Healthy eating habits/Sports drinks: are they really doing us good?

Background
The Australian Guide To Healthy Eating (AGHE) gives the public an outline on the quantity and quality of foods and beverages which should be consumed to maintain a healthy weight and optimal health. These guidelines are structured in a way that promotes the consumption of foods high in nutrients necessary to maintain health and wellbeing. The AGHE places sports drinks on the bottom right corner, amongst other food and beverages which are termed ‘discretionary’ implying that they should only be consumed in limited amounts.

Fluid Balance
The human body is made up of 60-70% water. That means that a male that weighs 70 kg would contain at least 42 litres of water. Out of these 42 litres, 28 litres would be found inside cells, 11 litres would be surrounding cells and blood vessels (interstitial fluid), and only 3 litres would be found in the blood as plasma (the blood without the red blood cells, white blood cells, platelets and other cells). A simpler way to put it is to say that water is found in either vascular (blood) space or tissue space. Males generally contain more water than females, because fat repels water and thus a body that is higher in fat tissue would result in a lower percentage of water. The opposite goes for lean muscle tissue, which holds water well.

Loss of fluid
Fluid is lost from the body via urine, faeces, sweat, evaporation, and breathing. The main cause of dehydration is when we lose fluid through sweat. Although we lose a lot of fluid through urine, it is greatly controlled and regulated to prevent the body from dehydration. The amount of sweat varies greatly between individuals, but also within individuals as it depends on activity level and surrounding climate. The fluid that makes up sweat comes from blood plasma (blood space) and it is passed on from the blood when it circulates past sweat glands. This loss in fluids from the blood needs to be replaced as it directly affects the blood pressure and strains the heart.

Sweat
Sweat is needed to cool the skin down when the body temperature rises. It is produced from sweat glands that gain its fluid from the blood passing by. Sweating depends on the body temperature that is affected by surrounding climate and exercise. If fluids are not restored it will lead to dehydration.



Exercise and fluids
During exercise our muscles create energy. Out of this energy 75% is released as heat energy, and the other 25% is in the form of ATP, which is a stored form of chemical energy. As it is mostly heat that is released from our muscles, it is important that it is removed from the muscle or the muscle would overheat. Therefore the heat energy is transferred to the blood. The heated blood stimulates our sweat glands to produce sweat, and when the sweat evaporates from the skin it cools the body down.

Dehydration
It is therefore very important to stay hydrated during exercise. During dehydration the blood runs more slowly through the body, which prevents the blood from efficiently removing heat that has been produced from the exercise. If heat is not being removed from the muscles it would eventually lead to increased core body temperature. An increase of just 2 degrees (from 37°C to 39°C) would create a state called hyperthermia (hyper = above normal, thermia = temperature). People that are dehydrated do not tolerate this state of increased body temperature very well and would fatigue or even collapse at temperatures between 38.5°C -39.5°C. Dehydration will result in dizziness, early fatigue and headaches. Dehydration will also prevent optimal muscle function and can reduce pleasure and performance, especially in hot climates, such as the Australian summer.

Fluid losses of about 2% of your body weight (which would be about 1.2 litres for a 60 kg woman) would be enough to notice a decrease in performance and if the losses were more than 2% it would increase the risk of dizziness, loss of coordination, nausea, vomiting, diarrhoea, and further gastrointestinal problems both during and after exercise. When dehydrated we also don't take up fluid as well from our intestines, making it even harder to restore fluid balance.

Drinking plan
Dehydration is common after exercise because we often sweat more than what we can replace during the training. People are often also unaware of how much they actually sweat, and therefore they don’t know how much fluid to drink to replace those water losses. A simple way to find out how much fluid is lost from exercise is to document the weight before and after a session and subtract the post weight from the pre exercise weight. It is recommended to have a drinking plan if exercising at higher intensities or in hot and humid climates, which would contain directions on how much to drink before, during and after exercise.

Drinking too much
It is also possible to drink too much fluid. If someone is exercising for long periods of time the losses of salt and other electrolytes through sweat in the combination of drinking only water could lead to dilution of remaining electrolytes. Electrolytes refer to the main minerals present in the body fluid: sodium (Na), potassium (K), chloride (Cl), magnesium (Mg), and calcium (Ca). Sodium is the most abundant of them. If sodium levels become too low it could give symptoms of headache and nausea. In extreme cases the low levels of sodium could cause fluid to move into the brain that would result in a swelling that would cause a state of feeling strange and mental confusion, and further cause general weakness, and then collapse, seizure, coma, and eventually death. The intake of fluids during exercise should aim to match the fluid lost from exercise. A good rule of thumb is to consume 150-200 ml of fluid every 15 minutes during exercise, and in sessions that lasts 60 minutes or less the best thing to drink is water.

Fuel for energy
Water is not the only thing you need to perform well. You also need fuel for the energy needed for muscle contractions. The main fuel is glucose that is also known as “blood sugar”. Glucose comes from the carbohydrate that we consume in the diet. During exercise glucose comes from a stored form of glucose called glycogen. Glycogen can be found in the liver and within muscles. When glycogen reserves are used up we solely depend on the sugar in the blood. When exercising within 60 minutes the glycogen is generally sufficient as an energy source and we don’t need any additional glucose from fast acting carbohydrate food. The main nutritional focus for exercise lasting less than 60 minutes is to have a good fluid balance.

