Appetite is more psychological then physical phenomenon. It denotes "an organic need represented in consciousness by certain sensations. It can be also be defined as a psychological desire to eat and is often related to specific foods. Unlike hunger, it is probably a learned response associated with pleasant tasting and satisfying food. It is an agreeable sensation that aids digestion by stimulating the secretion of saliva and other digestive juices. It also stimulates the desire to eat sufficient food to maintain the body and supply it with enough energy and nutrients to carry out its functions. However, as with other body functions, disorders of appetite occur. Excessive appetite may result in obesity, while diminished appetite is a sign common to many illnesses and may be a manifestation of stress.

Appetite serves to regulate adequate energy intake to maintain metabolic needs. It is regulated by a close interplay between the digestive tract, adipose tissue and the brain. Decreased desire to eat is termed anorexia, while polyphagia (or "hyperphagia") is increased eating. Dysregulation of appetite contributes to anorexia nervosa, bulimia nervosa, cachexia, overeating, and binge eating disorder.
Some people experience a loss of appetite; others have difficulty controlling theirs. When considering disturbances of appetite, it is important to remember that while hunger is a physical sensation, appetite is a psychological one. The hypothalamus area of the brain, which controls appetite, is closely connected with the emotions.
A poor appetite is not a disorder in itself, but usually a symptom of some other problem.  Lack of appetite is often due to continual munching, combined with drinking cold drinks, which depress Agni. Low appetite may also be due to emotional factors.
Alcohol, cigarettes, drugs, allergies, depression, emotional upset, illness, nutritional deficiencies, stress, and weather among other things can affect appetite. An undetected underlying illness, heavy metal poisoning, and/or nutritional deficiencies may be involved.
If you want to increase your appetite, more frequent small meals of healthy and nutritious foods may be more appetizing than two or three larger ones. Avoid fast food and processed foods, which offer little appeal and poor nutritional value. Instead, concentrate on eating a diet that contains a lot of fresh vegetables, fruits, and whole grains, which look and smell more tempting, are nutritionally safer choices, and are more likely to satisfy hunger.

SUPPRESSANTS
Eating fresh vegetables and whole grains as your primary foods will help you to feel full while furnishing your body with necessary nutrients.
Bergamot, fennel, and patchouli can decrease or regulate the desire for food, according to the body’s needs.
Stop using artificial sweetners and stop eating the sugar-free candies. The only purpose of these is to increase the appetite and make you hungrier. 2 Chromium Picolinate pills a day also helps.
Eating slowly and drinking plenty of water are important aspects of giving your appetite time to feel satiated and thus decreasing the need for additional food.
Apples and whole grains are examples of high-fiber foods requiring more time for chewing. Also, having a cup of bouillon 10 minutes before meals is helpful in reducing the appetite.
Flaxseed oil is the best known plant source of omega-3 fats but raw flaxseeds are even better, especially for appetite control.
Dark chocolates (containing less amount of sugar) can suppress your appetite.
Take chickweed herb to decrease the appetite.
Copious amounts of water are vital to satiating the appetite.
Soup is one of the best kept secrets to appetite control and weight loss.
Herbal teas are popular appetite suppressants. Pour boiling water over one teaspoon of dried herbs such as chickweed, dandelion or fennel and steep for 3 to 5 minutes. Chickweed in particular, which is sometimes considered a pesky weed, can be made into an herbal tea to help with weight loss by working to reduce the appetite. It also serves as a diuretic that flushes toxins from the body.
Take 1/2 ounce carrier oil, 10 drops fennel oil, 5 drops bergamot oil, 3 drops patchouli oil. Place the carrier oil in a clean container, add the essential oils, and blend. Massage the mixture over your stomach and abdominal area several times daily
In hunger pangs stop yourself and take ten slow breaths. Take deep breaths. This will work in controlling the cravings of overeating.  
Take 15 drops bergamot oil, and 10 drops fennel oil. Drop the bergamot and fennel oils into a small glass bottle with an airtight cover. Gently turn the bottle over a few times or roll it between your hands to blend. Inhale directly from the container as necessary. If you want to tame your appetite, breathe in Appetite-Suppressing Inhalation whenever you get the urge to eat between meals.
Whey protein powder has been used for years by dieters as an effective natural appetite suppressant. Whey protein powder is also excellent for muscle growth, which is crucial because muscle burns fat. You can drink it as a delicious shake or add it to smoothies or any variety of food recipes.
Try eating a small salad before a meal. Salad with spinach, mesculin, endives and cabbages -- all types of greens will help curb your cravings.
 
