It turns out that giving fruits and veggies a good night’s sleep isn’t the only way to make them better to eat. Researchers at Texas A&M have shown that carrots produce more antioxidants in response to the “stress” of being chopped or shredded, while scientists at the University of Florida are working hard to make a tastier and more nutritious tomato. Read more
In 400 BCE, the Greek admiral Androsthenes wrote* of a tree that
“opens together with the rising sun . . . and closes for the night. And the country-dwellers say that it goes to sleep.”
Over the next 2000 years, researchers discovered that the daily cycles first observed by Androsthenes fall into 24-hour periods similar to our own cycles of waking and sleeping . In plants, these circadian rhythms help control everything from the time a plant flowers to its ability to adapt to cold weather . Plants can even use their internal clocks to do arithmetic calculations to budget their energy supplies through the night .
But what happens when part of a plant is harvested for food? In a recent study, researchers at Rice University and UC Davis showed that cabbages can exhibit circadian rhythms as long as a week after harvest.
As with any plant, cabbages experience circadian rhythms while growing out in the field; however, cabbages stuck in the constant dark of a delivery truck or light of a 24-hour grocery store will inevitably lose their sense of time. Like travelers adjusting to a new time zone, cabbages deprived of cyclic light conditions suffer a severe bout of veggie jet lag. And just as travelers overcome jet lag by readjusting their sleep cycles, cabbages can “re-entrain” their circadian rhythms by being exposed to cyclic light conditions. This also works with spinach, zucchini, sweet potato, carrots, and blueberries, suggesting that post-harvest circadian rhythms are a general characteristic of many, if not all, fruits and vegetables.
The ability to re-entrain circadian rhythms in produce presents an intriguing new way to improve the palatability and even nutrition of our fruits and vegetables. In the wild, circadian rhythms can help plants defend themselves against hungry herbivores. The researchers showed that cabbages with re-entrained circadian rhythms use a similar mechanism to avoid becoming an afternoon snack for plant-eating larvae—with less damage from hungry larvae, re-entrained cabbages appear fresher and tastier than cabbages kept under constant light or dark conditions.
Cabbages fight off larvae and other pests thanks to molecules called glucosinolates. Any cabbage can produce these molecules, but re-entrained cabbages produce glucosinolates in sync with their circadian rhythms. Because larvae also experience circadian rhythms, re-entrained cabbages get an extra boost of molecular larvae-fighting power just when they need it the most.
While glucosinolates are bad news for larvae, they have valuable anti-cancer properties when consumed by humans. In fact, the very molecules that plants create to defend themselves against their environment are often beneficial for our own health. Future research will show whether such phytonutrients in other types of produce can also be reconditioned to accumulate in predictable 24-hour cycles. Taking advantage of circadian rhythms in fresh produce could then give us more control over the way phytonutrients accumulate over time, helping us maximize the nutritional benefits of our fruits and vegetables. Improving the nutrition of our food could be as simple as giving our produce a good night’s sleep.
*The original Greek passage comes from Botanische forschungen des Alexanderzuges  with a very special thank you to Tovah Keynton for the English translation. The drawings (also from Botanische) depict the tree leaves transitioning into and then assuming their “sleeping position.”
- McClung CR (2006) Plant Circadian Rhythms. PLANT CELL ONLINE 18: 792–803. doi:10.1105/tpc.106.040980.
- Kinmonth-Schultz HA, Golembeski GS, Imaizumi T (2013) Circadian clock-regulated physiological outputs: Dynamic responses in nature. Semin Cell Dev Biol 24: 407–413. doi:10.1016/j.semcdb.2013.02.006.
- Scialdone A, Mugford ST, Feike D, Skeffington A, Borrill P, et al. (2013) Arabidopsis plants perform arithmetic division to prevent starvation at night. eLife 2: e00669–e00669. doi:10.7554/eLife.00669.
- Bretzl H (1903) Botanische forschungen des Alexanderzuges. B. G. Teubner.
