Frozen peas and candy bars are both processed, and the difference matters

Key takeaways

• From 1998 to 2018, U.S. outbreaks linked to raw milk outnumbered those linked to pasteurized milk 202 to 9, though only 1% to 2% of adults drink raw milk in a typical week¹.
• In a two-year lab study, frozen produce held its vitamins about as well as fresh, and sometimes better than fresh produce that sat in the fridge for five days².
• Cornell scientists found that heating tomatoes for 30 minutes cut vitamin C by about 29% but more than doubled the lycopene they could extract³⁴.
• In a 2017 study in three U.S. regions, about 71% of the sodium people ate came from packaged and restaurant food, not from their own salt shakers⁵.
• Use the four-step ladder below to keep helpful processing, such as freezing, canning and fermenting, and to step away from products built mainly from refined ingredients.

From 1998 through 2018, U.S. health officials traced 202 foodborne outbreaks to raw, unpasteurized milk¹. Those outbreaks sickened 2,645 people and sent 228 to the hospital¹.

Pasteurized milk was linked to nine outbreaks in the same years, a few of them large, with 2,133 illnesses in all¹. The raw-milk count is the striking one, because researchers estimate that only 1% to 2% of adults drink raw milk in a given week¹.

Pasteurization is food processing. So is freezing peas, canning beans, fermenting cabbage and simmering tomato sauce. So is turning corn, sugar and dyes into a neon snack chip.

“Processed” covers all of it, which makes the word almost useless on its own. A better question is what a process does to a food. Does it make the food safer, keep it longer or free up nutrients? Or does it strip out fiber and pile on sugar, salt and refined starch?

This guide walks through that spectrum and ends with a four-step ladder, 10 swaps and a pantry list. Our companion article on ultra-processed foods covers the health research and policy fight over that category.

“Processed” runs from frozen peas to soda

A widely used scale for sorting foods by processing, called NOVA, was built by Brazilian nutrition researchers including Carlos Monteiro⁶. It doesn’t rank foods by nutrients. It sorts them by how much processing they’ve had and why⁶.

NOVA has four groups⁶:

• Group 1, unprocessed or minimally processed: fresh, frozen or dried fruits and vegetables, grains, beans, meat, fish, eggs, nuts, plain pasteurized milk and plain yogurt. Drying, freezing, chilling, grinding and pasteurizing keep a food in this group. Even pasta made from only flour and water counts.
• Group 2, kitchen ingredients: salt, sugar, honey, oils, butter and lard, used to cook group 1 foods rather than eaten alone.
• Group 3, processed foods: simple products made by adding salt, sugar or oil to group 1 foods. Think canned vegetables and beans, canned fish, cheese, cured meats, salted nuts and fresh bread from a bakery.
• Group 4, ultra-processed foods: industrial formulas made mostly from refined substances and additives, often with ingredients a home cook wouldn’t use. Examples include soft drinks, packaged snacks, sweetened cereals, packaged sliced bread, nuggets, sausages and instant noodles.

A few placements surprise people. Frozen spinach and plain yogurt sit in the same group as a carrot pulled from the garden. Fresh, unpackaged bakery bread lands in group 3, while many packaged loaves land in group 4⁶.

The line that matters isn’t between “natural” and “processed.” It’s between processing that serves the food and processing that replaces it.

Heating milk is processing that saves lives

Pasteurization heats milk to a set temperature for a set time to kill germs⁷. The Centers for Disease Control and Prevention (CDC) says pasteurized milk offers the same nutrition as raw milk without the risk⁷.

Raw milk can carry Campylobacter, E. coli, Listeria, Salmonella and other germs⁷. Most infections cause diarrhea, cramps and vomiting. Some lead to Guillain-Barré syndrome, a nerve disorder, or hemolytic uremic syndrome, which can cause kidney failure, stroke or death⁷.

Children carry much of the burden. In a CDC and FDA analysis of outbreaks from 2013 to 2018, 48% of raw-milk illnesses struck people under 20¹. Over those same years, states that expressly allowed raw milk sales had about 3.2 times as many outbreaks as states that banned sales¹.

The CDC also advises against drinking raw milk that could carry H5N1 bird flu, including as a way to build antibodies⁷.

