Are Pumpkins Cancer-Squashing Superfoods?

cancer-fighting pumpkins with vitamin a

We think of fruits as being sweet and juicy, yet the two fruits Americans love to eat most on Thanksgiving are neither. Intensely colorful and tart cranberries, despite being so dry and sour that they taste absolutely terrible in their natural state, are always invited to Thanksgiving dinner. But cranberries are not the only unusual fruits donning the Thanksgiving dinner table—what fall feast would be complete without a bright orange member of the squash family?

Squashes are fruits

We think of most squashes as vegetables because they are dry and starchy rather than sweet and juicy. However, because they contain seeds, they are actually fruits in disguise. The Cucurbita family (squash family) includes not only squashes, pumpkins, and gourds, but also zucchini, yellow squash, cucumbers, and melons. Let’s take a closer look at these vibrant autumn unfruity fruits.

Fruits vs. vegetables

Those of you familiar with my philosophy about vegetables know that I view them as untrustworthy and deserving of suspicion (see my Vegetables page)—but what about fruits? Plants that rely on animals to disperse their seeds tend to wrap their seeds in fruits to entice hungry mobile sorts. If all goes as planned, an unsuspecting creature will eat the seedy fruit, walk away, digest the fruit, and later deposit the seeds, along with a nice meadow-muffin of natural fertilizer, in just the right spot so they can germinate and grow into mature plants. Not the most romantic method of reproduction, but so effective that it's been around for hundreds of millions of years. Plants want and need animals to eat their fruits, so it would not be in their best interest to invest fruits with toxic compounds—it would be unwise to sicken or kill your reproductive helpers. Therefore, hypothetically speaking, the chemicals in fruits should be gentler on our systems than those in vegetables.

Pumpkins and other squashes are not particularly appealing fruits in their natural state—they generally need to be cooked in order to be palatable. Of course plants in the squash family also have vegetable parts—stems, roots, and leaves, but we don't tend to eat those parts, probably because they don't taste very good. In fact, even many fruits in this family don't taste very good—when was the last time you enjoyed a nice steaming helping of gourd?

Pumpkins and squashes, deconstructed

The Cucurbita moschata include several varieties of pumpkins and squashes, including butternut squash. The poor pumpkin family—they have had every inch of their beings, from stem to seeds, violated by scientists who hope to discover magical, life-saving ingredients. In this post we'll focus only on the fruit flesh of pumpkins and squashes, since that’s what we like to eat on Thanksgiving.

Does orange = vitamin A?

Carotenoids (such as alpha and beta carotene) are responsible for the beautiful orange color of pumpkins and squashes. We think of orange foods like carrots and sweet potatoes as excellent sources of vitamin A, but you may be surprised to learn that plant foods contain no vitamin A at all, at least as far as humans are concerned. Herbivores (vegan animals) and many other animals possess an enzyme that can convert carotenoids to vitamin A, but we don't. In our bodies, plant carotenoids have to jump through a series of biological hoops in order to become the active form of vitamin A (retinol) that our bodies can use.

Carotenoids in fibrous foods like pumpkin are trapped within plant cell walls made of indigestible cellulose (insoluble fiber), so that even after cooking and digesting pumpkin, a maximum of only 25% of the carotenoids are freed from its rigid fibrous matrix. Fat is then required to absorb carotenoids (pass the butter please), but even if we eat enough fat with our pumpkin or squash, we can only absorb about 8% of the carotenoids within. Furthermore, once it's inside our bloodstream, we can only convert about 50% of the beta carotene into active vitamin A. The conversion rate varies widely from one plant food to another. The National Institutes of Health estimate that it is 12 to 24 times more difficult for our bodies to extract vitamin A out of plant foods than from animal foods. Vitamin A from animal sources is in the form of retinyl esters, not carotenoids, and we easily convert these to active vitamin A; therefore, they are completely bio-available. Good food sources of vitamin A include egg yolks and dairy products, but the best source of vitamin A is actually liver. Unfortunately liver is not a pretty orange vegetable, but hey, looks aren't everything.

Can pumpkins cure cancer?

Well, maybe . . . if you drop one directly on top of a tumor . . .

Pumpkin’s latest claim to fame is cucurmosin, a chemical within pumpkin flesh that is toxic to cancer cells under laboratory conditions. Cucurmosin is a “Ribosome Inactivating Protein”, RIP for short. RIPs are aptly named because they are deadly. RIP’s kill cells by stopping their ribosomes dead in their tracks. Ribosomes are the protein manufacturing assembly lines within all cells (not just cancerous cells), so if they are taken out of commission, all cellular activity grinds to a screeching halt, killing the cell. Two especially potent RIPs are notorious poisons—Shiga toxin (from bacteria) and ricin (from castor beans). Luckily, cucurmosin is a kinder, gentler variety of RIP, because it has a harder time breaking into cells to get at their ribosomes. However, when it does, it is just as merciless as other RIPs. Pumpkins and squashes use cucurmosin to ward off invaders such as bacteria and viruses.

But wait . . . healthy cells also contain ribosomes—does cucurmosin kill them too?

It may be reassuring to know that, in laboratory studies, it takes a much higher dose of cucurmosin to kill healthy cells than to kill cancer cells. But most importantly, and very reassuringly, cooking destroys cucurmosin.

The bottom line

Happily I have found no evidence that compounds within the fruity flesh of pumpkins and related squashes are harmful to our health, provided we eat them cooked. This is in keeping with my theory that the fruity parts of edible plants are usually less likely to irritate our bodies than the vegetable bodies of plants. So chances are excellent that you can enjoy your beautiful, bountiful, colorful, giant pumpkins with wild abandon! Just remember to cook them first, use plenty of delicious fat, and keep the added sugar to a minimum:)

Next up, we explore the magical healing powers of our other holiday favorite in "Cranberries for UTI prevention: Crimson Crusader or Juicy Gossip?"


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