Inflated claims that sugar and fat can turn us into junkies highlight just how little is known about the science of addiction, argues Maia Szalavitz
IS FAST food addictive? That question has set alarm bells ringing across the food industry. If meals high in fat and sugar were found to work on the brain in the same way as nicotine or heroin, they could be classed as health hazards and taxed and labelled just like cigarettes (New Scientist, 1 February,p 26). Fast-food giants could follow tobacco companies in paying out huge sums in damages to people who claimed they had been made ill by their products.
But there is something wrong with this picture. The contention made by several neuroscientists, and repeated again and again in the media, is that fast food may be addictive because it affects the pleasure circuits in our brains in the same way recreational drugs do. Yet this is misleading and based on circular reasoning. Our brains have evolved to make food and sex pleasurable in order to spur survival. Drugs alter our desires and make us crave more by co-opting those systems. Arguing that food and sex are addictive because they affect the same brain circuits as recreational drugs is like claiming that humans are attracted to sex and sugar because they remind them of drugs: utterly backwards.
The misconception is indicative of how poorly addiction is understood by many of those writing and campaigning about it. It is a complex subject, and highly politicised — which is why we must get it right.
The real question is not how sugar and fat act like recreational drugs, but why some people get hooked and others don’t. For example, although you rarely hear about it, research consistently shows that only between 10 and 20 per cent of those who try heroin become addicts. (Here I am using the most commonly accepted definition of the term "addict": someone who carries on using compulsively despite ongoing negative consequences.) This means that it cannot be the substance alone that causes addiction, but rather a complex combination of substance, circumstance and vulnerable biology.
Scientists are right to note that certain foods, drugs and activities are more likely to induce such cravings. But not everyone who uses or engages in them will become addicted. Even the most addictive things only trap a minority of those who pursue them.
This confusion was part of the reason why tobacco companies managed to hold off paying huge damage settlements for so long. It is even harder for lawyers trying to prove that "big food" caused their clients’ obesity. There is nothing startling about the fact that we crave fats and sweets. In the environment in which humans evolved this was adaptive: those who ate more energy-rich foods when they were available and were better at storing fat were more likely to survive lean times. That fat could prove a health hazard in excess was not of concern in an environment of frequent famine and rare feast.
There are plenty more examples of how addiction is misunderstood. In an admirable attempt to destigmatise drug addiction and promote treatment rather than punishment, the US National Institute on Drug Abuse (NIDA) states: "Addiction is a brain disease because drugs change the brain." Those who argue that fast food is similarly addictive have picked up this argument, pointing to specific substances in food they say act like drugs and claiming that they, too, lead to loss of self-control.
But again, reality is more complicated. Ordinary learning also demonstrably changes the brain — but no one is arguing that learning is a disease. What’s more, brain researchers at NIDA have not compared drug addicts to casual users, merely to non-users. As a result, they cannot show whether the structural differences seen in the brains of addicts are what cause these people to use drugs heavily and lose control.
Much of the work on food is just as flawed. For example Neil Barnard, head of the Physicians Committee for Responsible Medicine, a non-profit group based in Washington DC that campaigns against unethical medical research and animal experimentation, argued recently that milk and cheese break down into substances that act like opiates and are thus addictive (see www.pcrm.org/news/commentary030519.html). However, a study published in the Journal of Dairy Science in 1994 (vol 77, p 672) found that when these substances were tested on rats, the animals did not act the way rats normally do when exposed to addictive chemicals.
Drug addiction, like overeating, results from the fact that our modern environment is very different to the one in which our ancestors evolved, when heroin and hamburgers were not widely available and the mechanisms of pleasure were designed to make the "on" drive stronger than the "off". To deal with compulsive behaviour today we need to unravel the complexity of this mismatch and the role of individual genetic differences and specific environments. Crying "addiction" in the face of any excess only clouds the picture further.
"The real question is not how sugar and fat act like recreational drugs, but why some people get hooked and others don’t"