Water

Water is the principle constituent of the body, comprising 50-70% of total body weight, depending on factors such as age, gender, physiological state and the proportion of body fat. This means an average 70 kg man is estimated to contain about 42 litres of water, whereas the body of an average woman would contain less because she has larger fat stores.

It's for this reason that we are always being encouraged to drink plenty of water and stay well hydrated. The body loses approximately 1 to 1.5 litres of fluid a day through obligatory fluid losses from the kidneys, gut, skin and lungs. Even more is lost during hot weather or if we exercise.

Water is also used up in metabolic processes within the body; this water is not lost, but it's not available to maintain hydration. So another 0.5 to 1 litre of water is needed each day to maintain good hydration levels, depending on the climate temperature and how active we are.

Generally, it is assumed that fluid intake takes care of itself because people respond to their thirst, but this is not always the case. Many people confuse feeling of mild hunger with mild thirst, which means they eat something instead of drinking.

Although some foods have quite a high water content (such as fruit and vegetables), they also provide calories, whereas water does not provide any calories. This means that drinking plenty of water and staying well hydrated is important for weight loss. Drinking plenty of water or low calorie drinks will help avoid these confused hunger feelings and water before and with meals helps you feel fuller so you eat less.

Staying hydrated

Although severe dehydration is rare in healthy people, a mild degree of dehydration can contribute to constipation, increase the risk of urinary tract infections, cause lethargy and headaches, and loss of concentration, especially at work or whilst driving.

The key to maintaining good hydration throughout the day is to drink small amounts of water throughout the day. First thing in the morning you need to replace some of the fluid that has been lost overnight whilst you have been sleeping.

Most people empty their bladder on waking because energy stores that are held in water have been used up and this water is then excreted from the body, so it is quite natural to wake up slightly dehydrated every morning.

If you ignore this, and do not have a substantial drink, the dehydration effects will last until you do drink. This is a common mistake many people make. They do not drink enough first thing in the morning and then turn to foods and snacks to make themselves feel better believing they need an energy boost, when in fact the real reason they feel tired and lethargic is because they are experiencing symptoms of mild dehydration.

Many people often complain that once they start to drink more water, they find themselves constantly running to the loo. This can be for two reasons. Firstly, the body needs to get used to taking in more fluids, after about 2 to 3 weeks the body should adapt to the increased intake and things should settle down again.

Secondly, they are probably drinking too much in one go. If you carry a large bottle of water around with you, you need to take small sips at regular intervals, about 50-100mls every half an hour. If you forget to drink during the morning then try to compensate by drinking half the bottle all in one go, the body won't be able to hang on to it all so a sizeable amount will be seem to ‘go straight through you'.

Once you have established good drinking habits; drinking with every meal, small regular sips between meals, you will notice a real difference to your energy levels, concentration and snacking habits, all of which should make weight loss easier. Not only should you be eating less (smaller meals, fewer snacks) but you should find exercising a lot easier also.

What about other drinks?

Water is the best choice for quenching your thirst between meals. It is totally calorie free and contains no sugars that damage teeth.

If you don't like the taste of plain water, you could try sparkling water, or add a slice of lemon or lime. You could also try adding some sugar-free squash or fruit juice for flavour.

Other drinks are an important part of a healthy balanced diet, because as well as providing fluid, they also act as vehicles for important nutrients; for example, minerals such as calcium in milk, antioxidants in tea and coffee, and vitamins such as folate and vitamin C in fruit juices.

Milk

Milk contains vitamins and minerals such as calcium, riboflavin and vitamin B12 and it doesn't damage teeth. For a healthy choice, choose semi-skimmed or skimmed milk. Be aware that flavoured milks, milkshakes, condensed milk and milk-based energy or malt drinks tend to contain added sugar, which can cause tooth decay.

Juices and smoothies

Fruit juice and fruit smoothies contain plenty of vitamins and antioxidants that are good for health, in particular they are a good source of vitamin C. A glass (150ml) of fruit juice counts as one of the five fruit and veg portions we should be having each day.

However, fruit juice also contains intrinsic sugars that can damage teeth, so they are best drunk as part of a meal to dilute the potential acid erosion effect.

The sugars found naturally in whole fruit are less likely to cause tooth decay, because the sugar is contained within the structure of the fruit. But, when fruit is juiced or blended the sugar is released. Once released, these sugars can damage teeth, especially if fruit juice is drunk frequently.

When you are choosing fruit juice, check the labels carefully to make sure you are buying 100% fruit juice and there is no added sugar. Also watch out for 'juice drinks', which contain as little as 5% fruit juice and contain a lot of sugar.

Soft drinks

Fizzy drinks, squashes and 'juice drinks' contain varying degrees of sugar, which can mean they are a lot more calorific but contain very few healthy nutrients. So try to keep these to a minimum. Diet drinks contain no or hardly any calories but the phosphoric acid they contain can still damage teeth and is associated with poor bone health , so don't try to stave off hunger pangs between meals with endless cans of diet coke.

If you or your children like fizzy drinks try diluting fruit juice with sparkling water instead. Remember to dilute squashes well for children and if they insist on having a sugary or fizzy drinks, it's best to have them with meals.

Research shows that children and young people in the UK eat too much sugar, and more of it comes from fizzy drinks than any other type of food or drink. Children who have lots of sugary drinks, such as fizzy drinks and squashes are more likely to be overweight and to put on weight.

Tea and coffee

Most people love their cup of tea or coffee and there is quite a lot of evidence to show that these plant-based drinks contain high concentrations of antioxidants that are beneficial for the heart.

Both tea and coffee contain caffeine and there is quite a lot of controversy surrounding the effects of caffeine, and its effect on health has been the subject of much research. Overall, the bulk of the evidence demonstrates that moderate consumption of coffee and other caffeine-containing beverages, such as tea and cola drinks, does not pose a risk to health in normal healthy individuals, with the exception of pregnant women.

However, there is confusion about the word moderate. The amount of caffeine in beverages will depend on the variety and the strength of the brew for tea and coffee. As a rough guideline, an average sized (150 ml) cup of instant coffee contains approximately 60 mg of caffeine, compared with about 80 mg for filter coffee, and 40 mg a cup for a cup of tea or a can of cola. The amount of caffeine that people can tolerate varies, depending on individual sensitivities; but on the basis of existing research, a daily intake of about 250-300 mg (4 or 5 cups of coffee) is considered to represent a moderate intake.

Caffeinated drinks such as tea, coffee and cola, can act as mild diuretics, which means they make the body produce more urine. The dehydrating effects of these drinks under normal circumstances are much less than commonly perceived.

Various studies on caffeine have concluded that doses of more than about 300 mg have a mild diuretic effect, whilst doses of less than 250 mg do not show any effect. In coffee drinkers, habituation can be developed, raising the minimum dose needed to cause mild diuresis.

Tea and coffee and iron

Tea and coffee contain compounds that can bind with iron making it less available for absorption. For this reason avoid drinking tea and coffee with meals or within 30 minutes after a meal. Pregnant women need to watch how much coffee they drink. And neither tea nor coffee are suitable drinks for children.