It is important for readers to be aware that graphs shown by Drewnowski in a recent commentary in this journal1 and previous publications2,4 carry a serious statistical artifact. Since energy is included in the numerator on one axis (kcal/g) and in the denominator on the other axis ($/kcal), a negative auto-correlation is created. To demonstrate this artifact, we took the energy content (measured in kcal/g) and weights for 212 foods from a supermarket in Melbourne, Australia (2008 data) and applied a random number for the price of each food. The foods included a range of products from different categories in the supermarket including breads, cereals, biscuits, frozen meals, milk, and yoghurt. The resulting scatterplot, illustrated in figure 1, exhibits the same negative auto-correlation as the figure presented by Drewnowski.1

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At the supermarket, shoppers are likely to face...

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