Beautiful women fixate over their faces. For buff men, it’s their bodies. What do underweight men fixate on? Their physique, of course.

Doctors say the safest way to lose weight is diet and exercise. It also turns out the safest way to gain weight is also diet and exercise. But it’s best if you consult with a doctor so you gain weight safely and in all the right places.

Chomping down willy-nilly on junk food, gulping down sugary beverages and packing on carbs is a recipe for heart disease and diabetes. You’ll gain weight but the weight you gain will be fat and not muscle.

A safe place to start is by determining if you’re really underweight. Use a Body Mass Index (BMI) calculator (there’s a lot of them online). If your BMI is less than 18.5, you’re underweight. Your doctor also can help determine if you’re underweight based on your height, weight, what you eat and your activity level.

Your doctor might place you on a weight gain program if you’re underweight. Healthy weight gain requires a balanced approach, just like a weight loss program.

The doctors at the Mayo Clinic recommend the following ways to safely gain weight the healthy way.

Eat more frequently. When you're underweight, you may feel full faster. Eat five to six smaller meals during the day rather than two or three large meals.

Choose nutrient-rich foods. Have an overall healthy diet. Choose whole-grain breads, pastas and cereals; fruits and vegetables; dairy products; lean protein sources and nuts and seeds.

Try smoothies and shakes. Drink smoothies or healthy shakes made with milk and fresh or frozen fruit. In some cases, a liquid meal replacement might be recommended. Stay away from diet soda, coffee and other drinks with few calories and little nutritional value.

Watch when you drink. Sip higher calorie beverages along with a meal or snack. For others, drinking 30 minutes after a meal and not during it may work.

Being underweight comes with its own set of risk factors, including injuries and falls, suicide from mental illness, and alcoholism and cirrhotic liver disease. DFID - UK Department for International Development, CC BY 2.0

Make every bite count. Have a bedtime snack such as a peanut butter and jelly sandwich, or a sandwich with sliced vegetables, and lean meat or cheese. Snack on nuts, peanut butter, cheese, dried fruits and avocados.

Have an occasional treat. Even when you're underweight, be mindful of excess sugar and fat. Most treats should be healthy and provide nutrients in addition to calories. Bran muffins, yogurt and granola bars are good choices.

And, yes, exercise. Exercise, especially strength training, can help you gain weight by building your muscles. Exercise also stimulates your appetite.