Nutrition is the process of providing and obtaining the nourishment necessary for optimum health and growth through food. As nutritionists, we advise people on how to modify what they eat according to individual requirements such as activity level, age, gender, current state of health and body type. If you are new to training or looking to improve your lifestyle, it is important to have the basic knowledge first in order to implement an effective plan.
The next three articles will be geared towards helping those who are just starting out/ those who are looking to make a change to their current lifestyle and those who want to brush up on their knowledge. The first of these articles will provide basic information about nutrition, followed by two more articles focusing on the gym and supplements.
WHAT IS A CALORIE?
A calorie is a unit of heat. One calorie equates to the amount of heat required to raise the temperature of 1g water by 1⁰C from a standardised initial temperature. One calorie is the equivalent of approximately 4.2 joules. There are 1,000 calories in a kilocalorie (kcal) and these are the units you will see used on food packaging. In general, kcal is what people are referring to when they talk of calories in a nutrient context.
Calories (kcal) per gram of macronutrients:
Lipids (fat): ~9kcal
If you want to keep track of your calorie intake and you consume a few alcoholic beverages during the week (people tend to forget that they drink calories too) it is worth knowing that alcohol provides 7kcal of energy per gram.
Carbohydrates are organic compounds consisting only of carbon, hydrogen and oxygen atoms. Carbohydrates are synthesised by plants from water and carbon dioxide during photosynthesis. In their simplest form, glucose (C₆H₁₂O₆), they are readily soluble and transported around the body to be oxidised back to carbon dioxide and water and used as energy for cellular metabolic processes.
If carbohydrates are not required for energy (in other words, you eat a surplus amount) they are stored as glycogen in the muscle and liver. Despite being principally a source of energy, carbohydrates are a diverse group of substances with varied chemical and physiological properties with differing importance to health. Cutting carbohydrates out of your diet is never the answer, but knowing which carbohydrate containing foods to include in your diet is.
Major dietary carbohydrates can be divided into three classes: sugars, oligosaccharides and polysaccharides. The word saccharide comes from the Greek word ‘sakkharon’ which means sugar. Within the sugar class, there are three sub-groups of carbohydrate; monosaccharides, disaccharides and polyols.
Monosaccharides are the building blocks of other longer chain sugars. The three principle monosaccharides are glucose, fructose and galactose. Free glucose and fructose can be obtained through the inclusion of raw fruit, dried fruit and vegetables such as carrots, onions, swede and turnip.
Starch is the most commonly known polysaccharide and is a storage carbohydrate found in cereals, rice, potatoes and other root vegetables. It is a long chain carbohydrate consisting only of glucose molecules linked together.
There are other ways in which carbohydrates are classified and these are the terms you are likely to hear more often.
Extrinsic and Intrinsic Sugars – Extrinsic sugars are those which are added to food by the consumer, manufacturer or chef in a bid to alter the taste. Syrups, honey and fruit juices are commonly sweetened with extra sugar even though they naturally contain sugar to begin with.
Intrinsic sugars are those which are naturally occurring (in plants for example) and are always accompanied by other important nutrients such as vitamins and minerals.
Total sugars – This is a food label designed to incorporate all sugars present in food regardless of whether they are intrinsic or extrinsic.
Complex carbohydrates – This term was introduced in 1977 to encourage consumption of more healthy foods such as fruit, vegetables and whole grain. Now the term has become equated with starch and is a key to establish how resistant to digestion the food is. Resistance to digestion slows down the energy released from food preventing an insulin peak post-ingestion and providing you with sustainable, nutrient-rich energy as opposed to a quick burst of energy followed by a low or ‘sugar crash’.
Glycaemic carbohydrates – It is important to distinguish between carbohydrates which do or do not directly provide glucose as an energy source following the process of digestion and absorption in the small intestine. Carbohydrates which provide glucose for metabolism are known as ‘glycaemic’ whereas those which pass to the large intestine prior to being fermented are known as ‘non-glycaemic’. Maltodextrins (oligosaccharide) and most mono and disaccharides are classed as glycaemic.
The extent to which carbohydrate in foods raises blood glucose concentrations has been used as a means of classifying dietary carbohydrates. It is commonly known as the glycaemic index, used in the GI diet.