Many people choose raw milk for reasons that deserve respect: taste, tradition, support for a local farm, a wish for food that hasn’t passed through a plant. The nutrition claims are the weak link. The Food and Drug Administration (FDA) reviewed them and found that pasteurization barely changes milk’s protein, calcium, fat or minerals⁸. Vitamin C drops somewhat, but milk was never a real source of it, at about 5 milligrams a cup⁸.

The FDA also notes that raw milk has no lactase, the enzyme that digests milk sugar, so it doesn’t fix lactose intolerance⁸. Yogurt helps some people because of the cultures added to make it, not because the milk started out raw⁸.

Raw milk is riskiest for children under 5, adults over 65, pregnant women and people with weakened immune systems⁷. If you’re in one of those groups, or feeding someone who is, choose pasteurized. If anyone gets sick after drinking raw milk, especially a young child, call a doctor and mention the milk.

Your freezer may keep vitamins better than your crisper drawer

Many shoppers assume fresh produce always beats frozen. A two-year study published in 2017 in the Journal of Food Composition and Analysis put that belief to the test².

Researchers measured vitamin C, folate and a form of beta-carotene (the plant pigment your body turns into vitamin A) in eight fruits and vegetables, from broccoli and spinach to blueberries². They compared fresh produce, frozen produce and “fresh-stored” produce kept in a refrigerator for five days, the way many households do².

Most comparisons showed no meaningful difference². When there was one, frozen beat fresh-stored more often than the other way around².

Read this research with the same eye you’d turn on any industry. The frozen-food industry’s trade group says the Frozen Food Foundation partnered with the University of California, Davis, on a related study⁹. That doesn’t make the findings wrong, but it’s worth knowing.

Federal advice lands in the same place. The 2025–2030 Dietary Guidelines for Americans, released in January 2026, say frozen, dried or canned fruits and vegetables can be good options when they have little or no added sugar¹⁰. The catch is what gets added: syrup on canned peaches, sauce packets in frozen vegetables, extra salt in some canned goods. Plain is the goal.

Heat can free up nutrients, as tomatoes show

Cooking is processing too, and it isn’t always a loss. In 2002, Cornell University food scientists led by Rui Hai Liu heated tomatoes to about 190 degrees Fahrenheit for 2, 15 and 30 minutes³⁴.

After 30 minutes, vitamin C was down about 29%³. But the amount of trans-lycopene, a form of the red pigment in tomatoes, that the team could extract rose 164%³⁴. Total antioxidant activity climbed 62%³.

The researchers credited heat with breaking down the tomato’s cell walls, which let more lycopene out⁴. That makes the pigment more bioaccessible, meaning freed from the food and available to be absorbed.

Keep the limits in view. This was a lab test on tomato pulp, not a study of what people absorb or whether their health improved⁴. The authors pointed to human studies showing better lycopene uptake from cooked tomato products⁴. That is a promising lead, not proof that sauce prevents disease.

So balance it: eat some produce raw for vitamin C, and enjoy sauces, soups and stews too.

Fermentation is old processing with new evidence behind it

Long before factories, people preserved food with salt, smoke, drying and microbes. Natural-health traditions have prized fermented foods such as sauerkraut, yogurt and miso for generations.

Stanford University researchers put fermented foods to the test in a 10-week trial published in Cell in 2021¹¹. They split 36 healthy adults by chance into two groups. One group added fiber-rich foods. The other added fermented ones: kefir, kimchi, kombucha, yogurt, vegetable brine drinks and fermented cottage cheese¹¹.

The fermented-food eaters ended up with a wider variety of gut microbes. Their blood tests also showed drops in 19 markers of inflammation, interleukin-6 among them, and people who ate more servings saw larger shifts¹¹. The fiber group saw no drop in any of those 19¹¹.

It was a small study in healthy people, and it measured blood markers, not disease¹¹. Still, the 2025–2030 Dietary Guidelines now name sauerkraut, kimchi, kefir and miso as foods that support a diverse gut microbiome, though they set no serving target¹⁰. It’s a rare case of traditional practice and federal advice moving toward each other.

Fortification belongs in the helpful column too. Since 1998, folic acid has been added to cereal and grain products to prevent neural tube defects, serious birth defects of the brain and spine¹². Our guide to vitamins and minerals covers how well that worked.

Where processing goes wrong: salt, sugar and stripped-out fiber

Trouble starts when processing adds what your body already gets plenty of and removes what it needs.

