The Green Power

With spring come seasonally grown local foods and green leafy vegetables (GLV) become more desirable for quality, and especially for their overall health benefits. Examples of GLV include salads, kale, broccoli, collard greens, spinach, mustard greens, etc. Although there is a large variety of GLV to choose from, most clinical scientific research focuses on broccoli and cruciferous vegetables.

Green Leafy Vegetables

GLV do not fall short when it comes to providing health benefits to many chronic health conditions. One of the foods listed as heart-protective by the Heart and Stroke Foundation of Canada are:

• GLV;
• Foods containing beta-carotene (e.g., carrots, tomatoes, squash, sweet potatoes); and
• Foods high in vitamin C (e.g., broccoli, red peppers, strawberries, oranges).¹

Furthermore, dietary nitrates found in GLV (as opposed to nitrates added in packaged foods) offer cardiovascular benefits through their conversion to nitric oxide, a vasodilator.

Effects of GLV on Heart Health and Cardiovascular Disease—What Studies Say

A review of human-intervention studies on the effects of dietary nitrate on blood pressure and endothelial function suggested an inverse relationship between dietary nitrate consumed and corresponding systolic blood pressure. Doses as low as 3 mmol of nitrate were reducing systolic blood pressure by 3 mmHg.²

A 14‑year observational study found an inverse relationship between vegetable nitrate intake and cardiovascular disease (CVD) mortality, independent of lifestyle and cardiovascular risk factor in men and women older than 49. All quartiles in groupings of greater than 69.5 mg/d of vegetable nitrate intake demonstrated a proportional lowered hazard ratio for CVD mortality.³

Another study investigated the effects of a GLV snack in 222 women aged 14–35 years. The study found that the snack containing 54.1 mg alpha-linolenic acid (ALA) from GLV, compared to a control snack with 4.1 mg ALA, led to a 24% increase in medium-chain erythrocyte DHA levels after 12 weeks of supplementation, and an inverse relationship with plasma homocysteine levels. Similar beneficial cardiovascular effects were also noticed in men with insulin resistance that were supplemented with green leafy vegetables along with their fat-rich meal.⁴

Broccoli and Cruciferous Vegetables

Broccoli and its chemical by‑products have a more clinical significance on chemoprevention, liver detoxification support, and promotion of healthy estrogen metabolism. Due to a particular sulfur-rich compound called sulforaphane, diets rich in cabbage, broccoli, and cauliflower suggest chemoprotective effect in certain cancer types⁵, and has given rise to pilot research.⁶

There are several human clinical trials investigated the impact of broccoli (500 mg/d), Brussel sprouts (250 mg/d), and other cruciferous vegetables on their ability to influence cytochrome enzymatic activity in the liver, hence enhancing its detoxification pathways. ⁷

Another benefit of broccoli and cruciferous vegetables is observed via their ability to reduce free radicals. This has implications for several diseases that are made worse from free-radical damage. It was for example observed in a randomized controlled trial study with autistic individuals, who experienced symptom reduction after 18 weeks of supplementation with the sulforaphane supplement. The young adults in the treatment group had a reduction in social dysfunction and behavioural issues as seen in the Aberrant Behaviour Checklist (ABC), Social Responsiveness Scale (SRS), and Clinical Global Impression Improvement Scale (CGI‑I) (p = 0.015–0.007). Both statistical and clinical relevance were observed in this study, and on discontinuation of the supplements, scores rose to pretreatment levels. This suggests that continued supplementation is likely required and suggests a dose-dependent relationship.

Apart from autistic spectrum disorders, any condition with high levels of oxidative stress and low antioxidant capacity—along with depressed glutathione synthesis, mitochondrial dysfunction, and higher lipid peroxidation/neuro-inflammation—has the potential to benefit from sulforaphane supplementation. However, more evidence and funding for research is needed.

Benefits of GLV on Hormone Health

Intestinal health and transit are important considerations in the prevention of hormone-related disorders. Enzymes secreted in the stomach and intestine break down nutrients, which are absorbed throughout the intestine. Some enzymes promote the healthy absorption of nutrients, but some ensure the adequate elimination of the by‑products of metabolism, such as hormones, medications, and other toxins. These so‑called detoxification enzymes are mostly found in the liver and in the intestines, but they are also found in other organs.

Without adequate fibre or with changes in the microbiome, the harmful by‑products or hormones that we would want out of the system, have a potential chance to get reabsorbed. This is what could potentially happen with estrogen, as its metabolism is tightly regulated with bowel health and with how the liver functions to break down estrogen.

Dietary indoles in cruciferous vegetables are known to induce cytochrome P450 enzymes and have prevented tumours in various animal models. Because estradiol metabolism is also cytochrome P450–mediated and linked to breast-cancer risk, indoles found in cruciferous vegetables may theoretically reduce estrogen-responsive tumours in humans.

The most potent inducer, indole‑3‑carbinol (I3C), was administered to humans (500 mg/d for one week). It significantly increased the extent (mean ± SEM) of estradiol 2‑hydroxylation from 29.3% ± 2.1% to 45.6% ± 2.1% (p < 0.001)⁹. These results indicate that I3C influences estradiol metabolism in humans and may provide a new chemopreventive approach to estrogen-dependent diseases. However, it was noted that isothiocyanates and indoles derived from the hydrolysis of glucosinolates, such as sulforaphane and indole‑3‑carbinol (I3C), have an anticarcinogenic mechanisms, but deleterious effects have also been reported in some experimental protocols, including tumour promotion over prolonged periods of exposure. Epidemiological studies indicate that human exposure to isothiocyanates and indoles through cruciferous vegetable consumption may decrease cancer risk, but the protective effects may be influenced by individual genetic variation (polymorphisms) in the metabolism and elimination of isothiocyanates from the body. Cooking procedures also affect the bioavailability and intake of glucosinolates and their derivatives.¹⁰

Along with I3C compounds, quercetin is a flavonoid found in various fruits and vegetables, including green beans and broccoli, and has health-promoting effects. And last but not least, green tea (although not a green vegetable per se, but it is green!) and its main active compounds, catechins, have also been studied in human clinical research for its antioxidant capacities. Overall, the various compounds in GLV target multiple pathways to better health.

To incorporate more greens into your lifestyle, here are a couple of my favourites!

Dr. Kaitlyn’s Greens Smoothie

• Handful of kale or spinach
• 1 ripe avocado
• A few ice cubes
• 1 banana
• 1 tsp. maple syrup or agave to sweeten

Easy Broccoli Stir-Fry

• 1 cup of broccoli
• Cashews
• Sesame oil, gluten-free soy sauce, or tamari

Sauté chopped garlic and ginger in sesame oil. Add in broccoli with a bit of water, and cashews at the end. Serve over brown rice.