It is a situation you may have faced at some point in your life. You have been living responsibly, exercising frequently and avoiding fatty food and desserts. You go for a party and eat a piece of cake. It tastes good, and you have another piece. The next day you feel hungry and crave for a sweet snack. You give in to temptation, as sugary snacks are within easy reach. Before you realise, several weeks have gone by and you have consumed a lot of sugar. You are under threat of a long period of high sugar diet . What would you call this behaviour?Even a decade ago, few people would have called such a habit an addiction. The word was reserved for more serious stuff: alcohol, drugs and nicotine. Eating sugar was a habit that came and went, thought scientists, and not as dangerous or permanent as drinking alcohol or smoking. In the last decade, some psychologists and neuroscientists have begun to change their opinion, after they studied people who consume junk food excessively and found several similarities with well-known addictive behaviour. Not just in what they do every day but also in how their brains respond to this behaviour.This is causing a change of mindset among some neuroscientists. Around the world, neuroscientists have seen that animals can be addicted to certain foods, and that this addiction can have serious consequences for them throughout life. "We observe in animals all the classic symptoms of food addiction," says Nicole Avena, assistant professor at the Icahn School of Medicine at Mount Sinai in New York. "We see binging, craving and withdrawal symptoms." Such findings are being extended to human beings, as neuroscientists observe similar behaviour in people as well. Some scientists are also researching ways to counter food addictions.Last year, a set of two papers published by scientists from the Queensland University of Technology (QUT), Australia, provided clues to food addiction and how to control it, in experiments conducted on laboratory animals.They found that long-term consumption of sugar produces changes in animal brains, somewhat like those produced by nicotine and drugs. They also found that it was possible to reduce an animal’s craving for sugar with drugs used commonly to treat nicotine addiction. The association between sugar and nicotine was unlikely to be accidental."Maybe we should think about sugar the way we think about nicotine," says Selena Bartlett, neuroscientist and professor at QUT.Other studies back up this finding. In a paper published last year in the journal PLOS One, Nicole Avena and her colleagues show that highly processed foods – which contain a lot of sugar — produce addictive behaviour. Avena, a research neuroscientist at the New York Obesity Research Center at Columbia University, had earlier shown in animal models that binge eating produced changes in the brain similar to those produced with addictive drugs. Avena is now at the forefront of the movement among neuroscientists to establish that food in general, and sugar in particular, is addictive. PLOS One is a peer-reviewed, open access scientific journal published by the San Francisco headquartered Public Library of Sciences (PLOS).Other laboratories around the world have been reporting similar findings. Three years ago, David Ludwig and other scientists from Harvard University showed that foods that raised blood sugar levels quickly lit up a part of the brain called nucleus accumbens, primarily because of their high sugar content. This portion of the brain is involved in addiction. Among others, Mark Gold of the University of Florida and Kelly Brownell of Stanford University have both pioneered the concept of food addiction, based on their own research in their labs. Gold had found that overeating reduces drug use in many people, which suggests that food itself might work as a drug.Not all neuroscientists agree with these definitions. There is not enough evidence to say that food is addictive, they say, because much of the research is based on animal models. They also say that sugar is part of food, and never eaten by itself like other addictive substances. "The idea of food addiction is a flawed idea," says Hisham Ziauddin, senior clinical research associate at Cambridge University neuroscience department. Ziauddin reviewed all recent research literature on the topic and found that the results are not yet convincing. He thinks that some standard aspects of drug addiction, like dose dependency, are yet to be evaluated fully.None of the substances normally thought as addictive — nicotine, alcohol, drugs — is necessary for survival. Food is necessary for survival, and sugar in small doses is also an important part of the diet. Can an essential substance be called addictive? Those who champion the idea of food addiction, however, say that the evidence is getting stronger by the day, and that the issue is largely one of semantics.While scientists wrestle with definitions, it is clear that some of the consequences of high sugar consumption are in no doubt. People like desserts