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Preparation & Everyday Use

Preparing and using functional foods: fresh, frozen and canned produce, whole fruit versus juice, pasteurized versus unpasteurized, and why we do not give home-fermentation instructions.

Content last updated . This page has not been medically reviewed.

Safety first. Supplements can cause side effects and interact with medicines. Read mushroom safety and interactions before you use any mushroom product.

Fresh, frozen and canned

A study that compared eight fruits and vegetables (corn, carrots, broccoli, spinach, peas, green beans, strawberries, blueberries) found frozen produce was often comparable and sometimes higher in vitamins such as ascorbic acid and alpha-tocopherol than fresh stored in the refrigerator. [1] Canned produce: proper evidence was not found in the sources we read; check sodium and added sugar on the label. [2]

Whole fruit versus juice

A meta-analysis of cohort studies found 100% fruit juice was not associated with type 2 diabetes, while non-100% juice was (RR 1.15); the authors note 100% juice lacked the beneficial association seen for whole fruit. [3] Juice has less fiber than whole fruit. See Whole fruit vs juice.

Pasteurized and unpasteurized

Pasteurized products are heat-treated to kill harmful microbes. In pregnancy, extension guidance advises avoiding raw milk and cheeses made from unpasteurized milk, and raw sprouts. [4] Pasteurizing sauerkraut did not remove its effect on the gut in a trial. [5]

Fermentation food safety

We do not give home-fermentation or canning instructions. Mistakes can make people ill, and we have not verified a method for every food. Use a tested recipe from a food-safety authority and follow it exactly.

Everyday use

  • Eat the food as food; do not use it in place of prescribed medicine.
  • Combine foods in a varied pattern; single-food results do not add up. [6]
  • Foods that interact with medicines: Safety.

Frequently asked questions

Is frozen as good as fresh?

For vitamins in the eight foods tested, frozen was comparable or better in many cases. [1]

References

  1. Bouzari A et al. Vitamin retention in eight fruits and vegetables: a comparison of refrigerated and frozen storage. J Agric Food Chem 2015. PMID 25526594.
  2. U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020–2025. Check the site for the current edition.
  3. Lee CW et al. Consumption of Fruit Juice and Risk of Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis of Prospective Cohort Studies. Am J Med 2025. PMID 40393612.
  4. Clemson Cooperative Extension. Food Safety for Pregnant Women and Their Babies. Extension fact sheet.
  5. Schropp N et al. The impact of regular sauerkraut consumption on the human gut microbiota: a crossover intervention trial. Microbiome 2025. PMID 39940045.
  6. American Dietetic Association. Position of the American Dietetic Association: functional foods. J Am Diet Assoc 2009;109:735-46. Cited through a bibliographic record; the later Academy of Nutrition and Dietetics edition should be checked.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.