Helminths, appetite and body weight
Helminths are clearly able to influence appetite.
Infectious agents, including parasitic worms, seem to be capable of overwhelming the mechanisms that regulate appetite and body weight.
* Appetite and parasite
The following study suggests a possible manipulation of appetite regulation in infected mice by larvae of the helminth, Taenia taeniaformis.
* Leptin, a tool of parasites?
Larvae of the nematode, Nippostrongylus brasiliensis, affected the degree of anorexia in rats at 8 days post infection, in a dose-dependent manner.
* Anorexia induced by the parasitic nematode, Nippostrongylus brasiliensis: effects on NPY and CRF gene expression in the rat hypothalamus
Helminths can also affect body weight and mitigate obesity.
Helminth infection or its derived molecules can mitigate obesity and Metabolic Syndromes (Mets) via induction of macrophage M2 polarization, inhibition of adipogenesis, promotion of fat browning, and improvement of glucose tolerance, insulin resistance and metabolic inflammation.
* Helminth and Host Crosstalk: New Insight Into Treatment of Obesity and Its Associated Metabolic Syndromes -- Full text | PDF
Helminths prevented weight gain in laboratory mice by boosting populations of bacteria that produce compounds which trigger increased energy consumption.
* Suppression of obesity by an intestinal helminth through interactions with intestinal microbiota -- PDF (Also reported by EurekAlert: Intestinal helminths boost fat burning: Japanese investigators show how)
Infection with the helminth, Trichuris muris, significantly reduced rates of weight gain in host mice.
* Feeding Immunity: Physiological and Behavioral Responses to Infection and Resource Limitation
Helminths suggested as safer, effective treatment for obesity and other metabolic disorders.
* Helminth infection protects against high fat diet-induced obesity via induction of alternatively activated macrophages
Helminth infections have been associated with hypophagia and weight reduction, as well as improvements in metabolic syndrome and type 2 diabetes.
* The interplay of type 2 immunity, helminth infection and the microbiota in regulating metabolism -- Full text | PDF
Therapeutic helminths and appetite
A number of people have reported a normalisation of appetite after commencing helminthic therapy.
One such self-treater reported an increase in appetite after she started taking HDC, and noticed the same change in her son after he also began using this species. 
Self-treaters using hookworms have reported similar results, including someone who became much more hungry between weeks 4 and 12 after inoculating with hookworms,  and several others have also reported an improvement in appetite, especially between days 39 and 51.
At 40 days post inoculation, another hookworm host found that she suddenly became able to eat all the food on her plate, after years of never quite managing to eat everything she put out for herself at mealtimes. At 47 days, someone with a history of food intolerance found herself responding unusually positively when she saw food on the television, and, at 51 days after a second dose of NA, yet another hookworm host began to experience strong hunger pangs verging on cramps in the early morning or after long gaps between meals. 
Below are more comments from hookworm users.
Some helminth hosts experience cravings for specific foods or food groups.
A brief period of reduced appetite sometimes follows the first inoculation.
Several people have found that the ability of helminths to normalise aberrant hunger/satiety responses has resulted in them eating less food.
Therapeutic helminths and body weight
Helminths appear generally to normalise body weight.
Some people gain weight.
And one individual experienced an increase in weight post inoculation with hookworms even though she appeared not to be consuming any additional food.
Others have lost weight after inoculating with helminths.
The use of non-therapeutic helminths for weight control
The beef tapeworm, Taenia saginata, has been used to reduce body weight in obese individuals, something that it does very efficiently. However, it does not meet the criteria for a therapeutic helminth (see Therapeutic helminths), which include causing no pathology in the host and posing no risk of infection to others. For more detail about T. saginata, see the following page.
The porcine (pig) tapeworm, Taenia solium, might also be effective as an aid to weight loss, but it is unsuitable for use by humans because it has a potential for mis-migration in our species. Once hatched, it travels through the bloodstream and can settle in the muscles, eyes or brain. Cysts in the muscles generally don't cause symptoms, but they can cause blurry vision if they lodge in the eyes and, in the brain, headaches, encephalitis, and seizures which can occur in up to 70 percent of infected patients.
- Helminth infection modulates number and function of adipose tissue Tregs in high fat diet-induced obesity
- The presence of (helminth) infection was able to prevent exacerbated weight gain in mice fed with high fat diet when compared to non-infected controls. In addition, infected animals displayed improved insulin sensitivity and decreased fat accumulation in the liver.