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.