For many underweight athletes, the struggle to gain weight is a constant frustration, equal to that of overweight people who are trying to lose weight. "I’m always eating. I spend too much money buying food. I wish I could just eat normally and look normal. I hate my spindly legs..."

Clearly, genetics plays a powerful role in a person’s physique. But so does "the fidget factor." Never sitting still and constantly moving around even when seated - burns calories (possibly an additional 700+ calories per day, equivalent to one or two meals. Mellow out and try some of the following weight gain tips.

Weight gain tips. Theoretically, you have to eat 500 to 1,000 calories per day to gain one to two pounds per week. Without question some people do gain weight more easily than others. Controlled weight gain studies have shown 20 lbs differences in subjects who were overfed the same amount of calories for the same time period. Why the difference? Maybe its fidgeting and perhaps its genetics. Keeping those factors in mind, here are five important rules to help with your quest for bulk.

1. Eat Consistently- Every day , have three hearty meals plus one to three additional snacks. Do NOT skip meals. You miss out on important calories that you need to accomplish your goals.

2. Eat larger then normal portions. Instead of having one sandwich for lunch, have two. Eat three potatoes at dinner, instead of only two. Have a taller glass of milk, bigger bowl of cereal, larger piece of fruit.

3. Select higher calories foods. Read food labels to determine which foods have more calories than an equally enjoyable counterpart. For example, cran-apple juice has more calories than does orange juice (170 vs. 110/8 ounces); granola has more calories than Cheerios (700 vs 100/cup); corn more than green beans (140 vs 40/cup).

4. Drink lots of juice and milk. Beverages are a simple way to increase your caloric intake. Instead of drinking water, quench your thirst with calorie containing fluids. One athlete gained 13 pounds in 3 months simply by adding six glasses of cranberry juice(1,000 calories) to his standard diet.

5. Do strengthening exercises (weight lifting, push-ups etc.) to stimulate muscular development so that you bulk up instead of fatten up. Some underweight people are afraid exercise will result in weight loss rather than weight gain. Remember, exercise tends to stimulate the appetite; you’ll want to eat more. Exercise also increases thirst; you’ll easily be able to drink extra juices.

Many athletes today are taking Creatine to gain weight. Creatine is a natural compound found primarily in meats. It is needed for immediate energy during short, intense exercise such as sprinting. If you are tempted to try creatine, I first recommended you pay attention to the above Weight Gain Tips. That is, you need to consistently eat more calories, drink more juices, and do strength training. No magic pill is going to replace these key steps.

Nancy Clark, MS, RD is nutrition counselor at SportsMedicine Associates in Brookline MA (617-739-2003). Her new Sports Nutrition Guidebook,Third Edition (2003; $24) and her Food Guide for Marathoners (2002; $20) are available via www.nancyclarkrd.com or by sending a check to Sports Nutrition Services, 830 Boylston St. #205, Brookline MA 02467.