By Shiyi Liang
Anorexia is an eating disorder where one loses appetite. Eating disorders affect people’s daily life and can lead to mortality and affects people from all age groups. Various physiological and pathophysiological conditions, as well as psychological problems may lead to anorexia (Yoshimura, Uezono and Ueta, 2015). Anorexia may cause multiple health risks, including low blood sugar, anaemia and more serious issues like organ failure and cardiac complications (Health Risks of Anorexia, 2021). This review will include several forms of anorexia in different groups of people.
For long term regulation of feeding behaviour, the hypothalamus plays an important role. Different neurons in the hypothalamus receive signals from organs and cells, they detect levels of hormones and nutrients to stimulate or suppress feeding. One example is that adipocytes secrete hormone leptin, encoded by the ob gene, to communicate with the brain and decrease appetite. The lack of leptin drives hunger and feeding, and in animals, it motivates them to eat abnormally (Bear, Connors and Paradiso, n.d.). Different neuropeptides found in the brain also facilitate feeding behaviour control.
Anorexia can be found in cancer patients, and it is one of the troublesome problems they experience which affects their nutrient intake and quality of life. Some patients with cancer may develop taste and smell changes due to cancer itself after anticancer treatment (Laviano, Koverech and Seelaender, 2017). Inflammatory peptides released from the tumours are demonstrated to affect appetite. As an example, Interleukin –1 leads to anorexia by enhancing the action of serotonin and stimulate corticotrophin-releasing factor in the hypothalamus. The increased level of lactate due to increased lactic dehydrogenase activity is a potential reason. Animal studies show similar results that lactate reduces or inhibits food intake (Ezeoke and Morley, 2015). Evidence supports that cancer anorexia is not simply a reduction of food intake but has a more complicated mechanism behind it (Laviano, Koverech and Seelaender, 2017).
Recently strategies are trying to relieve the suffering of patients. Drugs for cancer-related anorexia were developed like Anamorelin, Megestrol acetate (MA) and Thalidomide. The first two drugs showed significant improvement in patient body weight compared with placebo and MA also increased appetite (Zhang, Shen, Jin and Qiang, 2018). Acupuncture and Chinese herbal medicine were found to have effects but were not statistically significant.
Reduced appetite in elderly people can be described as the anorexia of ageing and has a variety of causes. Drugs for different diseases, such as Amiodarone, Psyllium and Penicillamine, may cause anorexia in older people. Taste and olfaction impairment among the elderly make meals less enjoyable because these sensations are important for the sensation of hunger. The levels of several hormones involved in feeding behaviour including CCK, PYY, GLP-1, and insulin, also control changes in feeding as people get older (Di Francesco et al., 2007). Caroline G Maclntosh et al. hypothesize that older people have a greater release of these hormones. They recruited 8 older men and 7 younger men, all healthy, with their BMI and mean energy intake recorded before the first day of the experiment. The subjects were intraduodenally infused with glucose or triacylglycerol emulsion at the start of the experiment and continued for 120 minutes. Venous blood was collected before and between certain periods to measure plasma cholecystokinin (CCK), glucagon-like peptide 1 (GLP-1), and peptide YY （PYY）using appropriate methods. They found that the older subjects have higher baseline fasting plasma CCK concentrations than the younger subjects and the difference remains throughout the infusion. For GLP-1 and PYY, however, the result did not show significant differences before and after intraduodenal nutrient infusions (MacIntosh et al., 1999). Another study suggested ageing affects leptin and ghrelin level in the body and may alter hunger. Their experiment provided meals to both old and young subjects and measured the feeling of hunger and satiety using a visual analogue scale. Blood samples were taken before and after meal to evaluate the level of leptin and ghrelin. Younger subjects have significantly lower serum leptin concentrations than the elderly subjects throughout the whole period, but no difference in ghrelin levels. However, they found no correlation between these two hormones and the sensation of hunger and satiety. They still hypothesize that leptin cooperates with CCK (Di Francesco et al., 2006).
A statistic in 2012 showed that almost 1-2% of adolescents in the US suffer from anorexia and suggested that teen anorexia happens because teenagers have unrealistic expectations of their body weight, and they cannot accept themselves being overweight (Teen Anorexia Statistics (Newport Academy, 2021). These features can be regarded as part of teen anorexia nervosa, where patients restrict energy intake and have a deep fear of gaining weight. For teenagers, this disorder is caused by a myriad of reasons. Ranging from psychological factors to cultural factors and can be influenced by social media, believing that thinner is better, or they experience depression, anxiety and/or perfectionism (Peterson and Fuller, 2019). The main treatments for this are divided into inpatient and outpatient. For inpatient treatment, the patient stays in the unit and unnecessary calorie expenditure is forbidden. A series of diet, activities and guidelines are set in meetings with the patient, family members, psychiatrist, nutritionist, and relevant workers. For outpatient treatment, the patient stays at home and the outpatient therapist supports them. The therapist would comfort helpless parents and supervise the treatment plan (Weaver, Sit and Liebman, 2012).
Anorexia has a bad influence on people’s quality of life and the patients are sometimes hard to come out from the shadow. The treatment for anorexia is not significantly effective so more research needs to be done to design treatments for each population or a treatment that can be commonly used.
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