Salt is the clearest case. In a 2017 study published in Circulation, a team led by Lisa Harnack of the University of Minnesota tracked where people’s sodium came from in three U.S. regions⁵. About 71% came from packaged and restaurant food⁵. Only 14% occurred naturally in food, and 11% came from salt people added while cooking or at the table⁵.

Hiding the salt shaker barely touches the problem. The 2025–2030 Guidelines set a limit of less than 2,300 milligrams of sodium a day for everyone 14 and older¹⁰.

Sugar comes next. The new Guidelines recommend no amount of added sugar and suggest keeping any single meal to 10 grams or less¹⁰. Flavored yogurts, sauces, cereals and drinks are common hiding places.

Refining is the third problem. The Guidelines call for sharply cutting highly processed refined carbohydrates, such as white bread, flour tortillas and crackers¹⁰. Refining removes the fiber-rich outer bran and the germ of the grain; our history of industrialization tells that story.

Fiber also goes missing when fruit becomes juice or a gummy snack. The Guidelines advise eating vegetables and fruits whole, in their original form¹⁰.

“Whole food” has no legal definition, but structure matters

No federal rule defines “whole food.” Even the new Dietary Guidelines, which put “real food” front and center, don’t formally define it¹⁰. A useful working idea: a food that still looks like what it came from, or a dish made from such foods with a few kitchen ingredients.

Why does form matter if the nutrients are the same? Scientists point to the food matrix, the physical structure of cell walls, fibers and proteins that holds nutrients in place. It changes how much your body takes in.

Nuts show this clearly. At a Department of Agriculture (USDA) lab in Beltsville, Maryland, scientists measured how much energy volunteers absorbed from nuts¹³. People got about 129 calories from an ounce of almonds, well short of the 168 to 170 that standard calorie math predicts¹³. Walnuts fell 21% short of their predicted count¹³.

Processing narrowed the gap. For whole raw almonds, the standard math ran 25% too high. Roasting cut that miss to 19%, and roasting plus chopping cut it to 17%¹³. The more the nut was broken up before chewing, the more energy the body pulled out.

So the matrix cuts both ways. Breaking tomato cell walls frees more lycopene, and breaking up almonds frees more calories⁴¹³. Either way, a whole food is more than its nutrition label.

The processing ladder: four steps and 10 easy swaps

This shopping ladder puts NOVA’s logic in plain terms⁶.

1. Step 1, whole or barely changed: fresh, frozen, dried, pasteurized or plain fermented foods. Make these the base of your plate.
2. Step 2, kitchen helpers: oil, butter, salt, sugar and honey. Use them to cook step 1 foods, in amounts you choose.
3. Step 3, simply processed: canned beans and fish, cheese, bakery bread and canned tomatoes. Good everyday foods; check the label for added salt and sugar.
4. Step 4, built from refined ingredients: products with long ingredient lists of things you wouldn’t cook with at home. Eat them less often, and let foods from steps 1 to 3 crowd them out.

Here are 10 swaps that each move a food down the ladder.

If you usually buy	Try instead	Why it helps
Flavored instant oatmeal packets	Plain rolled oats with frozen berries	Same grain, and you decide the sugar
Fruit-flavored yogurt	Plain yogurt with fruit and a little honey	Keeps the cultures while you control sweetness
Packaged sliced white bread	Bakery bread or a whole-grain loaf with a short ingredient list	Moves toward step 3, and whole grain adds fiber
Instant noodle cups	Plain pasta with frozen vegetables and olive oil	Pasta made from flour and water is step 1
Breaded chicken nuggets	Chicken pieces roasted with oil and spices	You set the salt and skip the coating
Flavored tortilla chips	Popcorn popped at home with oil and salt	A whole grain, seasoned your way
Fruit snacks or gummies	Fresh, frozen or unsweetened dried fruit	Keeps the fiber that gummies leave out
Bottled creamy dressing	Olive oil, lemon juice and herbs	Three ingredients you can name
Jarred pasta sauce with added sugar	Canned tomatoes simmered with garlic and oil	Cooking frees lycopene, with no added sugar
Ice cream every night	Frozen banana or berries blended with plain yogurt	A treat built from step 1 foods

How strong is the evidence?

