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Monday, 14 September 2009

How appetite is regulated

Appetite (the desire to eat) is regulated by many internal and external factors.

Internal factors:
(1) Appetite regulation centres in the brain stem and the hypothalamus play a central role in appetite regulation. There are two main pathways through which appetite related signals are transmitted between brain and periphery: appetite stimulating (orexogenic) pathway and central appetite suppressing (anorexogenic) pathway. Appetite stimulating pathway releases chemicals that encourage eating. The central appetite suppressing pathway, on the other hand, releases chemicals that inhibit eating

(2) Gastrointestinal tract: GI hormones (such as peptide YY and Insulin) can influence appetite

(3) Adipose tissue hormones: Adipose tissues (or body fat’s main role is to store fat as a form of energy) can secrete hormones (eg adipokines) that can influence appetite.

(4) Others: serotonin and cannabinoids can have an effect on appetite

External factors:
(1) Emotional and psychological factors: factors such as depression, stress, guilt and low self-esteem usually stimulate, but sometimes inhibit appetite. Factors such as cultural attitudes and peer influence can be important, too.

(2) Environmental factors: factors such as the taste, texture and presentation of food could affect appetite

(4) Drugs: Some drug act on central appetite centre. Appetite suppressant agents either stimulate brain catecholamic pathways (e.g. amphetamine can reduce signal to start eating), or effecting serotonin pathways (e.g. sibutramine which enhances the signals to stop eating). Some drugs (e.g. corticosteroids and tricyclic antidepressants) increase appetite.
Some drugs (eg metformine, levodopa, digoxin) can reduce appetite as a side effect of their main action. A large number of drugs can cause adverse GI side effects that can cause poor appetite.

Loss of appetite
Generally, appetite links to the amount of energy that body needs. It increases, for example during puberty and decreases in old age. Under-nutrition and weight loss are the risks of poor appetite.

Poor appetite could be due to many factors:
- Mental and emotional issues (e.g. depression, tiredness)
- Pain, minor ailments (e.g. cold), or some diseases (e.g. cancer, gastrointestinal conditions such as Crohn’s disease)
- Some medicines, drug and alcohol misuse
- Unappealing food (e.g. culturally inappropriate)
- It may also be signs and symptoms of eating disorders

Management of poor appetite usually depends on the underlying cause; however, paying attention to some points may help.
- Reduce portion sizes and increase the frequency of meals
- If appropriate, use more high energy foods (e.g. cream, sugar) and when people feel hungry or at their best
- Limit liquid intake during meals as it can be filling
- Vary the colour and texture of foods to make it more appealing
- Consider using a multivitamin and mineral supplement.
- Liquid oral nutritional supplements (e.g. Ensure) may also be beneficial.

Children appetites vary and they may go through phases of dislike particular foods, but generally if they have a normal BMI and continue to grow, there is little to worry about. But in these cases there are some ways to help:
- Some children may like to eat small snacks rather than a proper meal.
- Healthy snacks between meals are acceptable.
- Their involvement with choosing what to eat or preparing it may help
- Not giving food too much attention

In cases highlighted below it is important that the patient is referred to:
- People who are acutely ill and have not eaten or unlikely to eat for more than five days
- People with a BMI < 18.5 kg/m2
- People with unintended weight loss (more than 10 per cent of body weight in three to six months)
- People with a BMI or 18.5-20 and unintended weight loss of 5-10 percent of body weight over three to six months.
- Infant and children who are failing to eat and failing to grow appropriately

Extracted from:
Mason P. (2008). Dealing with loss of appetite. The Pharmacy Journal, 281, pp: 395-398.


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