Ppeople who are most successful in preventing weight gain, and dieters who lose weight and keep the pounds off, have made major changes in their in diet and exercise routines. Big behavioral changes do stave off weight gain. Small daily changes, say using the stairs, are enough to prevent incremental weight gain that can lead to obesity. Much larger life-style changes — say exercising 60 to 90 minutes a day — are needed to prevent weight regain.