Why eat fruit and vegetables?

Most of us know that we should eat 5 portions of fruit and vegetables every day, but how many of us know why or even how many should be fruit and how many should be vegetables? And moreover, what is a portion?
Nobody really knows where the actual origin of the “5-a-day” comes from, there has been much speculation, but it certainly isn’t from nutritional science. Different countries around the world set their targets differently, some up to 9 or 10 portions. But in the UK, we’ve kept it at 5 for one good reason: we think that’s manageable, not because we think it’s best for optimal health. The University College of London have recently announced that we should be considering at least 7 portions per day, and that vegetables should take precedence over fruit (1).

In nutritional medicine, we often suggest selecting a wide range of colours when buying vegetables, which should include at least one dark leafy green. The purpose for that is to enable the body to have access to a wide range of minerals and a plant chemical called “phytochemicals”. There are hundreds of these in plants with many more being discovered all the time; some of which are responsible for the plant colour and thus tend to be rich in the skin of fruits and vegetables. Some phytochemicals have been linked to the reduction in chronic diseases, because they have an antioxidant capability (2). Our bodies are constantly at battle with environmental stressors such as traffic fumes, sun radiation, chemicals from industry to name but a few. These are known as “free radicals”, and phytonutrients in vegetables and fruits help keep them from causing too much damage to our cells, which can lead onto chronic diseases and cancer (3).

Fruit and vegetables, if eaten as a whole food (that is, they’ve not been juiced) are relatively low in energy and therefore they help with a calorie-deficit style diet. When people diet, they often forget the essential nutrients our bodies need in terms of vitamins and minerals – particularly if they are watching their carbohydrates. Potassium is one particular element that we can easily miss out on, and yet this is abundant in fruit and vegetables (4). Potassium, along with magnesium, helps keep blood pressure stable, which is potentially protective to the heart (5).
Finally, fruit and vegetables are great sources of dietary fibre, particularly soluble fibre, which is the type that has been shown in many clinical trials to stabilise the body’s cholesterol levels and protect the heart. Eating a good range of vegetables with whole grains is great way to improve blood cholesterol (6).

Portion size
A single portion of fruit or vegetable is around 80g. Nutritionists are wary about including juices and smoothies simply because the act of pulping fruit and vegetables releases their sugars and breaks down the fibres – and therefore we lose a degree of their health-giving properties. Potatoes don’t count at all. Many of us do believe that both white and sweet potatoes are good sources of vitamin C and potassium, and so there’s no good reason why they cannot be part of the 5-a-day. They just need to be baked and not fried or roasted (or eaten as crisps!).

Fruit Vegetable Juice
½ grapefruit 3 sticks of celery 150ml glass of unsweetened fruit or vegetable juice (any more is still 1 portion)
5cm slice melon 1 med tomato or 7 cherry tomatoes
Large slice pineapple 3 heaped tablespoons of frozen carrots/peas/sweetcorn
2 slices of mango 5cm piece of cucumber
30g dried fruit (about 1 heaped tablespoon) 8 cauliflower florets
1 apple 2 brocolli spears
1 banana 4 heaped tablespoons kale/spinach/greens
1 pear 3 heaped tablespoons Beans or pulses (but 6 tablespoons is still 1 portion!)
1 orange
2 plums
2 satsumas
2 kiwi fruits
3 apricots
7 strawberries
14 cherries

Buying and preparing vegetables

We often believe that fresh is best, but is it? Actually, the way you cook your vegetables makes most of the difference. If we think of vitamins belonging into two groups, one that is water soluble and one that isn’t, it helps understand why cooking can change the health-giving properties of food. Most B vitamins and vitamin C are water soluble, there are only 4 vitamins that are not: A, D, E and K. Vitamin A is not destroyed by cooking, but vitamins C and B can leach into the water (as do minerals in vegetables). So if you steam vegetables, you will lose less of their water soluble content. Tomatoes are an exception, cooking tomatoes actually increases their health giving properties – so go for tinned (or better still, cartons) when making pasta sauces (7) (8) .
The modern issue we have with fresh vegetables is that many of us buy them from supermarkets, and we have no idea how long they have been in storage. The longer a fruit or vegetable has been from its original source, the more nutrients it loses. Similarly, buying vegetables pre-prepared (cut, cubed) also speeds up nutrient loss. Frozen vegetables tend to be frozen at source, and retain their nutrients for longer. If you buy fresh, it’s always best to get them locally and in season.
That said, any vegetable is better than no vegetable – so explore them, and make them part of your every day nutrition.

Further Reading:
Visual guide to portions: http://www.nhs.uk/Livewell/5ADAY/Documents/Downloads/Poster%5B1%5D.pdf
NHS Choices: http://www.nhs.uk/Livewell/5ADAY/Pages/Portionsizes.aspx

1. Oyebode O, Gordon-Dseagu V, Walker A, Mindell JS. Fruit and vegetable consumption and all-cause, cancer and CVD mortality: analysis of health survey for England data. Journal of Epidemiology & Community Health. 2014 April; doi:10.1136/jech-2014-203981.
2. Scalbert A, Manach C, Morand C, Remesy C, Jimenez L. Dietary polyphenols and the prevention of diseases. Critical reviews in food science and nutrition. 2005; 45(4).
3. Liu RH. Health benefits of fruit and vegetables are from additive and synergistic combinations of phytochemicals. American Journal of Clinical Nutrition. 2003; 78(suppl).
4. Slavin JL, Lloyd B. Health benefits of fruits and vegetables. Advances in Nutrition. 2012 July; 3.
5. Crowe FL, Roddam AW, Key TJ, Appleby PN, Overvad K, Jakobsen MU, et al. Fruit and vegetable intake and mortality from ischaemic heart disease: results from the European prospective investigation into cancer and nutrition (EPIC) heart study. European Heart Journal. 2011; 32.
6. Threapleton DE, Greenwood DC, Evans CEL, Cleghorn CL, Nykjaer C, Woodhead C, et al. Dietary fibre intake and risk of cardiovascular disease: systematic review and meta-analysis. British Medical Journal. 2014; 347.
7. Bernhardt S, Schlich E. Impact of different cooking methods on food quality: retention of lipophilic vitamins in fresh and frozen vegetables. Journal of Food Engineering. 2006; 77(2).
8. Dewanto V, Wu X, Adom KK, Liu RH. Thermal processing enhances the nutritional value of tomatoes by increasing total antioxidant activity. Journal of Agricultural and Food Chemistry. 2002; 50(10).