Bill Bryson: we shouldn’t take calorie counting too seriously

The author of The Body explores the strange history of how a 19th century 'calorimeter' chamber came to inform nutritional science (but hasn't always worked).

Bill Bryson

We all know that if we consume too much beer and cake and pizza and cheeseburgers and all the other things that make life frankly worth living, we will add pounds to our bodies because we have taken in too many calories. But what exactly are these little numerical oddments that are so keen to make us round and wobbly?

The calorie is a strange and complicated measure of food energy. Formally it’s a kilocalorie, and it is defined as the amount of energy required to heat 1kg water by 1°C, but it seems safe to say that no one ever thinks of it in those terms when deciding what foods to eat. Just how many calories each of us needs is pretty much a personal matter. Until 1964, the official guidance in the United States was for 3,200 calories per day for a moderately active man and 2,300 for a similarly disposed woman. Today those inputs have been reduced to about 2,600 calories for a moderately active man and 2,000 for a moderately active woman. That’s a big reduction. Over the course of a year for a man that would be almost a quarter of a million fewer calories.

Americans today consume about 25 per cent more calories than they did in 1970 (and, let’s face it, they weren’t exactly going without in 1970).

It probably won’t come as a surprise to hear that in fact the inputs have gone in exactly the other direction. Americans today consume about 25 per cent more calories than they did in 1970 (and, let’s face it, they weren’t exactly going without in 1970).

The father of caloric measurement – indeed of modern food science – was the American academic Wilbur Olin Atwater. A devout and kindly man with a walrus moustache and a stout frame that showed he was no stranger to the larder himself, Atwater was born in 1844 in upstate New York, the son of a travelling Methodist preacher, and studied agricultural chemistry at Wesleyan University in Connecticut. On a study trip to Germany he was introduced to the exciting new concept of the calorie and returned to America with an evangelical urge to bring scientific rigour to the infant science of nutrition. Taking a position as professor of chemistry at his alma mater, he embarked on a series of experiments to test every aspect of food science. Some of these experiments were a touch unorthodox, not to say risky. In one, he ate a fish poisoned with ptomaine to see what effect it would have on him. The effect was that it nearly killed him.

Calirometer Chamber
The interior of Wilbur Atwater's respiratory calirometer

Atwater’s most celebrated project was the building of a contraption he called a respiratory calorimeter. This was a sealed chamber, not much larger than a large cupboard, in which subjects were confined for up to five days while Atwater and his helpers minutely measured various facets of their metabolism – inputs of food and oxygen, outputs of carbon dioxide, urea, ammonia, faeces, and so on – and so calculated caloric intake. The work was so exacting it took up to sixteen people to read all the dials and perform the calculations. Most of the subjects were students, though the lab janitor, Swede Osterberg, was also sometimes drafted in; quite how voluntarily is unknown. Wesleyan’s president was mystified by the point of Atwater’s calorimeter – the calorie was an entirely new concept, after all – and especially appalled at the cost. He ordered Atwater to take a 50 per cent pay cut or hire an assistant at his own expense. Atwater chose the latter and, undeterred, worked out the calories and nutritional values of practically all known foods – some 4,000 in all. In 1896, Atwater produced his magnum opus, The Chemical Composition of American Food Materials, which remained the last word on diet and nutrition for a generation. For a time he was one of the most famous scientists, of any type, in America.

Atwater’s most unsettling discovery – to himself as much as to the world at large – was that alcohol was an especially rich source of calories, and thus an efficient fuel.

Much of what Atwater concluded was ultimately wrong, but that wasn’t really his fault. Nobody yet understood the concept of vitamins and minerals or even the need for a balanced diet. To Atwater and his contemporaries all that made one food superior to another was how well it served as fuel. So he believed that fruit and vegetables provided comparatively little energy and needed to play no part in the average person’s diet. Instead he suggested that we should eat a lot of meat – two pounds (almost 1kg) every day, 730 pounds (330kg) a year. The average American today eats 268 pounds (122kg) of meat a year, about a third of Atwater’s recommended amount, and most authorities say that is still too much. (The average Briton, for purposes of comparison, eats 185 pounds (84kg) of meat a year, almost 70 per cent less than Atwater’s recommended amount. That’s still too much.)

Atwater’s most unsettling discovery – to himself as much as to the world at large – was that alcohol was an especially rich source of calories, and thus an efficient fuel. As the son of a clergyman and a teetotaller himself, he was appalled to report it, but as a diligent scientist he felt his first duty was to the truth, however awkward. In consequence, he was swiftly disowned by his own, devoutly Methodist university and its already scornful president. Before the controversy could be resolved, fate intervened. In 1904, Atwater suffered a massive stroke. He lingered for three years without recovering his faculties and died aged sixty-three, but his long efforts secured the calorie’s place at the heart of nutrition science, evidently for all time.

You've been reading an extract from The Body: A Guide for Occupants by Bill Bryson, publishing 3rd October 2019.

The Body
The Body


'A directory of wonders.' – The Guardian

'Jaw-dropping.' – The Times

'Classic, wry, gleeful Bryson…an entertaining and absolutely fact-rammed book.' – The Sunday Times

'It is a feat of narrative skill to bake so many facts into an entertaining and nutritious book.' – The Daily Telegraph

‘We spend our whole lives in one body and yet most of us have practically no idea how it works and what goes on inside it.
The idea of the book is simply to try to understand the extraordinary contraption that is us.’

Bill Bryson sets off to explore the human body, how it functions and its remarkable ability to heal itself. Full of extraordinary facts and astonishing stories The Body: A Guide for Occupants is a brilliant, often very funny attempt to understand the miracle of our physical and neurological make up.

A wonderful successor to A Short History of Nearly Everything, this new book is an instant classic. It will have you marvelling at the form you occupy, and celebrating the genius of your existence, time and time again.

What I learned is that we are infinitely more complex and wondrous, and often more mysterious, than I had ever suspected. There really is no story more amazing than the story of us.’ Bill Bryson

Sign up to the Penguin Newsletter

For the latest books, recommendations, author interviews and more