the powers of whole, unprocessed foods. One of his patients, a woman from the UK, was raised on a low-carbohydrate, high-fat and high-protein Atkins diet and “has one of the healthiest MRI scans that I’ve ever seen. Almost all of her organs were free of visceral fat, and she had strong, protective muscle”. He uses this case study to demonstrate the importance of fuelling the body with a diet rich in healthy fats and protein, rather than relying on “excessive levels of carbohydrates and sugars, that can spike insulin levels and increase visceral fat storage over time”.
Healthy fats such as olive oil, fatty fish, avocados, nuts and seeds can reduce levels of inflammation and help cells to use insulin more efficiently, reducing the spikes that promote visceral fat storage. Meanwhile, protein (from lean meats, eggs, fish and legumes) supports muscle mass, which can boost metabolism and encourages the body to burn fat rather than store it.
Alongside a wholefood approach, Dr O’Mara advocates for a diet rich in fermented foods. “Humans have eaten these for thousands of years and they are linked to a range of improved health outcomes,” he says. “My research shows that one of the best ways to get rid of visceral fat is through an improved microbiome and, as we know, fermented foods are linked to better gut health.”
One 2019 study found that miso (fermented soybean paste) had the power to reduce visceral fat accumulation in mice more effectively than exercise alone. The researchers believed that, as miso is fermented, it produces bioactive peptides, isoflavones and other metabolites that might influence fat metabolism, inflammation and insulin sensitivity. Meanwhile, a 2024 study on mice found that fermented fruits could help reduce obesity and fat accumulation by improving lipid metabolism and boosting the gut microbiome. Of course, further research on humans is needed to confirm these findings.
Dr O’Mara promotes a reworked version of the carnivore diet, which he calls “the living diet”, because of its heavy focus on meat in combination with “live” fermented foods. It involves high-quality animal foods such as grass-fed meat, fatty fish and eggs, alongside fermented vegetables and dairy, such as kimchi, sauerkraut and kefir. Seed oils, alcohol, refined sugars and carbohydrates, ultra-processed foods (UPFs) and additives are all restricted. He believes this way of eating is the key to better gut health, reduced inflammation and visceral fat reduction.
“I have worked with patients who had visceral fat accumulating around their lungs, their heart and even their colon,” says Dr O’Mara. “In 20 years, if they hadn’t already died from a heart attack or cancer, they would be wearing nappies [because of the excess pressure on their abdomen and other organs, which can cause pelvic floor prolapse and incontinence issues].
“However, the good news is that visceral fat is a lifestyle disease, which means it can be tackled and reversed through targeted lifestyle interventions like stress management, consistent movement throughout the day, strength training and a balanced diet, for a longer and healthier life.”