Why ‘Calories In, Calories Out’ Failed Us 

Why Calories Don’t Decide Your Weight — Hormones Do 

For years, anyone who struggled with their weight was told the same simple story: eat less, move more. Calories in, calories out. If the scales did not move, the implication was obvious — you must be cheating, miscounting, or lacking willpower. 

But is this really true? 

People were eating less than they used to, skipping meals, choosing ‘low-calorie’ options [aka low fat] and still finding themselves heavier, not lighter. If weight were really governed by basic arithmetic, this would not be happening on a population scale. The maths would work. It doesn’t, because the human body is not a furnace. It is a hormonal system. 

One of the most important challenges to the calorie model has come from the work of Dr Jason Fung and others who focus on insulin and metabolic hormones rather than food quantity alone. His central point is disarmingly simple: it is not how much you eat that determines whether you store fat, but which hormones are switched on when you eat.  

And the hormone that matters most in this scenario is insulin. 

Insulin is not a villain. It is essential to life, moving glucose out of the bloodstream and into cells and storing excess energy for later. But it has one effect that is crucial for weight regulation: when insulin is high, fat burning is switched off. You can be eating very little, but if insulin is high, your body remains in storage mode. The door to your fat stores stays locked. 

This is why the type of food matters far more than its calorie count. Different foods trigger radically different hormonal responses, even of the calorific value is the same. Refined carbohydrates and ultra-processed foods raise blood sugar quickly, which provokes a strong insulin release. Insulin then pushes glucose into cells and channels excess energy into fat, while simultaneously blocking the release of fat for fuel. Protein raises insulin a little but also triggers powerful satiety hormones, telling the brain that the body is fed. Fat barely raises insulin at all, allowing fat burning to continue. 

So, a bowl of pasta and an omelette may contain the same number of calories, but they send completely different messages to the body. One says, ‘store energy and lock fat away’. The other says, ‘you are nourished, you can relax and burn fat’. 

Insulin also quietly blunts another key hormone: leptin, which tells the brain that you are full and safe. When insulin remains high for long periods, leptin signalling becomes blunted. The brain does not register satiety properly. Hunger rises, metabolism slows, and cravings increase even while the body is actively storing fat. People are left eating less, feeling worse, and becoming heavier. This is not a failure of discipline. It is a body being hormonally overridden. 

This is why calorie-restricted dieting so often backfires. When insulin stays high but food intake drops, the body reads the situation as a threat. Fat remains locked away, energy availability falls, and metabolic rate slows. Hunger intensifies. Eventually, the drive to eat wins, and when it does weight is rapidly regained, often with interest.  

Long before insulin was identified, traditional herbal systems already understood that metabolism was about regulation rather than arithmetic. They worked with the liver, blood sugar handling, digestion, bitter taste receptors, stress hormones, and the nervous system’s role in appetite. This is why herbs like cinnamon, berberine, Gymnema and digestive bitters keep reappearing in metabolic care; not because they ‘burn calories’, but because they help change the signals the body responds to. 

The most liberating truth in all of this is that struggling with weight is not a moral failure. Our bodies have been doing exactly what they were told to do by the hormonal environment it lives in. Change the signals, not just the calories, and our bodies will begin to change.