Squash, summer

What’s new and beneficial about summer squash

• The WHF rating system uses 29 nutrients to rank the quality of our 100 profiled foods. It’s not surprising to see that many well-known vegetables rank very high in overall nutrients. For example, spinach earns 23 different nutrient rankings of either excellent, very good, or good. Broccoli earns 24 such rankings, and kale gets 19. Yet, it might be surprising to learn that summer squash is another vegetable quite high up on this list with 20 different nutrient rankings of either excellent, very good, or good. Several recent studies have focused on one key area in the overall nutrient richness of summer squash— namely, its mineral content. These studies confirm the strong mineral profile that we include for summer squash on our website. They show this vegetable to be a valuable source of copper, manganese, magnesium, phosphorus, potassium, calcium, and iron. Interestingly, one of the studies has also found a greater potential for mineral richness in zucchini varieties of summer squash (as compared with straightneck, crookneck, and pattypan varieties).
• Summer squashes—and especially the yellow-skinned varieties—have long been recognized for their richness in carotenoids. However, the extent of this richness has been underscored in a recent study from Korea. This large-scale study looked at all foods consumed by over 8,000 participants, and then analyzed the percentage of various carotenoids that was provided by each food. (Note that this study did not differentiate between summer and winter squashes, as both were included in the analysis.) For lutein and zeaxanthin, squash emerged at the top of the list, providing 36% of the lutein+zeaxanthin provided by all foods combined! For the carotenoid beta-cryptoxanthin, squash placed second (behind persimmon) with 18% of total daily beta-cryptoxanthin. And for beta-carotene, squash placed third (behind sweet potatoes and carrots) with 9% of total daily beta-carotene. These findings encourage us to remember that when we are thinking about carotenoids and vegetables like carrots and sweet potatoes come to mind, we ought not to forget about squashes—including those mildly sweet yellow summer varieties.
• While we are on the topic of carotenoids, it is well worth noting a recent study that compared carotenoids in the outer skin versus inner flesh of summer squashes. At WHF, we typically recommend enjoyment of whole vegetables including the skin since this part of the food can be uniquely concentrated in nutrients. (This approach on our part is also connected with our recommendation of certified organic vegetables, which are much more likely to have lower levels of unwanted contaminants on their skin.) In this recent study, researchers compared the levels of lutein, zeaxanthin, beta-carotene, and total carotenoids in the epicarp (skin) and mesocarp (flesh) of summer squashes. Carotenoid richness was typically 2–10 times higher in the skins than in the flesh of 22 different varieties that were analyzed. These results are a reminder that the skins of vegetables can be well worth eating, as long as care is taken to select vegetables that have not been exposed to unwanted contaminants during cultivation or post-harvest.

Recommendations

If you are enjoying green varieties of summer squash like zucchini, we recommend that you treat these varieties as part of your daily green vegetable intake. At WHF, our outstanding level of green vegetable intake is 8 servings of green vegetables per day. A variety of days in our WHF Meal Plan provide this outstanding amount, without compromising the delicious balance of textures or flavors in our WHF Meal Plan Recipes. Alongside of zucchini, many different types of green vegetables are available to provide you with exceptional nourishment. Included here are dark green leafy vegetables from the cruciferous group (for example, mustard greens, turnip greens, kale, or collards); green vegetables from the parsley/umbelliferous group (like fennel and celery); green allium vegetables like leeks, green lettuces like romaine; and leguminous vegetables like green peas and green beans. Rather than relying exclusively on any one of these subgroups, we recommend that you choose a variety of green vegetables—including, of course, green summer squashes like zucchini.

If you decide to enjoy yellow varieties of summer squash, we recommend that you treat them as part of your yellow/orange vegetable intake. At WHF, our minimum daily goal for vegetable intake from this yellow/orange group is 1/2 cup per day. A more optimal intake level would be one cup per day. Alongside of yellow summer squash, yellow/orange vegetables like sweet potato, carrots, and yellow bell peppers can contribute to your daily yellow/orange total.

Summer Squash, sliced, cooked
1.00 cup
(180.00 grams)

Calories: 36
GI: very low

NutrientDRI/DV

 copper21%

 manganese17%

 vitamin C13%

 phosphorus10%

 magnesium10%

 fiber9%

 folate9%

 vitamin B17%

 vitamin K7%

 potassium7%

 vitamin B67%

 omega-3 fats6%

 vitamin B36%

 zinc6%

 pantothenic acid5%

 calcium5%

 vitamin B25%

 iron4%

 choline3%

 protein3%

Food Rating System Chart

• Health Benefits
• Description
• History
• How to Select and Store
• Tips for Preparing and Cooking
• How to Enjoy
• Nutritional Profile
• References