STIMULANTS
Mix fresh lime juice in a glass of water and 1 tsp of ginger juice and little bit salt and drink it daily for loss appetite.
One part each of cloves, nutmeg and long pepper, 3 parts of Indian gooseberry and 8 parts of ginger. Grind the mixture to obtain a fine powder. Add sufficient sugar to make it tasty enough to eat. Consume a spoonful of this mixture twice or thrice a day helps in improving lost appetite.
Fennel, like its cousin caraway (both belong to the Umbelliferae family of herbs), is a familiar digestive aid, both for relieving stomach upset and for boosting the appetite.
Take equal parts of mustard seeds, asafetida, ginger, cumin seeds and black salt and grind the mixture to a fine powder. Add this mixture to a glass of buttermilk and drink it an hour before meals for increasing the appetite.
Eating sour grapes is also effective in treating the problem of anorexia.
Basil tea and peppermint tea helps in increasing appetite.
Several other oils bergamot, chamomile, juniper, myrrh, palm Rosa, and orange also arouse the appetite.
Extract a cup of pomegranate seed juice. Add a pinch of rock salt and a spoonful of honey. Sip it slowly and it removes the bad taste from the mouth and increases your appetite.
Take 1/2 ounce carrier oil, 4 drops basil oil, 4 drops orange oil, 4 drops thyme oil, 3 drops coriander oil, 3 drops rosemary oil and place the carrier oil in a clean container, add the essential oils, and blend well. Massage the mixture over your stomach and abdominal area as needed. This remedy is for enhancing appetite.
Any grouping of Horse radish, garlic, safflower, hops, goldenseal, oat straw, barberry, parsley, and ginseng will help increase appetite.
Kernels of fully-grown mango seeds are to be dried. Add a few curry leaves and a few pepper corns to the kernels (1-2 seeds) and grind them to a fine paste using water. Mix the paste in buttermilk. Add a pinch of salt to taste. This is then added to rice and taken. Tender mango leaves can be used in place of mango kernels. This brings about good appetite and helps sensitize the taste buds.
Three or four cloves of raw garlic should be boiled in a cup of water. This soup can be reinforced with the juice of half a lemon and taken twice daily. This helps in boosting appetite.
Soak tamarind in a glass of water, soak for at least 1 hour, then mash it and strain it so as to extract its pulp. Now to this tamarind pulp add salt and black pepper powder for taste.
In a ratio of 1:4 grind rock salt and unrefined sugar. After meals take this mixture with hot water. This effective home remedy to enhance your appetite.
The juice of sour grapes is another effective remedy for anorexia. The juice of these grapes should be used in kneading the flour before preparing chapattis.
Mix in equal parts cinnamon bark, small cardamom, coriander seeds and fennel seeds. Soak the mixture in cold water overnight. Strain this blend with a tea strainer. Drink this early in the morning for better appetite.
On orange slices sprinkle black salt and dried ginger powder. This home remedy is effective in treating appetite loss.
Take a thiamine supplement along with zinc, vitamin A, niacin, B-complex, and biotin to increase appetite.
Drop the essential oils 8 drops clary sage oil, 6 drops coriander oil, 4 drops black pepper oil, 3 drops ginger oil and 1 drop peppermint oil into a small glass bottle with an airtight cover, and gently turn the bottle upside down a few times or roll it between your hands to blend. Inhale directly from the container beginning thirty minutes to one hour before mealtime, can help in enhancing appetite.
At least half an hour before meals application of ice bag on stomach is also helpful in treating anorexia. Even drinking a glass of ice water 1 hour before meals is also beneficial in treating loss of appetite.
Take small quantity of caraway seeds and roast them and make a powder of it. To this powder add salt to your taste. With water take this mixture after eating your meals.
Bitter greens consist of arugula, radicchio, collards, kale, endives, escarole, mizuna, sorrel, dandelions, watercress, and red/green mustard, which help, in increasing appetite by improving digestion.
5-HTP is an herb that balances out the serotonin in your brain, thus helping to calm an overactive appetite. It also helps you sleep better at night.
Hot pepper increases metabolism and the appetite.
Flintstones vitamins will increase your appetite, whether you are a child or an adult.
Essential oils that come from culinary herbs, including basil, clary sage, coriander, ginger, marjoram, rosemary, and thyme, are particularly good for stimulating appetite.