Turning your body into a fat-burning furnace sounds like classic fitness hype, but it’s not far from reality. Deep inside your body lies brown adipose tissue (BAT), better known as brown fat — a specialised type of fat that burns calories to generate heat through a process called thermogenesis. Unlike ordinary white fat, which hoards energy, brown fat cells are loaded with mitochondria that convert fatty acids into heat.

For decades, scientists believed this process relied almost entirely on a protein called UCP1 (uncoupling protein 1). But a new Nature study has revealed a hidden backup system powered by peroxisomes (pronounced per-rock-sis-shomes) and the enzyme ACOX2. These cellular components can take over when UCP1 isn’t doing its job — meaning your body has a built-in Plan B for fat oxidation and heat production.

What Is Brown Fat and Why It Burns Calories

Brown adipose tissue is mostly found around your collarbones, spine and upper chest. It’s rich in mitochondria, the cell’s energy factories, which use fatty acids to create heat — a process called non-shivering thermogenesis. When triggered by cold exposure, hormones or exercise, brown fat boosts your energy expenditure, helping regulate body temperature and metabolism.

Although most adults have only small amounts of brown fat, studies have linked active BAT to lower body fat percentage, improved insulin sensitivity, and healthier glucose metabolism. Simply put, people with more active brown fat tend to be leaner and metabolically healthier.

UCP1 vs Peroxisomes: Two Ways to Burn Fat

Traditionally, UCP1 was seen as the only way brown fat produced heat. The new study turns that idea on its head. Researchers found that peroxisomes, cell structures best known for detoxification, can also generate heat.

By using the enzyme ACOX2 (acyl-CoA oxidase 2), these peroxisomes oxidise fatty acids and release energy as heat — even in the absence of UCP1. In lab tests on mice missing the UCP1 gene, those with active peroxisomes could still stay warm. It’s a discovery that expands our understanding of metabolic flexibility and how the body adapts to cold or energy demands.

Why the Discovery Matters

If scientists can safely activate this peroxisome-driven thermogenesis, it could open a new front in the battle against obesity and metabolic disease. Drugs that enhance ACOX2 activity might allow people to burn more calories without extreme cold exposure or exhausting workouts.

But it’s not as simple as flipping a metabolic switch. Peroxisomes play a role in many cellular processes, and overstimulation could cause unwanted side effects. Still, the finding changes how researchers view energy balance, showing there’s more than one way to burn fat and generate heat.

How to Activate Brown Fat Naturally

While scientists figure out how to harness this new pathway, there are ways to boost your existing brown fat right now:

• Cold exposure: Regular cold showers, ocean swims or just turning down the thermostat can trigger brown fat activation.
• High-intensity training: Exercise increases the hormones that wake up brown adipose tissue.
• Diet hacks: Foods with capsaicin (chilli), catechins (green tea), and resveratrol (grapes) may mildly stimulate brown fat activity.
• Better sleep: Healthy circadian rhythm supports hormone balance linked to metabolism.

These methods won’t replace training and nutrition, but they can complement them by nudging your body’s thermogenic system into gear.

Key Takeaway

Scientists have discovered a backup heater in brown fat that doesn’t rely on UCP1. Instead, peroxisomes use ACOX2 to burn fatty acids and produce heat — a finding that could one day revolutionise how we fight obesity and boost metabolic health. Until then, your best fat-burning strategy is still the old-fashioned one: move more, eat smart, recover well, and stay cold once in a while.