Because of nutritional yeast's high nutrient content, vegetarians will sometimes use it as a supplement. In vegan recipes, nutritional yeast also makes a good substitute for Parmesan cheese. But nutritional yeast isn't that high in calories, so it isn't likely to cause weight gain. If you're trying to gain weight, you're better off choosing other foods -- including higher-calorie dishes that contain nutritional yeast as an ingredient. Check with your doctor before adding a significant amount of nutritional yeast to your diet, as it contains purines, which may bring on symptoms of gout for those who suffer from this condition.
Calories in Various Kinds of Yeast
The number of calories in yeast depends on the type of yeast. Typically, nutritional yeast has the fewest calories of all the main types of yeast people consume, with about 15 to 20 calories per tablespoon, depending on the brand. This is somewhat fewer than the 23 calories per tablespoon found in regular baker's yeast and fewer than the 28 calories per tablespoon in brewer's yeast, which is also sometimes used as a supplement to provide B vitamins. It's also slightly fewer than the 21 calories per tablespoon found in Parmesan cheese.
You need to consume an extra 3,500 calories to gain a pound, so it would take quite a lot of nutritional yeast to cause weight gain. Since nutritional yeast typically isn't eaten in very large quantities, it isn't likely to cause weight gain. If you've added it to your diet and have gained weight, it is more likely that some other food you're eating is causing the weight gain.
Potential Health Benefits
While any extra calories will help with weight gain, filling your diet with nutrient-rich foods, like nutritional yeast, is the best approach. Nutritional yeast provides fiber, protein and B vitamins, including vitamin B-12, as it is frequently fortified with this vitamin. For example, one brand provides 9 grams of protein and 4 grams of fiber, as well as 150 percent of the recommended dietary allowance for vitamin B-12, in just a three-tablespoon serving. Typically, vitamin B-12 is found only in animal foods, making it a difficult nutrient for vegans to get in their diet, but it's essential for making red blood cells, as it keeps your nerve cells healthy and is essential for forming DNA. Getting enough protein in your diet will make it more likely you'll gain muscle instead of fat, and fiber is important for digestive health -- as it helps prevent constipation -- and may lower your risk for stroke and heart disease by reducing your cholesterol levels.
Use in a Balanced Diet
If you're using nutritional yeast as your main source of vitamin B-12, check the label to make sure you choose one that's fortified with B-12. You can sprinkle nutritional yeast on top of foods to give them a nutty, cheesy flavor. Use nutritional yeast on popcorn, cooked vegetables, scrambled eggs, pasta, salads or anywhere else you would usually use Parmesan cheese. While it isn't recommended to consume more than 1 to 2 tablespoons of brewer's yeast per day, you don't need to worry about using too much nutritional yeast, unless you're allergic to it, and then you should avoid it completely.
Other Foods for Weight Gain
If you're trying to gain weight, avoid sweets or highly processed junk foods, and choose foods that are high both in calories and in nutrients. Good choices include avocado, nuts, seeds, olive oil, whole grains and foods that contain lean protein. Adding a tasty topping, such as nutritional yeast, to foods that are relatively bland may make it easier for you to eat more and gain weight. It's also helpful to eat more often, rather than trying to eat larger meals. Consider drinking a smoothie or eating a handful of nuts with a piece of fruit, or serve whole-grain pitas with hummus for a snack between meals to increase your chances of gaining weight.