Seasonal Nutrition: Why Eating Locally Matters

Nutrient Content and Harvest Timing

Fruits and vegetables are not static products. Their nutrient content changes depending on harvest timing, storage duration and transport conditions. Rickman et al. (2007) showed in a comprehensive review in the Journal of the Science of Food and Agriculture that fresh vegetables continuously lose nutrients after harvest. Vitamin C is particularly sensitive. Spinach can lose up to 50% of its vitamin C content within 7 days at refrigerator temperature. Folate and B vitamins also degrade measurably during storage.

The reason lies in plant biochemistry. After harvest, metabolic processes continue. Enzymes break down vitamins, while light and oxygen accelerate oxidation. Temperature is the most important factor: the warmer the storage, the faster the degradation. Vegetables consumed immediately after harvest therefore deliver the highest nutrient values.

Why Seasonal Foods Can Be More Nutritious

Seasonal vegetables from the region are typically harvested at the optimal point of ripeness. Tomatoes that ripen in summer under natural sunlight contain more lycopene than greenhouse tomatoes in winter. Strawberries in June deliver higher vitamin C values than imported strawberries in January, which are harvested unripe and transported over thousands of kilometres.

Barrett (2007) documented in the Journal of Food Science that fruits and vegetables destined for long-distance transport are frequently harvested before full ripeness. This directly affects nutrient content because many vitamins and secondary plant compounds are only formed in the final days of ripening. An apple that ripens on the tree is not only more flavourful but also contains more polyphenols than one picked prematurely.

Short Transport Routes: Nutrients and Climate

Regionally grown vegetables offer a double advantage. First, the short time span between harvest and consumption minimises nutrient losses. A head of lettuce from the weekly market is often just a few hours old. Imported lettuce from southern Spain or North Africa, by contrast, has been in transit for several days.

Second, the carbon footprint of regional products is significantly lower. Strawberries flown in from overseas cause many times the emissions compared to Swiss open-field strawberries. However, the calculation is not always straightforward. Heated greenhouses in Switzerland can have a higher carbon footprint in winter than open-field vegetables from southern Europe transported by truck. Seasonality and regionality therefore belong together.

Frozen vs. Fresh: A Surprising Comparison

Frozen vegetables deserve a better reputation than they often receive. Bouzari et al. (2015) compared the nutrient content of fresh and frozen fruits and vegetables in a study published in the Journal of Food Composition and Analysis. The result: frozen products were equivalent or even more nutritious than fresh supermarket produce in most cases.

The reason is simple. Frozen vegetables are harvested at optimal ripeness and blanched and flash-frozen within a few hours. Blanching inactivates enzymes that would break down nutrients. Flash-freezing halts biological degradation almost completely. By comparison, fresh vegetables in the supermarket had often been sitting on display for several days already.

Peas, beans, spinach and broccoli performed particularly well in their frozen form. Vitamin C, riboflavin and alpha-tocopherol showed no significant differences. In some cases, the vitamin A content of frozen vegetables was actually higher than in the fresh variant.

Preservation Methods Compared

Freezing is not the only preservation method that affects nutrient content. Here is how different approaches compare.

Freezing

Best nutrient retention among all preservation methods. Enzymes are inactivated by blanching, and degradation is halted by cold. Vitamin C losses range from 10 to 30%, with most other nutrients even lower.

Fermenting

Lactic acid fermentation can actually increase certain nutrients. Sauerkraut contains more vitamin C than raw white cabbage because lactic acid bacteria inhibit breakdown. Additionally, probiotic cultures are produced that can support the gut microbiome.

Drying

Water removal concentrates minerals and fibre but destroys heat-sensitive vitamins. Dried apricots contain more iron per gram than fresh ones but less vitamin C. Gentle air-drying at low temperatures preserves more nutrients than high-heat drying.

Canning (Heat Preservation)

Heating above 100 degrees Celsius destroys a significant portion of heat-sensitive vitamins. Vitamin C and folate losses range from 50 to 80%. However, minerals, fibre and fat-soluble vitamins (A, D, E, K) are largely retained. Canned tomatoes actually deliver more bioavailable lycopene than raw tomatoes.

Seasonal Calendar for Switzerland

The following table shows which vegetables and fruits are in season in Switzerland at different times of year. The information refers to open-field cultivation.

Season	Vegetables	Fruit
Spring (March to May)	Asparagus, rhubarb, radishes, spinach, wild garlic, spring onions, head lettuce	Strawberries (from May)
Summer (June to August)	Tomatoes, courgettes, aubergines, peppers, beans, cucumbers, corn, chard	Cherries, apricots, blueberries, raspberries, redcurrants, plums, peaches
Autumn (September to November)	Pumpkin, beetroot, celeriac, leeks, Brussels sprouts, kale, carrots, parsnips	Apples, pears, grapes, quinces, walnuts
Winter (December to February)	Lamb’s lettuce, chicory, savoy cabbage, white cabbage, salsify, Jerusalem artichoke, potatoes (stored)	Apples (stored), pears (stored), citrus fruits (imported)

Some vegetables such as carrots, potatoes and onions are available from Swiss production nearly year-round thanks to good storage properties. Stored vegetables are kept in modern cold storage facilities with controlled atmosphere, which slows nutrient degradation.

Practical Implementation

Eating seasonally does not require a radical lifestyle change. A few simple strategies help.

• Visit weekly markets: At Swiss weekly markets, the vegetables come straight from the field. The sellers know what is currently in season.
• Use frozen vegetables as a supplement: In winter, frozen vegetables are a sensible alternative to imported fresh produce. Nutrient content and price are right.
• Hang up a seasonal calendar: A seasonal calendar on the fridge door serves as a reminder of what is currently available when writing the shopping list.
• Preserve and ferment: Those who preserve the summer harvest also have regional foods in winter. Fermented vegetables additionally provide probiotic cultures.
• Stay flexible: Eating seasonally does not mean never buying an avocado or banana. It is about the general direction, not perfection.

Conclusion

Seasonal and regional nutrition is not a nostalgic trend but scientifically well-founded. Harvest timing measurably influences nutrient content. Short transport routes reduce losses and emissions. Frozen vegetables are an underrated alternative that can match fresh produce in terms of nutrients. And preservation methods like fermentation can even increase nutritional value. Those who orient their menu around the seasonal calendar make a simple decision with measurable benefits.

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Sources:

• Rickman JC, Barrett DM, Bruhn CM (2007). Nutritional comparison of fresh, frozen and canned fruits and vegetables. Part 1. Vitamins C and B and phenolic compounds. Journal of the Science of Food and Agriculture, 87(6), 930-944.
• Bouzari A, Holstege D, Barrett DM (2015). Mineral, Fiber, and Total Phenolic Retention in Eight Fruits and Vegetables: A Comparison of Refrigerated and Frozen Storage. Journal of Agricultural and Food Chemistry, 63(3), 951-956.
• Barrett DM (2007). Maximizing the Nutritional Value of Fruits and Vegetables. Journal of Food Science, 72(9), R133-R144.