Health benefits

Broad overall nutrient benefits from summer squash

In terms of nutrient richness, many people would not place summer squash on their list of “attention grabbing” vegetables. Much more likely to be included in this list would be vegetables like kale or spinach or broccoli. However, summer squash is a vegetable with remarkable nutrient richness that spans all nutrient categories: vitamins, minerals, macronutrients (like fiber and protein) as well as phytonutrients like carotenoids. At WHF, we rate summer squash as an excellent source of two minerals (copper and manganese) and very good or good source of six additional minerals (magnesium, phosphorus, potassium, zinc, calcium, and iron). We would also add that recent studies have confirmed the remarkable nutrient richness of summer squash. Interestingly, one study that we reviewed showed greater potential for mineral richness in zucchini-type summer squashes (when compared with straightneck, crookneck, and scallop varieties).

In the vitamin category, it’s striking to see the number of B-vitamins provided by summer squash in very good or good amounts. These B-vitamins include B1, B2, B3, B6, pantothenic acid, choline, and folate. (The only unranked B-vitamins for summer squash are B12 and biotin.) Other vitamins provided by summer squash in “very good” or “good” amounts include vitamin C and vitamin K.

In terms of macronutrients, summer squash earns a ranking of “good” for both protein and fiber in our WHF rating system. In the case of fiber, we are talking about 2.5 grams per 1 cup serving and only 36 calories. In this macronutrient category, summer squash also achieves a “good” ranking for its omega-3 fatty acid content. At 150 milligrams per serving, the total amount of omega-3s is not high here. But it’s important to remember that you are getting these 150 milligrams in only 36 calories of food. By comparison, consider a food like salmon that is normally singled out for its omega-3 content. From salmon, you get 1,300 milligrams of omega-3s for 158 calories. When you do the math here, you get about 8 milligrams of omega-3s per calorie of salmon, and about 4 milligrams of omega-3s per calorie of summer squash. While this per-calorie amount is twice as high in salmon as in summer squash, many people would not expect summer squash to show up anywhere on the omega-3 radar screen, and so this is impressive.

The best-studied phytonutrients in summer squash are carotenoids. The focus here has been on lutein, zeaxanthin, beta-cryptoxanthin, and beta-carotene. In terms of summer squash varieties, yellow straightneck, yellow crookneck, yellow zuccihini, and yellow patty pan are your best choices for total carotenoids. The skins of these squashes can be especially important to consume if you are seeking to make the most of summer squash carotenoids. One recent study has compared carotenoid content in the skins (epicarp) and flesh (mesocarp) of summer squashes and found that carotenoid richness was typically 2–10 times higher in the skins than in the flesh. In this study, 22 different varieties of squash were analyzed. One good way to avoid unwanted potential contaminants on the skins of summer squash is to purchase certified organic versions of this vegetable.

The carotenonoid richness of squash has recently been underscored in a large-scale study from Korea. When all foods consumed by over 8,000 participants were analyzed for their carotenoid content, squash came out remarkably well. (It’s important to note here, however, that this study did not differentiate between summer and winter squashes, even though both were included in the analysis.) For lutein and zeaxanthin, squash came out in first place and provided 36% of the lutein+zeaxanthin from all foods combined! For another carotenoid— beta-cryptoxanthin—squash placed second (behind persimmon) with 18% of total daily beta-cryptoxanthin. And for beta-carotene, squash placed third (behind sweet potatoes and carrots) with 9% of total daily beta-carotene.

Other health benefits from summer squash

Ordinarily, strong evidence would be expected for the health benefits of summer squash for decreasing your risk of several health problems. For example, we would expect decreased risk of blood sugar problems, given the strong B-vitamin, good fiber, and good protein content of this vegetable. Decreased risk would also be expected of problems related to oxidative stress since the antioxidant profile of summer squash is a notable one. Here is a food that earns an excellent rating for manganese and a rating of “good” for zinc, two key antioxidant minerals. In addition, summer squash gets a rating of “very good” for its richness in vitamin C—one of the premiere antioxidant nutrients. And on top of these benefits is the antioxidant richness of summer squash in terms of its carotenoids. Each of the key antioxidants provided by this vegetable—lutein, zeaxanthin, beta-cryptoxanthin, and beta-carotene—has been shown to have unique antioxidant properties.

Unfortunately, however, there are just too many limitations at this point in the research findings for us to provide you with the kind of evidence that we would expect to see. These limitations stem from two basic tendencies in the scientific research. A first tendency is to include both summer and winter varieties of squash in the study sample. For example, pumpkin is very frequently included in squash studies alongside of other squashes. Some of this overlap between summer and winter squashes in research studies is based on the potential closeness of these squash varieties from a science standpoint. The genus/species Cucurbita pepo, for example, includes field pumpkin as well as zucchini!