Dietary fibre – Consisting of non-starch polysaccharides, dietary fibre is the indigestible portion of plant foods and is divided into soluble and insoluble fibre. Soluble fibre dissolves in water and tends to slow down the movement of food through the digestive system. Insoluble fibre does not dissolve in water, it absorbs water as it moves through the digestive system easing digestion and promoting regular bowel movements.
The minimum amount of carbohydrate required per day to avoid ketosis is ~50g/day because ~130g/day can be produced in the body from non-carbohydrate sources by gluconeogenesis. Glucose is an essential energy source for the brain and red blood cells and the daily requirement for this is ~180g/day. A state of ketosis means that the body relies on ketones derived from fatty acid oxidation as a source of energy. It is undesirable as it impairs cognitive function and is particularly harmful to pregnant women as the foetus may be adversely affected. Diets which exclude the intake of carbohydrates are not healthy, particularly if you are exercising regularly to work towards a better physique.
Fats are essential because they are a storage unit for energy. Gram for gram fats are the most efficient source of energy we can consume with 1g of fat providing 9kcal of energy. This does mean that less is more when it comes to portion sizes, but it also means that small amounts of fat keep us energised! Fat is also a vital part of the membranes surrounding every cell in your body, which means that without it your cells would not be able to function properly. When levels of fat are too low, brain and nervous function is compromised with is why you hear people talking of fish being ‘brain food’.
Without fat, we would also not be able to absorb many of the vitamins we rely on to maintain health. Vitamins A, D, E and K are all fat-soluble. We could also find ourselves in a hormonal mess should fat levels fall below the recommended requirements. Fats are structural components of prostaglandins which regulate many of the body’s functions. They also regulate the production of sex hormones, which is why females who are dangerously underweight/too lean experience problems with menstruation.
If you want your skin to have a healthy, youthful glow then consuming fats is important. Fatty acid deficiency results in dry, flaky skin. In addition to the skins surface, the layer of subcutaneous fat (beneath the skin) helps to regulate body temperature. This is why those with very low body fat are more sensitive to cold and obese individuals struggle in hot weather.
So basically, if you want to avoid fluctuating moods, stay mentally alert, fight fatigue, control weight and take care of every cell and organ in your body, you need to be consuming those healthy fats!
The amount of fat you require to maintain optimum health is dependent upon lifestyle, weight, age and current health status. Essentials of Human Nutrition (2007) recommends the following:
- Dietary fat should provide at least 15% of total energy and 20% for women of reproductive age.
- Upper limit of dietary fat should be 30% for an average adult.
- 10% or less of dietary fat consumed should be in the form of saturated fat.
- Trans-fats should only make up 1% of total dietary fat intake.
Despite what you may have heard, fat isn’t always the bad guy! Trans and saturated fats are guilty of inducing health issues if eaten in excess of guidelines. They can cause weight gain, cholesterol build up, heart problems and more. But, monounsaturated and polyunsaturated fats have the opposite effect and are definitely not to be considered the enemy!
These fats are ‘saturated’ with hydrogen which is where the name comes from. The carbon atoms that make up the base structure of this fatty acid are bonded to the maximum number of hydrogen atoms possible. The structure of these fats makes them solid (in general) at room temperature. Foods with high levels of saturated fat include red meat, processed meat, cheese, butter and nuts.
Trans fat can be found naturally at low levels in foods such as meat and dairy products, but on the whole they are man-made through the process of hydrogenation. Typically, this involves the addition of hydrogen atoms to a polyunsaturated vegetable oil using a nickel catalyst. This type of fat has a longer shelf life than other fats. Foods with high levels of trans fat include tinned soup, margarine, cakes, biscuits, frozen food and fast food.
This fat is unsaturated as the molecular structure contains one carbon-carbon bond. These carbon atoms could bond with more hydrogen atoms if they were not in this double bond. The word ‘mono’ is used because there is only one of these bonds in the entire molecular structure. Monounsaturated fats are generally liquid at room temperature. Foods high in monounsaturated fat are avocadoes, peanut butter and olives.
Now you know what the structure of monounsaturated fats is, it isn’t difficult to work out what a polyunsaturated fat is like. ‘Poly’ means that there are two or more carbon-carbon bonds within the molecular structure. The most famous polyunsaturated fats are probably omega-3 and omega-6. The 3 and 6 denote where on the structure the double bond is (in case you were wondering).
Within this category, there are essential (EFA’s) and non-essential fatty acids (NEFA’s). Essential fatty acids are those which cannot be synthesised in the body and have to be consumed through diet.
