Thread by @MedCrisis

Shall I eat these fancy hospital biscuits?

[science thread]

Important vote 🍪🍪🍪

The packet tells me that each biscuit has 300kJ = kilo joules
Or 72kcal = kilo calories, ie 72,000 calories

But the box says "72 calories per biscuit"

So what's that about?

The official SI unit for energy is the joule. Which is equivalent to 1 newton metre. ie the work done on an object when a force of 1 N acts on it in the direction of its motion through a distance of one metre (1 N⋅m)

Another definition is the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second.

Not particularly intuitive as a unit for food, right?

The calorie, as you probably know, is defined as the energy needed to heat 1g (1ml) of water by 1 degree Celsius at 1 atmosphere.

Food's calorific content used to be worked out by doing just this - burning it and seeing by how many degrees the temp of some water would rise.

Confusingly, 1 KILOcalorie is the same as 1 Calorie - the modern food usage just dropped the kilo to make things simpler. Which is fine, but it did give me a bit of a shock (see below).

But I doubt anyone burnt these biscuits to come up with the figures above. Or that salad dressing you had at lunch. Or the tiramisu you'll have tonight.

Instead food labs and manufacturers use the Atwater system, developed by the father of American nutrition, Wilbur Olin Atwater

Atwater co-invented the respiration calorimeter, to measure precisely the energy provided by food and created a system to measure that energy in units, known as food calories (the concept of a calorie already existed, but not previously applied to nutrition)

Before Atwater, many experiments on calorie intake & expenditure had been conducted on animals. During this period, there was a widely held belief that the 1st law of thermodynamics (conservation of energy) applied to animals but not humans because we're so #special.

Atwater showed that if energy consumed in food was not used, it would be stored. He stated different types of food produced different amounts of energy. In 1896 a chemical analysis of 2600 American foodstuffs was published.

Atwater stressed the importance of an inexpensive and efficient diet that included more proteins, beans, and vegetables in place of carbohydrates.

Atwater concluded ~1900 that Americans consumed too much fat and sweets and did not exercise enough. How times change.

Atwater was an active supporter of temperance (abstinence from alcohol). Ironically, it was he that inadvertently proved alcohol contains energy and found his work being used by liquor producers to promote their drinks as "nutritional"

His work led to major initiatives to alleviate childhood malnutrition in the USA. His other major legacy (not forgetting the numbers on my biscuits) is giving birth to the science of nutrition, enthusiastically adopted in the sporting world as well.

Back to my biscuits. We said the numbers are not derived from actual burning, but the Atwater scale, which works by first knowing the total amount of carbohydrates, fat and protein in the foodstuff. The energy contained is then calculated using average values for each.

Each of my biscuits has 8.8g of carbohydrate, given a value of 4kcal per gram. Therefore (4x8.8) = 35.2kcal of the energy in 1 biscuit comes from carbohydrates
+
3.6g fat at 9kcal/g = 32.4kcal
0.8g protein at 4kcal/g = 3.2kcal

= 70.8kcal

+ misc = 72kcal/biccie

What was that shocking realisation I mentioned earlier? Because we don't use the kilo when talking about food Calories, we don't realise how much energy is in our food.

There are around 72,000 calories in 1 of my biscuits. Not 72.

That means (wait for it) that my little packet of 2 biscuits could heat 2 litres of water from room temperature to almost boiling!

(1kcal can heat 1L of water by 1C, therefore each biscuit can heat 1L of water by 72C)

By my estimation (not factoring in solutes etc), a can of Coke contains enough energy to heat a can of Coke by...421 degrees Celsius!!

So did I eat the biscuits? Of course not. I could've saved myself all this working out because the answer was obvious. No self-respecting human should ever eat anything with white chocolate. Because it's disgusting.