Three years ago, I stopped eating sugar. My plan was to have a sugar-free month, just to see if it made a difference. I had done similar experiments before – a month without caffeine, or alcohol, or reading news online. Aside from chocolate, I wasn’t a big eater of sugar, I thought, so I didn’t expect to notice any change. But I did.

Giving up sugar set me free. And so, what began as an experiment has become my new life. I have changed in ways that I had not thought possible.

I used to get “hangry” – that grumpy, urgent craving that demands prompt attention. To stave it off, I carried bags of almonds or dried fruit. Back when I ate sugar, I couldn’t go running in the morning – if I tried, I would get dizzy, and anyway, my legs felt as if they were made of stone. I would have slumps in the afternoon – my head would get foggy – so if I was working from home, I would take a nap. I had mood swings, joy alternating with despair. I had assumed that all of these things were simply part of life, of how I was, a frustrating aspect of my makeup. And now all of them are gone.

For the first two weeks of my unsweetened life, though, I was in a foul temper. At first, I attributed this to the darkness and gloom of the winter days. But as I started to feel better – calmer, happier, more even-keeled – a more sinister thought began to nag at me. Had I been in withdrawal?

My decision to stop sugar was taken on a whim. Back then, aside from its role in tooth decay, I knew little about its possible effects on health. But when I discovered how much better I felt without it, I became curious – and began to read.

To a chemist, sugar refers to a class of molecules made of hydrogen, carbon and oxygen; some of these serve particular biological roles. Lactose, for example, is found in milk; deoxyribose gives the “D” to DNA. But in daily life, the main sugars one meets are glucose, fructose and sucrose – which is a marriage of the other two. That is, each molecule of sucrose is one glucose linked to one fructose. Interestingly, the two simple sugars have the same chemical formula – six atoms of carbon, 12 of hydrogen, six of oxygen – but different chemical structures. The human tongue detects this: fructose tastes sweeter.

Glucose is synonymous with blood sugar, since it is transported in the blood and delivered to cells to fuel their energetic needs. But you can also find it, along with fructose, in fruits and vegetables. Sucrose is extracted from sugar cane or beets, and is usually encountered as the white crystals of table sugar. When most people speak of “sugar”, they mean sucrose. High-fructose corn syrup, the most common sweetener of non-diet soft drinks, is a mixture of glucose and fructose. So is honey – though honey is a complex concoction that contains many other compounds.

The history of sugar is full of darkness. The European appetite for sweetness drove the slave trade; according to one estimate, in the Americas, two-thirds of enslaved Africans worked on sugar cane plantations. Sugar is also implicated in lung cancer. How? Because the tobacco in blended cigarettes has typically been soaked in sugar syrups; this makes the smoke easier to take into the lungs.

The grim harvest does not stop there. A growing number of doctors blame sugar consumption for a long list of medical woes. These include diabetes, obesity, hypertension, heart disease, gout, non-alcoholic fatty liver disease, many cancers and perhaps even Alzheimer’s. Some researchers have even linked the eating of sugar in childhood to the development of myopia, arguing that the spikes in insulin secretion caused by sugar consumption interfere with the normal development of the eyes. In short: the recent medical literature about sugar makes alarming reading.

Such connections are, of course, disputed. But as an evolutionary biologist, as well as someone who has felt the immediate benefits of a sugar-free lifestyle, I find the claims persuasive. For most of human history, after all, milk, honey and fruits have been the main sources of sweetness. When cane sugar first made its way to Europe around 1,000 years ago, it was treated as a spice, a medicine and a preservative.

In 1700, the average sugar consumption in the United Kingdom was around two kilograms per person per year. Today, the figure is 10 times that amount. Over the past 300 years, sugars have thus gone from an occasional luxury to a substantial component of the average western diet. The present sugar glut is an anomaly in human experience. We have changed the world to suit our appetites; but our bodies cannot accommodate the change.

Different foods have different effects on the body. To see this, look no further than sugars. Intake of glucose directly stimulates the production of the hormone insulin; that of fructose does not. Fructose, instead, is metabolised in the liver, where it is turned into fat. Indeed, evidence is mounting that fructose is a major player in metabolic illness. When you consume table sugar, you get both fructose and glucose, because the sucrose is chopped into its component parts. Repeatedly consuming vast quantities of these substances – as when you eat lots of sugary food or drink lots of sodas – could thus cause a double whammy of metabolic disturbance.

In my new life, I don’t eat foods with added sugar. Some of these are obvious: cakes, cookies, ice creams, doughnuts, muffins, candies. Some are less so. Vinegar, weirdly, often has added sugar. So do pickles. I no longer eat sushi – the rice has usually been sweetened. I steer clear of maple syrup. I also avoid super-sweet fruits – grapes, persimmons, dates. Fruit juice? No thanks.

I don’t substitute other sweeteners; I just eat differently. Chocolate is still on the menu – but only if it is 100% cacao. This can be hard to find – but luckily, a small shop around the corner from where I live has a large variety. With the sugar gone, the taste of the chocolate itself is revealed. And just as coffee grown in different places and handled in different ways can have different flavors, so too with chocolate. Abstaining from sugar has also made me more sensitive to notes of sweetness in otherwise savory foods, such as cashews.

In abandoning sugar, I have become aware how ubiquitous it is. Want to eat something on the go? Almost everything for sale contains sugar. Even recipes for vegetables often call for adding it. In fact, until three years ago, I was guilty of such practices myself, often adding a spoonful of sugar to the cooking water of green beans, peas and sweetcorn (sweetcorn!), a practice I now look back on with astonishment.

The social pressure to eat sugar is enormous; whole meals are geared around the stuff. In many countries, breakfast is an orgy of sugar; cake at tea time was a fixture of my childhood. I still attend meetings where someone is always designated to bring sweet food for everyone. Halloween has become a festival of candy. Then there’s the sugar propaganda. It’s everywhere. Clothes for little girls covered with pictures of lollipops. Giant knitted ice cream cones as cuddly toys. Soaps formed to resemble cup cakes. Candlesticks in the form of ceramic doughnuts, complete with icing. Cut-out books of paper desserts.

I’m not so militant in my avoidance that I interrogate restaurant chefs about which vinegar they use, or whether they add sugar to the cooking water. On special occasions – an anniversary, perhaps, or a birthday – I will eat a mouthful of, say, lemon meringue pie. But only as a rare treat, perhaps five or six times a year. Always in the past, after one of my experiments, I would take up the old habits. But not with sugar. It’s not just the long shadow of possible illness. It’s that – like others I know who have stopped – I feel so much better without it. I like knowing that, if I need to, I can hike all day without eating. I enjoy being free of rampaging hunger. Running in the mornings has become a delight. I prefer feeling more serene, less prone to mood swings or afternoon fatigue. My mind feels clearer. I can’t imagine going back. Life is more savory this way.