A second tendency in the squash research is to analyze an isolated component of the food instead of the whole vegetable. For example, squash seeds and their oils have a reasonably good track record in animal research. However, this type of research cannot reliably be used to draw conclusions about people enjoying fresh summer squash in their meal plans. Eventually, large-scale, human research studies that focus attention on summer squash and that find important health benefits for this vegetable along the lines described above.

Description

Summer squash belongs to a very large family of plants usually referred to as the gourd family. Since the science name for this family is Cucurbitaceae, members of this family are also sometimes referred to as “cucurbits.” Along with summer squashes, winter squashes, and melons belong to this same family of plants. Cucurbits profiled among our 100 WHF include summer squash, winter squash, cantaloupe, watermelon, and cucumbers. The list presented below will give you more details about the Cucurbitaceae family and show you how summer squash fits in from a science perspective:

• Cucurbita genus
  • winter squashes
  • summer squashes
• Cucumis genus
  • cantaloupe
  • cucumber
  • casaba melons
  • Crenshaw melons
  • honeydew melons
  • muskmelon
• Citrullus genus
  • watermelons
  • bitter apple

The name “summer squash” can be a bit confusing. Both “summer” and “winter” squash are warm season crops. However, summer squashes are typically harvested before full maturity (within a period about approximately 50-70 days) and are intended for market as quickly as possible after harvest. “Winter” squashes, by contrast, are allowed to fully mature (in a time frame that may take 90-120 days) and develop a much thicker outer skin allowing for storage over many months and thus “winter storage.” At WHF, this emphasis on freshness in summer squash has led us to recommend no more than one week (at the most) of summer squash storage in the refrigerator after purchase.

While highly diverse, summer squashes commonly enjoyed in the United States can be placed into three basic groups: (1) zucchini-type squashes, (2) straightneck and crookneck squashes, and (3) scallop-type, “patty pan” squashes.

Zucchini varieties with dark, richly green skins are widely available in supermarkets and they are usually solid in color. However, zucchini-type squashes may also be striped or speckled, and can be not only dark green but also light green or yellow in color. Zucchini summer squashes are fairly long, cylindrical, and have a noticeable stem at their flower end. Popular varieties of zucchini in the U.S. include Cocozelle, Black Beauty, Spineless Beauty, Greyzini, Raven, Ambassador, and Contender. Yellow-skinned zucchini-type squashes include Gold Rush and Golden Dawn.

Virtually all of the straightneck and crookneck summer squashes that you will find in the supermarket are yellow in color. Like their name suggests, crookneck varieties have a bend in their thinner neck region. However, this bend can be fairly slight and also fairly gradual, making some crookneck varieties appear very similar to their fellow straightneck varieties. Early Prolific is one of the most popular straightneck varieties. Golden Summer and Early Summer are two very popular crookneck varieties.

Scallop-type summer squashes get their name from their scallop-like shape. These varieties are also called “patty pan” squashes. Early White Bush, Yellow Bush, and Bennings Green Tint are some popular varieties of scallop-type summer squashes.

In the United Kingdom and parts of New Zealand and Australia, you might hear the terms “marrow” and “courgette” being used in conjunction with squashes. Generally speaking, the French term “courgette” is used to refer to smaller and less mature squashes, and the term “marrow” is used to refer to larger and more mature forms.

All summer squashes commonly sold in the U.S. belong to the science genus/species Cucurbita pepo. This genus/species is native to North America, even though it is now widely cultivated.

History

Summer squash is native to North America, and especially to the central and southern regions of what is now the United States. Wild varieties of summer squash also still grow in the more northern parts of Mexico. Fairly quickly, summer squash was domesticated and grown throughout North America, Central America, and South America; today it is widely cultivated worldwide. Within the United States, Florida, California, New York, and Michigan produce the most summer squash. However, a large amount of summer squash is also imported into the U.S., predominantly from Mexico.

On a worldwide basis, China, India, Russia, the United States, Mexico, and Iran are among the top squash-producing countries (when both summer and winter squashes are included). Squash also plays an important role in food systems throughout the Pacific Islands region, including islands like Tonga, Fiji, New Guinea, and the state of Hawaii.

How to select and store

When purchasing summer squash, look for ones that are heavy for their size and have shiny, unblemished rinds. Additionally, the rinds should not be very hard since this indicates that the squash are over-mature and will have hard seeds and stringy flesh. Purchase summer squash that are of average size since those that are overly large may be fibrous, while those that are overly small may be inferior in flavor.

At WHF, we encourage the purchase of certified organically grown foods, and summer squash are no exception. Repeated research studies on organic foods as a group show that your likelihood of exposure to contaminants such as pesticides and heavy metals can be greatly reduced through the purchased of certified organic foods, including summer squash. In many cases, you may be able to find a local organic grower who sells summer squash but has not applied for formal organic certification either through the U.S. Department of Agriculture (USDA) or through a state agency. (Examples of states offering state-certified organic foods include California, New York, Oregon, Vermont, and Washington.) However, if you are shopping in a large supermarket, your most reliable source of organically grown summer squash is very likely to be summer squash that display the USDA organic logo.

