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Chris van Tulleken has a medical degree from Oxford and a PhD in molecular virology from University College London. He is a practising infectious diseases doctor and an associate professor at University College London. His new book is Ultra-Processed People: Why We Can’t Stop Eating Food That Isn’t Food.

In the spring of 2019, a paper was published in the medical journal The Lancet with an unremarkable-sounding title: “Health Effects of Dietary Risks in 195 Countries, 1990–2017.” It soberly presented associations between food and health from most countries on Earth. But buried on Page 9 of the analysis, there was a startling finding: Poor diet is responsible for more deaths globally than any other cause, including the previous No. 1 risk – tobacco.

That food is a daily struggle for most of us – what, when and most importantly how much to eat – is reflected in some grim statistics; most of us, including me, live with extra weight or obesity. But what study after study has shown is that health outcomes related to food are not just about obesity. Even for the minority of Canadians who live at a “healthy weight,” food is still a huge cause of sickness and early death.

To me, the problem has always felt like it was me. My failure to resist unhealthy products, my failure to be more active and burn off those excess calories, my failure, even as a doctor and a scientist, to understand the deluge of information about nutrition: This internalization turns all discussions of food into discussions about shame, guilt and stigma.

So it may reassure you to know that the science is now very clear: The problem isn’t me, or you – it’s the food. Or rather the food-like substances that now make up most of the calories consumed in Canada. Because, over the past 150 years, food has become … not food. We now mostly eat a set of products called ultraprocessed foods, or UPFs.

There’s a long, formal definition of ultraprocessed food, but it boils down to this: If it’s wrapped in plastic and contains an ingredient you don’t find in a typical home kitchen, then it’s a UPF. Much of it will be familiar to you as “junk food,” but there’s plenty that’s also sold as healthy, nutritious, environmentally friendly or useful for weight loss. It’s another rule of thumb that almost every food that comes with a health claim on the packet is a UPF. Almost all supermarket bread is UPF, likewise breakfast cereal, along with soda pop, packaged snacks, reconstituted meat products and frozen dishes. All belong in the ultraprocessed category.

To understand how this new food is harming us, we need to look at the history of eating from a biological perspective. After all, living organisms have only two projects: reproduction, and the process of extracting energy from the world to fuel that reproduction (also known as eating.) Everything else merely serves those agendas.

I think of eating in three distinct, but overlapping ages, all of which are still going on today.

Let’s go back to the very beginning. The Earth is approximately 4.5 billion years old, but life emerged much quicker than was previously thought. By the time the Earth was a billion years old, there were small but unmistakable signs of microbial life, which we’ve been able to observe thanks to microfossils in a band of prehistoric iron deposits in northern Quebec. These bacteria ate iron, breathed carbon dioxide (as opposed to oxygen) and produced rust as waste, which they deposited into the geologic record in vast bands hundreds of metres thick.

This First Age of Eating, in which organisms consume food that has never been alive, continues today. Bacteria are still eating rocks, and we are still trying to understand the fundamental processes at play in their consumption habits.

But at some point, perhaps when access to resources such as raw iron became too competitive for comfort, a shortcut evolved: let someone else get their energy from rocks or the sun, and get your own energy by eating these simpler lifeforms, or their waste products, instead. And so, during the Second Age of Eating, living organisms started to eat other living organisms. This has been going on for hundreds of millions of years (and for around two million years for humans).

Exactly when this Second Age began isn’t clear, and the scientific literature is entertainingly rancorous, but there is general agreement that one day, around 560 million years ago, an oval-shaped and rug-like creature, about the size of your finger, crawled slowly through some mud at the bottom of the sea, at the edge of the ancient continent of Rodinia. Though it lacked a skeleton, limbs or eyes – anything but the most basic nervous system – by the standards of the day it was fabulously complex, the apex of billions of years of evolution. And it was eating bacteria in the mud. The rug, later named Dickinsonia costata, is one of the earliest pieces of evidence of the Second Age of Eating. These creatures evolved – via the shrew-like creatures that survived whatever it was that killed off the dinosaurs – into you and me.

We eat, then, as part of a set of interlinking, entangled arms races, competing for energy flowing between life forms. Like all arms races, this competition has generated complexity, and so, everything about eating is complex.

Consider the project of being a cow, or its ancestral wild equivalent, an auroch. Herbivores like these need to get precisely enough energy to stay alive without gaining so much weight that they can’t move, or losing weight so much weight that they waste away. But they need to simultaneously acquire the construction materials – the elements and molecules – needed to build and maintain their bodies.

The auroch’s world didn’t contain handy nutritional information labels about energy and minerals. They had to chase the rain, avoid the carnivores and eat the right amount of, for example, the mineral selenium, all whilst precisely maintaining body weight. How did they do it? Through a system of such staggering complexity that we are only just beginning to understand it.

Inside the auroch, and inside you, is a vast array of nerves and hormones that are able to regulate energy consumption and nutrient intake entirely subconsciously, and with extraordinary precision. This system is the legacy of the half-billion years or more of the Second Age of Eating. It’s why, if we eat foods from the Second Age (also known simply as food), we can largely ignore words printed on packets and nutritional guidance. Obesity is unknown in wild animals not because food is simply hard to come by, but because of this internal system.

For almost all of the Second Age of Eating, food has been consumed raw, fresh and often still alive. But, around two million years ago, a single species started to externally process its food: grinding, milling, pounding, fermenting, drying, salting, cooling and cooking.

