The most likely alternatives, butter and pig fat, were ruled out using a technique called isotope-ratio mass spectrometry, which measures the molecular weights of the chemicals in a sample.

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But accurately working out Mathilde's volume (necessary because density is the ratio of mass to volume) was harder.

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The AMS paper will report the positron-electron ratio in the mass range of 0.5 to 350 Gigaelectronvolts.

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All models were required to have a body mass index -- a ratio of height and weight -- above 18, the minimum limit considered healthy by the World Health Organization.

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Although the trial has several limitations, children in the low sugar group scored significantly lower across multiple measures of obesity, including BMI, weight, skinfold-thickness measurements, waist-to-height ratio, and fat mass.

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The studies measured the participants' body mass index (BMI), a ratio of their height and weight, but it wasn't able to take into account their body fat composition, or how much of their overall body weight was made up of fat versus muscle.

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Body Mass Index (BMI) is defined as the ratio of weight (in kg) to height (in meters) squared and is an inexact measure of body fat, though it supposedly establishes cutoff points of normal weight, overweight, and obesity.

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Even in cultures without access to mass media, the optimum waist-to-hip ratio for women is around 0.7, which corresponds most closely to an hourglass shape, and is linked to fertility.

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