भूख
भूख उस समय अनुभव होती है, जब खाना खाने की इच्छा होती है। परितृप्ति भूख का अभाव है। भूख की अनुभूति हाइपोथैल्मस से शुरु होती है जब यह हार्मोन छोड़ता है। यह हार्मोन यकृत के अभिग्राहक पर प्रतिक्रिया करती है। हालांकि एक सामान्य वयक्ति बिना भोजन के कई सप्ताहों तक जिंदा रह सकता है। भूख की अनुभूति भोजन के कुछ घंटों बाद शुरू हो जाती है और व्यक्ति असहज महसूस करने लगता है। भूख शब्द का इस्तेमाल व्यक्ति के सामाजिक स्तर को बताने के लिए किया जाता है।
जब अमाशय में मरोड़ देने लगता है। भूख का मरोड़ अक्सर भोजन के बारह से चौबीस घंटे के पहले शुरू नहीं होता है। भूख का एक मरोड करीब 30 सेकेंड तक रहता है। और यह लगाता 30–45 मिनटों तक होता रहा है। इसके बाद भूख 30-150 मिनटों तक कम हो जाता है The fluctuation of leptin and ghrelin hormone levels results in the motivation of an organism to consume food. When an organism eats, adipocytes trigger the release of leptin into the body. Increasing levels of leptin results in a reduction of one's motivation to eat. After hours of non-consumption, leptin levels drop significantly. These low levels of leptin cause the release of secondary hormone, ghrelin, which in turn reinitiates the feeling of hunger.
Some studies have suggested that an increased production of ghrelin may enhance appetite evoked by the sight of food, while an increase in stress may also influence the hormone's production. These findings may help to explain why hunger can prevail even in stressful situations.
Hunger appears to increase activity and movement in many animals - for example, an experiment on spiders showed increased activity and predation in starved spiders, resulting in larger weight gain. This pattern is seen in many animals, including humans while sleeping. It even occurs in rats with their cerebral cortex or stomachs completely removed. Increased activity on hamster wheels occurred when rats were deprived not only of food, but also water or B vitamins such as thiamine. This response may increase the animal's chance of finding food, though it has also been speculated the reaction relieves pressure on the home population.
On June 19, 2009, it was reported that world hunger hit one billion people, about a sixth of the world's total population.
There were 923 million hungry people in the world in 2007, an increase of 80 million since 1990. The world already produces enough food to feed everyone - 6 billion people - and could feed the double - 12 billion people. The Meals On Wheels Association of America Foundation (MOWAAF) has found that hunger is a serious threat facing millions of seniors in the United States, and that understanding the problem is a critical first step to developing remedies. In 2007, MOWAAF, underwritten by the Harrah's Foundation, commissioned a research study entitled "The Causes, Consequences and Future of Senior Hunger in America". The report was released at a hearing of the U.S. Senate Special Committee on Aging in March 2008 in Washington, D.C.
The study found that in the United States, over 5 million seniors, (11.4% of all seniors), experience some form of food insecurity (i.e., were marginally food insecure). Of these, about 2.5 million are at-risk of hunger, and about 750,000 suffer from hunger due to financial constraints. Some groups of seniors are more likely to be at-risk of hunger. Relative to their representation in the overall senior population, those with limited incomes, under age 70, African American, Hispanic, never-married, renters, and seniors living in the Southern United States are all more likely to be at-risk of hunger. While certain groups of seniors are at greater-risk of hunger, hunger cuts across the income spectrum. For example, over 50% of all seniors who are at-risk of hunger have incomes above the poverty threshold. Likewise, it is present in all demographic groups. For example, over two-thirds of seniors at-risk of hunger are Caucasian. There are marked differences in the risk of hunger across family structure, especially for those seniors living alone, or those living with a grandchild. Those living alone are twice as likely to experience hunger compared to married seniors. One in five senior households with a grandchild (but no adult child) present is at-risk of hunger, compared to about one in twenty households without a grandchild present. Seniors living in non-metropolitan areas are as likely to experience food insecurity as those living in metropolitan areas, suggesting that food insecurity cuts across the urban-rural continuum.
A food craving is an intense desire to consume a specific food, as opposed to general hunger. Similarly, thirst is the craving for fluids. Withdrawal craving is a "hunger" for administering addictive drugs.