Nutrition (21 page)
Natural mineral water is bottled at a single, identified and protected source and has a guaranteed consistent composition.
The most important role of water is to act as a solvent for certain mineral salts. When these salts dissolve in water they separate to produce electrically charged particles known as electrolytes. The concentration of different electrolytes in different parts of the body draws water in and out of fluid compartments and maintains the electrical potential across cell membranes, which is vital for life. If fluid or electrolyte levels fall outside narrow limits, metabolic functions are affected in potentially dangerous ways. A low blood calcium level, for example, can cause muscle paralysis, while a high level can cause heart-rhythm abnormalities; a low blood potassium level can cause mental confusion and muscle weakness, while a high blood potassium level can cause the heart to stop beating.
The level of each electrolyte within your cells, the watery part of your blood (serum) and the interstitial fluids bathing your cells is closely regulated in a process known as homeostasis. Homeostatic control mechanisms involve all your internal organs – especially your lungs, liver and kidneys – your endocrine glands and your nervous system.
Blood calcium levels are maintained within a very tight range by calcium-sensing receptors in your parathyroid glands. These trigger the release of parathyroid hormone to increase the amount of calcium released from your bone stores, or calcitonin hormone, which increases the deposition of excess calcium in bones.
Blood water balance is maintained by hormones, which regulate how much urine is lost via your kidneys, and by thirst receptors, which encourage fluid intake. Blood salt levels are regulated by the amount of electrolytes excreted via the kidneys. Hormones such as aldosterone and vasopressin tell the kidneys how much water and electrolytes to reabsorb or excrete. This regulation is closely linked with your blood-pressure control, which is maintained by hormones (renin-angiotensin system) that regulate water and salt balance, by control of your heart rate and through blood-vessel dilation or contraction.
Acidity
Water (H
2
O) ionizes into hydrogen ions (H
+
, which are also known as protons) and hydroxyl ions (OH
-
). It is the concentration of positively charged protons that determines the acidity, or pH, of a fluid. The higher the concentration of protons, the higher the acidity, and vice versa.
2
O) ionizes into hydrogen ions (H
+
, which are also known as protons) and hydroxyl ions (OH
-
). It is the concentration of positively charged protons that determines the acidity, or pH, of a fluid. The higher the concentration of protons, the higher the acidity, and vice versa.
The pH scale of a fluid ranges from 0 (highly acid) to 14 (highly alkaline). This is a logarithmic scale, which means that each number represents a tenfold difference in concentration from the numbers on either side. So a liquid with a pH of 5 is 10 times more acidic than a liquid with a pH of 6, and 100 times more acid than a liquid with a pH of 7.
When protons and hydroxyl ions are present in equal proportions, the pH of a fluid is considered neutral with a pH 7 (for example, water). If more H
+
ions are present than OH
-
ions, then the fluid is acidic (such as stomach acid). If more OH
-
ions than H
+
ions are present, the fluid is alkaline (such as pancreatic secretions).
+
ions are present than OH
-
ions, then the fluid is acidic (such as stomach acid). If more OH
-
ions than H
+
ions are present, the fluid is alkaline (such as pancreatic secretions).
Many carbonated soft drinks have a pH of 3, making them 10,000 times more acid than water (pH 7). This means they are capable of dissolving tooth enamel and can contribute towards tooth decay.
Dietary acids and enamel
Tooth enamel is the hardest substance found in the body, and forms a thin layer over the surface of each tooth that is up to 2.5 mm thick. Despite its hardness, it readily dissolves on contact with acid substances with a pH of less than 5.5. The acidity of common foods and drinks is surprisingly high. All the substances listed in the chart below have a pH that can harm your teeth with prolonged contact. In fact, someone who eats citrus fruit more than twice a day is 37 times more likely to experience dental erosion than someone who eats citrus fruit less frequently.