Carbohydrates
Most sports drinks contain 6-8% (i.e. 6-8 grams per 100 grams) of sugar, also known as carbohydrates. Research shows that this amount is beneficial during exercise. Sports drinks that contain more than 8% of carbohydrates will result in slower absorption of the sugar. This means it will take longer to reach the working muscles and may potentially remain in the stomach when needed the most – when muscle glycogen stores are depleted. Sports drinks containing less than 6% sugar are unlikely to provide muscles with adequate fuel.

Sodium
Sodium in sports drinks is beneficial in a number of ways. Most importantly, it acts to replace the salts that we lose when we sweat. As mentioned above, the amount we sweat varies greatly between individuals. However, most people don’t realize how much they actually sweat. This is because it quickly evaporates from the skin’s surface during exercise in non-humid conditions. Sodium also enhances fluid absorption from the stomach, making it available to the body as quickly as possible. Sodium makes us want to drink more because it drives our thirst mechanism. This also happens when we eat foods containing high amounts of salt such as salted nuts. The physiological response to consuming large amounts of salt is to drink more. This is beneficial when we exercise to keep us well hydrated.

Potassium
Potassium is another electrolyte that we lose through sweat and is also important to replace since low potassium concentration may result in muscle weakness and mental confusion.

Other ingredients
Sports drinks can contain other ingredients like protein, and certain vitamins and minerals such as calcium, iron and vitamin C. Further research is needed to clarify whether or not these nutrients are beneficial during exercise.

Examples of sports drinks
Ingredients in common sports drinks
 * Gatorade Endurance contains more sodium than other sports drinks as it was made specifically for very long endurance sessions (4-8 hours in length).

During exercise
Sports drinks provide carbohydrates to the working muscles. They are then converted into energy to enable the muscles to continue to work. Sports Dietitians Australia recommend people consume 30-60g of carbohydrate per hour of exercise, to help delay fatigue. This however, is only applicable to those who exercise for longer than 60 minutes, or those who exercise in extreme heat. People who exercise less than 60 minutes, generally do not need to consume carbohydrates during their session, since the body’s carbohydrate stores are usually adequate to fuel this amount of exercise.

Following exercise
Sports drinks consumed after exercise will aid in full rehydration. This will not occur until all sodium losses have been replaced. Following exercise, they can be beneficial for people who can’t tolerate solid foods straight after training. Any food or drink that contains carbohydrate is recommended, as it will assist in refueling carbohydrate stores in the body. This will help in recovery and stop you from feeling tired and lethargic after exercise.

Who will benefit from sports drinks?

 * Recreational athletes: those who perform continuous aerobic activity for more than 60 minutes
 * Elite and endurance athletes: those who train for more than 2 hours per day
 * High-intensity training athletes: eg. sprinters will benefit from a sports drink after only 30 minutes of training
 * Tired athletes: are likely to have depleted carbohydrate stores
 * Athletes exercising in the heat: will lose more fluid and electrolytes, and will burn carbohydrate at a faster rate
 * Cramping athletes: there is some evidence suggesting that cramping may be caused by dehydration and large losses of salt.

Negative aspects of sports drinks
The main ingredient in sports drinks is sugar. By comparison to a regular soft drink, the sugar content does not differ greatly. When sugar is consumed in excess, the body will store it as fat. If an exercising program lasts 60 minutes or less, there is no need to consume a sports drink. If this is done over long periods, this may result in a person gaining weight. The sugar in sports drinks may also contribute to dental caries. This problem is exacerbated by the acidity in sports drinks. If consumed over prolonged periods, this will contribute to the erosion of the enamel which cannot be replaced. From an economical perspective, sports drinks cost more than filling a water bottle up at the gym. The cost of a 600ml bottle of sports drink varies between $2.50 to $4.50.

Alternatives to sports drinks
For any exercise session no longer than 60 minutes, water is recommended as the fluid of choice. Some may find water bland so to enhance the taste, some lemon or lime may be added to give the water some flavor. This low sugar alternative does not increase an individual’s total energy intake. It is cheaper than buying a sports drink or bottled water from the gym and is environmentally friendly as a new plastic bottle is not purchased every second day. For a pre workout snack, foods high in carbohydrates and low in fat are recommended. This could be slice of toast with jam/honey or a smoothie or a glass of juice. Having a snack about 30 minutes before an exercise session can help the individual improve their exercise session as well as prevent a person from feeling ‘weak’ or ‘dizzy’ during their exercise session. During an exercise session, which last 60 minutes or shorter, water is recommended. It is essential to keep hydrated throughout the session as most individuals lose more fluid through sweat than they consume during the exercise session. After exercising, the aim is to consume foods which aid in refueling and rehydration. The two most important macronutrients required after exercise are carbohydrates and protein. A quick snack right after an exercise session could be a muesli bar or a few salted almonds. These options are high in protein which provides satiety and the salted nuts will provide some sodium to aid in electrolyte rebalance. It is essential to consume water which rehydrates the body.