For those suddenly diagnosed with health issues due to weight gain, there is hope that can recover. Some conditions will only require them to make small changes over time, so avoiding extreme measures will be possible. The idea their physician wants them to have is that crash diet and exercise programs will only lead them further down the bad path they have taken, so depending upon them is like counting on leaky brakes going down a steep hill. They might find they are out of control at any time, so getting the issue fixed before traveling is for the best.
Diets that promise a person will lose a great deal of weight in a short time are often those that cut out entire food groups, and this is a bad idea for those who want to be happy with their health. They will often see immediate results, but remaining on this type of diet can have its own unhealthy consequences. They might suddenly find they are unable to resist cheating, and they can gain back more weight than they have lose, or they might find their body beginning to shut down.
Fatigue is often a symptom of an extreme diet change, and avoiding it is a good way to get rid of the weight while giving the body time to adjust. Making small changes that cut out excess or empty calories in a balanced manner will do more to sustain a person until they reach a reasonable goal. Those who know there are no quick fixes for weight that has been added over the years are better off than the people craving a fast weight loss so they can go back to their original bad habits.
It takes time to make a good diet work, and the person trying to lose weight should occasionally reward their efforts when they reach their goals. There should be a few intermediate steps between the beginning and the end of their program so they can look forward to those rewards as a motivation to keep going.