Intentional exposure to tapeworms is one of the oldest forms of extreme dieting known, but using a tapeworm for weight loss is a dangerous thing to do. Some varieties of tapeworm can directly harm their human hosts as they spread out beyond the intestinal tract. In all cases, using a tapeworm for weight loss places the dieter at serious risk of malnutrition. As with all crash diets, the rapid weight loss resulting from tapeworm infection is apt to prove temporary once the infection is cleared up through treatment.
Tapeworms normally live in the digestive tracts of large herbivores, typically cattle and pigs. Humans are often exposed to tapeworms when poor sanitation allows the eggs produced by the parasite to survive and be ingested, but people long ago realized that tapeworms could also be introduced into the body intentionally as an extreme form of dieting. Tapeworms alter the functioning of the human digestive tract, decreasing its efficiency, which leaves food for the tapeworms to digest and reduces the amount of energy and nutrition that the human host can extract.
A tapeworm infection poses only a few direct threats to the body. Both cow and pig tapeworms can cause damage to a human host, although direct damage from cow tapeworms is rare and normally comes only in the form of intestinal blockage. Pig tapeworms can infect other parts of the body and cause damage to various organs and systems.
Using a tapeworm for weight loss exposes a human host to many indirect health risks. Tapeworms so drastically decrease the body's ability to process food that a host with a normal diet is likely to suffer from malnutrition as the body becomes unable to absorb sufficient vitamins and minerals. The very fact that using a tapeworm for weight loss prevents the body from absorbing many calories can also cause problems, as the human body alters its metabolic processes in times of food crisis. In this altered metabolic state, the body begins burning muscle for energy, which reduces the amount of energy that it makes available for normal activity, leading to listlessness and a very low energy level.
As with any extreme weight loss measure, using a tape worm for weight loss is likely to cause the body to overreact when the diet ends. This response is, in part, psychological. Dieters return to old eating habits after a diet's end. The process can be especially pronounced in people who never actually changed their eating habits as part of a diet. This boomerang effect can have a physiological aspect as well since using a tapeworm for weight loss causes the body to react as if it were starving, which leads to a greater accumulation of stored energy when the tapeworm diet is concluded.