Summer squash is very fragile and should be handled with care as small punctures will lead to decay. It should be stored unwashed in an air-tight container in the refrigerator, where it will keep for about seven days.

Here is some background on why we recommend refrigerating summer squash. Whenever food is stored, four basic factors affect its nutrient composition: exposure to air, exposure to light, exposure to heat, and length of time in storage. Vitamin C, vitamin B6, and carotenoids are good examples of nutrients highly susceptible to heat, and for this reason, their loss from food is very likely to be slowed down through refrigeration.

While it can be frozen, this will make the flesh much softer. Freezing is not recommended as a routine storage method. Yet, it is a great process to turn to if you have amounts larger than you will be able to consume (for example, if you grow summer squash in your garden and have a bounty of it). The fact is that the freezing of summer squash can be an excellent storage process in terms of nourishment. A recent research study has shown excellent retention of the antioxidant activity in frozen summer squash.

Begin by slicing your summer squash and steaming for three minutes. Steaming is prefereable to the more traditional boiling method as it minimizes water contact and therefore minimizes nutrient loss. Remove squash from steamer and let cool thoroughly before placing in freezer bags and storing in the freezer.

Tips for preparing and cooking

Preparation

Wash summer squash under cool running water and then cut off both ends. You can then proceed to cut it into the desired size and shape for the particular recipe.

Cooking for nutrient retention

Of all of the cooking methods we tried when cooking summer squash, our favorite is Healthy Sauté. We think that it provides the greatest flavor.

Healthy Sauté—similar to Quick Boiling and Quick Steaming, our other recommended cooking methods—follows three basic cooking guidelines that are generally associated in food science research with improved nutrient retention. These three guidelines are: (1) minimal necessary heat exposure; (2) minimal necessary cooking duration; (3) minimal necessary food surface contact with cooking liquid.

To Healthy Sauté summer squash, heat 3 TBS of broth (vegetable or chicken) or water in a stainless steel skillet. Once bubbles begin to form add sliced squash, cover, and Healthy Sauté for 3 minutes (1-1/2 minutes on one side, and then 1-1/2 minutes on the other side) on medium heat. Transfer to a bowl and toss with Mediterranean Dressing. See our 3-Minute Healthy Sautéed Summer Squash recipe for details on how to prepare this dish.)

How to enjoy

Serving ideas

• Sprinkle grated zucchini or other summer squash on top of salads and sandwiches.
• Enjoy an easy to make ratatouille by healthy sautéing summer squash, onions, bell peppers, eggplant and tomatoes and then simmering the mixture in tomato sauce. Season to taste.
• Serve raw summer squash with your favorite dips.

Recipes that feature summer squash

• Any Time Frittata
• Italian Tofu Frittata
• Zesty Mexican Soup
• Southwestern Cod Saute
• Primavera Verde
• 5-Minute Healthy Sauteed Summer Squash
• Calabacitas (Mexican-flavored vegetable side dish)
• Steamed Vegetable Medley
• Tahini and Crudites Appetizer

Nutritional profile

One cup (180g) at 36 calories provides copper (21% DV), molybdenum (18.1% DV), manganese (17% DV), vitamin C (13% DV), magnesium (10% DV), phosphorus (10% DV). Additional nutrients include folate (9% DV), fiber (9% DV), potassium (7% DV), vitamin B6 (7% DV), vitamin K (7% DV), vitamin B1 (7% DV), zinc (6% DV), omega-3 fats (6% DV), among others. While not often considered as a premiere food source of antioxidants, summer squash can provide you with unique amounts of antioxidant nutrients, including the carotenoids lutein and zeaxanthin. While summer squash contains very little overall fat (only 1/2 gram per cup), the fat in summer squash (mostly stored in its edible seeds) is unique in composition and includes omega-3s (in the form of alpha-linolenic acid), monounsaturates (in the form of oleic acid), and also medium chain fats (in the form of lauric and myristic acids).

Summer squash is our food of the week

This week we celebrate the coming of summer by featuring summer squash while it is in the peak of its season, has the best flavor, and is the least expensive. With its soft shell and creamy white flesh, it takes just minutes to prepare and is a great summer addition to your Healthiest Way of Eating. It is rich in powerful antioxidants, which promote healthy immunity, and its concentration of beta-carotene provides anti-inflammatory properties.

• Learn how to prepare summer squash, step-by-step, Cubed Zucchini
• Why is the food of the week among the WHF?
• Healthy Eating with the Seasons

Individual concerns

“Can you tell me what oxalates are and in which foods they can be found?”