Alpha-Linolenic Acid (ALA), short chain Omega-3’s and Omega-6’s and Linolenic Acid (LA) are all essential fatty acids.
Long-chain Omega-3’s and Omega-6’s, Arachidonic Acid (AA), Eicosapentaenoic Acid (EPA) and Docosahexaenoic Acid (DHA) are all non-essential fatty acids as they can be synthesised from other fatty acids.
Foods which are high in polyunsaturated fats include oily fish(salmon, trout, sardines), walnuts, sunflower oil, sesame oil and low levels can also be found in leafy green vegetables.
The bottom line is simple; don’t go no-fat, focus on the good fats. Try to eliminate trans fat from your diet, limit your intake of saturated fat and ensure you include essential fatty acids in your diet every day.
Proteins are fundamental structural and functional elements within every cell in the body and undergo extensive metabolic interaction. Following water, protein is the next most abundant molecule in the human body and accounts for approximately 16% of our total body weight. Proteins are made up of amino acids joined together by peptide bonds to form polypeptides.
Proteins taken in the diet are broken down into amino acids in the process of digestion and absorption. Absorbed amino acids contribute to the amino acid pool of the body, from which all proteins are synthesised. The proteins of the body are constantly turning over through processes of protein synthesis and breakdown. The rate of this will increase following exercise which is why those who are building muscle require surplus amounts of protein in their diet.
The structure and function of all proteins is related to amino acid composition. There are 20 amino acids; 11 of which are non-essential and 9 of which are essential as they cannot be synthesised in the human body, they have to be ingested.
There are 3 branched chain amino acids: leucine, isoleucine and valine. Branched chain amino acids (BCAA’s) are highly prominent in muscle tissue, accounting for 14-18% of its amino acid makeup. BCAA’s are metabolised differently than other amino acids and can be oxidised in the muscles during exercise for energy. Adequate BCAA levels can increase carbohydrate availability, protecting the muscles from exercise-induced protein breakdown.
Protein intake varies dependent on gender, training status and the like, but as a guide the Department of health supports a dietary intake of 1.2-2.0g per kg of bodyweight for those trying to build muscle, 1.2-1.7g per kg bodyweight for endurance athletes and between 0.6-1.1g for maintenance in a relatively sedentary adult. The varying sources from which protein can be ingested and their biological value also have a great impact on how they are digested, absorbed and utilised by the body but I will discuss this further in the Beginner’s Guide to Supplements.
Alcohol is the only substance which is both a nutrient and a drug which affects brain function. Alcohol is not consumed in pure form (ethanol) but in aqueous solutions in alcoholic beverages. Alcohol is readily absorbed in unchanged form and distributed throughout total body water. Almost all of the alcohol consumed will be metabolised by the liver, which is why binge drinkers or those with alcohol addictions suffer from severe liver damage and disease.
Pharmacologists class pure alcohol as a central nervous system depressant which puts it in the same group as general anaesthetic. Alcohol provides 7kcal of nutrients per gram and is appetite suppressing. Alcohol is one of the leading causes of nutrient deficiency and the common nutrients which become depleted as a result of heavy alcohol intake are folate, thiamin, niacin, B-vitamins and vitamin A.
A unit of alcohol is ~8g or 1cl of alcohol. As a rough guide for how to calculate units a 12% 250ml glass of wine equates to 3 units, a 3.6% pint of beer equates to 2 units and a single shot of spirit equates to 1 unit.
Government guidelines recommend that men should not consume more than 3-4 units per day and women should not consume more than 2-3 units per day. It is also recommended that you do not drink up to this limit on successive days for a long period of time.
Properties resulting from a hydrogen-bonded structure make water an essential constituent of all known life forms on the planet. The average adult contains ~35-45L of water which accounts for 50-70% of their overall body weight dependent on the amount of body fat they have.
The intake of water is vital to the chemical reactions that occur in the body to utilise energy, aid muscle repair and prevent damage to cardiovascular, skeletal and digestive systems. It is also one of the most effective aids to weight loss. Drinking a glass or two of water prior to a meal will satiate you and result in you eating less of your meal/reducing portion size. Drinking water also helps to prevent you from overindulging in caffeinated, high-sugar or diuretic beverages which cause dehydration every time you feel thirsty. Water is lost through sweat, evaporation, faeces and urine and it needs to be replenished if you want your body to function optimally. You will notice particular issues when training or during digestion if you have not taken in enough water.
