It's not easy to lose weight if it was, then there would be little demand for these various diet regimens.
GM diet was a diet plan developed by General Motors for their staff and then made popular. Initially, it was a non-vegetarian diet plan, now they have a vegetarian plan too. You or anyone can get one over the internet, so I won't waste time is typing it once more.
Initially, there may be a weight gain and once you finish the diet plan, if you go back to your old habits, then you will start gaining weight back again. Avoiding alcohol during this regimen is advisable.
Diet alone will not be useful. You also need to have a gradual increase in exercising also I I don't' know your age, weight and exercise tolerance levels). This can include jogging, treadmill, yoga or swimming. A lot of people start running a lot to exercise and lose weight, if you overdo it, you'll hurt your knees.
Avoid the foodstuffs rich in sugar and calories ( sweets, dairy products, junk food and preserved/ready made food ( ready-made parotas etc). Please watch out for liquid calories, many people on a liquid diet drink pre-packaged juices, add sugar or eat too many ripened bananas or mangoes (1 medium sized mango can have up to 150 calories).
The best practical approach is a combination of diet and exercise and remembering to keep realistic targets and once weight loss is achieved, we need to maintain it.