very much, and it is easy to lose control of your urges when eating sweet stuff. "People want to stop," says Ashley Gearhardt, assistant professor of psychology at the University of Michigan. "But they repeatedly fail. It is not due to lack of desire to stop that they fail." Interestingly, the more you get exposed to sugar, the more difficult it is to control eating more of it. Your brain starts responding less and less to the pleasure of eating sweet stuff, forcing you to eat more and more. Even at the level of common sense, these are parallels with drugs of abuse. Common sense, though, is not considered technical evidence in science.There is another aspect of sugar consumption that is also beyond doubt: sugar is bad for you. Although it is self-evident, medical scientists have only recently realised how bad sugar is for the human body. Sugar’s role as a disease-causing agent got worldwide attention when Robert Lustig, a professor of paediatrics at the University of California in San Francisco, gave a lecture that went viral on YouTube in 2009.Sugar these days is a term commonly used to describe sucrose, the white substance that we add to desserts and beverages. It is half glucose and half fructose. Glucose can go all over the body and be processed in all cells. Fructose can be processed only in the liver. So eating too much of sugar — even in unrefined form like jaggery or in disguise like in fruit juice — can tax the liver too much and cause many metabolic diseases. Obesity, diabetes, heart disease and cancer are mentioned frequently in combination with eating sugar.In technical parlance, sugar is a term used for a variety of biochemicals with a specific structure. In this sense, glucose is a sugar. So is lactose — found in milk — or maltose, formed when enzymes break down starch. Our story is applicable to sugar in both senses, but especially to the common variety that we add to our desserts. High-calorie food contains sugars in plenty, and can raise glucose levels quickly. Any food that raises glucose levels quickly is a potential addictive substance, according to scientists that argue in favour of food addiction. Such foods provide energy for the body and pleasure for the brain. Eat them too much and too quickly, and you have a serious problem.The big advance in our understanding of food in recent times has come from one fact, now accepted nearly universally by the medical research community. Not all calories are the same. A hundred calories from protein or fat have a different impact on the body when compared with 100 calories from carbohydrates. Different kinds of carbohydrates with the same amount of calories also produce different biological effects. And the difference in impact is not just on the body. It is on our brains as well.As the Harvard study three years ago showed, the total amount of calories in the food did not matter to the brain. The brains of individuals in two groups, each given a glass of milkshake with the same amount of calories and tasted no different, responded differently to the drink because they raised the blood sugar levels at different speeds. One had a special kind of starch that raised it quickly, while the other had a different kind of starch that was absorbed slowly. The addiction area in the brain, the nucleus accumbens, lit up in the brains of people whose blood sugar spiked.This was strong evidence that the so-called high glycaemic foods were bad. The brain rewarded eating high glycemic foods by making their consumption pleasurable, but in an environment where people are generally not short of energy. It is a good reason for addiction, although high-glycaemic foods are eaten regularly. The jury is still out on the technical use of the term, according to some neuroscientists, but the evidence is getting stronger by the day.Semantics does not always matter in science, but in this case it does. The consequences of eating sugar or high-glycaemic foods are different if we call the process as addictive or not. Addictive behaviour gets gradually worse over a period of time. So a head start in exposure is the worst thing you can do. "The risk of addiction is considerably lower if you get exposed to a substance at 25 years of age compared with 16 years of age," says Vivek Benegal, professor of psychiatry at the National Institute of Mental Health and Neurosciences (Nimhans) in Bengaluru. Benegal studies addiction, especially alcohol addiction.We could interpret this finding in the context of food addiction. It is rare for a child to get exposed to a substance of abuse, like drugs or nicotine, or alcohol. But even toddlers are exposed to sugary snacks in modern lives. If you give them too much junk food early in life, they are in danger of developing a life-long liking for high-calorie food. Eating sweet snacks can be even worse, and set them on a course for disease very early in life. Changing course can be difficult in adult life, even for those with the knowledge of the risks. After all, every addict is aware of the dangers of their behaviour.