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Healthy Interaction Between Cruciferous Vegetables and Your Digestive Tract

When we think about the health benefits of foods like cruciferous vegetables, most of the time we think about the nutrients they provide. In the case of cruciferous vegetables, for example, we might think about their great fiber content, or their vitamin C, or their unique phytonutrients like glucosinolates. But did you know that the health benefits from cruciferous vegetables include their supportive interaction with your digestive tract? And more specifically, did you know that intake of cruciferous vegetables significantly changes the composition of bacteria that help you digest food?

Researchers at the Fred Hutchinson Cancer Research Center in Seattle, WA have recently conducted a fascinating study on cruciferous vegetables and bacteria in our digestive tract. Participants in the study rotated between 4 different diets: (1) a low-quality diet that contained only 9 grams of fiber and no vegetables or fruits of any kind whatsoever; (2) a higher quality diet that included about 400 grams (or approximately 2-3 cups) of cruciferous vegetables; (3) a higher quality diet that included about 800 grams (or approximately 4-6 cups) of cruciferous vegetables and about 29 grams of total fiber; and (4) a mixed diet containing about 400 grams of cruciferous vegetables and another 200-300 grams of other vegetables (including carrots and celery). The cruciferous vegetables used in the study were broccoli (45% of the total cruciferous vegetables), cauliflower (35%), cabbage (16%), and radish sprouts (4%). The sprouts and the cabbage were consumed in raw form, and the broccoli and cauliflower were consumed cooked. All participants in the study consumed the same total number of daily calories (about 2,280) regardless of the different diet type.

While rotating the study participants through the four different types of diets, the researchers took a very careful look at the participants' intestinal bacteria. They used a highly specialized technique—called molecular fingerprinting—to look at DNA in the genes of the bacteria, and to determine very specifically what happened to different groups of bacteria in the gut. What they found was fascinating. First, each individual participant had his or her own unique mixture of bacteria when starting the study. Second, the gut bacteria changed in a dramatically different way when participants followed the low-quality fruit- and vegetable-free diet versus the diets containing cruciferous vegetables. Third, the intake of cruciferous vegetables brought about consistent types of changes in the gut bacteria, even though each participant still ended up with his or her own unique balance.

The changes in gut bacteria were especially interesting because some of the bacteria groups becoming much more plentiful following consumption of broccoli, cauliflower, cabbage, and radish sprouts were groups of bacteria that are known to metabolize glucosinolates, lignans and fiber. All of these nutrients are found in cruciferous vegetables! In fact, the ability to metabolize glucosinolates (and convert them into cancer-preventive isothiocyanates) may be a very important factor in prevention of certain cancers, including cancers of the digestive tract. It's amazing to think that cruciferous vegetables like broccoli not only bring with them key phytonutrients like glucosinolates, but also the ability to shift bacterial populations in the gut in a way that optimizes the value of these glucosinolates for our health!

One additional point seems worth mentioning, and that involves the issue of raw versus cooked cruciferous vegetables. The chopping and immediate cooking of cruciferous vegetables has traditionally been regarded as a practice that denatures the myrosinase enzymes found in these raw vegetables. Since these myrosinase enzymes are needed to convert the vegetables' glucosinolates into isothiocyanates, chopping and immediate cooking has traditionally been viewed as a practice that might rob us of the full benefits of vegetables like broccoli or cabbage by preventing the conversion of glucosinolates to isothiocyanates by myrosinase enzymes found in fresh, raw broccoli. This new research suggests that vegetables like broccoli or cabbage might have the ability to increase the numbers of gut bacteria with myrosinase enzymes such that the conversion of glucosinolates to isothiocyanates has a much better chance of occurring in our digestive tract when we eat cooked broccoli, cabbage, or other cruciferous vegetables.

WHFoods Recommendations

Never underestimate the miraculous benefits of whole, natural, nutrient-rich foods! Even when we cook foods and change their raw chemical composition, they may be able to bring about changes in our digestive tract that result in optimal nourishment. In the case of cruciferous vegetables like broccoli, you may not need to worry about consuming these vegetables in raw versus cooked form due to fears about heat deactivation of myrosinase enzymes and loss of potential phytonutrients (isothiocyanates) that can help protect you from cancers. These lightly cooked vegetables may be able to bring about shifts in your gut bacteria so that you have plenty of bacteria with myrosinase enzymes of their own, giving you additional cancer protection.

References

  • Fei Li, Meredith A J Hullar, Yvonne Schwarz et al. Human Gut Bacterial Communities Are Altered by Addition of Cruciferous Vegetables to a Controlled Fruit- and Vegetable-Free Diet. J Nutr. 2009 Sep;139(9):1685-91. 2009.

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