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The latest bit of conventional weight loss wisdom to be debunked by science is the need to create a 3500-calorie deficit to lose one pound (0.45kg) of body weight.

The 3500-calorie myth

Why this conventional weight-loss wisdom seldom achieves real-world success

The latest bit of conventional weight loss wisdom to be debunked by science (well, mathematics to be exact) is the need to create a 3,500-calorie deficit to lose one pound (0.45kg) of body weight. It’s yet another theory predicated on the over-simplified theory of energy balance; a theory where all calories are considered equal.

This theory, expounded by health and fitness professionals for some five decades, first gained traction in 1958 when Dr Max Washnofsky wrote a paper in the American Journal of Clinical Nutrition concluding that “3,500 calories is the caloric value of one pound of body weight lost.”

This figure also gave rise to the 500-calorie-a-day-deficit guideline as it neatly broke that ‘magical’ figure of 3,500 into seven – seven days in a week to deliver sustainable, healthy weight loss of up to 0.45kg a week.

While it’s not entirely wrong, real-world application of this theory is often far removed from the controlled lab environment where a pound of body mass will liberate 3,500 calories of energy in accordance with the first law of thermodynamics.

Complex process

The truth is that the environment within the human body is far more complex. There are multiple factors at play, all of which influence your ability to metabolise ingested and stored energy for fuel, the primary source of that energy, and the rate of metabolism of that fuel.

Factors such as your current weight, your hormonal balance, enzyme function, the composition of your gut bacteria, your current nutritional status, your daily activity levels and the intensity of that activity, and the composition of your diet all affect your metabolism and therefore influence your ability to effectively lose weight and keep it off.

In fact, as we’ve covered before, when a person restricts calorie intake and increases energy expenditure to create a 500-calorie deficit, their body perceives this reduced availability of energy as a threat due to possible starvation and acts to ensure their survival. The various hormonally-driven biological and the numerous physiological process that ensues effectively lower your daily metabolic rate through a process known as metabolic adaptation or adaptive thermogenesis. These include an increase in mitochondrial efficiency, which effectively means we’re able to burn fewer calories to meet our energy requirements, with a concomitant increase in the production and release of hormones that promote catabolism and hunger, and a decrease in hormones that promote anabolism (tissue growth), energy expenditure, and satiety.

Diminishing returns

As a result, a daily deficit of 500 calories produces slightly less of an effect on each subsequent day of your diet. While the impact of this diminishing effect is negligible at first, the more weight we lose the greater this response becomes. It’s the reason why many people lose a significant amount of weight initially, especially obese individuals, but then plateau.

The impact of this metabolic adaptation is so profound that over a 12-month period you can only expect to lose 50 percent of the weight that the 3,500-calorie rule estimates. This effectively means that you would then need to create a 7,000-calorie deficit to lose the same amount of weight that was achieved in the initial stages of a diet, which is extreme and unsustainable.

While the math can become quite complicated and the law of individual difference (and the resultant individualised response) dictates that this won’t be the same for everyone, the general consensus is that the longer you diet, the greater the calorie deficit will need to be to keep seeing the same degree of results.

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