We seem to be addicted to everything these days: phones, sex, shopping … and junk food. There is, of course, a vast difference between serious clinical addiction and figure-of-speech addiction ("I'm totally addicted to sherbet lemons at the moment"). Of course we need food to live, but can we become dependent on certain unhealthy foods in the same way that we can on drugs?
Rats can't resist junk food
About a decade ago, a group of American psychiatrists studying obesity decided to look into whether some people's anecdotal claims of food addiction could be proven. They devised a series of studies in which rats were offered highly palatable sugary or fatty food (they had the option of their regular healthy food, too, but that didn't get a look-in). Nicole Avena was one of the researchers: "We found signs of tolerance, withdrawal, craving and measurable changes in neural chemicals such as dopamine and opioid release," she says. In short, it looked very much as though the animals were addicted to a drug, even tolerating "foot shock" (running over an electric grid) to get their fix.
Today, the food addiction model is still relatively young and controversial. However, says Avena, "additional studies have been conducted that validate these initial findings. And there's been some studies done in humans now that have really begun to characterise this." I wondered whether it is the taste or the nutrient (ie sugar or fat), once digested, that is making us high. It could be both. Avena's studies have involved rats getting the taste of sugar but not the nutrient and vice versa, and dopamine is released either way, which means that the two together result in a dopamine double whammy.
What's the most addictive food?
So far, empirical research has focused on fat and sugar, rather than specific products such as cereal or toffee. We do know, however, that fat and sugar produce different responses in the brain's reward system. With sugar, rats show clear signs of withdrawal: shaking, sweating, changes in body temperature, anxiety and, says Avena, "they show changes in the brain in terms of release of chemicals such as dopamine and the opioids." Fat doesn't have this effect, but this doesn't necessarily mean it is less potent than sugar. Avena points out that cocaine addicts don't show signs of withdrawal like heroin addicts do.
There have been surveys on the foods people say they find addictive. Many of the human studies into food addiction have been based around the Yale Food Addiction Scale (pdf), a questionnaire used to determine whether someone could be classified as a food addict. One of its questions is about which foods the subject finds most problematic, and Ashley Gearhardt, the co-creator of the scale, has shared the top 10 nasties. Crisps, chips, sweets, chocolate and biscuits crop up – no surprises there. White bread and pasta also feature, and number one is ice-cream.
What constitutes addiction anyway?
This is a subject of ongoing debate. Avena and colleagues used the diagnosis criteria in the standard American guide for psychiatrists, The Diagnostic and Statistical Manual of Mental Disorders. This stipulates that three of the following must have applied to an individual over the past year to qualify them as addicts:
• The substance is often taken in larger amounts than intended.
• A persistent desire or unsuccessful efforts to cut down substance use.
• A great deal of time is spent in activities necessary to obtain the substance.
• Important activities are given up or reduced because of substance use.
• Substance use is continued despite knowledge of having a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by the substance.
But the manual itself has lost credibility of late, attracting a revolt from many psychiatrists and ridicule for including such things as "internet addiction disorder" and "caffeine withdrawal". And, as an aside, there are substance addictions (which are often treated by psychiatrists) and behavioural addictions such as gambling (which are not). It is not clear who should be treating "food addicts" and how, although Avena has been pursuing microbiological studies into food addiction, mindful of potential future pharmacological treatments.
One thing is for sure: if food addiction is real, it cannot be a blanket blame for obesity. As Gearhardt says, "Most people don't become addicted to any addictive substance. For example, only about 10% of people become addicted to alcohol, but around 90% drink it."
Paul Fletcher, professor of health neuroscience at Cambridge University, is baffled by the "apparently uncritical acceptance of food addiction." In his opinion, it is way too early for it to be taken as a valid or useful concept. While the rat studies are sound, he says, the degree to which they can be extrapolated to humans is limited. And the rest of the research results are inconsistent. He also wonders what, precisely, the addictive substance in food is: sugar, salt, fat or just anything that tastes good?
Meanwhile, his colleague Hisham Ziauddeen jokes in a surprisingly amusing stand-up routine (yup, there is an academic stand-up scene), about the legislative implications of food addiction. Parents who feed their and, gasp, other people's children cake become child abusers overnight? The chocolate market is driven underground?
Fletcher says: "We are finding that 'addiction' is a handy term to be applied to lots of human behaviours now: sunbed addiction? Facebook addiction?" Does the concept of food addiction ring true to you? Has sugar withdrawal given you the sweats or shakes? What foods do you find it hardest to resist?