By Jessica Brown
When we’re hungry, just about any food will do, but a craving can leave us fixated on a particular food until we get our hands, or indeed mouths, on it.
Most of us know what it feels like to experience food cravings. We usually crave higher calorie foods, which is why cravings are associated with weight gain and increased body mass index (BMI). But the story we tell ourselves about where these cravings come from could determine how easily we give into them.
It’s widely believed that cravings are our body’s way of signalling to us that we’re deficient in a certain nutrient – and for pregnant women, their cravings signal what their baby needs. But is this really true?
Much of the research into cravings has instead found that there are probably several causes for cravings – and they’re mostly psychological.
In the early 1900s, Russian scientist Ivan Pavlov realised that dogs anticipated food in response to certain stimuli associated with feeding time. In a series of well-known experiments, Pavlov taught the dogs to respond to the sound of a bell by drooling.
Food cravings largely can be explained by this conditioning response, says John Apolzan, assistant professor of clinical nutrition and metabolism at Pennington Biomedical Research Center.
“If you always eat popcorn when you watch your favourite TV show, your cravings will for popcorn will increase when you watch it,” he says.
The 15:00 slump is another example of this response in practice. If you crave something sweet in the middle of the afternoon, there’s a chance this craving is stronger when you’re at work, says Anna Konova, director of the Addiction and Decision Neuroscience Laboratory at Rutgers University in New Jersey.
That is because cravings arise from particular external cues, rather than our body calling out for something.
Chocolate is one of the most common food cravings in the West – which supports the argument that cravings don’t stem from nutritional deficiencies, since chocolate doesn’t really contain high levels of anything we could be deficient in.
It’s often argued that chocolate is such a common craving because it has high amounts of phenylethylamine, a molecule that triggers the brain to release feel-good chemicals dopamine and serotonin. But many other foods we don’t crave nearly as often, including dairy products, contain higher concentrations of this molecule. Also, when we eat chocolate, an enzyme breaks the phenylethylamine down, so it doesn’t go into the brain in significant quantities.
Chocolate, which is craved twice as much among women than men, has been found to be the most craved food in the West by women before and during menstruation. But while blood loss can increase the risk of some nutritional deficiencies, such as iron, scientists say chocolate wouldn’t restore iron levels anywhere near as quickly as red meat or dark, leafy greens.
One would assume that, if there was any direct hormonal effect causing a biological need for chocolate during or before menstruation, this craving would alleviate after the menopause. But one study only found a small decrease in the prevalence of chocolate cravings in post-menopausal women.
It’s much more likely that the association between PMS and chocolate cravings is cultural, due to its prevalence in Western society. One study found that women born outside the US were significantly less likely to link chocolate cravings to the menstrual cycle, and experienced fewer chocolate cravings, compared to those born in the US and to second-generation immigrants.
Women might associate chocolate with menstruation, researchers have argued, because during and before their periods is the only time they feel it’s culturally acceptable for them to eat “taboo” foods. This, they say, is because Western culture has a “thin ideal” of female beauty that creates the perception that craving chocolate must be justified with a good excuse.
Another paper argues that food cravings are caused by the ambivalence or tension between desiring a food and wanting to control food intake. It’s assumed, the paper states, that women in particular resolve this by not having the food in question – which increases their chance of craving it as they’re more likely to notice cues.
This can be problematic, Hill says, because cravings are fuelled by negative feelings.
“If eating a craved food follows a craving, then those restricting what they eat to lose weight will feel they've broken a dietary rule and feel bad about themselves,” he says.
“We know from studies and clinical observations that negative mood can trigger more eating and, for some, become an eating binge. This pattern has little to do with a biological need for food or physiological hunger. Rather, it's the rules we set regarding eating and the consequences of their transgression.”
Research also indicates that, while chocolate cravings are prevalent in the West, they’re not common at all in many Eastern countries. There are also differences in how urges for different foods are communicated and understood; only two-thirds of languages have a word for cravings, and in most cases, this word only relates to drugs, and not food. “When you can articulate that a craving exists, you can identify and define it, which means you can experience it,” says Nicole Avena, assistant professor of neuroscience at the Mount Sinai School of Medicine in New York.
“Having a definition means cravings are real, whereas if cravings aren’t well defined or ingrained in a culture, people won’t automatically assume cravings are happening to them – they’re more elusive.”
Even in languages that do contain a word for craving, there is still is a lack of consensus around what a craving actually is. This, Konova argues, is a barrier to understanding how to overcome cravings, since we may be labelling several different processes as cravings.
There is evidence suggesting that the trillions of bacteria in our guts can manipulate us to crave, and eat, what they need – which isn’t always what our body needs.
This is because microbes are looking out for their own interests, says Athena Aktipis, assistant professor at Arizona State University’s department of psychology. And they’re good at doing this.
“The gut microbes that are best at surviving inside us end up being more frequent in the next generation. They have the evolutionary advantage of being better at affecting us in ways that get us to preferentially feed them,” she says. (Find out more about how microbes affect our bodies in our recent BBC Future series Microbes and Me).
Different microbes in our guts prefer different environments, such as more or less acidic, and what we eat affects the ecosystem in our guts and what’s available for the bacteria to survive on. They can manipulate us into eating what they need in a few different ways.
They can send signals from the gut to the brain via our vagus nerve and make us feel under the weather if we’re not eating enough of a certain nutrient, or make us feel good when we eat what they want, by releasing neurotransmitters such as dopamine and serotonin. They can also alter our taste receptors so we consume more of something to get the same taste of sweetness, for example.
No one has observed this happening yet, Aktipis says, but it’s based on scientists’ understanding of how microbes behave.
But, she adds, these microbes aren’t always necessarily signalling for us to eat things that are good for us. After all, some bacteria cause disease and death.
“There’s a notion that the microbiome is part of us, but if you have an infectious disease making you feel sick, you would say that microbe is invading your body, not that it’s part of your body,” she says. “You could be getting hijacked by an impaired microbiome.”
But if you eat a diet with lots of complex carbohydrates and fibre, you will cultivate a more diverse microbiome, Aktipis says. This probably means that a healthy diet, which leads to a healthy microbiome, means you crave healthy food.
Cut your craving
Since our environment is full of cues that could tap into our cravings, such as advertising and photos on social media, overcoming them isn’t so straightforward.
“Everywhere we go, we see adverts for food with lots of added sugar, and it’s easy to access these foods. This continual bombardment of advertising affects the brain – and smelling these foods primes the brain to want to eat them,” says Avena.
Since there’s no realistic way to reduce the stimulus of something like chocolate in an environment where we’re surrounded by it, researchers are studying how we can overcome the conditional model of cravings using cognitive strategies instead.
A number of studies have found that mindfulness techniques, such as being aware of cravings and not judging these thoughts, can help reduce cravings overall.
Research has found that one of the most effective ways to curb cravings is to cut the craved food from our diet – which runs counter to the argument that we crave what we need.
In one study, researchers carried out a two-year trial where they randomised more than 300 subjects to one of four diets with different levels of fat, protein and carbohydrates, and measured their cravings and food intake. All the groups lost weight, but when they ate less of a certain food they craved it less.
The researchers say their findings show that, in order to reduce cravings, people should eat the food they crave less often – possibly because our memories associated with that food fade over time.
It’s largely agreed that more work needs to be done into defining and understanding cravings, and developing ways we can overcome the conditional response we develop for unhealthy food. In the meantime, there are several mechanisms suggesting that the healthier our diet, the healthier our cravings.