Eating a salad for lunch sounds like a healthy enough choice. Indeed, it’s an easy go-to for many people who are trying to cut calories — not just for the midday meal, but anytime. But where’s the real nutritional value in all those leafy greens? And is buying bagged greens worth the convenience? Read on for the answers — some of which may be surprising.

Beware the pre-wash

Often, bagged greens are pre-washed, which adds to the convenience factor but can actually be a detriment in the long run, as many of the essential vitamins are water-soluble. Buy a whole head of lettuce instead, chop in advance (see below for more details on why), and wash as you go. It won’t take too much extra time, and the nutritional value will be largely retained.

The effects of cutting

Interestingly enough, damaged plants may actually be able to produce more polyphenols, which can protect against osteoporosis, heart disease, and even certain cancers. So don’t worry about losing nutrients through chopping in advance.

Check the dates

This is an important habit to develop, no matter what the product: Look for the best-by date, and select a package with the latest date available. The fresher the product, the better the quality, particularly when it comes to produce.

The packing process: help or hindrance?

Packaged greens are bagged using a “modified atmosphere” technique, which essentially reduces the amount of surrounding oxygen, thereby allowing the greens a longer shelf life. Does this harm the product? Interestingly, no: Studies have shown that beta carotene, folate, and vitamin C are all aided by the modified atmosphere process. In addition, it keeps the vegetables looking good for a longer period of time, meaning they’re less likely to be pitched out due to wilting or browning.

So, to bag or not to bag?

The answer depends largely on when you’re planning on eating the greens. For same-day or next-day cooking, the pre-packaged product is fine. If, however, the plan is to eat a salad every day for a week, it’s best to buy whole heads and prepare them in the method described above. The nutrient loss in packaged greens occurs at a more accelerated rate, so they’re best consumed as soon as possible. If, however, the choice is between packaged greens or no greens at all, it’s always prudent to go with the former.