The problem with other diets has been multifaceted and usually falls into a few common categories.
Just Plain Wrong:
The number one reason why most diets fail is that they ignore science and ignore research. They just don’t work. You can’t lose weight eating a low fat diet. You can’t lose weight eating lots of whole grains. You can’t lose weight eating baked potatoes or sweet potatoes. You can’t lose wight exercising like crazy. It just doesn’t work! So the number one reason why most diets don’t work, is because they just don’t work. The science isn’t there.
Some diets require the dieter to do too many calculations, adding up points and calories, or weighing of food. Some people just can’t do that or think it’s too much work. They end up failing before they even begin. And the notion that reducing calories will cause weight loss is simply wrong. You will still be fat and gain even more weight. Research has shown that people on severely restricted calorie diets, even as low as 400/day, store more fat, have lower metabolism, and either maintain their current weight or gain weight. Your body goes into self preservation mode trying to store every calorie as fat and trying to spare every ounce of fat you have by causing you not to burn any calories. Your body will even start breaking down muscle and converting it to fat.
Sometimes diets fail because the dieter reaches their goal and thinks they are okay to return to previous eating habits. They end up putting the weigh back on. You breathe every day, you eat every day, you should be on a diet every day. Diets aren’t temporary. They are lifelong.
Another common reason is that the dieter can’t stay on that diet. If you hate protein, you should not be on a high protein diet. Or find protein that you like. You shouldn’t choose a diet that is unpalatable. You should choose one that incorporates foods that you like. Now this may be difficult to do, but you can make it work if you have to. If you hate protein, you might be able to tolerate protein shakes or other forms.
Fast Fad Diet:
One common reason that a diet fails, is because it is a fad diet. Some diets claim that if you drink their juice or shakes for a month (or a few days) that you will lose a ton of weight. Or that if you take certain herbs for a short period of time, that you will lose weight. Any diet that makes claims of quick fast weight loss is a fad diet. Do not try any of these fad diets. A lot of times these are scams and or companies trying to turn a quick profit and go out of business. Or worst yet, sell you dangerous substances which can cause heart defects and heart failure.