Author Jo Robinson explores the agricultural history of phytonutrients, while Harvard researchers move us a step closer toward understanding how the resveratrol in red wine and chocolate could be hindering the aging process. Read more
If you take a look at the Nutrition Facts panel on your favorite snack, you can learn a lot about the different molecules in your food. These molecules—fats, proteins, carbs, vitamins, and minerals—are essential for our health: they provide energy for our bodies and can be recycled to form the molecular building blocks of our cells. Many of these molecules even promote specific molecular processes: Vitamin C helps build the collagen in connective tissue , while iron allows oxygen to bind red blood cells and be transported through the body .
But there’s an entire class of nutrients you won’t find listed in the Nutrition Facts: phytonutrients. While phytonutrients (also called phytochemicals) are not essential for our survival, they can have beneficial effects on our health. Trendy “superfoods” are often high in phytonutrients like resveratrol, flavonoids, or antioxidants.
This fruit smoothie recipe from Dr. Dena Herman packs a big punch of antioxidants thanks to a generous serving of antioxidant-rich berries. Antioxidants are a large group of chemicals that have the ability to counteract a process called oxidation. A material is “oxidized” when it loses electrons through a chemical reaction; antioxidants can impair this process by giving up electrons and becoming oxidized themselves. For example, apples that are cut and exposed to the air will quickly turn brown as oxygen interacts with and oxidizes molecules in the fruit’s tissue. Lemon juice can prevent this oxidative browning because it contains antioxidant molecules like Vitamin C.
In our bodies, oxidation can lead to cellular damage by breaking down important molecules like proteins, fats, and even DNA. Molecules that promote oxidative damage not only come from environmental factors like air pollutants, smoke, and UV radiation, but can also come from our own bodies as a byproduct of many cellular and metabolic processes. Our bodies are equipped to deal with moderate amounts of damage; however, extensive “oxidative stress” can wreak havoc on our cells and may contribute to the development of cancer, insulin resistance, and several cardiovascular and neurological diseases [3,4]. Consuming foods rich in antioxidants is thought to help counteract such harmful oxidative stress.
Makes about 4-6, 8 oz glasses
1 package silken tofu or soft tofu
2 cups mixed frozen berries*
2–3 tbsp apple juice concentrate
Water or unfiltered apple juice, enough to blend
*Other types of frozen fruit will work, but do not include citrus as it will curdle with tofu. Berries are used in this recipe because they are a great source of antioxidants.
- Blend all ingredients in a blender until smooth.
- Adjust to desired consistency by adding more water or unfiltered apple juice.
- Serve immediately and enjoy!
- USDA Agricultural Research Service, “Phytonutrient FAQs”
- Harvard School of Public Health, “Antioxidants: Beyond the Hype”
- NIH MedlinePlus, “Antioxidants”
- Scientific American, “Is the Free-Radical Theory of Aging Dead?”
- NIH Research Radio Podcast on Resveratrol
- Van Robertson WB, Schwartz B (1953) Ascorbic acid and the formation of collagen. J Biol Chem 201: 689–696.
- Dallman PR (1986) Biochemical basis for the manifestations of iron deficiency. Annu Rev Nutr 6: 13–40. doi:10.1146/annurev.nu.06.070186.000305.
- Houstis N, Rosen ED, Lander ES (2006) Reactive oxygen species have a causal role in multiple forms of insulin resistance. Nature 440: 944–948. doi:10.1038/nature04634.
- Figueira TR, Barros MH, Camargo AA, Castilho RF, Ferreira JCB, et al. (2013) Mitochondria as a Source of Reactive Oxygen and Nitrogen Species: From Molecular Mechanisms to Human Health. Antioxidants Redox Signal 18: 2029–2074. doi:10.1089/ars.2012.4729.
Nutrition specialist Dr. Dena Herman introduced UCLA students to the molecules of food and nutrition as part of our 2013 Science and Food course. We learned all about essential nutrients, were introduced to the exciting new world of phytonutrients, and even got to make smoothies! Check out the highlights: