What are the biological processes behind the sensation of "being hungry"? [closed]

Question

I'm trying to work out if there is a particular diet or habits around eating that would minimize the sensation of "being hungry".

Is "being hungry" a psychological sensation determined simply by the habit of eating at specific times during the day? Are there any observable biological processes associated with hunger? Is it driven by an empty stomach or some other biological process? Are there any particular hormones associated with hunger?

Answer 1

Hunger is the physiological drive to eat, influenced by hormones, nutrient levels in the body, and eating patterns. Scientists differentiate this from appetite, which is the psychological drive to eat. I wont discuss appetite here. Scientists also differentiate between hunger and satiety (fullness), because they are regulated by different centres. I will discuss both of these, because they directly affect each other.

The hypothalamus (HT) contains centers that tell you if you're hungry or satiated. Although they are separate centres, the hunger centers inhibit the satiety centers (i.e. when you're hungry you feel less full), and vice versa. When the hunger centers are activated, activity in your sympathetic nervous system decreases, which signals you to eat. The opposite occurs when the satiety centers are activated.

To "decide" which of these centers should be activated, the hypothalamus receives input from a few sources:

• The gastrointestinal (GI) tract (the stomach and intestines)

  • Cholecystokinin (CCK) is a hormone released by the small intestine in response to fat entering the small intestine. It decreases activation in the hunger centres of the HT (i.e. it makes you less hungry), and increases activation in the satiety centres (i.e. it makes you feel more full).
  • Peptide YY is a hormone release by the small and large intestines in response to eating. There is some evidence that protein consumption increases peptide YY release. It also inhibits your hunger centres. Relevance to weight control: Between CCK and Peptide YY, both fat and protein consumption decrease hunger.
  • Ghrelin is a hormone released by the stomach in response to emptiness. It stimulates the hunger centres in the HT (i.e. makes you feel more hungry). Since an empty stomach causes hunger, you can see how it would be beneficial to slow down the stomach's emptying. The hormones CCK (as mentioned above, it is released in response to fat) and GIP (released from the small intestine in response to food) both delay gastric emptying. Fiber has also been shown to delay gastric emptying. Relevance to wight control: High fiber and high fat meals may help delay the next onset of hunger. Smaller meals also slow gastric emptying, but I'm not sure if it's enough to compensate for the fact that the meal is smaller.

• From nutrients in the blood

  • When glucose enters the the blood stream, the hormone insulin is released. Insulin inhibits the hunger centres of the HT (i.e. it makes you less hungry). Any carbohydrates you eat will enter the blood stream as glucose, however, complex carbohydrates (think whole grain foods) enter the bloodstream more slowly, causing a lower but more sustained level of insulin than simple carbs do (think sugary treats), which will cause a spike and drop in insulin. Relevance to weight control: Complex carbs keep you more satiated than simple carbs.

• From body fat stores

  • Stored body fat releases a hormone called leptin, which tells the HT that you're gaining body fat. If you gain fat (increasing leptin), it decreases your hunger and increases your satiety, and the opposite happens if you lose fat. Relevance to weight control: some people have a disorder in their production or reception of leptin, making it easy to gain weight uncontrollably.

There is also evidence that orexin, a hormone involved in sleep/wakefulness cycles, stimulates hunger. Sleep deprivation has been shown to increase food intake. Relevance to weight control: Get enough sleep.

(source)

Answer 2

"Feeling hungry" is a chemical and physiological response to lack of nutrients in the bloodstream. When the bloodstream is sufficiently filled with nutrients for the body's use, the brain slows the digestive process in the stomach. When the nutrients in the blood are absorbed or used (turned to fat or burned), then the brain resumes the digestive process. When the digestive tract is activated without sufficient nutrients for it to absorb, we "feel hungry" and our stomach starts growling. (Source)

Drinking a glass of water will often relieve the hungry feeling that we get. Additionally, protein and fiber take longer to process than fats and carbohydrates, and will thus "stick with us" longer. So having more protein and fiber in your diet and less carbohydrates and fats will decrease the amount of time you spend feeling hungry. See this document on preventing hunger pangs and food cravings.

It is my understanding that taking HCG (human chorionic gonadotropin) injections will eliminate food craving and hunger pangs from a physical standpoint, although I've known people on it to experience extreme food boredom. I don't advise anyone to take hormone injections unless specifically instructed to by their physician. If you do start HCG, it is absolutely imperative that you follow every step of the diet including the retraining phase for 3 weeks after the HCG regimen is ended. I have known people that have successfully lost significant amounts of weight while taking HCG; however, the Journal of the American Medical Association and the American Journal of Clinical Nutrition both claim that it is ineffective and unsafe as a weight-loss aid.