Food/drink | pH |
Lemon/lime juice | 1.8 to 2.4 |
Fizzy cola drinks | 2.7 |
Orange juice | 2.8 to 4.0 |
Apples | 2.9 to 3.5 |
Grapes | 3.3 to 4.5 |
Mayonnaise | 3.8 to 4.0 |
Tomatoes | 3.7 to 4.7 |
Black coffee | 2.4 to 3.3 |
Vinegar | 2.4 to 3.4 |
Black tea | 4.2 |
Once tooth enamel has dissolved away, it can’t be recovered and the softer, underlying parts of the tooth soon start to decay.
Tips to protect your teeth
You don’t want to avoid eating fruits and drinking fruit juices altogether, as they form a vital part of a healthy diet. The erosive potential of fruit juices may partly be reduced by diluting them with water, but this may make drinks unacceptable due to their reduced taste and colour. Try to decrease the frequency with which you consume acidic foods or drinks, and consume them quickly, rather than sipping or chewing daintily. Using a straw positioned towards the back of your mouth lessens the contact time between your teeth and the drink compared with using a cup, and may reduce the erosion caused by soft drinks. It also helps to rehydrate your mouth regularly by sipping water. Sluice your mouth out after drinking tea, coffee, cola, sports drinks, wine and other alcoholic drinks. In fact, this is another good reason – apart from responsible drinking – to have a glass of water after each alcoholic drink. You can neutralize acids in your mouth with foods containing calcium and phosphate – some dental experts suggest holding a piece of cheese in your mouth for a few minutes after eating a fruit salad, for example. Another tip is to select fruit juices fortified with added calcium, as this significantly decreases their erosive potential.
You could also brush your teeth with a fluoride toothpaste
before
eating. Don’t brush your teeth immediately after eating, as abrasion by a toothbrush after consuming an acidic drink or acidic food may increase loss of enamel. In fact, rinsing your mouth with a glass of water is better than brushing immediately after eating. You could also use a fluoridated mouthwash with a neutral pH.
before
eating. Don’t brush your teeth immediately after eating, as abrasion by a toothbrush after consuming an acidic drink or acidic food may increase loss of enamel. In fact, rinsing your mouth with a glass of water is better than brushing immediately after eating. You could also use a fluoridated mouthwash with a neutral pH.
Floss your teeth regularly to remove the acidic, bacterial plaque that builds up around the teeth. Interdental brushes that clean between your teeth are another new alternative to flossing. As well as reducing gum disease, people who floss regularly appear to be less likely to die from coronary heart disease. As odd as it may seem, this is because having inflamed gums allows mouth bacteria to enter the circulation, where they are believed to trigger arterial disease.
Other health problems associated with an acidic diet
Your body works hard to keep your blood, and the interstitial fluids that bathe your cells, within a very tight pH range of 7.35 to 7.45, which is slightly alkaline. This is achieved by buffering acids with proteins, bicarbonate and other electrolytes such as phosphates; controlling the amount of protons (H
+
) and bicarbonate ions (
) eliminated through your kidneys; and regulating the amount of acidic carbon dioxide gas exhaled through your lungs.
+
) and bicarbonate ions (
) eliminated through your kidneys; and regulating the amount of acidic carbon dioxide gas exhaled through your lungs.Even slight movements outside this narrow blood pH range will severely affect cell function by changing the three-dimensional shapes adopted by important cell proteins and enzymes, and by affecting the electrical balance of nerve and muscle cells.
Your diet strongly influences the amount of acid your body has to process. When a food is broken down, the metabolism of its various building blocks – proteins, carbohydrates and fats – results in either the net production or consumption of protons – the basic unit of acidity. If the metabolism of a food results in the production of excess protons, it is classified as an acid food, although ‘acid-forming’ is a more accurate description. If the metabolism of a food uses up more protons than it produces, however, then it is classified as an alkaline-forming food.