Claim	Evidence level	What the research shows
Pasteurization prevents illness from milk	Strong evidence	Raw milk caused far more outbreaks than pasteurized milk over two decades, though few people drink it17
Pasteurization strips milk of meaningful nutrition	Evidence says no, or unsafe	FDA found little change in protein, calcium, fat or minerals, and raw milk carries real infection risk8
Frozen produce is about as nutritious as fresh	Promising but early	One careful two-year lab study, in a field partly backed by industry29
Cooking tomatoes makes lycopene more available	Promising but early	Clear lab results; human absorption studies are smaller4
Fermented foods calm inflammation	Promising but early	One 10-week trial of 36 people found lower inflammatory markers11
A food’s structure changes how much you absorb	Promising but early	USDA feeding studies found people absorbed fewer calories from nuts than standard formulas predict13
All processed food is unhealthy	Evidence says no, or unsafe	Pasteurizing, freezing and fortifying protect health1212

Questions readers ask

The bottom line

Processing isn’t the enemy of natural eating. Heat made milk safe, freezing holds summer’s vitamins for winter, fermentation is as old as farming, and tomato sauce offers lycopene a raw tomato keeps locked away. Those processes serve the food.

The processing to step away from strips out fiber, adds salt and sugar, and builds products from refined pieces. Build meals on step 1 foods, use steps 2 and 3 wisely, and let step 4 products become the exception rather than the base of your diet.

Related reading

• The case against ultra-processed food keeps growing, though defining it is harder
• The ingredient list is a ranking, and most people miss it
• Why “natural” on a food label guarantees almost nothing
• Industrial life brought clean water and white bread, and history shows which to keep
• A healthy month of groceries, priced by the government

Sources

1. Koski L, Kisselburgh H, Landsman L, et al. “Foodborne Illness Outbreaks Linked to Unpasteurised Milk and Relationship to Changes in State Laws – United States, 1998–2018.” Epidemiology & Infection, 2022. cambridge.org
2. Li L, Pegg RB, Eitenmiller RR, Chun JY, Kerrihard AL. “Selected Nutrient Analyses of Fresh, Fresh-Stored, and Frozen Fruits and Vegetables.” Journal of Food Composition and Analysis, 2017 (abstract via Montclair State University). researchwith.montclair.edu
3. Cornell University. “Cooking Tomatoes Boosts Disease-Fighting Power.” Cornell Chronicle, 2002. news.cornell.edu
4. Dewanto V, Wu X, Adom KK, Liu RH. “Thermal Processing Enhances the Nutritional Value of Tomatoes by Increasing Total Antioxidant Activity.” Journal of Agricultural and Food Chemistry, 2002. pubmed.ncbi.nlm.nih.gov
5. University of Minnesota School of Public Health. “Majority of Sodium in American Diet Comes From Packaged, Restaurant Foods” (on Harnack LJ, et al., Circulation, 2017). UMN, 2017. sph.umn.edu
6. Louzada MLC, Ricardo CZ, Martinez Steele E, et al. “The Share of Ultra-Processed Foods Determines the Overall Nutritional Quality of Diets in Brazil.” Public Health Nutrition, 2018. cambridge.org
7. Centers for Disease Control and Prevention. “Raw Milk.” CDC Food Safety, 2025. cdc.gov
8. U.S. Food and Drug Administration. “Raw Milk Misconceptions and the Danger of Raw Milk Consumption.” FDA, 2024. fda.gov
9. American Frozen Food Institute. “UC Davis Study Reinforces the Nutritional Benefits of Frozen Fruits and Vegetables” (industry statement, cited only for industry involvement). AFFI, 2010. affi.org
10. U.S. Department of Health and Human Services and U.S. Department of Agriculture. “Dietary Guidelines for Americans, 2025–2030.” HHS and USDA, January 2026. cdn.realfood.gov
11. Stanford Medicine. “Fermented-Food Diet Increases Microbiome Diversity, Decreases Inflammatory Proteins, Study Finds” (on Wastyk HC, et al., Cell, 2021). Stanford Medicine News, 2021. med.stanford.edu
12. Centers for Disease Control and Prevention. “Achievements in Public Health, 1900-1999: Safer and Healthier Foods.” MMWR, 1999. cdc.gov
13. USDA Agricultural Research Service. “Going Nuts Over Calories.” AgResearch Magazine (Tellus), 2018. scientificdiscoveries.ars.usda.gov