Fat has finally overcome its bad reputation. It has even become trendy to add it to food and drinks for health reasons—whether that’s putting butter in your coffee for its purported health and energy benefits benefits, or swapping that low-fat, low-calorie salad dressing for a drizzle of bacon grease. In reality, when does adding fat make sense, and when is it a bad idea?

Fats Have Different Properties

Unfortunately, although often good, none are magical.

There are devotees of coconut oil, olive oil, you name it. There is always an expert exhorting you to work more of it into every meal you can. But are any of these oils really special?

Different oils typically become trendy on the basis of their fatty acid content: if you heard it’s good to put flax oil on your food, that’s because it’s rich in a type of omega-3’s. As wonderful as that may be, we get more bio-available omega-3’s from fatty fish.

Any oil or any fatty food is going to include a mix of fatty acid types. For example, lard contains a lot of saturated fatty acids but also a lot of monounsaturated fatty acids.

Fats can be broken down into a few different types:

Saturated fatty acids were once demonized, but are now earning back some respect. These are a major component of animal fats and are found in butter, cream, lard, and bacon.

Medium-chain fatty acids, found in coconut oil and in “MCT oil” supplements, are metabolized a little differently than the other fatty acids and may have some mild fat-burning properties if you use them in place of other fats, although as with all things nutrition related it is not that simple and there are some caveats to that.

Monounsaturated (omega-9) fatty acids are considered heart-healthy “good” fats. Their best-known sources include olive oil and avocados.

Polyunsaturated fatty acids include the omega-3’s found in fish and fish oils and, in a less potent form, in some nuts and seeds, and omega-6’s, found in seed-based oils like corn and canola. Both are required in our diet for different reasons: omega-3’s are made into anti-inflammatory hormones, and omega-6’s are made into pro-inflammatory ones. Some conventional nutrition philosophies lump both together as “good” fats. Newer evidence emphasizes how important the ratio between the two is: most of us should get more omega-3 and less omega-6.

Trans fatty acids, at least the artificial, man-made, highly processed version found in cheap pastries and canned frostings, are pretty much universally agreed to be bad for you.

The innate problem with adding fats to food is that the “good” and “bad” designations tend to come from research that substitutes the fats for each other, rather than eating the same meal with or without fat. It becomes important and relevant to make sure that your meal could really use the extra fat; and then, if that proves to be the case, choose the fat that best meets your goals.

If you feel you have a need for more omega-3’s in your diet, and if you’re sitting down to a meal that is low in fat to begin with—say a salad, or some lean protein with vegetables—a drizzle of flaxseed oil would be a fine addition to that dish.

On the other hand, if the meal already has a reasonable amount of fat in it, adding more is just going to add calories without necessarily conveying any benefits. In that case, consider swapping out one type of fat for another that fits your goals better. This could look like using  a healthier, cleaner option like coconut rather than pro-inflammatory canola oil as you fry up the vegetables.

Fat Helps Vitamin Absorption

Adding fat to a meal can help you absorb some of the vitamins in it. Vitamins are small organic molecules that form a necessary part of your diet, and need to be ingested as they cannot be made by the body. If you eat a varied, healthy diet in reasonable amounts and take a few high-quality supplements, you probably get plenty of all the vitamins your body needs. If you were to eat super low-fat meals, though, that would interfere with your digestive system’s ability to get those vitamins out of your food and into your bloodstream.

If you tend to be the type of person who eats lots of salads and vegetable dishes (low fat or otherwise) and are concerned about your vitamin intake, you are probably a healthy eater who is not at risk for a vitamin deficiency. Just saying. But biochemically speaking, does adding fat to food help vitamin absorption? The answer is a resounding yes.

Vitamins A, D, E, and K are all fat-soluble, so you need at least a little fat in a meal to help absorb them. (This is not the case for Vitamin C or any of the B vitamins, which are water soluble.) Tests on salads with fat-free, low-fat, and high-fat dressings have shown that you absorb more carotenoids (like Vitamin A) from a salad with a high-fat dressing. The same is true of salads that contain eggs, since the yolk contains fat.

It becomes reasonable to assume that these principles apply to other vitamin/fat combos, like eating broccoli with butter or cheese.

Fat in Beverages Is Mostly Useless

There is much hype around the benefits of fat-infused beverages such as butter coffee and FatWater, an emulsion of fat droplets in water.

The health claims tacked onto these products do not always make much sense, as food science researchers have noted: While MCT oil may lead to slightly more fat burning when swapped for other oils, adding a tablespoon or two to a beverage isn’t likely to have the same effect. Meanwhile, the only thing fat has been shown to help you absorb is fat-soluble compounds like the vitamins we discussed; it does not improve hydration like as the infused waters may imply. If you are looking to simply boost your energy (calorie) intake, these are good options.

If the beverage under consideration about is a smoothie, there is more reason to add fat. A smoothie is essentially food in liquid form. Too often, smoothies just contain carbohydrates, but a healthy, filling smoothie should contain protein and fat too. Almond butter (or other nut butters) contain both, and taste great; full-fat dairy (if you are able to tolerate it), including kefir or yogurt, is another option that provides that one-two punch. These additions make the smoothie more filling, and slow down the carbohydrate rush into your bloodstream.

Some Meals Need More Fat

Due to decades of bad advice, we got used to thinking of low-fat food as healthy; and it is true that it can be lower in calories. However, fat is a necessary and beneficial component of a nutrition plan: it helps with satiety (especially when combined with protein), and counteracts the “carb coma” that can follow after a meal heavy in sugars and starches. That means that a diet with a healthy amount of fat may help you eat less food in the long run.

Extremely low-fat meals result in you missing out on vitamins, are unsatisfying, leave us feeling hungry a short time later and, in my opinion, are just plain unbalanced. Go ahead and add some grass-fed butter to your vegetables but be mindful – you are filling out a healthy ratio of nutrients for you and your body and providing it with the tools it needs to accomplish your goals. Remember, it tastes great and is good for you but when adding fat, you are not applying a magic elixir.