Picture: iulianvalentin/iStock
Picture: iulianvalentin/iStock

A commentary on fad diets published in the medical journal The Lancet has managed to explain exactly why they don't work in just two charts.

Being sceptical and derisive of the latest fad diet is easy, usually because they're already quite ridiculous sounding and so require little work to be dismissive.

Yet, they persist, and are taken up by hundreds if not thousands of people at a time. The idea that they don't work is usually spoken as received wisdom, not by scientists who understand how weight loss happens but by other laymans who mock the fad diet, without understanding why it's so off the mark.

Luckily for us naysayers, The Lancet is here to help. Using data originally published in the Journal of the American College of Nutrition, the Lancet showed how the effects of a fad diet (such as low carb or low fat intake) are immediate, but short lived. The second chart highlights the fact that dieters can't sustain a huge drop in the number of calories they consume.

Picture: The Lancet

Graph A shows the low fat dieters and low carb dieters over two years. The average weight loss at the end of the experiment is a little under 2 kg, a near negligible amount given the other effects a fad diet may have had on the dieter's quality of life. Moreover, Graph A shows that the difference between these fad diets was also negligible, proving that one fad which cuts out fat, and one which cuts out carbohydrates, is not much more effective than the other.

For comparison, graph B shows that 'fad diets' are also futile because we never stick to them. The large curve shows how calorie intake creeps up on us, and the dashed lines show the discrepancy between actual weight measurements and the calorie intake that dieters recall. We lie to ourselves about whether or not we're sticking to the diet, rendering it redundant - or it would do so if the results weren't already so insignificant.

The commentary written for The Lancet was by Yoni Freedhoff and Kevin D Hall.

HT Julia Belluz

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