Whey protein provides all the essential amino acids and is easy to digest, although supplemental protein for toddlers usually isn't needed.

Vegans tend to be thinner than meat eaters, but a few tweaks to your diet can help you add extra pounds to your frame. While you can gain weight through food alone, a vegan weight-gain supplement serves as any easy source of calories if you fill up too quickly or have a hard time eating regularly.

Your lifestyle, certain medications and illness can squash your appetite, leading to possible unintentional weight loss that endangers your health. If you are too thin and have a body mass index of less than 18.5, this can compromise your immunity, energy, hormonal function and bone health.

Gaining weight can take as much effort as losing it. A caloric surplus, which involves consuming a greater number of calories than you burn, helps you put on pounds. No specific vitamin, regardless of its claims, will make you gain weight -- vitamins don't contain calories.

If you're lifting heavy and working out hard, you may be looking for ways to up your calorie intake to help build more mass. Weight-gain products such as Weight Gainer 1850 may help provide the calories you need. This high-calorie supplement may not be appropriate for everyone, however.

You need zinc for forming proteins and DNA and for proper immune function. Getting extra zinc in your diet isn't likely to cause weight gain if you are already getting the recommended amount, although some studies have shown beneficial effects on weight gain in people who are zinc deficient.

You need vitamin D to help absorb calcium and keep your bones healthy, but it also plays other roles in the body, including promoting immune function, cardiovascular health and limiting inflammation.

When you're working out but struggling to gain muscle, you might turn to supplements for help. Creatine is a dietary supplement used by athletes to improve performance and promote weight gain.

You might be the envy of your friends, but a high metabolism that makes it difficult to gain weight isn't always a gift, especially if you want to gain a few pounds. Weight-gain supplements might be a convenient way to add calories to get your weight up, but they might cause side effects in some people.

To put on pounds the healthy way, you'll need to increase your calorie intake and do some strength training. You may have tried a weight-gain supplement as an easy way to boost calories but then found the flavor to be lacking.

Weight gainers and muscle gainers are two names for products that offer the same thing -- extra calories from a mix of carbs, protein and fat to help you gain weight. These products are generally marketed to bodybuilders looking to add more muscle to their frame.

Magnesium is an essential mineral that plays a role in more than 300 functions in your body, many related to the way you metabolize energy. As a mineral, it has no calories and can't directly cause you to gain weight.