I will admit that my weight has been a struggle for much of my life. I was a slightly chubby kid, and being kind of shy and awkward, this only made things worse while I was growing up (at least that's how I saw it). Although I lost weight when I hit my growth spurt, by the time I was in college, my weight had started to creep back up (hitting nearly 200 pounds my senior year). During my adult life, my weight has ranged from 165 to about 190 pounds (with the exception of my senior year of college), and I would say that my healthy weight range is 170-175. Since I tend to become consumed by whatever activity I am focused on, it is easy for me to get wrapped up in school or work, and to not make time to eat healthy meals. Over time, this usually results in my gradually gaining weight when I am not actively focused on keeping myself healthy.
In my attempts to slim down, I have tried a pretty good number of the diets out there, including everything from intense exercise to counting nutrients to low carb to "tricking" my brain by drinking flavorless oils. I even tried eating slowly for a while (this actually worked pretty well while I kept it up). Overall, I have lost weight and eventually gained it back at least three or four times in the past ten years. By following the Four Hour Body Diet (from the book of the same name by Tim Ferriss) for the past few months, I managed to get my weight back down to where I like it, but more importantly, I have done a pretty careful analysis of what weight loss tactics do and don't work for me.
So what are the most important things that I have learned?
First of all, it's important to eat at least three meals, particularly breakfast and lunch (dinner is occasionally skippable). I have found that when I skip breakfast or lunch, I go into the next meal famished, which typically results in my eating far more calories than I would have otherwise. If I eat a healthy breakfast and lunch, I can often have a small dinner and be satisfied. It is also important to eat your meals at fairly regular times. Make sure you eat breakfast within an hour of waking up, and try to eat lunch no more than four hours after eating breakfast (this is the old "eat before you are hungry" credo). I don't find that eating more than three meals does much to reduce hunger. However, skipping snacks is definitely helpful for me.
Also, exercise alone is not a good way to lose weight. Your body has a finely tuned equilibrium, and it resists changes to that equilibrium. If you up your exercise level significantly without changing your diet, you will become uncontrollably hungry, and will consume enough calories to make up for the additional burn. You may gain muscle and lose a bit off your waistline, but the changes will likely be minor. There has been a bunch of recent scientific research that corroborates this.
Despite the advice of some dieting experts, a calorie is not a calorie. I do know people who have lost weight with strict calorie-restricted diets, but these haven't worked well for me. I just get too hungry when I calorie restrict, and find that this actually causes my body to go into starvation mode. Eventually I crack, and I gain the weight back from the resulting binge. One guy that I knew in San Francisco lost over 100 pounds through a calorie-restricted diet, and seems to have kept it off quite well. So I'm not saying that counting calories can't work, just that it hasn't worked very well for me.
Trick Your Brain to Lose Weight
What I have found is that you need to find a way to trick your brain into letting you lose weight. Your brain is trying to keep your weight constant, so willpower alone probably won't be enough for the long-term (scientific research has actually shown that you "use up" your willpower over time, so willpower probably isn't enough for any sort of long-term effort). There are a number of ways to "trick" your brain. Some people believe that you can alter your "set point" by consuming flavorless calories (read The Shangri La Diet for more information). I tried this diet for a couple of weeks, and found that it didn't work very well. However, you may experience very different results, so it might be worth a try.
I have found the most effective path to losing weight (at least for me) is to eliminate high-density carbs and sugar, and to make sure I get enough healthy protein and vegetables. I have a terrible sweet tooth, but if I can eliminate sugar from my diet, the cravings quickly disappear. If you are willing to count grams of macronutrients (protein, carbs, fat), The Zone Diet works pretty well. If not, you might want to try the Paleo or Four Hour Body Diet (which essentially involve a bit of estimation and a number of fairly simple rules). I personally have found that the sugar content in fruit makes me hungry, so I need to pretty much eliminate it (although one piece a day probably won't kill you).
I am also going to put in a plug for Weight Watchers. It is not my cup of tea, but my mother (who has kept herself thin for her entire adult life with a careful combination of diet and exercise) is a strong proponent. It combines a systematic approach to food selection with a live support group, and for some people this works great. I find that I don't really need the support group, and counting food units isn't really sustainable for me (I need to be able to follow simple rules).
Eat Healthy Foods
I believe that whatever diet you choose, you need to make sure that you are eating healthfully. Eating "healthy foods" isn't enough - you can stay fat if you eat healthy foods in the wrong ratios. However, there are definitely diets that will cause you to lose weight but aren't healthy to your heart or body. The Atkins diet will cause you to lose weight, but some adherents manage to do this while still eating garbage (eggs covered with cheese and surrounded by slabs of bacon come to mind). My mother needed an emergency appendectomy while on the Atkins Diet, and from what I have read, this is more common than you would expect. There is some research that indicates a link between The Atkins diet and colon cancer. Dr. Atkins himself suffered multiple heart attacks while eating his own diet, and while they didn't kill him, I'm guessing they were related to his eating style. A lot of this can be avoiding by limiting saturated fats, and by eating plenty of green vegetables (which can be done even on an Atkins-related diet).
Make Sure to "Cheat"
Also, it is important to cheat every once in a while. If you always adhere to a strict diet with no exceptions, you will eventually slip off the bandwagon. I have found that a weekly cheat day actually makes me want to eat healthfully for the rest of the week (I get lethargic and woozy-headed about mid-day on my cheat day). Then I'm ready to go until some time near the end of the week, at which point I'm only a day or two from my next cheat day. Also, instead of a single cheat day where you go crazy, you could eat one "cheat item" every day (for example, you could have a few fries or a small amount of dessert with your dinner). My friend who lost weight by calorie-restricting didn't include alcohol calories in his tally, although I believe that he did put some limits on his alcohol intake.
Finally, I do believe that it is important to combine diet with some form of exercise. You can go to the gym, or if that isn't your cup of tea, play a sport. If you live in a walking city, you can do this by skipping the subway every once in a while. Sure it may take half an hour to walk to work, but if you do this just a few times every week, you are pretty close to your exercise requirements. I recently bought a FitBit, and use it to track my daily steps.
Also, I haven't really talked about stress and happiness, but I have found that they correlate highly with my weight. During the periods that I have been the least happy and the most stressed, my weight has been the highest (I will admit to being something of a stress eater). Likewise, when I am happy and relaxed, I tend to lose weight (either actively or passively). For some reason, every time I go on a 10-day meditation retreat, I lose at least 5 pounds I'm not sure whether this is caused by the meditation or the healthy, vegetarian diet - probably a combination of the two. In fact, whenever I notice my weight increasing, I start to ask myself whether it is being caused by stress, and typically the answer is yes.
Overall, to keep your weight down, you need to find a sustainable system that works for you. There are a lot of diets and systems out there, and it is important to If you are a vegetarian, going to a meat heavy diet may not be the best solution (but there are plenty of plant-based diets that are supposedly healthy). Likewise, something that requires you to count grams of protein and carbohydrates may be hard if you don't like to cook.