Are local foods more nutritious?

This is one of the most frequently asked questions about eating locally grown and processed foods. While it would be nice to be able to make a claim of nutritional superiority of locally produced foods, the answer is not that simple. However, there are several points to be made that relate to the question.

Let’s focus in produce since when people ask the question, most of the time they are wondering if locally grown fruits and vegetables are more nutritious.

When fruits and vegetables are allowed to reach their peak ripeness, they will likely be of the highest possible quality. “Quality of vegetables” is an illusive concept that is difficult to define although it can be discussed in terms of four basic characteristics of food: 1. Color or eye appeal; 2. Taste and smell; 3. Texture or feel; and, 4. Nutrient content. Numbers 1, 2, and 3 can be evaluated with human senses and have the greatest chance of being at their peak if the product is allowed to ripen fully, is handled carefully after harvest, and reaches the consumer in the shortest time possible. This situation is most probable when produce is consumed near the place it is grown. Since we all are likely to consume fresh fruits and vegetables in great quantities when they are of the highest quality, locally produced foods stand to improve the nutritional quality of total dietary intake regardless of differences in nutrient content of a particular fruit or vegetable.

However, the importance of good post-harvest food handling cannot be over-emphasized. Wonderful, highly nutritious, flavorful and very local fruits and vegetables can be of very poor quality, and suffer significant nutrient loss. Ways to prevent this from happening would be: remove field heat shortly after harvest, hold at proper temperature and moisture levels, and protect from direct sunlight when selling at local markets. To retain maximum nutritional value, produce should be frozen or canned within 24 hours of harvest.

Sun and Vitamin C

There is some evidence that certain foods at their peak ripeness offer superior nutritional benefits. The synthesis of vitamin C is closely associated with carbohydrate in vegetables which is influenced by variation in light intensity during growing and ripening. Glucose in the edible plant part is activated by UTP, and then oxidized to the activated form glucuronic acid, the direct precursor of vitamin C. All processes that promote the synthesis of UTP or ATP and glucose favorably influence the synthesis of ascorbic acid. The most important factors in this respect are light intensity and potassium supply. Light intensity is directly involved in photosynthetic ATP synthesis and all synthetic processes of the plan. So, this would suggest that allowing vegetables to obtain maximum sun exposure to achieve ripeness will maximize the vitamin C content.

While this is indeed true, we also need to keep in mind that this “more sun, more vitamin C” argument holds up only for fruits (including tomatoes and some melons) that are routinely harvested before they are ripe, and continue to ripen after harvest. Tomatoes come to mind as important examples since they alone make up nearly a quarter of total vegetable consumption among U.S. consumers. That said, it is important to keep in mind that most fresh produce can be harvested only when it reaches peak ripeness and would therefore, ordinarily receive maximum “sunning.” Most fresh produce just begins the decomposition process after harvest, which is slowed when handled gently and kept a appropriate cool temperatures and humidity.

It is important not to exaggerate the claim that “local produce is picked when ripe.” With the exception of tomatoes, bananas, pears and some other fruits, all produce is picked when ripe, whether on a local farm or anywhere on the planet. It has to be. You can’t pick a green bean, pea, apple, eggplant, head of broccoli, or bunch of greens earlier or later – you have to pick it when it’s ready and then make sure you have a system in place to keep it in excellent condition until it is eaten.

Given the current infrastructure of our global food system, the big growers and distributors shipping around the country and the world have the resources and subsidies to keep things cool, while the many small, local growers may not have adequate coolers.

All this said, the overall quality of locally grown produce picked in the morning, kept chilled and out of the sun, cannot be beat by the most efficient trans-continental trucking.

Variety in the diet

We’ve all heard this phrase from the time we could hold a fork and say, “More peas, please!” Eating a varied diet has been the foundation of the dietary guidance since such guidelines were first developed. In the Health Eating Index, the USDA Center for Nutrition Policy and Promotion reports that less than one-third of people achieve the recommended amount of variety in dietary patterns. According to USDA Agriculture Research Service (ARS) Continuing Survey of Food Intake by Individuals (CSFII) U.S. food consumption data, only about 10 different vegetables account for nearly 85 percent of total vegetable intake among Americans – potatoes, tomatoes, head lettuce, onions, carrots, sweet corn, snap beans, broccoli, cucumber, and peas. A similar situation exists for fruits. Not only is it striking that so few different fruits and vegetables make up such a large proportion of total intake but for any given vegetable, the diversity in terms of plant varieties is quite limited. This results in a very narrow genetic diversity in our consumption of fruits and vegetables, and hence less diversity in our agriculture systems.

Many fruits and vegetable varieties have been developed that are useful for the globalized food system. In other words, tomatoes with delayed ripening that can be harvested green, transported long distances and withstand the pressures of storage and transportation. In more localized food systems, where fruits and vegetables will be marketed and eaten near the farms that produce them, farmers are likely to choose varieties (not just one) based on their climate and what would work the best in local soils as well as what the diverse preferences of their respective market might demand.

Farmers may also wish to increase diversity in the farming system to increase stability and protection against potential threats to which a system with limited generic diversity would be more susceptible. By choosing from the local food system, the, we are more likely to consume more variety within each of the food groups which through greater genetic diversity in the diet would lead to a broader set of nutritional compounds.

So if I can’t say for certain that local foods are always more nutritious, what can I say?

Plenty! Eating locally grown processed (value-added) foods is one very tangible step people can take to strengthen local community-based food systems. Community food systems promote food-related enterprises in proximity to food production, marketing and consumption. Such systems enhance agricultural diversity, strengthen local economies (including farm-based businesses), add to farmland protection, and protect the viability of farming as a livelihood. And who doesn’t love to see farms in the rural landscape?

Keeping the market strong for what farmers are growing keeps farmers on the land and enhances the aesthetic quality of the landscape. Local food systems mean less long distance shipment of a lot of water packaged in the produce we enjoy. This means a decreased use of non-renewable fossil fuels for food distribution, lower emission of resulting pollutants, less wear on transcontinental highways, ect.

Finally, perhaps the idea of a healthy lifestyle should include eating with the seasons from the local harvest. In order to sustain a healthy lifestyle, the health of the food producing natural resources needs to be protected. Our food choices, when local and seasonally varied, tend to enhance the local agriculture an food system environment burden by shortening the distance food is transported (and hence the energy needed to move our food around), and by protecting agricultural landscapes.

By eating locally, we also encourage sustainable farming practices because we’re sending the message that it’s important to keep local farmland productive and vital.