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If you鈥檝e ever tried to lose weight, there鈥檚 a good chance you鈥檝e been told it all comes down to a simple 鈥渃alories in, calories out鈥� formula: burn more calories than you consume, and the kilos will disappear.

And it鈥檚 easy to see the appeal of breaking weight loss down into simple maths 鈥� just follow the formula, and you鈥檒l achieve success. It鈥檚 also believable because many people do lose weight when they first adopt this approach.

Indeed, the diet industry鈥檚 reliance on the 鈥渃alories in, calories out鈥� concept is why society blames people for being overweight. Anyone who can鈥檛 follow this simple energy formula is only overweight because they lack the willpower to eat less and exercise more.

But the only simple truth here is that it鈥檚 time to bust the 鈥渃alories in, calories out鈥� myth as the only way to lose weight. Here鈥檚 why.

The many calorie-counting apps and online calculators available make it seem effortless. Simply enter your sex, age, height, weight, body composition and activity levels and they鈥檒l tell you exactly how many calories you should eat daily to lose weight.

Unfortunately, no matter how accurate these calculators claim to be, they rely on averages and can鈥檛 determine the calorie intake appropriate for you with 100 percent accuracy. They can only estimate.

Similarly, our metabolic rate 鈥� how much energy we burn at rest 鈥� also varies from person to person based on many factors, including body composition or how much muscle and fat we have. Complicating things further, our metabolic rate also alters when we change our diet and lose weight.

Calculating the calories in food 鈥� the other part of managing 鈥渃alories in鈥� 鈥� is also far from accurate.

While Australian food standards require foodstuffs to display Nutrition Information Panels showing energy in kilojoules, there are no requirements for information accuracy other than it must not be misleading. A worrying听听for the values shown on labels.

In practice, the variation can be much more than this. One Australian study found food contained anywhere听听energy or nutrient components than its packaging stated.

Another reason the simple 鈥渃alories in, calories out鈥� formula is not so simple is our bodies don鈥檛 consume every calorie the same way. What鈥檚 shown in your calorie counter is not what鈥檚 actually absorbed in your body.

Different calorie sources also have different effects on our hormones, brain response and energy expenditure, changing how we respond to and manage our food intake.

For example, while eating 180 calories worth of nuts is the same as eating 180 calories of pizza in terms of energy intake, the way these foods are absorbed and how they affect the body is very different.

While we absorb most of the calories in a slice of pizza, we don鈥檛 absorb about听听in nuts because their fat is stored in the nut鈥檚 fibrous cell walls, which don鈥檛 break down during digestion. Nuts are also packed with fibre filling us up for longer, while a slice of pizza has us immediately reaching for another due to its low fibre content.

The biggest failing of the 鈥渃alories in, calories out鈥� formula is it ignores that the body adjusts its control systems when calorie intake is reduced. So while the formula can support people achieving weight loss initially, the reduction in energy intake is听听that ensure lost weight is regained.

Namely, when your body registers a sustained decrease in the calories you consume, it believes its survival is threatened. So it automatically听听to protect against the threat, reducing our metabolic rate and burning less energy.

This stems from our hunter-gatherer ancestors, whose bodies developed this response to adapt to periods of deprivation when food was scarce to protect against starvation.

Research also suggests our bodies have a 鈥溾��: a听听our bodies try to maintain regardless of what we eat or how much we exercise.

Our bodies protect our set point as we lose weight, managing biological signals from the brain and hormones to hold onto fat stores in preparation for future reductions in our calorie intake.

The body achieves this in several ways, all of which directly influence the 鈥渃alories in, calories out鈥� equation, including:

• slowing our metabolism. When we reduce our calorie intake to lose weight, we lose muscle and fat. This decrease in body mass results in an expected decrease in metabolic rate, but there is a听听beyond what can be accounted for, further disrupting the 鈥渃alories in, calories out鈥� equation. Even after we regain lost weight our metabolism听. Our thyroid gland also misfires when we restrict our food intake, and听, also changing the equation by reducing the energy we burn at rest

• adapting how our energy sources are used. When we reduce our energy intake and start losing weight, our body听听to carbohydrates and holds onto its fat,听听at rest

• managing how our adrenal gland functions. Our adrenal gland manages the hormone cortisol, which it releases when something that stresses the body 鈥� like calorie restriction 鈥� is imposed. Excess cortisol production and its presence in our blood听.

Our bodies also cleverly trigger responses aimed at increasing our calorie intake to regain lost weight, including:

• adjusting our appetite hormones. When we reduce our calorie intake and deprive our bodies of food, our hormones work differently,听听and telling us to eat more

• changing how our brain functions. When our calorie intake reduces, activity in our hypothalamus 鈥� the part of the brain that regulates emotions and food intake 鈥� also reduces,听听and judgement over our food choices.

The 鈥渃alories in, calories out鈥� formula for weight loss success is a myth because it oversimplifies the complex process of calculating energy intake and expenditure. More importantly, it fails to consider the mechanisms our bodies trigger to counteract a reduction in energy intake.

So while you may achieve short-term weight loss following the formula, you鈥檒l likely regain it.

What鈥檚 more, calorie counting can do more harm than good, taking the pleasure out of eating and contributing to developing an unhealthy relationship with food. That can make it even harder to achieve and maintain a healthy weight.

For long term weight loss, it鈥檚 important to follow evidence-based programs from health-care professionals and make gradual changes to your lifestyle to ensure you form habits that last a lifetime.

This article originally appeared in the 听 is a member of the Charles Perkins Centre.

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