A comment such as, "You've gained weight!" could be the best thing that ever happened to you. A study done at the University of Colorado and reported in the American Journal of Clinical Nutrition indicates that for a majority of weight-loss maintainers success was usually preceded by a "trigger event or critical incident." These events could be medical (a doctor tells you to lose weight), emotional (someone makes a derogatory comment about your weight) or a life event (a divorce).

So, what are some of the more common trigger events, and do they work to sustain weight-loss?

MEDICAL DIAGNOSIS

Examples: Cardiovascular disease, diabetes, hypertension, sleep apnea, low-back pain.

How it works: You're willing to change your ingrained behaviors because you want to avoid the health consequences. You want to live longer, and with a high quality of life.

Will it last? Probably. "Hearing that you have high blood pressure or that a close friend has just been diagnosed with diabetes can be an extremely powerful, teachable moment for making changes in your eating and exercise behaviors," says Amy Gorin, assistant professor of psychiatry at Brown Medical School and the Miriam Hospital.

Make it last: Don't think that a "death threat" will carry you to the gym every morning. This is a strong motivator, but you still need to come up with a strategy that will last forever.

SPECIAL EVENT OR LIFE CHANGE

Examples: A wedding or divorce, a school reunion, birthday, college graduation or a new job all can trigger a determination to lose weight.

How it works: You're highly motivated, with a crystal-clear goal — you'll do almost anything to reach your objective. But this often means using behaviors that are probably only temporary.

Will it last? Once the goal for a special event is achieved, it can be difficult to maintain motivation, says Kristi J. Ferguson, an associate professor at the University of Iowa Carver College of Medicine.

Make it last: Use the special event as a kicking-off point, but plan in advance what you're going to use as a motivator beyond the special event to maintain your weight-loss.

VANITY

Examples: A terrible photo that makes you look heavier than ever; running into an old friend who comments on your weight; not being able to fit into your "fat" pants.

How it works: Vanity can serve as a negative motivator, meaning that you will do whatever you can to move away from the negative stimulus. Or, the desire to be able to fit into different clothes can act as a positive motivator.

Will it last? Probably. But the desire to be attractive must be more important than any distraction. It must be one of the more central themes in your life.

Make it last: It's not a good idea to use that terrible photo just to get you pumped up so that you'll have more willpower to resist tempting foods. Instead, use it as motivation to plan how you will not only lose weight but keep it off permanently.

DIET PUSHER

Examples: A spouse, family member or friend pushes you to lose.

How it works: You're pestered to lose weight (and/or stop smoking or drinking), and you give it your best shot to get the nudger off your back.

Will it last? Having the diet police looking over your shoulder every minute can create resentment. If you lose weight for another person, you'll probably start stuffing doughnuts down your throat the first time you get angry at that person.

Make it last: Sit down with your family and have a rational discussion. Make it clear that you know you have to lose weight, but you don't want them watching your food choices or telling you what you should or shouldn't eat — that will only annoy you and make it less likely that you'll do what you know you should be doing. Explain that they don't have to modify their own lives, but they should at least support your objective.

COMPETITION OR SUCCESS

Examples: Friends, family or co-workers decide to lose weight; a walking or weight-loss contest among your colleagues at work; seeing people you know succeeding at losing weight and keeping it off.

How it works: They make it look "doable." In terms of a contest, you're just plain competitive and want to win.

Will it last? Probably. There is strong motivation in seeing others succeed at losing weight, and competitions are also helpful.

Make it last: Seeing others succeed can be a great start, but make sure you use their example as the inspiration to create a plan of your own. Don't just copy their diet or method — find out what diet works for you.

EMOTIONAL

Examples: Overhearing a co-worker call you a fat slob; being charged for two seats on an airplane.

How it works: You're embarrassed and use revenge as a motivator.

Will it last? Very possibly. Humiliation is long-lasting, and if you channel your energies into eating better and increasing physical activity, you will likely lose weight and keep it off.

Make it last: Use this strong inspiration wisely. Don't go to extremes. Set yourself up with eating and activity behaviors that are realistic for your current situation, especially in the beginning, while the memory of the humiliation is still fresh in your mind.

Charles Stuart Platkin is a nutrition and public-health advocate, and author of "Breaking the FAT Pattern" (Plume, 2006). Sign up for the free Diet Detective newsletter at www.dietdetective.com.