Fat as an Organ: How Visceral Fat, Brown Fat, and Hip Fat Shape Health and Ageing

Overview

The Guardian Science Weekly episode reframes fat as an active, dynamic organ rather than a static energy reserve. Host Maddie introduces adipose tissue as a connective tissue distributed under the skin (subcutaneous fat) and around internal organs (visceral fat), and explains that fat exists in several cellular forms with distinct roles. The discussion features Ian Sample, the Guardian science editor, and Professor Declan O'Regan, who elaborate on adipose tissue’s hormonal signaling, inflammation, and its broad influence on health, ageing, and disease risk.

"fat is actually intricate and dynamic, constantly in conversation with the rest of our body" - Ian Sample, Guardian science editor

Types of Fat and Their Functions

Listeners learn about white fat as the main energy store, brown fat that generates heat through mitochondrial activity, and beige fat, which can behave like brown fat. Brown fat is especially important in newborns for temperature regulation, while its proportion decreases with age. The episode emphasizes that fat is a living ecosystem that senses nutrients and other factors, releases hormones, and communicates with the brain via nerve signaling. This reframes fat as a central player in metabolism, inflammation, and ageing rather than a mere bystander.

"it's not simply inert tissue waiting to be used, it's a dynamic tissue and affects the whole body" - Declan O'Regan

Visceral Fat, Inflammation and Ageing

The discussion turns to visceral fat, which surrounds organs and contributes to mechanical and inflammatory health risks. Using UK Biobank data, Declan explains that visceral fat is a key indicator of accelerated cardiovascular ageing, driven by chronic, low-grade inflammation that affects heart muscle stiffness and arterial health. Inflammatory markers such as glycaem-related measures rise with increasing visceral fat, linking fat distribution to systemic ageing processes beyond mere weight.

"visceral fat was one of the most important indicators for driving this accelerated ageing of the heart in the circulatory system" - Declan O'Regan

Hips, Thighs and Protective Fat Distribution in Women

The episode highlights a sex difference: fat stored around the hips and thighs in women appears to be protective, contrasting with visceral fat’s harmful effects. Possible explanations include oestrogen-driven distribution and adiponectin-like hormones that may counteract inflammation. This protective pattern is most evident in pre-menopausal women, which raises questions about whether hormone therapies might sustain certain protective effects after menopause.

"women's body fat distribution, when it's on the hips and the thighs is protective" - Maddie

Measuring Fat and Health Implications

The podcast notes the challenges of assessing fat-related health risk. Traditional BMI is imperfect because it does not capture fat location or differentiate fat from muscle. MRI remains the gold standard for precise measurement, while simpler tools like waist-to-height ratio offer better proxies for visceral fat risk. The conversation also touches on the limits of liposuction for improving health, with evidence suggesting that removing subcutaneous fat does not yield equivalent health benefits to losing the same amount of adipose tissue through diet and exercise, sometimes even allowing fat to return in different areas.

Practical Takeaways and a Call to Rethink Fat

The episode closes with a candid reflection on the obesogenic environment and the difficulty of addressing obesity purely as a fat problem. It underscores that fat can be linked to multiple health outcomes, ageing, and the need for strategies that improve overall health rather than fixating on weight alone. The takeaway is a more nuanced view of adipose tissue as a complex organ that interacts with health and ageing, inviting readers to rethink self-perceptions and health strategies in a more holistic way.

"we actually really need to think about fat differently" - Maddie