We don’t need reminding that fruits and vegetables are an important part of our diet, especially for those trying to conceive. Most of us, certainly me, need to do a better job of making sure we’re getting enough of both. Juice can be a convenient way of getting some of those nutrients; a single glass of juice can contain the vitamins and minerals from several pieces of fruit and vegetables. On the downside, that glass of juice will also have all the sugar from those fruits and lack most of their fiber, so it is not a complete dietary solution. That being said, juice tastes good and, in moderation, can be a good part of our diets.

Does the manner in which the juice is made matter? We have our standard store-bought juice, heat pasteurized for safe storage. There is also fresh made at home, either in a food processor or a specialized juicer. And now also available in some markets is cold-pressed; juice made with a cold extraction followed (often) by a pasteurization method that doesn’t use heat. These different methods result in different products, but is there is a measurable health difference?

Many years back there was an omnipresent infomercial on TV in which gray-haired but disturbingly energetic Jay Kordich pitched the “Juiceman Juicer.” Jay would admonish against store-bought, pasteurized juice. “Heating kills the enzymes!” he’d excitedly – and repeatedly – exclaim to his midnight audience.

I was in graduate school at the time, immersed in a thesis project which entailed extracting enzymes from bacteria. While I made sure my cold press extraction of RNA polymerase from 50 gallons of E. coli stayed cold, I often repeated his mantra to myself. “Heating kills the enzymes!” I’d say as I scraped large, smelly masses of centrifuged bacteria into the large press with a huge spatula.

It’s true, heat (and air, and time and a lot of other factors) will kill the enzymes. This matters if you’re trying to make RNA polymerase for your next set of experiments. Does it matter when choosing a juice?

Most nutrients and minerals in juice are not affected much by heat pasteurization. Vitamin C is one of the less stable nutrients, and is sometimes used as a measurement of how much a juice extraction method affects the nutrient content of the juice. Heat pasteurization removes a measurable fraction of the vitamin C (anywhere from one third to just a few percent, depending on the method). However this still leaves most of the vitamin C present. One glass of orange juice, fresh or pasteurized, gives you more than the recommended daily amount of vitamin C, so the difference between the methods isn’t very important.

That’s the story for vitamin C, at least. Every nutrient is different, however, and needs to be studied on their own. A few nutrients are more susceptible to heat than vitamin C. Some are sequestered by fiber, which means juice with more fiber has less of that nutrient available for your body. Heating can increase the availability of some nutrients by making them more digestible. And while Jay Kordich was right that heating will kill the enzymes, so will your own digestive system. There is little evidence that active enzymes from our food are an important part of our diet.

What is certain is that food safety is very important, especially for women who are trying to conceive. No food is healthy if it is not safe, and there are several relatively common bacteria found in foods that can be very dangerous to pregnant women. So whatever juice you choose, make sure that you have confidence in its freshness or preservation. And unless you’re trying to extract active enzyme for your PhD thesis, I wouldn’t worry too much about your juice extraction methodology.