By James Collier RNutr, Co-Founder & Head of Sustainable Nutrition

Food cravings are unavoidable. Everyone experiences them. We crave certain foods and some of us are more susceptible to stronger cravings than others. Craving food when it’s nearing mealtime is understandable, as discussed in our article How to Control Your Cravings, but it’s often the case that we crave more foods than we actually require at meals, especially sweet and fatty foods, and cravings can be particularly strong when we’re feeling stressed, bored or our mood is low. Why is this?

Having it easy

We live in a time where there’s a more-than-plentiful supply of food. We have it easy: if we fancy something to eat, we simply go to the cupboard and grab something, or we nip to the shop and buy what we want. In the west, most of us can enjoy pretty much whatever comes to mind. Life, however, was considerably harder for our hunter-gatherer ancestors; food was difficult to come by, so they relied on the memory of foods previously eaten to help motivate them to find food.

How our ancestors went supermarket shopping

“Mary” – a forager ancestor of ours – is looking for food in the African Savannah and she stumbles upon some pineapples. Immediately her mouth starts watering as she remembers the sweet, delicious taste and succulent texture of pineapple from when she last enjoyed pineapple a few months ago. The signal is there for Mary to eat as much pineapple as she can right now. If she were to leave them, those baboons she saw a mile-or-so away might find and eat her pineapples by the time she comes back with the rest of her tribe. So, Mary eats as much pineapple as she can until she’s full, and then she carries as many as she can back to her camp. Not long later, however, the craving for pineapple returns which acts as a signal for her to eat as many as possible before the pineapples go bad in the hot Savannah sun.

Developing a sweet tooth

The craving for sweetness, therefore, evolved to be advantageous for humans. Those who didn’t have such a strong memory for sweetness weren’t so readily motivated to search for energy-dense, nutritious foods, hence they had less of a chance of passing on their genes to their offspring. A genome that included genes related to motivation to seek food, therefore, had an evolutionary advantage. Mary, and those like her who were more motivated to seek sweet food, passed their genes down to us.

Similarly, we’re hard-wired to crave other flavours that we subconsciously associate with nutrients we require; for example, umami (savouriness) when we need protein from meat, and saltiness when we are low on electrolytes. The evolutionary cues for tasty foods naturally available have stayed with us. These days, however, it’s not only foods like pineapples that we crave: we have processed high sugar and fat foods only an arm’s reach away, products that have been designed in such a way to be optimised for flavour and texture, not nutrition. Not only that, but these foods are low in vitamins, minerals and fibre; not great choices!

What is hunger?

Hunger is the sensation we experience when we have the need to eat. There are two ways we can think of hunger: physiological (also known as “stomach” or “true”) hunger where your body requires food, and psychological (or “mouth”) hunger which happens when you fancy something to eat. It is the latter type that’s related to cravings. In order to understand hunger, we’ll briefly look at a few of the hormones and neurotransmitters that are involved in the hunger process (NB: other chemicals are also involved, but these are of less relevance for this article).

The role of hormones

Hunger is primarily controlled by a hormone called leptin. Leptin is released from fat cells and the cells of the small intestine. It causes appetite to drop by signalling a region in the brain called the hypothalamus^[1].

More fat → More leptin → Stimulates the hypothalamus → Reduces appetite

Ghrelin, often called the hunger hormone, is released from the stomach and is also involved in regulating appetite, but the other way around. When our stomach is empty, ghrelin signals to the brain that it’s time to eat^[2]. One of ghrelin’s actions is to stimulate the release of dopamine which, in turn, is involved in the motivation to acquire food^{[3, 4]}.

Dopamine is a neurotransmitter that gives rise to positive feelings relating to pleasure. The happy sensations we experience in relation to dopamine may result from a number of activities; for example, from purchasing something we desire or looking forward to going on holiday. One of dopamine’s most important roles is its involvement in motivating us to acquire food through feelings of pleasure, by increasing our appetite and giving us the impetus to hunt and gather food^[5]. These days, as most of us don’t need to hunt and gather our food, these dopamine urges mean nipping to the cupboard to grab a chocolate biscuit!

