Have you ever been craving or dreaming awake about a cheese pizza, creamy-filled doughnuts, a lava chocolate cake, a juicy steak with french fries, coffee, bread, macaroni & cheese, alcohol, ice or salty foods ?

Well, let me tell you… You’re not alone.. A Canadian study from McMaster University performed with 1,000 undergraduate college students revealed that 97 % of women and 68 % of men experienced food cravings, being chocolate the most craved food, especially among women. A food craving is an intense and uncontrollable desire for a specific food.

Since a long time ago, science has related cravings with nutritional deficiencies or food restrictions. For example, a craving for chocolate may indicate a deficiency of magnesium, L-tryptophan and phenylethylamine. Magnesium is a critical mineral involved in more than 300 biochemical reactions. L-tryptophan is an essential aminoacid that is converted to serotonin, a key hormone that stabilizes our mood, feelings of well-being, happiness, and even sleep (melatonin precursor). Phenylethylamine is a stimulant substance for the brain associated with energy, euphoria, romantic love and overall wellbeing.
A severe deficiency in vitamin C led sailors to scurvy in long sea journeys, which was relieved with “ extraordinary pleasure ” once they had access to fresh fruits and vegetables.

Pregnant women have the most weird cravings due to hormonal imbalance, enhanced sense of smell and taste and/or lack of micronutrients. Some of them crave for ice that relieves the inflammation of mouth and tongue due to iron deficiency anemia. Others have Pica, an unsual behavior where they have a intense desire to eat non-food substances such as dirt, crayons or laundry starch due to zinc or iron deficiencies.

Despite the said above, there is no evidence that all cravings are necessarily caused by deficiency of certain nutrients. Several studies have found that dieting or calorie restriction results in decreased food cravings, particularly among dieters participating in very-low-calorie (e.g., 200 kcal/day to 800 kcal/day) or monotonous diets.

It is known that food cravings arise to satisfy emotional needs such as calming stress and reducing anxiety

SO, WHAT CAUSES FOOD CRAVINGS ?

It is believed that food cravings arise from a combination of social, cultural, emotional and psychological factors. Unlike United States, where chocolate is the most craved food, in Japan women are more likely to crave for sushi and rice, while in Mexico they would crave for tacos. This reflects  the influence of family traditions and cultural differences around the world. Actually, some studies have linked cravings with emotions and desire (stress eating). For example, is more probable that  you want sugary foods after a bad day at work  because you had a discussion with your boss or maybe after breaking-up with your boyfriend or girlfriend.  It is known that food cravings arise to satisfy emotional needs such as calming stress and reducing anxiety.  Allison Childress, a nutrionist at Texas Tech University, says “because cravings are typically psychological and not physiological (unlike hunger), they tend to be satisfied by a feeling or sensation that is gained from eating certain foods”. Food cravings have been shown to be related with higher levels of stress.

            Additionally, some personal cues, like smells, pictures, sounds, memories of foods, associated with our childhood or past experiences can trigger cravings.

            From the Buddhist perspective, craving is “expecting things to be different from how they currently are”. This means that when we  have a sense that something is missing or absent, we can fill that void with food, music, sex, gambling, drugs et al, in order to feel comfort, reward or to satisfy our emotional needs. All these stimuli work in the same way, activating  the release in our brain of a chemical called dopamine that contributes with the feelings of pleasure or satisfaction as part of the reward system.  

                        A study made in 2004 with functional magnetic resonance imaging (fMRI) by the Monell Chemical Senses Center in Pennsylvania, found that certain areas of the brain were activated (lit up), when the participants thought about the foods they liked. Specifically the hippocampus, the insula and the caudate nucleus, which are key areas of the dopamine reward system involved in cravings. They found that brain regions activated by food craving overlap with areas implicated in drug craving. The reward mechanisms involved in cravings are very similar to those associated with addictionsThis is why sugar has the same  effect as cocaine, but  with the difference that it is eight times more addictive. The reward regions are connected to areas associated with memory and behavior.  In daily life, this means that when you finish a meal (cue ) and find it pleasurable (reward), our brain will remember it and will try to repeat  the experience again and again (behavior).

Kent Berridge, professor of biopsychology and neuroscience at the University of Michigan, says that the hunger system works a little separate from the craving area that is located in the center of the brain. According to Berridge the dopamine system  is activated by cues, whether emotional or environmental.

