Ever wanted all the chips, chocolates, or jelly beans in the bag in a single sitting? You are not alone, and studies report cravings are present up to 90 percent of the population.
What Causes Cravings?
There is no straightforward cause of cravings, and we all experience them somewhat differently. Let’s take a look at some common causes, then some solutions to help limit and possibly avoid these powerful biological urges.
We do know from the literature that all of the following can influence cravings.
- Type of food
- Time of day
- Gender differences
- Gut-brain signals
- Sress, and
- Biological needs
Type of Food
The type of food you are eating, especially foods like chocolate (the most craved food), or other high-calorie, sweet and savory foods, can increase your cravings for those foods (see Meule, 2020 for review). Studies show these cravings can be unlearned following long-term energy restriction, which suggests a conditioned food response (e.g. think: Pavlov’s dog). In addition, how strong the craving is, not current hunger, seems to predict higher salivary flow and higher chocolate consumption.
Cultural differences can also influence cravings, for example rice in Japan, suggesting cravings are directly related to what you eat.
Time of Day
The time of day is also a factor, as cravings for savory and sugary foods tend to increase into afternoon and evening, while cravings for healthier foods like fruits tend to decrease. A study from 2015 showed just 5 days of sleep deprivation led to increased energy expenditure by 5%, and resulted in gaining almost a pound, despite changes in hormones that signal excess energy stores. Participants then reported delays going to sleep and waking up earlier. Therefore even though our energy needs increase slightly at night, our energy intake often exceeds needs (see Meule, 2020 for review).
Gender differences also play a role, with studies showing overweight and obese females are 1.1 times more likely (i.e. twice as likely) to report eating relieves negative emotional states than males, and females experience more food cravings despite similar rates of binge eating and obesity. Women deprived of sleep for 5 days also showed a decline in dietary restraint and weight gain compared to males. Women have also been found to have significantly more cravings for chocolate and sweets than men, and eat more calories and more sweet food in response to stress. Another study found cravings occured in 77% of women who experienced stress, and were associated with altered hormone levels (e.g. higher leptin), larger hip circumference, and altered body composition.
In men, diets high in protein up to 25% of overall calories show reductions in cravings up to 60%.
For women, it is important to know we are more susceptible and should take steps to get enough sleep and avoid stress.
In the 1800’s, a physician treating a gunshot injury at close range noted the rate of digestion was slowed when the patient was angry or irritable, indicating that his emotional state affected the stomach – suggesting a ‘gut-brain’.
Formally referred to in the literature as the ‘gut-brain axis’, many people may have experienced how mental or emotional states can influence the stomach, and the other way around (e.g. overeating in response to stress). This system of nerves, hormones and receptors in the gut, together with the gut microbiota (tiny organisms that live in the gut), communicate with the brain as digestion continues from the stomach to the small intestine.
- First, special sensors in the gut (called mechanosensors) send signals to the brain through the vagus nerve to sense fullness, often credited for our ‘gut feelings’. An empty stomach triggers the mucus in the gut to release the hormone ghrelin. This hormone then acts on reward systems in the brain resulting in a powerful drive to eat, including areas such as the hippocampus involved in spatial learning and memory.
- Next, hormones such as cholecytokinin and the vagus nerve continuously send signals to the brain about fullness to establish meal patterns, with the brainstem and hypothalamus helping promote feelings of satisfaction and happiness (see Berthould, 2008 for review).
- Finally as the stomach fills, it releases the hormone leptin to signal fullness (see Coll et. al, 2007 for review).
Cravings and the Brain
Many brain areas signal the stomach to eat, including the reward areas, cognition, and learning. The body’s need to maintain consistency (called ‘homeostasis) leads to many complicated changes that regulate energy use from food and the signals back to the brain.
For example, hormones released by the fat cells, gut, and pancreas act on the hypothalamus (fullness), the brainstem, and autonomic nervous system to affect appetite. Human studies show reduced cognitive performance and brain activity in areas such as the thalamus, hypothalamus, and amygdala following disruptions in gut microbiota. In patients with irritable bowel syndrome (IBS), a brain imaging study (fMRI) showed reduced activation of the amygdala and frontolimbic regions and gut bacteria after negative emotional stimuli.
Because your brain and gut are connected, there is a feedback loop and what you typically eat your body is going to want, regardless of nutrient value (see Meule, 2020 for review). This gut-brain and can bypass any higher thinking areas in the brain for more primitive, immediate needs for survival. This system of energy storage evolved for feast or famine and protects against unevenness of food supply, and is an advantage against the risk and cost of obtaining food. We are therefore prone to obesity in an environment where energy-dense foods are readily available in large portions (see Rogers & Brunstrum, et. al, 2016 for review).
Calorie Restriction & Hunger
Cravings can serve a biological function to prepare the body for digestion and consumption (e.g. salivary flow) and motivate food seeking behaviors. Cravings for a specific food, or ‘selective hunger’ can also be distinguished from hunger (‘nonselective’), where any food will do (see Meule 2020 for review).
