Summer Squash

Health Benefits
(Source: World's Healthiest Foods, George Mateljan)

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 WHFoods, 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 WHFoods 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, we would expect to present you with strong evidence 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. We would also expect decreased risk 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, we do not believe this type of research can be used to draw conclusions about people enjoying fresh summer squash in their meal plans. Eventually, we do expect to see 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.

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