As well as dopamine being associated with pleasure received from eating tasty foods, it’s also linked to the memory of the pleasure derived from eating these scrumptious foods^[5]. These pleasure sensations contribute to the future desire to eat these foods again. When we think of a food being “moreish”, blame dopamine! These feelings of happiness and pleasure mean, in the wrong circumstances, we crave eating things that are bad for us.

Empty stomach → Ghrelin released → Stimulates the hypothalamus → Increases appetite → Dopamine released → Pleasure recollection experienced → Motivation to seek food

Another chemical involved in the hunger process is the hormone insulin. Insulin is released when the level of glucose in our blood goes up. Our blood glucose (sugar) rises following a meal that contains carbohydrates or protein^[6]. The response is larger after we eat sugars or simple carbs with a high glycaemic index (GI). When the rate of blood sugar increase is rapid, we release more insulin^[6]. Read more about this in our article What is Glycaemic Index and Load?

Higher levels of insulin may be associated with a greater degree of pleasantness derived from sweet-tasting foods^[7]. This means, not only do we want to eat, but what we most want to eat are sweet calorie-dense foods.

Hyperinsulinemia is when levels of insulin in the blood are habitually raised, and may be associated with conditions like type 2 diabetes, obesity and metabolic syndrome. In these conditions, people are predisposed to a number of potential adverse health conditions, like heart disease and stroke, and they have a preference for foods that would further exacerbate their condition^[8]. Hyperinsulinemia may result from a bad diet and lifestyle or for other reasons, and has been shown to be linked to stress^[9].

Food, Pleasure and Fulfillment

Hedonia refers to the happiness associated with short-term pleasure, and examples include unwrapping a birthday present you’ve been eagerly awaiting and the gratification experienced from enjoying eating tasty foods. Hedonic pleasure is related to dopamine. However, hedonic pleasure is short-lived and the positive feelings soon wear off. Eudaimonic happiness is derived through meaning and purpose and is related to more sustained positivity. Both hedonia and eudaimonia are important for leading a happy life, but people too often chase hedonic pleasure, especially when they feel stressed, bored or their life feels less fulfilled in general.

If your life has more eudaimonic fulfilment, you will be able to rely less on hedonic pleasures, including that which is derived from eating junk food. However, we realise that life can be complex and that many people struggle to feel fulfilled. If this is you, strategies like mindfulness, meditation and keeping a gratitude log may be worth looking into. Good nutrition will also help.

Serotonin is another hormone and neurotransmitter that’s relevant here; it’s linked to feelings of contentment and happiness, is related to popularity, cooperation and respect, and is a key contributor to eudaimonia^[10]. Some people have lower levels of serotonin which may be a result of their genetic make-up, what happened when they were in their mother’s womb or adverse life events^[11-13]. Certain psychological interventions may help increase their serotonin levels and happiness, as will certain antidepressant drugs^[14].

What is often overlooked, however, is the effect that good nutrition can have on serotonin levels^[15]. In particular, foods rich in omega-3 fats, choline, low-GI carbs and soluble fibre may be beneficial^[16]. More recently, it’s been discovered that most of the serotonin produced in the body is not in the brain, but actually in the enteric nervous system, i.e. the nervous system of the intestines^[17]. This is partly linked to the gut microbiome which may support a healthy production of serotonin. Soluble prebiotic fibres (like those found in oats, pulses and some fruits) and probiotics, can support a healthy gut microbiome^[18].

Comfort Eating

Your psychological make up can be linked to food cravings and some people are more susceptible to them than others^[19]. When we feel stressed, we look to do things that can help alleviate some of that stress, and we’re predisposed to seek pleasures that will help to cheer ourselves up, like eating foods we enjoy. Not only does eating give us pleasure in the moment, but we also derive pleasure through the memory of eating it^[20]. This is why food is a great topic of conversation and why we like talking about our favourite foods and cooking.

Similarly, when we’re bored, we look for things that will occupy us, and snacking is one thing that we know we enjoy that will help ease boredom.

Furthermore, if you have a high level of insulin, as is the case in hyperinsulinemia, you’re likely to be predisposed to feeling hungry more often and the satisfaction you receive from snacking, especially from sugary foods, is greater^[7]. But snacking increases insulin levels further which risks you wanting to continue snacking and chasing the dopamine surge that you get from snacking. As well as this, people feel guilty about having “bad” foods, especially when they want to avoid them, and this can further worsen mood, and the cycle continues. This is why snacking can have addictive qualities^[21]. If this is you, then some of the tips in our article How to Control Your Cravings may be useful.

