Winter Squash

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

Broad-based Nutrient Support from Winter Squash

Enjoyment of winter squash can help boost your nutrient intake in every major nutrient category. Among the macronutrients, you get about one-fourth of our daily recommended fiber from a single one-cup serving. You also get about 10% of our daily recommended intake level for a very important type of fat—namely, omega-3 fat—from this same one-cup serving. On our website, 27 of 100 foods rank as excellent, very good, or good sources of omega-3s. Among these 27 foods most concentrated in omega-3s, winter squash ranks 13th!

In the vitamin category, B vitamins are a winter squash specialty. Here we are talking about the role of winter squash as a very good source of vitamin B6, and a good source of vitamin B2, vitamin B3, folate, and pantothenic acid. Also important to mention in this vitamin category is vitamin C, which winter squash provides in a very good amount; and of course vitamin A, which winter squash provides in an excellent amount due to its rich array of carotenoids. Vitamin K is also provided in a good amount by winter squash.

One final piece of information in this vitamin category for winter squash involves its vitamin E content. While present in exceedingly small amounts in the flesh of winter squash, more substantial amounts of vitamin E are provided by the seeds of this vegetable. Included here are the members of the vitamin E family known as the gamma-tocopherols. These important forms of vitamin E are one reason to consider saving and lightly roasting the seeds of winter squash if you decide to scoop them out of this vegetable before cooking. We've found that an oven temperature of 160-170°F (about 71-77°C) for 15-20 minutes works well for this purpose. We've also found it helpful to make a single layer of the winter squash seeds across a cookie sheet when preparing the seeds for light roasting.

Minerals provided by winter squash also play an important role in its nutrient benefits. This vegetable achieves rankings of very good for manganese and copper, and ranking of good for potassium and magnesium. Smaller amounts of zinc, iron, and calcium are also provided by winter squash.

In terms of phytonutrients, the star quality of winter squash is definitely its carotenoids. The carotenoid-richness of winter squash is responsible for the placement of this vegetable in our WHFoods Top 10 for vitamin A. While the carotenoids beta-carotene and alpha-carotene usually account for the greater percentage of carotenoids in winter squash (especially in those varieties belonging to the Cucurbita moschata genus/species), the complete list of identified carotenoids in winter squash is a long one and spotlight carotenoids are listed below:

  • alpha-carotene

  • auroxanthin

  • beta-carotene

  • beta-cryptoxanthin

  • flavoxanthin

  • luteoxanthin

  • neoxanthin

  • neurosporene

  • phytofluene

  • taraxanthin

  • violaxanthin

  • zeaxanthin

Studies have also confirmed the presence of antioxidant phenols in winter squash, including lignans like secoisolariciresinol. In terms of quantity, the amount of total phenols in winter squash usually ranges from 25-80 milligrams of total phenols (when measured as chlorogenic acid equivalents) in about 3.5 ounces (100 grams) of fresh, uncooked winter squash.

When all of these nutrient categories are combined—macronutrients, vitamins, minerals, and phytonutrients—what you end up with is very broad-based nutrient support from a vegetable that is all-too-often overlooked as too starchy and high-carb to be providing such comprehensive nutrient benefits.

Blood Sugar-Related Benefits from Winter Squash

Over recent years, several areas of nutritional research have overlapped to provide us with a clearer view of winter squash and its impact on our blood sugar. Winter squash has long been established as vegetable with a low or medium glycemic index (GI) value. The difference between medium GI and low GI depends on the GI cut point of 55 that is typically used to differentiate between low and medium GI. We've seen studies on winter squash that show GI values between 55-65 as well as studies that show lower GI values between 50-55. At WHFoods, we classify winter squash as a low-GI food based on a value of 51 that we believe best corresponds to our preferred method of cooking winter squash—namely, short-term steaming (7 minutes). It is worth noting here, however, that many factors that can influence the GI value for winter squash, including the variety of winter squash, season of harvest, length of storage, preparation method, and cooking method. Whatever the factors involved, however, it's clear that winter squash scores lower on the GI scale than other equivalently starchy vegetables (for example, potatoes). Its lower GI values make winter squash a vegetable that is relatively easy on our post-consumption blood sugar levels and beneficial in this regard.

In fact, recent studies have shown that winter squash can help steady the release of sugar inside of our digestive tract after being eaten. (Researchers refer to this set of events as "post-prandial glycemic response.") Scientists are not yet completely certain about the reasons for this blood sugar-related benefit. But one key to this blood-sugar benefit may involve the pectin content of winter squash.

Pectin is an unusual fiber component that is built around special molecules called galacturonans. Galacturonans are polysaccharide-like molecules that contribute to the cell wall structure in many plants. The key galacturonans in pectin are homogalacturonan, rhamnogalacturonan, arabinogalacturonan, and xylogalacturonan. (In fact, these molecules are often referred to as the "pectic polysaccharides.") Research on pectin has shown it to have antidiabetic properties and to help lower the release of sugar from our food into our digestive tract following a meal. This research makes the pectin in winter squash a very likely candidate for the blood sugar-related benefits from this vegetable.

Yet, it's also important not to lose the forest through the trees here. As mentioned previously, winter squash achieves a ranking of "very good" in our WHFoods rating system and provides us with nearly 6 grams of fiber per cooked cup! Pectin definitely makes an important contribution to this total fiber content. At the same time, we would expect most foods that rank as "very good" fiber sources to be helpful foods for regulating blood sugar since fiber intake has long been known to help steady digestion and sugar metabolism in our digestive tract.

Before leaving this area of blood sugar benefits, it's also important to mention the great B-vitamin profile of winter squash. We're talking about a vegetable that we recognize as a very good source of vitamin B6 and a good source of vitamin B2, vitamin B3, folate, and pantothenic acid. These B vitamins play important roles in carbohydrate metabolism and are likely to provide us with blood sugar-related benefits for this reason.

Other Potential Health Benefits from Winter Squash

Because winter squash is a vegetable that has not been studied extensively by food and health researchers, we only have bits and pieces of research evidence for other potential benefits from winter squash.

Several factors combine to suggest that winter squash may be a vegetable that provides us with important antioxidant benefits. These factors include its very good level of vitamin C, the vitamin E contained in its seeds, and of course its amazing carotenoid richness. Added to these factors would be its total phenol content and its antioxidant-related minerals including manganese and copper. However, we have yet to see any large-scale human studies that specifically link intake of winter squash to antioxidant benefits in the body. We fully expect future studies to demonstrate these benefits, however. In parts of the world where intake of winter squash plays an especially prominent role in overall food intake, these antioxidant benefits might be of special importance.

As described earlier, pectic polysaccharides are naturally occurring food fibers known to help benefit blood sugar events following a meal. These polysaccharides have also been shown to help increase satiety (food satisfaction after eating) and also to help lower total blood cholesterol levels. However, research studies have yet to clarify exactly how much food-based pectin would be needed to help lower total cholesterol levels over time. We suspect that future studies will show intake of winter squash to be helpful in this regard, but perhaps in an intermediate way.

The omega-3 fatty acids provided by winter squash—together with its carotenoids and phenols—also make anti-inflammatory benefits from this vegetable a distinct possibility. However, large-scale human studies are definitely needed in this area.

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