These processes are not just a part of our culture – they’re part of our physiology. We occupy a unique dietary niche: we are the only obligate processivores. Our bodies bear witness to this long history of food processing. It’s evident in the number of genes we have for enzymes to digest starch, milk, sugar and alcohol, and in the size of our eating apparatus: The human digestive tract is remarkably short for an animal our size because it extends out of the body and into the kitchen. Processing is necessary for our survival and has made us human. Our internal systems are able to regulate nutrient intake with processed food very effectively, making obesity in humans in the Second Age of Eating extremely rare.

But most of the humans in Canada have entered what I call the Third Age of Eating. Starting in this era, a single species (and their pets and livestock) started to eat food products that were manufactured using novel molecules and previously unknown industrial processing techniques. These molecules created ultraprocessed foods, a category that has become so dominant in the modern food system that most of our calories now come from food products containing synthetic molecules that are never found in nature. This Third Age of Eating is just a few decades old, which is why it is useful to think about UPFs in the context of the very long history of how humans have stayed alive.

The anno domini of the Third Age is a matter of debate, but 1879 is a good candidate – it’s the year that the non-nutritive sweetener saccharin was discovered as an extract of coal tar. Over the next century, thousands of new molecules entered our food system. Today, in industrialized countries such as Canada and Britain, each of us ingests around eight kilograms of food additives per year. To put this in perspective, on average we only buy two kilograms of flour each year for home baking.

The additives are troubling, but the main point is not that they are themselves harmful – it’s that they are a proxy for the ultraprocessing of food that we now know is linked to disease.

Ultraprocessing includes a huge range of industrial techniques. Milk can be unprocessed – drunk straight out of the cow. Or it can be processed to become other foodstuffs – when manually churned, it becomes butter (first done more than 5,000 years ago). But ultraprocessing uses relatively new and novel techniques such as deodorizing (using steam to get rid of smells), interesterification (rearranging the molecules of fatty acids to preserve their nutritional value), and emulsification (a chemical process that helps oil and water stick together). Combined, these methods transform plant oils into fake butter, or margarine, which was one of the first ultraprocessed foods to enter into wide use.

UPF products are often fake versions of traditional foods, made using cheap commodity crops and deconstructed into their constituent molecules, which are then further modified, combined with additives, and assembled using industrial food-shaping techniques such as moulding and extrusion. This creates a nearly limitless range of textures, flavours and products that are proprietary, have extremely long shelf lives and are easily transported via global supply chains.

Almost every aspect of these foods is harmful to the body and the planet. The destruction of the food structure by processing means that UPFs are, in general, soft – think supermarket bread or a doughnut. UPFs are also dry, which prolongs their shelf life and often means they are calorie-dense. This combination of calorie density and softness means that you can eat far more calories per mouthful than the internal regulatory systems from the Second Age of Eating can keep up with. As a result, you inevitably eat too much.

UPFs also have drastically reduced levels of phytochemicals – the thousands of molecules in plants that are essential for dietary health as well as all those emulsifiers, modified starches and other additives that damage and inflame the gut’s microbiome. Plastics from the packaging of UPFs have a range of potential health consequences, including cancers and infertility.

The effect of all this is not just weight gain, but higher instances of strokes, heart attacks, cancers, Type 2 diabetes, high blood pressure, fatty liver disease, inflammatory bowel disease, depression, dementia and, of course, early death.

And the evidence shows that UPFs are not simply salty, fatty, sugary foods that are low in fibre. It is the processing itself that is the problem. Fatty, salty, sugary homemade lasagnas and cakes are very different from those we buy from the freezer aisle.

There are now growing calls to remedy the health problems caused by UPFs. If the food is too soft, causing us to eat too much of it too quickly, perhaps it can be made chewier. If it’s damaging the microbiome, perhaps it could be supplemented with probiotics. This approach is known as reformulation – but it’s already been going on since the 1980s, when we started replacing sugar with sweeteners and fat with modified starches. It doesn’t work. It misunderstands the purpose of UPFs – they are made for profit.

Each UPF product has been reiterated through so many cycles of marketing and taste testing that it has become very hard for humans to stop eating them. For many people, UPF products are as addictive as cigarettes or drugs. If there are foods you struggle with, they are probably made in a factory.

So what do we do?

One neat trick to alleviate the hold UPFs have over your brain is to eat while you read, which is similar to a well-evidenced approach to quitting smoking: Eat a UPF product and try to enjoy it as you read the ingredients. As you drink, think about the phosphoric acid in your cola, leeching the minerals out of your bones. As you chew, think of the Xanthan gum in your ice cream, promoting the growth of novel bacteria in your gut. Many people have found that they simply stop wanting the food. If you’re lucky, you may have the resources and time to quit UPFs and eat real food. This approach of abstinence is what I’ve found easiest.

Policy makers have a harder task. It’s not easy to regulate the universe of products that makes up most of the Western diet. You can’t tax UPFs, because for many people, they are the only affordable and available food.

We need deep systemic changes in the food system to make real food affordable and available. Like all public health initiatives, tackling UPF consumption should start with policies that reduce poverty and inequality. When people can afford to eat better, they do.

In the meantime, the first step is to include information about ultraprocessing in Canada’s national eating guidelines, with the advice to severely limit intake. This may seem small and bureaucratic, but it’s a really important first step, because it’s something that scientists, doctors and lawmakers can point to. The next step is to stop the kid-centric marketing of UPFs, including all those colourful cartoon characters on the packets.

Then, we need to use labelling to demonstrate what constitutes healthy food. When people realize what healthy food actually is – and that they can’t afford to eat it – that’s when the revolution begins.