Summary

An understanding of the neurophysiology of food cravings allows us to alter our relationship with food. Eating a diet that’s low in sugar, avoids processed fats, is high in fibre, vitamins and minerals, and with regular meals that avoids snacking will have an impact on your mental state and you can read more in our article Can Food Boost Your Mood?

Understanding what food cravings are and why they occur allows us to do something about them. That something involves eating a diet that’s low in sugar and processed fats, while being high in fibre, vitamins and minerals. Regular meals with minimal snacking will also help to put you in control and have a positive effect on your overall wellbeing.

References

1. Kelesidis T, et al. Narrative review: the role of leptin in human physiology: emerging clinical applications. Annals of internal medicine. 2010; 152(2):93-100.
2. Delporte C. Structure and physiological actions of ghrelin. Scientifica (Cairo). 2013; 2013:518909-.
3. Perello M, et al. Ghrelin signalling on food reward: a salient link between the gut and the mesolimbic system. J Neuroendocrinol. 2015; 27(6):424-34.
4. Abizaid A. Ghrelin and dopamine: new insights on the peripheral regulation of appetite. J Neuroendocrinol. 2009; 21(9):787-93.
5. Volkow ND, et al. Reward, dopamine and the control of food intake: implications for obesity. Trends Cogn Sci. 2011; 15(1):37-46.
6. Wilcox G. Insulin and insulin resistance. Clin Biochem Rev. 2005; 26(2):19-39.
7. Rodin J. Insulin levels, hunger, and food intake: an example of feedback loops in body weight regulation. Health Psychol. 1985; 4(1):1-24.
8. Han JC, et al. Insulin resistance, hyperinsulinemia, and energy intake in overweight children. J Pediatr. 2008; 152(5):612-7.e1.
9. Yan Y-X, et al. Investigation of the Relationship Between Chronic Stress and Insulin Resistance in a Chinese Population. J Epidemiol. 2016; 26(7):355-60.
10. Dfarhud D, et al. Happiness & Health: The Biological Factors- Systematic Review Article. Iran J Public Health. 2014; 43(11):1468-77.
11. Bleys D, et al. Gene-environment interactions between stress and 5-HTTLPR in depression: A meta-analytic update. Journal of Affective Disorders. 2018; 226:339-45.
12. Velasquez JC, et al. Placental serotonin: implications for the developmental effects of SSRIs and maternal depression. Front Cell Neurosci. 2013; 7:47-.
13. Frick A, et al. Overlapping expression of serotonin transporters and neurokinin-1 receptors in posttraumatic stress disorder: a multi-tracer PET study. Molecular Psychiatry. 2016; 21(10):1400-7.
14. Bleys D, et al. Gene-environment interactions between stress and 5-HTTLPR in depression: A meta-analytic update. Journal of Affective Disorders. 2018; 226:339-45.
15. Briguglio M, et al. Dietary Neurotransmitters: A Narrative Review on Current Knowledge. Nutrients. 2018; 10(5):591.
16. Huang Q, et al. Linking What We Eat to Our Mood: A Review of Diet, Dietary Antioxidants, and Depression. Antioxidants (Basel). 2019; 8(9):376.
17. Yano Jessica M, et al. Indigenous Bacteria from the Gut Microbiota Regulate Host Serotonin Biosynthesis. Cell. 2015; 161(2):264-76.
18. Holscher HD. Dietary fiber and prebiotics and the gastrointestinal microbiota. Gut Microbes. 2017; 8(2):172-84.
19. Kalon E, et al. Psychological and Neurobiological Correlates of Food Addiction. International review of neurobiology. 2016; 129:85-110.
20. Mela DJ. Eating for pleasure or just wanting to eat? Reconsidering sensory hedonic responses as a driver of obesity. Appetite. 2006; 47(1):10-7.
21. Lemeshow AR, et al. Food and beverage consumption and food addiction among women in the Nurses' Health Studies. Appetite. 2018; 121:186-97.