There is a lot of confusion around the concept of acid and alkaline foods. This is because the acidity of a food refers to its effect on the acidity (pH) of your urine
after
it has been fully processed in your body. Put simply, it’s the effect of the ‘ash’ remaining after that food has been processed to release its energy, micronutrients and salts. It does not refer to whether or not the food itself is acidic or alkaline in quality, nor the effect it has on the acidity of your digestive system or even your blood. In fact, many acid-tasting foods such as lemons, oranges and tomatoes actually have an alkaline effect on the body.
after
it has been fully processed in your body. Put simply, it’s the effect of the ‘ash’ remaining after that food has been processed to release its energy, micronutrients and salts. It does not refer to whether or not the food itself is acidic or alkaline in quality, nor the effect it has on the acidity of your digestive system or even your blood. In fact, many acid-tasting foods such as lemons, oranges and tomatoes actually have an alkaline effect on the body.
It may seem illogical that acidic-tasting fruits, such as lemons and limes, have an alkaline effect on your urine, but this is easily explained. The types of acid present in fruits, such as citric acid and malic acid, are weak acids. This means they do not separate out into their ions to release protons (H
+
) to any great extent. Instead, they are readily neutralized by the large amount of potassium and sodium also present in the fruit to form salts such as potassium citrate and potassium malate. During metabolism, these salts react with sodium, water and carbon dioxide in your cells to form sodium bicarbonate, which has an alkaline effect on urine. Adding sugar to fruit juices reduces the buffering effect of potassium, however, so sweetened fruit juices become acid-forming.
+
) to any great extent. Instead, they are readily neutralized by the large amount of potassium and sodium also present in the fruit to form salts such as potassium citrate and potassium malate. During metabolism, these salts react with sodium, water and carbon dioxide in your cells to form sodium bicarbonate, which has an alkaline effect on urine. Adding sugar to fruit juices reduces the buffering effect of potassium, however, so sweetened fruit juices become acid-forming.
Protein-rich foods such as meat and dairy products are the main acid-forming foods in your diet. This is because the amino acids they contain are broken down to produce excess protons, which your body excretes via your urine. These are therefore classed as ‘acid’ or ‘acid-forming’ foods. When healthy, your liver, kidneys and lungs can process acid-forming foods without undue difficulty.
Having to process excess acid-forming foods can lead to some loss of bone-mineral density when phosphate salts are leached out to buffer excess acids in the body. Phosphate is stored in your bones and teeth as calcium phosphate, so when phosphate is used to buffer acid-forming foods, calcium is left behind which, in some cases, may contribute to the formation of kidney stones. Eating an acid-forming diet may also increase the level of inflammation in the body, thus increasing the risk of a number of health conditions.
A growing body of research now suggests that the long-term consumption of an acid-forming diet may have other adverse effects on health. This becomes more of a problem as you get older, when your kidney function naturally declines and becomes less able to secrete the excess acid from your body.
Acid diet and osteoporosis
There is growing evidence that an acid-forming diet is harmful for bones. The average Western diet supplies notable quantities of acid (50 to 100 milliequivalents acid per day), which contributes to a low-grade, long-term metabolic acidosis. Because bone is used to buffer this excess acid, it leads to gradual dissolution of bone mineral and reduced bone mass. In healthy male volunteers, for example, eating an acid-forming diet increased their urinary calcium excretion by 74 per cent compared to when they consumed an alkaline-forming diet. This extra calcium was essentially leached from their bones. Studies in which bone density has been measured by ultrasound or dual-energy X-ray absorptiometry has also shown a correlation between the nutritional acid load and bone health. To help protect your bones, aim to consume less acid-forming foods (protein-rich foods) and more alkaline-forming foods such as fruit and vegetables, which are associated with a more alkaline environment and have been shown to have a beneficial effect on bone health. In addition, drinking an alkaline, bicarbonate-rich water has also been shown to have a beneficial effect on reducing bone loss and, in those with an acid-forming diet, mineral-water consumption has been suggested as an easy and inexpensive way of helping to prevent osteoporosis.
Acid diet and liver health
Excess intakes of acid-forming foods have been associated with a build-up of fat in the liver, which is involved in processing proteins from which the acidic protons are released. In adolescents, females with the most acid-forming diets are 4.5 times more likely to show liver enzyme changes associated with non-alcoholic fatty liver disease than those with the least acid diet. Further studies are needed to confirm these findings.
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