If ancient Romans didn't understand calories, how was their theory of nutrition so accurate?

Macronutrients, calories, and antioxidants all seem like very modern concepts, and, today, we certainly know a lot more about nutrition than the ancient Romans did. But while the Romans didn’t understand the science as well as we do now, they absolutely had an intuitive understanding of many of the key concepts behind how best to fuel ourselves.

Across the Roman empire, ancient thinkers developed a sophisticated theory of nutrition which allowed them to understand some of the basic principles behind the science of food and diet long before the discovery of recommended daily allowances and other modern standards.

Speaking on the HistoryExtra podcast, Dr Claire Bubb, assistant professor in the study of the ancient world at New York University, explains that “there are parallel ideas [in ancient Roman thinking] that are expressed with different words, observing some of the same things, but within a totally different theoretical construct of how food and nutrition works.”

The Ancient Roman theory of nutrition was surprisingly intuitive

Roman ideas about nutrition centred on the blood. They generally thought that food went into the digestive system after it was eaten, and then broken down. Then, “the bits that are useless, we would excrete”, Bubb explains. “But anything in food that could potentially be relevant to our bodies, we would digest and turn into blood.

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“So your food becomes your blood and then your blood becomes any part of your body that it needs to – the building block of your body,” she says. “Say if I'm wearing down my muscles because I'm using them all the time, the blood will go to the muscles, and it'll build new muscle.”

Romans classified foods by their qualities, not their nutrients

The ancient Romans associated different properties of foods with different impacts on the body, whether that was healing or strengthening. Rather than thinking about the amounts of protein or vitamin C in a food, they were “thinking about the qualities in food.”

Some foods were thought to be more nourishing than others, and able to help build muscle. This is what we would think of as protein, Bubb says. Meanwhile, other foods were thought of as “drying,” or as having “good juices in them”.

“Some foods have really good humours in them, and that leads to good blood versus bad blood that might make you unhealthy,” she says.

The theory of humours suggested that people’s bodies were ruled by four fluids in the body – blood, phlegm, yellow bile, and black bile. Each humour was associated with the elements: blood was air, phlegm was water, yellow bile was fire, and black bile was earth.

And different balances of each humour created different qualities – warm, cold, moist, or dry – which led to various diseases.

For example, people with diseases that were seen as hot and dry would benefit from eating foods that were seen as cold and wet.

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Whether foods were cold or hot, wet or dry, was based on flavour and texture. Cucumbers were cold and wet, for example, whereas bread and roasted meat were dry and hot. Foods with a bit of a kick to them, like onions, garlic, and rocket, were hot, too.

Because they believed that the body was ruled by what people ate, they also believed that foods had the power to transfer their characteristics to whoever ate them.

Their ideas are understandable, if not scientific

“The cool thing about it is how intuitive it is. You can understand if you eat too much, you feel full and kind of gross the next day,” Bubb says.news

“It's not surprising that they noticed things that we're also noticing. There are some foods that are refreshing and some foods that really sit heavily in your stomach and are harder to digest, and the ancient Romans experienced those same feelings.

“These are intelligent people who are really paying close attention … It's a very empirical approach to how all of this works and how health works.”

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“What they got wrong is in how they explained these things that we still observe – the methodologies that they had. They didn't have microscopes; they didn't have the ability to send things to a lab and figure out what they're composed of.”

Instead, they thought about the composition of food in terms of the elements. It may seem “crazy for us to think about there being little bits of fire in our food,” Bubb remarks, but she notes that we talk about calories – which we convert into heat.

“They just think about it in a way that, when you really boil down exactly what they're saying, feels just odd and difficult for us to imagine,” she says.

The way the Romans thought about food fed into their greater worldview

The system of humours didn’t just apply to food and medicine – humours were also thought to rule people’s personalities and emotions.

People who had too much blood in them were thought to be cheery and friendly; those with too much yellow bile were considered bitter and daring; too much black bile meant you were melancholic and fearful; and too much phlegm made people placid and forgetful.

The way that the ancient Romans thought about food also influenced how they thought about different people in society, about age, and about seasons.

Older people were seen as colder, and so needed less warmth and less food, while growing people (such as children and athletes) needed more warmth and more nourishment. They thought people in general should eat more in winter and spring, when the body needs to produce more warmth and therefore, they believed, needed more nourishment.

The Romans knew less about food science than we do now, and many of their ideas seem misguided to the modern perspective. But thinking about food, medicine, wellness and constitution as all interlinked is a surprisingly modern way of thinking, paralleling how we think about nutrition today.

Claire Bubb was speaking to James Osborne on the HistoryExtra podcast. Listen to the full conversation.