There are always lot of issues with fad diets, I wouldn't recommend them generally, but some are better than others. Here is some information on them: http://www.everydiet.org/fad_diets.htm
Some of the side effects of a sugar heavy diet is obesity and diabetes.
Optifast is a quick weight loss program that works for many people, but there are some side effects that are important to note. Some users regain their weight in a short amount of time because of the low calorie diet. Once the diet phase is over, many dieters gain the weight back because they begin to binge on unhealthy foods. The formation of gallstones is another risk of following the Optifast liquid diet. Before beginning this program, dieters should speak with their doctor about medications to prevent the development of gallstones. Mild side effects of a liquid diet can occur such as fatigue, nausea, muscle cramping constipation and diarrhea.
The HCG diet does not have any negative side effects. The only problem is that it can be quite difficult to maintain.
Ellen Coleman, a registered dietician and author, said the diet may have serious side effects for some people.
Some common side effects of the HCG diet include insomnia and high blood pressure. Consult your doctor about it.
The most significant side effects of an elimination diet are nutritional disorders resulting from a prolonged, highly restrictive diet, and the risk of a serious reaction as suspect foods are re-introduced to the diet.
The side effects are going to be very similar to that of starvation. The primary effects are going to be headache and dizziness.
The HCG diet is a popular weight loss program that helps users lose weight quickly. With any new diet, there comes benefits and side effects. The HCG has both. The main benefit is rapid weight loss. Does that outweigh the risk of side effects? The most common side effects of the HCG diet include light-headedness, irritability, fatigue, and headaches. These are due to the low calorie diet and your body having to use stored fat as energy. Before starting any diet, consider the side effects and how the HCG diet may effect your body.
There are no serious side effects. The main problem is that it has low variety and is difficult to maintain.
Diet/exercise.
Practitioners of the Wigmore diet warn people to expect certain side effects from detoxification, which is considered a key principle in the Living Foods lifestyle.
Diet pills can affect people differently and have side effects that include headaches, high blood pressure, diarrhea, and nervousness. The worst side effects are increased heart rate, heart attacks, and death in some cases.