Different types of food produce different amounts of energy.

Our awareness of the link between body weight and food intake began in 1896 when Wilbur Atwater (1844-1907), an American agricultural chemist, showed that different types of food produced different amounts of energy and the efficiency of a diet should be measured in food calories (or kilojoules if you prefer the metric term).

In Atwater’s time knowledge of the nutrients and their functions was very limited: carbohydrates and fats provide energy; proteins build and repair tissues; vitamins were unknown and only a few minerals such as calcium and phosphorus were recognised as essential but their role was unknown. With his colleague, E. B. Rosa, a physicist, Atwater developed a calorimeter to measure the calorific value of different foods. Atwater’s measurements mark the beginning of the quest for scientific understanding of nutrition.

In 1919 American scientists J. Arthur Harris and Francis Benedict devised an equation for calculating how many calories we need to consume each day. The Harris-Benedict equation determines a person’s ideal calorie intake by taking into account age, gender, height and weight (Google ‘Harris-Benedict equation’ to search online calculators to work out your basal metabolic rate or BMR, a scientific term for ideal calorie intake).

Once you know your BMR, fighting the battle of the bulge is a simple task: all you have to do is to strike a balance between two variables, diet and exercise. In her book, Calculus Diaries, science writer Jennifer Ouellette, has turned the simple arithmetic of diet and exercise into calculus by introducing another variable: the ‘tastiness’. To Ouellette, ‘tastiness’ is ‘the pleasure we derive from our food intake, given a fixed number of calories we can consume per day and a fixed amount of money we can spend on groceries.’

‘So if we know what we’re eating each day now, what small change can we make in our diet to optimize how much we enjoy mealtimes?’ she asks. To record the small, incremental change recommended by her, requires a graph pad, a pencil, a good knowledge of calculus and singing ‘You take a function of diet and you call it yummy’ to the right tune. Wouldn’t you rather eat that chocolate doughnut, now?

© Surendra Verma 2019

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