ARE HUNGER AND FOOD CRAVINGS THE SAME?

Hunger and cravings are two different sensations easily recognizable from each other. The first one is regulated by the body and the last one is powered by the mind. Cynthia Dsauza, professor of addictive disorders and recovery studies at Texas Tech University says that hunger manifests with stomach rumbling, mild headache or feelings of weakness and generally doesn’t go away with the passage of time. Meanwhile, cravings can be triggered by external influences like a problem with your boss, an argue with your wife or boyfriend, the loss of a beloved one, gambling,financial problems, having  sex or assisting to a party.

Our hunger (appetite) and satiety sensations are cycles regulated by several hormones that interact with the hypothalamus, a very important regulatory brain center involved also with  thirst, sleep and sex drive.

Once our stomach is empty and blood sugar and insulin levels are low, it releases ghrelin – the appetite-increaser hormone– that signals the hypothalamic arcuate nucleus to produce neuropeptide-Y which potentiates the food intake. Ghrelin is called so because it’s considered as a Growth Hormone-releasing peptide  (GHR). Normally, ghrelin levels are higher before meals and lower after eating. Stress stimulates its production

Another hormone called leptin (from the Greek, leptos, “thin”), made by fat cells and enterocytes -cells in the small intestine- counterbalances the actions of ghrelin. It inhibits hunger when it binds to receptors in the lateral hypothalamus and stimulates satiety when it acts in the medial hypothalamus.

Since sleep is also regulated by the hypothalamus, when we don’t have enough sleep, ghrelin levels rise and leptin level fall, leading to a spike in appetite and an increase in hunger. This emphasizes the extreme importance of sleeping well overnight (quality and quantity) in order to avoid hunger and cravings.

Ghrelin and leptin are known as the hunger and satiety hormone respectively. They’re both produced in the periphery and act in the brain (centrally) via our blood stream, crossing the blood-brain barrier , but also communicating through the vagus nerve.

While ghrelin is a fast-acting hormone produced in the stomach and duodenum that increases hunger, leptin -the appetite suppressor – has long term effects on energy balance and appears to be the big player, regulating ghrelin according to some studies. Besides being produced in fat cells, leptin is also secreted in the stomach, heart, placenta and skeletal muscles.

Normally, both hormones correlate with how well-fed you are; before a meal, ghrelin is high and leptin is low and after eating, is the opposite, leptin goes up and ghrelin comes down. Leptin is related to fat mass, the more body fat you have the more leptin you produce in order to tell your brain to stop eating and start burning it. This is a called a negative feedback loop.

Researcher, Judith Altarejos, Ph.D, from Sanford-Burnham Prebys Medical Institute at San Diego, California says that “obesity results when brain becomes  ‘deaf ’ to leptin signals.” This means that the brain hears only ghrelin and keeps telling you to eat without being stopped.

Obese people have a lot of fat and therefore high levels of leptin, but somehow the brain doesn’t respond to the normal leptin signaling of not overeating. This is called leptin resistance which is very similar to insulin resistance. Both are present in obesity.

According to the Sleep Foundation, not sleeping enough hours (sleep deprivation) produces a imbalance between both hormones with an increase in ghrelin levels and a decrease in leptin, a combination that leads to overeating and potential obesity. This fact pinpoints that sleep quality and quantity are critical to keep an optimal eating behavior and body weight regulation.

Other key issue is to know the chemistry of foods and their interaction with hunger, satiety and other hormones. For example,  high fructose corn syrup or HCFS is a cheaper sugar developed from genetically modified corn and present in a great number and variety  of processed foods ( sweet sodas, fruit juices, ketchup, mayonnaise, sauces, bread, pastries, etc. ).  Regular sugar contains glucose and fructose. Glucose is metabolized by each cell of our body while fructose is only processed in the liver. High amounts of fructose in the liver accumulate as fat (cholesterol and triglycerides)  causing what is known as non-alcoholic fatty liver disease (NAFLD), called like this because it looks just like what happens in the livers of people that drink too much alcohol.  

 

According to Harvard Medical School, NAFLD was practically unknown before 1980 and now is present in almost 1/3 of the adults in the US and other developed countries, and between 70 to  90 % of those who are obese or have diabetes. This is mainly due to the excess of fructose in the US food industry with the use of HFCS.