Variety Matters With Fruit & Veg

Research continues to reveal the astonishingly wide range of different phytonutrients in fruits and vegetables (F/V), and that we need a variety of these in order to protect different parts of our bodies. Variety and not just quantity is something we would do well to consider carefully if we want to do the best for our bodies and minds.

Study 1

An October 2011 study 1  looked at whether increased intake of different F/V would have a positive effect on decreasing the risk of specific colorectal cancers (CRC).

The study concluded that: “…the association between intake of F/V and CRC may be different according to the location of the cancer:

  • the risk of proximal colon cancer seemed to be decreased with increased intake of brassica vegetables
  • the risk of distal colon cancer seemed to be decreased with increased intake of brassica vegetables, apples, and dark yellow vegetables
  • the risk of rectal cancer was increased by increased intake of fruit juice

Discussion

It may be a surprise to you that fruit juice is associated with an increased risk of cancer – in this case rectal cancer – but it’s been known 2 3 4 5  for a quite some time time that fruit juice is not a healthy option – you may as well drink Coke 6 !

Study 2

An August 2012 study 7 looked in some detail at how each vegetable contains a unique combination of phytonutrients and, thus, the authors encourage us to eat a great diversity of vegetables to ensure that our diet includes a combination of these phytonutrients and that we thereby reap their health benefits.

A glimpse at the variety of phytonutrients in vegetables

  • the Apiaceae family (e.g. celery, parsley, carrot) is rich in flavonoids, carotenoids, vitamin C, and vitamin E
    • celery and parsley for example are among the best vegetables sources for the flavonoid apigenin and vitamin E 8
    • carrots have an unique combination of three flavonoids: kaempferol, quercetin, and luteolin9 10 11
  • the Asteraceae or Compositae family (e.g. lettuce, chicory) is rich in conjugated quercetin, flavonoids, and tocopherols
    • different lettuce cultivars contain significant variations in flavanol content 12
  • the Cucurbitaceae family (e.g. pumpkin, squash, melon, cucumber) is rich in vitamin C, carotenoids, and tocopherols 13
    • different melon groups have up to a 50-fold variation in ascorbic acid content 14
    • bitter gourd (Momordica charantia) has anti-diabetic properties and can be used to ameliorate the effects of type-2 diabetes 15
  • the Chenopodiaceae family (e.g. spinach, Swiss chard, beet greens) is an excellent source of folate 16
    • these veg can inhibit DNA synthesis in proliferating human gastric adenocarcinoma cells, hence helping to prevent stomach cancer 17
    • the Chenopodiaceae veg are high in oxalates which, if they become too concentrated in body fluids, can crystallise and cause health problems such as kidney calcium oxalate stones. [However, as Dr Greger has repeatedly pointed out 18 19 , it’s only if you are eating huge quantities, specifically of Swiss chard or spinach, that there’s any possible worry about kidney stones being caused by eating these wonderfully healthy plants. So don’t skimp on these greens, especially kale. Their benefits far outweigh any potential deficits if eaten to excess.]
  • the Fabaceae or Leguminosae family (that is, all the legumes, such as beans, peas, soybeans, chickpeas, lentils) are good sources of dietary fibre and isoflavonoids 20