However, excess energy storage (a.k.a. fat) can start to act on its own to influence appetite. Commonly called ‘starvation mode’, as fat on the body increases (picture a bathtub), eventually the amount the stomach can hold (picture a saucepan), is negligible in comparison, and hunger is then related to temporary appetite (see Rogers & Brunstrom et. al, 2016 for review). Studies in rats show fat sends signals to the brain to reduce feeding frequency. Over time, resistance to leptin (hormone that senses fullness) disrupts the negative feedback of body fatness on appetite (also Geliebter et. al, 2004), and after repeatedly consuming large meals increases tolerance to the filling effect of food.
So while most people and health professionals assume that hunger is related to depleted energy stores (also Assanand et. al, 1998) the relationship between hunger and appetite seems to be weaker than originally thought. For example, symptoms of low blood sugar reported by athletes competing in marathons include feeling sudden fatigue and loss of energy as liver and muscle glycogen stores are depleted, but rarely report normal hunger. Others report symptoms of hypoglycemia like sweating and shakiness, which are also relieved by carbohydrates but are rarely accompanied by reports of feeling ‘hungry’. In addition, Kahathuduwa et al, 2017 reviews studies showing that cravings decrease following extended caloric deprivation, and seem to be more related to perceived deprivation rather than actual nutrient deficiencies.
Whereas ‘appetite’ (a desire to eat), is the emptiness of the upper gut combined with the anticipated reward for food, hunger has an association with energy depletion (for review, see Rogers & Brunstrom et. al, 2016). In an environment of energy-dense and easily available foods, our cravings do not seem to be related to actual hunger but are linked to obesity through increasing appetite (i.e. desire to eat).
Since we cannot control this gut-brain mechanism, we can purposefully engage in healthy eating and take probiotics when recommended by a nutritionist or physician.
Stress is associated with increases in the hormone cortisol, which can lead to low blood sugar and ‘emotional eating’. Because we are very sensitive to changes in blood sugar due to homeostasis, the very act of not eating is also associated with cortisol release, activating the ‘fight or flight’ mechanisms and reducing blood flow to the stomach.
To stimulate the body to find food, the release of cortisol then suppresses hunger, slows digestion, and draws blood to the extremities. When cortisol levels go down, you feel a ‘crash’ as blood sugar also drops, bypassing hunger and increasing cravings for more high-caloric sweet and savory foods. For example, restrained eaters experience more intense and frequent cravings, and dieters have reported having more food cravings than non-dieters. Cortisol is also associated with increased cholesterol and heart disease, causes cravings and increases BMI (Body Mass Index) and increases abdominal fat.
Furthermore, dieting has been shown to be effective in only 10% of people, whereas weight loss surgery is 50% effective by targeting fullness signals in the upper gut (see Berthoud, et. al, 2008 for review). As a result, many insurance programs only pay for surgery. Studies show that diets are easy to break, and the effort it takes is distracting and can lead to feelings of failure. Because we are adapted to an uncertain food supply, overeating and undereating is common, and dietary restraint is difficult to sustain and can lead to disordered eating.
How to Avoid Cravings
To avoid this cycle of indulgence and dread, try thinking of your body as a machine that needs fuel, and that when depleted will send signals that it needs nutrients and calories. Like a dashboard on a car, monitor the signals to help your body burn fat and build muscle efficiently.
Clear your pantry.
Avoid sugary beverages, cereals, sweets, sodas, and dairy, since these interfere with normal blood sugar signals. Processed foods are often called ‘foods with no breaks’ because they do not tell you when to stop (remember the Lay’s commercial, I bet you can’t eat just one!). Our cravings are subject to talented and highly paid marketers and fancy packaging with misleading claims, so it takes self-discipline and is easier said than done. Similar to smoking in the 70s, companies are not being honest with consumers about the known dangers of their foods to our health.
Start eating healthy foods.
Choose healthy ingredients since you will crave what you eat, and these foods will tell you when you are full. Depending on your body type and size, aim for a range of 20 to 30 grams of protein (e.g. 3-4 eggs) each meal. Include green veggies and some good fat on the plate (e.g. oil or food source), a serving of beans and/or rice or sweet potato for starch. For athletes and to help burn fat around workouts, include additional protein sources like eggs, beans and rice, or quinoa.
Eat meals at regular intervals.
Aim for 3-4 balanced meals per day before 8:00pm. Eating regular meals will give your body the nutrients it needs throughout the day, reduce stress, and help avoid cravings for unhealthy foods high in sugar and fat. Just making the commitment to yourself will help you will feel better, look better, and be healthier from the inside out!
Reduce stress & get more sleep.
Try to identify points in your day or parts of your life that are stressful, and do your best to avoid them. Start a yoga or mediation routine, even just 5 minutes a day. Try starting a sleep routine about 1 hour before bedtime (e.g. reading, tea) to improve sleep quality.
KATY HARRIS, MSPH, CSCS
Katy Harris MSPH, CSCS is a Master of Public Health, Certified Strength & Conditioning Specialist, health and wellness business owner, and ultimate player who runs the WellLife Studio in Chapel Hill, NC.
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