The concept of "calories" has long been a cornerstone in discussions about diet, weight loss, and metabolism. But did you know that the calorie was originally invented for steam engines, not human nutrition? The term "calorie" was coined in the 19th century by French scientist Nicolas Clément as a unit of energy to measure steam. It was later applied to food energy in an effort to quantify how much energy we consume and expend. However, this mechanical, one-size-fits-all approach to energy has led to misconceptions about how our bodies actually function, especially in relation to metabolic health.
While calorie counting has become a mainstream obsession, it oversimplifies the complex metabolic processes that govern how our bodies use fuel. Your body has the remarkable ability to burn either glucose or fat for energy, depending on insulin levels, which is the hormone responsible for deciding which fuel source to prioritise. When insulin is low, like during fasting or low-carb eating, your body burns fat (including belly fat) for energy. This metabolic flexibility means your body can efficiently shift between fuels, but calorie counting often ignores these important nuances.
Interestingly, the brain can also run on either glucose or ketones. Ketones—produced when your body burns fat—are actually the brain's optimal energy source. This is why individuals with neurological conditions like depression, migraines, epilepsy, Parkinson’s, and Alzheimer’s often experience improvements on low-carb diets, as they help reduce insulin resistance and improve brain metabolism.
When you have low insulin for around 16 hours, your liver begins to burn fat, including its own stored fat, and converts excess fat into ketones. These ketones provide a powerful fuel for your brain, and any excess that your body doesn’t need will be excreted through urine and sweat, essentially “wasting” calories. The key takeaway here is that metabolic flexibility, or your body’s ability to use both glucose and fat for fuel, is far more important than rigid calorie counting.
The traditional mantra of "Eat less, exercise more" may seem like a good idea, but it’s a perfect recipe for hunger and frustration. Programs like The Biggest Loser, which focused on caloric restriction, showed that participants regained all the weight they lost and damaged their metabolism in the process. Cutting calories while keeping insulin levels high (through high-carb, low-fat diets) leads to constant hunger and weight regain. Conversely, when insulin is low, your body naturally burns fat, and hunger dissipates as your metabolism becomes more flexible.
Instead of forcing yourself to control calories through sheer willpower, focus on eating foods that lower insulin, such as healthy unrefined fats and oils. These fats keep you full and provide sustained energy without triggering insulin spikes. As you lower your insulin levels, your body will regulate your calorie intake naturally, making you feel full faster and reducing your overall hunger.
The flawed science of calorie counting is rooted in outdated ideas about energy, and it oversimplifies the complexity of human metabolism. By focusing on the quality of your food, particularly healthy fats, and optimising insulin levels, you can achieve metabolic flexibility. This will allow your body to burn fat more efficiently, regulate hunger naturally, and move away from the calorie-counting obsession. Instead of worrying about every calorie, focus on foods that support metabolic health, and let your body take care of the rest.