    • total, soluble and insoluble fibre and fermentability characteristics of various legumes have been shown 21 to vary significantly, as have levels of iron, zinc and calcium within different legumes
  • the Brassicacea or Cruciferae family (the cruciferous vegetables, including cabbage, broccoli, cauliflower, Brussels sprouts, kales, kailan, chinese cabbage, turnip, swede/rutabaga, radish, horseradish, rocket, watercress, mustards) are the best sources of glucosenolates in the human diet
    • major research has shown 22 that a crucifer-rich diet is likely to protect humans against colon, rectum, and thyroid cancers
    • when cruciferous veg at consumed with other phytonutrient-rich veg, the combination was also shown by the same research to protect against cancer in other organs.
    • broccoli, cabbage, Brussels sprouts, and kale have been shown 23 24 25 26 27 to protect against lung, prostate, breast and chemically induced cancers
    • diets rich in broccoli specifically have been shown 26 27 to have potential in reducing the risk of prostate cancer. [Remember that chopping the broccoli and leaving for at least 40 mins before cooking/eating raw is far, far more effective in making the sulphoraphane available to your body, as discussed in some detail in an earlier blog 28
    • research suggests 29 that there are significant differences in the health benefits among crucifers
    • within 65 cultivars of broccoli, there’s a 27-fold variation in glucoraphanin levels 30
    • between 21 cultivars of red cabbage and 6 cultivars of white cabbage, there was shown 31 to be a considerable variation in the concentration of the individual glucosenolates, with red cabbage cultivars being found to contain a lot more glucoraphanin than white cabbage cultivars
    • white cabbage cultivars contained significantly higher (and, once again, varying) levels of glucoiberin when compared to red cultivars
  • the Alliaceae family (allium vegetables, including garlic, onion, leek and chive) are rich sources of a wide variety of thiosulfides, which vary significantly in content between different alliums
    • alliums have been linked to reducing various chronic diseases
    • they are also high in flavonoids: anthocyanins in red onions and flavonols like quercetin and kaempferol in most yellow onions
    • onions also contain chromium which is linked 32 to diabetes prevention
    • onions are particularly rich in two types of fibre – inulin and neokestose (types of fructans). These have been demonstrated 33 34 to have prebiotic properties which encourage the proliferation of beneficial gut bacteria such as Lactobacilli and Bifidobacteria.
    • these frutans in onions also promote the absorption of calcium and are considered to be useful in the prevention of osteoporosis 35
    • also, high fructan diets have also been shown to lower blood concentration of cholesterol, triacylglycerol, phospholipids, glucose and insulin 36 and to have anti-diabetic potential 37
    • there’s a strong link between onion consumption and reduced risk of of stomach and intestine cancers 38 as well as colon, ovary, larynx, and mouth cancers 39
    • garlic consumption is associated with a reduction in the incidence of oesophageal and stomach tract cancers 40 , the reduction in the incidence of preneoplastic lesions occurring in the gastric mucosa of individuals infected by Helicobacter pylori 41 , and a reduced cancer risk of colorectal and prostate cancers 42 43
    • some studies have shown 44 45 46 that regular intake of alliums is associated with reduced incidence of breast, endometrium and lung cancers
  • the Solanaceous or nightshade family of vegetables have significant differences in phytonutrient content and have been studied for many decades (if not centuries) for their health-promoting properties. Amongst them are tomatoes, potatoes, sweet and hot chillies, and aubergines/eggplants
  • Tomatoes are a low energy dense food with unique health-benefiting phytonutrient constituents – specifically their carotenoids (lycopene, phytoene, neurosporene, and carotenes), levels of which vary between processed (sauce, paste, juice, and ketchup) and fresh tomatoes – again varying depending on whether eaten raw or cooked with different methods for different periods of time
    • tomatoes provide high levels of provitamin Avitamin A and potassium in the modern Western diet 47 48
    • tomatoes are an excellent source of ascorbic acid and vitamin C, and contain small but significant amounts of lutein, α-, β-, γtocopherols and conjugated flavonoids 49
    • in one study of 20 tomato cultivars, total flavonoid content varied between 1.3 to 22.2 mg/kg with about 98% present in the skin 50
    • in fresh tomatoes, flavonoids are only present in the conjugated form as quercetin and kaempferol 51 , but in processed tomato products there are also significant amounts of free flavonoids
    • the flavonoid content of tomatoes varies with cultivar and culture (e.g. cherry tomatoes have a more flavonoids than standard or beef tomato cultivars, and field-grown tomatoes have higher flavonoid content than greenhouse grown 52
    • tomatoes vary in levels of vitamin C, vitamin A, lycopene (high levels of which produce the bright crimson tomatoes) and anthocyanin (high levels of which produce purple tomatoes)
    • research has shown an inverse relationship between plasma/serum lycopene concentrations and risk of pancreatic cancer 53 , cervical cancer 54 , digestive tract cancers 55 , bladder cancer 56 , lower prostate cancer 57 , stomach cancer 58 , and lung cancer 59 , stomach and rectal cancers 60cognitive dysfunction, Alzheimer’s, Parkinson’s disease and vascular dementia 61 62 63  , cardiovascular disease 64 , osteoporosis and body weight 65 66 , lung cancer 67
    • consuming diets with large amounts of antioxidants from plant foods, such as tomatoes, is thought to inhibit the oxidative process of low density lipoprotein (LDL cholesterol – the ‘bad stuff’) 68 69 70 , thus reducing the risk of cardiovascular atherosclerotic disease
  • potatoes are an excellent source of carbohydrates and essential amino acids
    • the main carbohydrate in potatoes is starch, and a small but significant part of this is resistant starch. Because it resists digestion by enzymes in the stomach and small intestine, this resistant form reaches the large intestine virtually intact. This has positive health benefits as dietary fibre:
      • provides bulk
      • protects against colon cancer
      • improves glucose tolerance
      • improves insulin sensitivity
      • lowers plasma cholesterol
      • lowers triglyceride concentrations
      • increases satiety
      • reduces fat storage 71 72 73
    • preparation method affects the amount of available resistant starch –  for instance, cooked potato starch contains about 7% resistant starch, which increases to about 13% upon cooling 74
    • it’s a fallacy that eating potatoes will make you obese. It’s been demonstrated that you can still lose weight and include potatoes in your diet 75
    • the GI (glycaemic index) of potatoes is usually regarded as being high, and so it’s often advised that they are removed from low-GI diets. However, the GI of a potato varies significantly depending on its type (e.g. red or white), where it was grown, how it was prepared (hot or cold, mashed, whole, cubed, etc)
    • the protein content of potatoes (around 6%) is among the highest quality found in vegetables, being high in essential amino acids ( such as lysine, and other metabolites that might improve protein utilisation), and compares with the protein content of cow’s milk 76 77 78
    • potatoes accumulate significant amounts of vitamins, minerals, and a wide range of phytochemicals, including phenols (such as chlorogenic acid), phytoalexins, and protease inhibitors 79
    • a medium-size 150 g potato with the skin provides 27 mg of vitamin C (45% of the daily allowance), 620 mg of potassium (18% of daily allowance), 0.2 mg vitamin B6 (10% of daily allowance) and trace amounts of thiamine, riboflavin, folate, niacin, magnesium, phosphorus, iron, selenium and zinc
    • different parts of the potato have different phytonutrient content, with nearly 50% of the total phenolic compounds being located in the peel and adjoining tissue, but decreasing toward the centre 80
    • antioxidants in potatoes include α-tocopherol, lutein, and β-carotene 81
  • peppers are excellent sources of vitamins C, K, carotenoids, and flavonoids 82
    • antioxidant vitamins A and C help to prevent cell damage, cancer, and diseases related to aging, and they support immune function and reduce inflammation like that found in arthritis and asthma
    • vitamin K promotes proper blood clotting, strengthens bones, and helps protect cells from oxidative damage
  • red peppers are a good source of lycopene
    • lycopene is increasingly thought 83 to help prevent:
      • prostate cancer
      • bladder cancer
      • cervical cancer
      • pancreatic cancer
    • different pepper cultivars and species have different levels of vitamin C, provitamin A (α and β-carotene), quercetin and luteolin (the major flavonoids in peppers)
    • red bell peppers have significantly higher levels of nutrients (including lycopene) than green. The high levels of vitamin C and beta carotene in red bell peppers have been shown to be protective against cataracts and are promoted for individuals with high cholesterol levels
    • all bell peppers contain many different powerful phytochemicals which have been shown to prevent blood clot formation and reduce the risk of heart attacks and strokes (probably due to their content of substances such as vitamin C, capsaicin, and flavonoids)
    • hot chilli peppers contain even higher amount of these substance, with the major phytochemical group being capsaicinoids (responsible for putting the ‘hot’ into ‘hot pepper’)
      • significant variations in the capsaicinoids are found between and within pepper species 84
      • capsaicin in hot peppers has been shown 85 to:
      • decrease blood cholesterol and triglycerides
      • boost immunity
      • reduce the risk of stomach ulcers (probably by killing bacteria that lead to ulcers)
      • provide analgesic, anti-bacterial, and antidiabetic effects
    • hot peppers have incredibly high levels of vitamins and minerals (including vitamin C, vitamin B6, vitamin A, iron, copper, and potassium 86 , as well as being good sources of vitamins B1, B2 & B3 (thiamine, riboflavin and niacin) and potassium, manganese, iron, and magnesium
    • both hot and sweet peppers have been shown to increase the body’s heat production and oxygen consumption for about 20 minutes after eating – hence burning extra calories, and helping with weight loss
  • aubergine/eggplant contains lots of a vitamins, minerals and important antioxidant phytochemicals, including phenolic compounds (e.g. caffeic and chlorogenic acid) and flavonoids (particularly nasunin – the major phytochemical in aubergine)
    • nasunin, an important antioxidant, is part of the anthocyanin purple pigment found in the peel of aubergine, purple radish, red turnip, and red cabbage 87
    • by chelating 88 iron, nasunin lessens free radical formation with a variety of beneficial results, including:
      • protecting blood cholesterol from peroxidation
      • preventing cellular damage that can promote cancer
      • lessening free radical damage in joints – a primary factor in rheumatoid arthritis
    • the major phenolic compound found in all cultivars is chlorogenic acid. This is one of the most potent free radical scavengers found in any plant 89 , and which has many beneficial activities, including:
    • antimutagenic (anti-cancer)
    • antimicrobial
    • anti-low density lipoproteins (bad cholesterol)
    • antiviral
    • the phenolic acids in aubergines are responsible for some eggplants’ bitter taste and the browning that results when sliced (with the enzyme polyphenol oxidase triggering a phenolic reaction that produces the brown pigments)
    • aubergines contain several other antioxidants including:
      • carotenoids (lycopene, lutein, and α-carotene)
      • flavonoids (myricetin and kaempferol) 90
    • aubergines also contain good levels of dietary fibre, bone-building manganese, enzyme-catalysing molybdenum, heart-healthy potassium, bone-building vitamin K and magnesium, heart-healthy coppervitamin C, vitamin B6, vitamin B9 (folate), and vitamin B3 (niacin91
    • studies show 92 93 aubergine is effective in treating high blood cholesterol

