Eating to win: activity, diet and weight control
Eating to win: activity, diet and weight control

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6.1 Water intake

Water plays a key role in sustaining life and in the effective performance of your mind and body. The adult male and female body consists of around 60 and 50 per cent water, respectively. Approximately two litres of water are lost from the body every day, but this will vary depending on factors such as activity level and environmental conditions. General hydration guidelines suggest that men should consume two litres (about ten 200 ml glasses) of fluid per day and women should consume 1.6 litres (about eight 200 ml glasses) of fluid per day (British Nutrition Foundation, 2017). An active person in a hot climate may need to consume between five and ten litres a day (McArdle et al., 2012). Figure 7 shows the ways in which the body gains and loses water. You can also scroll over the parts of the body on the diagram to view some of the effects of dehydration (when water loss exceeds intake) in different parts of the body.

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Figure 7 Water intake and loss
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Some of the effects of dehydration (when water loss exceeds intake) include:

  • dizziness and headache
  • rapid heartbeat and impaired cardiac function
  • reduced blood flow to the muscles
  • impaired kidney function
  • decreased ability to sweat
  • loss of muscle glycogen stores.

During physical activity dehydration results from sweating, so it is important to ensure that the body is sufficiently hydrated before and during exercise. Fluid loss must also be replaced to rehydrate the body after exercise and to prevent further dehydration. In the following activity, you will explore fluid replacement strategies and how fluid intake can be combined with carbohydrate intake for energy replacement.

Activity 4: Think about your drink!

Timing: Allow about 20 minutes

Watch the film How beverage composition affects athletic performance [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] which introduces you to fluid and carbohydrate replacement strategies. As you watch the film, answer the following questions:

  1. What are the three main phases of fluid replacement?
  2. What factors can affect individual sweating rates?
  3. What types of drinks are recommended for fluid and carbohydrate replacement?
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Discussion

  1. The three main phases of fluid replacement are fluid intake (getting fluid into the body for hydration), fluid delivery (replacement of fluid loss or rehydration) and retention (keeping fluid in the body).
  2. Significant dehydration (more than 2 per cent weight loss) impairs the body’s ability to regulate temperature and can decrease endurance and team sport performance. Sweating rates can be affected by factors such as genetics, exercise intensity and environmental conditions (i.e. temperature, wind and humidity).
  3. For exercise lasting an hour or longer, 30–60 g carbohydrate per hour is recommended for fuel. A drink formulated with a 6–7 per cent solution of maltodextrin, sucrose or glucose can exit the stomach and absorb into the bloodstream as quickly as water. For endurance athletes exercising over 2–3 hours it is recommended that a small amount of fructose is added to the solution. Higher carbohydrate drinks can be more beneficial for endurance athletes up to a certain point, however beyond this returns diminish and can even become negative because of slower absorption and potential for increased gastrointestinal distress. It is also important to include the electrolyte sodium in the drink because it helps to maintain blood sodium levels and promotes the retention of water in the body.

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