When you’re trying to gain weight, the key is to take in more calories (energy) than you’re burning off. But how you do this matters, and some methods are healthier than others. All food provides energy, but some foods are much more “energy-dense” than others. This means they pack a lot of energy into a smaller amount.

For example, half a cup of walnuts has around 400 calories—this is energy-dense! On the other hand, you’d need about 16 cups of broccoli to get the same 400 calories, and while broccoli is healthy, it’s not very energy-dense. If you’re looking to gain weight, focus on foods that are high in healthy fats like nuts, seeds, peanut butter, salmon, avocados, and olive oil.

A good strategy is making smoothies with whole milk yogurt, peanut butter, and fruit, or adding avocado to your eggs and olive oil to your veggies. These will give you more calories without needing to eat huge portions.

It’s also important to be cautious with “pre-workout shakes.” A lot of these products have added ingredients like caffeine, creatine, and taurine, which are meant to boost performance during exercise. But here’s the catch: most of these supplements aren’t regulated (which means they are not tested), so they might contain stuff that isn’t safe and might have harmful ingredients.

The best way to gain weight safely is to stick with real food and drinks—things where you know all the ingredients.