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Dr Des Corrigan counts the Christmas calories and looks at the properties of that most controversial of vegetables — the Brussels sprout

Over the years I have written in the December issue about the positive health benefits of the many plants used in our Christmas celebrations, so to include the calorie-fest that is our typical festive dinner might at first glance seem counter-intuitive.

One UK website estimates that the average Christmas dinner provides up to 6,000 calories, with the main course accounting for around 956 of those. Add in a slice of cake for 259, on top of Christmas pudding with cream at 587 (heaven knows what a dollop of brandy butter would add). Just three chocolates from the ubiquitous selection boxes accounts for 133. Even confining yourself to one large glass of red wine (214), a glass of white (190) and a tot of Irish Cream liqueur (320), one can see how the calories mount up to twice the recommended daily intake for a man and three times that for a woman. According to the highly-reliable source that is the Daily Mirror, that intake could reach 7,000 if one adds in the pre-dinner nibbles and bubbles and post-meal chocolates and liqueurs.

On that basis, the health effects are largely to the downside. The possible exception is an unlikely one and is that most controversial of Christmas vegetables, the Brussels sprout. People either love it or loathe it, whether or not it is just served boiled or cunningly disguised with crispy lardons or roasted chestnuts, etc.

Although sprouts have been around since the 13th Century according to the records that suggest that they originated from near the Belgian capital — hence the name — their inclusion on the Christmas dinner plate is more recent. As is the case with much of our Yuletide traditions, we owe a lot to the Victorians, who were obsessed with the exotic and thus were delighted to include these miniature cabbages as part of their roast-based feasting. As ever, timing is everything and sprouts are thought to be at their sweetest after frost, so they are a quintessential winter green vegetable.

As miniature cabbages they are part of the Brassica group that also includes broccoli, kale, red cabbage, cauliflower, cabbage, mustard, cress and kohlrabi. The characteristic compounds in these Brassicas are organosulfur-containing molecules collectively known as glucosinolates. These typically consist of glucose bonded to the sulphur component, usually an isothiocyanate. The most abundant isothiocyanate is sulforaphane, abbreviated to SFN. The corresponding glucosinolate is called glucoraphanin (GLR). This is chemically stable, but biologically inert. It is converted to the biologically-active SFN when it comes in contact with an enzyme called myrosinase when the Brassica is chewed or bitten. GLR can also be transformed into SFN by bacteria in the gut. The highest levels of SFN are reported in broccoli and kohlrabi, but Brussels sprouts have more SFN than even trendy kale when antioxidant activity is measured, being second only to broccoli florets.

The type of Brassica determines the level of SFN, but equally, the way in which the vegetable is cooked or processed also has a huge impact. Myrosinase is heat labile and is destroyed by cooking or even steaming or blanching for more than a minute. So boiling sprouts to within an inch of their lives on Christmas day means that little or no SFN survives.

There has been huge scientific interest in SFN, with 2,315 articles published since it was first discovered in 1948. In 2020 alone, there were 250 papers published. SFN was originally investigated as an antibiotic and found to be active against H.Pylori.

Most attention has focused on the anti-cancer effects of SFN, based largely on epidemiological data supported by extensive in vitro and in vivo research on a variety of tumour models. SFN promotes apoptosis, induces cell cycle arrest, inhibits angiogenesis, reduces inflammation, alters susceptibility to carcinogens, reduces invasion and metastasis, and has antioxidant activity in cell and animal-based studies. It also has anti-ageing, neuroprotective and anti-diabetic activity.

Studies have shown the benefits of Brassica intake in terms of decreasing allcause mortality (Clinical Nutrition 2019), cardiovascular mortality (J Am Heart Assoc 2020), type 2 diabetes (Diabetes Investigation 2016), renal carcinoma (PLOS One 2013), and mortality due to breast (Cancer Research 2020) and lung cancer (Science Reports 2015). There are also strong indications of reduced risk of bladder cancer based on a meta-analysis in the World Journal of Urology in 2013.

A review in Current Medical Science (2021) described SFN as a promising natural molecule for cancer prevention and treatment, referring to the extensive in vitro and in vivo evidence and some recent human studies, for example a 2015 study where patients with recurrent prostate cancer were given a SFN-rich broccoli extract for 20 weeks. The time needed for the PSA levels to double was significantly increased during treatment, but only one of the 20 patients had a 50 per cent reduction in PSA levels, which was the primary outcome measure. RCTs in patients with breast cancer and melanoma are ongoing.

Studies have shown the benefits of Brassica intake in terms of decreasing all-cause mortality

The role of SFN in protecting against chronic kidney disease based on its powerful ability to activate a key transcription factor (NRF2) that induces expression of enzymes that combat the effects of oxidative stress relevant to CKD was reviewed in a 2018 article in Drug Design, Development and Therapy (2018). That effect on NRF2 is also cited as a factor in the ability of glucoraphanin and SFN to fight obesity through effects on insulin resistance, adipocyte differentiation and lipolysis.

Other reviews have suggested benefits in a variety of neurological conditions, including Alzheimer’s, Parkinson’s and Huntington’s. Its value as a safe and effective treatment in autism spectrum disorder was the subject of a 2020 review in EXCLI (Experimental and Clinical Sciences) journal.

The downside (apart from objections to the taste and smell of sprouts) arises from excess consumption that can lead to hypoglycaemia in diabetics, gastric irritation, IBS, diarrhoea, abdominal pain and flatulence due to the high fibre content. Some isothiocyanates can be goitrogenic, leading to hypothyroidism. There is also a risk of the vitamin K content of sprouts interfering with INR levels in patients on warfarin who consume large quantities of sprouts over a period of time.

Overall, SFN looks to be a highly interesting molecule with apparently enormous potential as a chemopreventative. Dosage and bioavailability are challenges, as is the cost of the largescale clinical studies needed and that surprisingly have not been done to date. For those of you still trying to decide to ‘sprout or not to sprout’ on 25 December, you may want to note that typical dietary intake of SFN is likely to be way below the bioactive/cytotoxic dose needed to prevent or treat cancer. No matter what you decide, I hope your Christmas Day will be a peaceful and happy one and that 2023 brings you the success and happiness you deserve.