It’s not fat causing your weight gain, it’s insulin.

For decades, conventional weight-loss advice centred on one message: eat less fat and consume fewer calories. Yet obesity and type 2 diabetes have continued to rise despite widespread adoption of low-fat products. Increasingly, many researchers argue that the conversation has overlooked one of the body's most powerful metabolic hormones: insulin.

That doesn't mean calories suddenly don't matter. Rather, it suggests how your body stores and uses those calories is heavily influenced by hormones—particularly insulin. Understanding this relationship may help explain why some people struggle to lose weight despite carefully counting calories.

The Hormone That Decides What Happens to Your Food

Insulin is produced by the pancreas whenever blood glucose rises, particularly after eating carbohydrates. Its primary job is essential: move glucose from the bloodstream into cells where it can be used for energy or stored for later.

However, insulin also acts as the body's primary fat-storage hormone. When insulin levels remain elevated for long periods—a state known as hyperinsulinaemia—it becomes more difficult to access stored body fat for fuel. Instead, the body continues storing excess energy while signalling increased hunger and reduced fat burning.

This has led many metabolic researchers to argue that chronically elevated insulin may be an important driver of weight gain rather than simply being a consequence of it. Recent reviews have strengthened this view, suggesting that persistently high fasting insulin may independently contribute to obesity, although scientists continue to debate exactly how large this effect is compared with overall calorie intake and energy expenditure.

Why Fat Isn't Necessarily the Problem

Dietary fat has often been blamed for obesity because it contains more calories per gram than carbohydrates or protein. But fat has relatively little effect on insulin compared with refined carbohydrates and sugary foods.

Foods such as white bread, sugary drinks, sweets, pastries and many ultra-processed snacks produce rapid rises in blood glucose, triggering larger insulin responses. If this pattern occurs repeatedly throughout the day, insulin may remain elevated for much longer than our ancestors would have experienced.

Healthy fats—from olive oil, nuts, seeds, avocados, oily fish and eggs—tend to be much more satiating while producing a far smaller insulin response. This partly explains why many people feel fuller for longer when replacing refined carbohydrates with whole-food sources of fat and protein.

The Experts Leading This Conversation

Few topics in nutrition generate as much debate as insulin and obesity. Several researchers and clinicians have helped bring the discussion into mainstream health conversations.

Dr Jason Fung, nephrologist and author of The Obesity Code, argues that obesity is primarily a hormonal disorder driven by chronically elevated insulin. His work popularised intermittent fasting as a strategy for reducing insulin levels.

Professor Benjamin Bikman, a metabolic scientist at Brigham Young University, focuses much of his research on insulin resistance. Through his book Why We Get Sick, he explains how chronically elevated insulin may contribute not only to obesity but also to metabolic syndrome, fatty liver and type 2 diabetes.

Professor Robert Lustig, paediatric endocrinologist and author of Metabolical, has spent years highlighting the metabolic effects of excess sugar—particularly fructose—and how modern processed foods may disrupt insulin regulation.

Researchers such as Professor Nicola Guess, Professor James Johnson and others have also contributed important recent evidence examining whether chronic hyperinsulinaemia itself may promote fat accumulation. While debate remains, there is growing agreement that insulin deserves far greater attention than it has traditionally received.

So... Do Calories Still Matter?

Yes—but hormones help determine what your body does with those calories.

Most experts now recognise obesity as a complex condition involving appetite regulation, hormones, genetics, sleep, stress, physical activity, food quality and total energy intake. The question is no longer whether calories matter or insulin matters. Both do.

For many people with insulin resistance, simply eating less may prove far more difficult because elevated insulin can increase hunger while reducing access to stored body fat.

Supporting Healthy Insulin Function Naturally

Lifestyle remains the foundation of healthy blood sugar control. Regular resistance exercise, daily walking, adequate sleep, stress management and reducing intake of refined carbohydrates all improve insulin sensitivity.

Several supplements also show promising evidence for supporting healthy glucose metabolism, although they work best alongside a balanced diet and healthy lifestyle rather than replacing them.

• Berberine – One of the most researched natural compounds for supporting insulin sensitivity and healthy blood glucose regulation.
• Chromium – May help improve insulin function in individuals with poor glucose control.
• Magnesium – Low magnesium status is associated with insulin resistance, and correcting a deficiency may improve glucose metabolism.
• Alpha-lipoic acid (ALA) – An antioxidant that has shown potential benefits for insulin sensitivity and glucose utilisation.
• Soluble fibre – Slows carbohydrate absorption, helping reduce post-meal blood sugar spikes.

Anyone taking medication for diabetes should consult their healthcare professional before introducing blood sugar-support supplements, as they may enhance the effects of medication.

The Bottom Line

Weight gain isn't simply about eating fat. For many people, the bigger issue may be chronically elevated insulin driven by modern eating patterns, refined carbohydrates and insulin resistance.

Although scientists continue to refine our understanding of obesity, the evidence increasingly suggests that successful long-term weight management isn't just about reducing calories—it's also about improving metabolic health and helping the body regulate insulin more effectively.

Rather than fearing healthy fats, focusing on whole foods, limiting highly processed carbohydrates, building muscle, staying active and supporting healthy insulin function may prove a far more sustainable strategy for lifelong weight management.

References:
Guess N. et al. (2026). Hyperinsulinaemia as a Cause of Obesity and Cardiometabolic Diseases. Nature Reviews Endocrinology.
Fung J. (2016). The Obesity Code. Greystone Books.
Bikman B. (2020). Why We Get Sick. BenBella Books.
Lustig R. (2021). Metabolical. Harper Wave.
American Diabetes Association. (2026). Standards of Care in Diabetes.
Mayo Clinic. (2026). Insulin and Weight Gain.