Diet is a 4-letter word ... but it basically boils down to mean "what you eat" on a regular basis. It can be a good diet (balanced) or a bad diet (heavy in saturated fats, carbs, sugar, salt, and low in vitamins, antioxidents, minerals, etc.) it can be high calorie or low calorie, it can be deficient in certain areas, it can be good for you, or it can be unhealthy ... but your diet is what you eat. You can't go "on a diet" - you are already on one. But, you can make adjustments to your diet to make it healthier.
The best thing you can do is eat a balanced diet, decrease your daily caloric intake, and increase your daily exercise level. One pound = 3,500 Calories - for every 3,500 calories more than your body needs you gain a pound, for every 3,500 calories burned over what you consume, you lose a pound.
Rapid weight loss diet plans only work for a while before your body's metabolism changes - and the weight loss stops. When that happns, and you change your diet, you can put the weight you lost right back on and then some because you body is anticipating the next "period of famine". A slow, steady weight loss is sustainable ... raipd weight loss is not.
A couple of things to consider:
1. If you eat a balanced diet and decrease your calories by just 500 calories a day, and walk briskly for about 30-minutes after supper - you'll probably drop a pound a week. Jogging doesn't burn any more calories than walking - it just burns them quicker - but you have to be in shape to jog. Swimming is probably the best exercise for burning calories, followed by riding a bicycle without gears - the old "one speed" bikes most of use grew up with before the 3-speed and 10-speed became so popular. If you haven't been exercising for a while you have to work up to it ... NO ONE SHOULD EVER START AN EXERCISE PROGRAM WITHOUT TALKING TO YOUR DOCTOR FIRST!!!!! And, I can't emphasize that enough!!! You may have other health issues that would limit or moderate your exercise regimen (you may need to get in shape walking before you can start bike riding, for just one example).
2. DON'T go jumping on the scales every morning!!! You will not see any difference, and it will only discourage you. Weight once a week on the same day, in the morning after you empty your bladder, without clothes, and before eating or drinking anything. Women, especially, go through cycles of water retention ... men do too but to a lesser degree. What you are looking for is "trend" over several weeks/months - not just this week vs the previous week.