Specific fruit & veg receptors

The fact that different F/V (with all the inherent variations in cultivar, species, origin, preparation method, etc) have different effects on our bodies reveals the fascinating fact that there are specific receptors and proteins for specific substances within specific plants 94 . These receptors are just waiting for the appropriate substance from the appropriate plant. If don’t feed yourself with the relevant plant, the specific receptors don’t respond and your body may suffer as a result.

As one study 95 commented: “It has been shown that phytochemicals bind to specific receptors and proteins for exhibiting biological and physiological activities.

Dr Greger discussed 96 the research showing that there’s a specific receptor for broccoli.

And, just to show you how incredibly complex and specialised this whole subject is, there’s a specific receptor for the EGCG in green tea 97  and even a specific receptor for the concentrated nutrient in apple peel 96 !

Variety is key

And it’s the variety of F/V that’s important, not just the amount you eat. One study that looked at the effects of F/V consumption on the effects of tobacco smoking stated 98  that: “Independent from quantity of consumption, variety in fruit and vegetable consumption may decrease lung cancer risk.” Which, as Dr Greger commented 99 , means that “…if two people eat the same number of fruits and vegetables, the one eating a greater variety may be at lower risk.

This applies to the prevention of all types of diseases. For instance, a study looking at F/V variety and type 2 diabetes 100 concluded that: “...a diet characterized by a greater quantity of vegetables and a greater variety of both F&V intake is associated with a reduced risk of T2D.

This was echoed by the authors of the above study where we looked at the various ingredients of different vegetables (alliums, potatoes, etc). The authors of that study 7 concluded that: “Because each vegetable contains a unique combination of phytonutriceuticals (vitamins, minerals, dietary fiber and phytochemicals), a great diversity of vegetables should be eaten to ensure that individual’s diet includes a combination of phytonutriceuticals and to get all the health benefits.

Final thoughts

The foregoing is only a tiny selection of F/V and of the plethora of essential substances therein contained.

However, what applies to all of them is that there appears to be no substitute for eating the whole F/V. Pills with chemicals extracted from the plants simply do not do the same ‘magic’ as the whole plant.

And we’re only starting to appreciate the vast complexity of the thousands of substances within F/V and the millions of interrelations between difference substances within the same plant and between different plants when consumed together. It’s mindbogglingly complex and it unlikely to ever be fully documented or understood.

But so what? The important thing is ensuring that we do all we can to maintain healthy minds and bodies; and it’s becoming increasingly clear that we achieve this by allowing our bodies to work out the chemistry. All we have to do is ensure we feed ourselves with a wide variety of F/V. This is something that is now much easier for us to achieve, with the year-round supply of a vast range of F/V available at our local stores.

Over millions of years, evolution has done the hard work in producing such amazing bodies as we humans possess. Is it really asking such as lot of ourselves to just feed those bodies with a wide range of wonderful-tasting and health-promoting fruits and veg?


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