Everywhere I go I hear someone talking about this diet or that diet. There is scientific evidence to support this and testimonials to support that. All of these people write a book saying their system is the best and the really smart ones have a line of food or at least cook books and cooking accessories. All of this is pretty dumb IMO.
We need to talk about 4 things differently: nutrition, calories, fitness and body fat.
Nutrition is pretty obvious. Things like whole grains, fruits, veggies and lean protein are good and sugar, fat and alcohol are not so good. Nutrition affects body fat/ weight. Eating junk makes you sluggish and lazy while healthier stuff will keep you full for longer and fuel your body. I have never seen someone down 4 cheese burgers and a plate of fries then go for a long run.
There are so many fad diets. Some make sense and others are just silly. People will often loose weight on any fad diet, at least for awhile. Part of the reason for this is that the change shocks their system. Also I believe the bigger issue is that these people, for the first time in awhile are in some way or another monitoring what they eat. Just about any sort of portion control is better than none!
I am a huge believer in calories in vs calories out. If you burn more calories than you take in you will lose weight. If you burn fewer than you are taking in you will gain weight. Too easy. I have never seen a person who genuinely followed that simple plan consistently and did not achieve results. The reason nobody talks about it is that it is simple and will not lead you to buying their book. Invariably diets that are successful are compatible with this theory. A person could get fat on a diet of vegetables, granted they might have to eat a 5 gallon bucket of them but it is possible. Conversely a person who ate reasonable amounts of all sorts of food could lose weight. It would be very difficult to convince me that any diet can defy the calories in vs calories out rule.
Exercise improves your overall physical condition. Of course going from obese to not obese will make it a lot easier to do everything diet alone will not make you fit. Walking, hiking, running, body control exercises and weight bearing movements will make you stronger, faster and able to endure more physical hardships.
Starting to exercise helps a lot but be ware that unless you are exercising a truly crazy amount (think Michael Phelps or Ultra Marathoners) you still have to pay attention to what you eat. As Jillian Michaels said recently on the TV "a slice of pizza is 500 calories which is an hour on the treadmill." Personally I have experienced and observed this to be true. It is easy to think "oh I am exercising a lot now so I can have a bit bigger dinner/ whatever" and depending on your goals it might be. A young guy who wants to put on 25lbs to go from JV to Varsity could couple his heavy strength training with a couple more small snacks and a second helping at dinner. That kids parents who are doing an exercise program of walking, hiking and calisthenics in order to improve their fitness and get to a healthy weight would not be advised to follow their meat head son's diet.
Body fat/ weight is an issue that holds many people back in terms of fitness. I am not going to get into it just being bad for you but well it is. Unless you are a world class athlete those 5-10 vanity pounds are not going to slow an average sized person down significantly or hurt them in body control exercises (push ups, pull ups, etc all) but a 30lbs spare tire sure will. I have known plenty of guys who were not exactly skinny and had a waistline which noted their liking of cheese burgers a bit but were in darn good shape. However it is hard to be fit when you are just plain fat. Hauling around unproductive mass makes it more difficult to move. Also that weight puts a lot of stress on knees and backs. A lot of (but certainly not all) bad knees and backs would go miraculously heal if their owners got to a healthy weight!
I find eating a healthy, reasonable amount of food and starting an exercise program work well together. Doing either in isolation doesn't seem to but they both sort of motivate me to do better with the other.
GET OFF OF THE COMPUTER AND GO FOR A WALK!!!