Water is necessary to clear toxins from the body, reduce excess sodium and liberate fat stores so that they can be utilised for energy. Daily water intake required by an individual varies dependent on body weight, age and the level of activity you participate in each day. The National Institute of Clinical Excellence (NICE) recommends that 18-60 year old adults need 35ml of water per kg of bodyweight per day and those over 60 years old need 30ml of water per kg of bodyweight per day.
Dietary minerals are chemical elements required by living organisms (aside from carbon, hydrogen, nitrogen and oxygen) that are present in common organic molecules.
Major minerals include calcium, phosphorus, potassium, sulphur, sodium, chlorine and magnesium. Trace minerals (required in less abundance) include iron, copper, zinc, selenium and iodine.
Rather than insert a table with a list of minerals (which would be boring to read and time consuming to create) I am going to focus on two of the major minerals required by the body and needed in the diet and one trace mineral. Minerals (like vitamins) are classed as micronutrients because we do not need to consume them in large dietary amounts like the macronutrients carbohydrates, fat and protein.
The skeleton contains 99% of the body’s calcium and we need an adequate intake of dietary calcium to grow and maintain healthy bones and teeth. Ordered movement of calcium ions plays a critical role in regulating muscle contraction, nerve conductivity, enzyme activation, blood clotting and the secretion of hormones.
Hypocalcaemia (low blood calcium levels) can cause seizures, tingling and numbness due to the negative impact low calcium levels have on neuromuscular activity.
Hypercalcaemia (high blood calcium) results in thirst, loss of appetite, mild mental confusion, irritability, weakness and fatigue.
If dietary intake of calcium is low, bone calcium will be mobilised to maintain blood calcium levels which leaves bones weaker and more at risk of injury and disease.
Recommended daily intake of calcium differs depending on age, gender and whether a woman is pregnant or lactating. An average adult requires ~1000mg/day.
Magnesium is involved in hormone secretion, vitamin D metabolism, bone function and protein synthesis. It has close interrelationships with calcium, potassium and sodium. Good dietary sources of magnesium include green vegetables, cereal, dairy products and meat. On average, 40-60% of dietary intake is absorbed. Dietary deficiency is very unlikely to occur in people eating a normal varied diet as it is such an abundant mineral.
Iron deficiency is the most common nutrient deficiency in humans. Approximately 500-600 million people suffer from anaemia (severe iron deficiency) and many are at risk of developing it. The total body content of iron is usually about 50mg/kg. Iron is most abundant in the haemoglobin of red blood cells but it is also present in the liver (stores), myoglobin in the muscles and in enzymes.
Dietary iron can be consumed from many food sources including meat, dairy, vegetables and fruit. Adult men require ~18mg/day. Women require differing levels depending on whether they are menstruating (43mg/day), post-menopausal (18mg/day) or lactating (24mg/day).
A vitamin is an organic compound required by organisms as a vital nutrient. Vitamins cannot be synthesised in sufficient amounts within the body and therefore dietary intake in small amounts is required.
Vitamins are classified as being either water-soluble or fat-soluble. B-vitamins and vitamin C are water-soluble vitamins which dissolve easily in water and are readily excreted from the body. Because of this, a more consistent intake of these vitamins is necessary in comparison with fat-soluble vitamins. Vitamins A, D, E and K are fat soluble meaning they are absorbed in fat globules which travel through the small intestine and enter into general blood circulation from there. These vitamins then become stored by the body and tend to remain as they are. Therefore, a high intake of fat-soluble vitamins can lead to hypervitaminosis. The most commonly known vitamin is probably vitamin C.
Water-Soluble Vitamin C:
Vitamin C is integral to the formation and maintenance of collagen, found in the skin and joints (connective tissue). It is grossly understated for its role in the formation of Carnitine, a potent fat mobiliser (aids fat burning), and for its role in nervous transmission allowing for more intense muscle contractions. Vitamin C is vital for the absorption of iron, a fundamental component of haemoglobin which is needed for oxygen delivery to the muscles! It is also a potent anti-oxidant which reduces the oxidative process (damage to your body) due to elevated free radical levels.
Fat-soluble vitamin K:
Vitamin K promotes the synthesis of a special amino acid with three carboxylic acids groups. The enzyme responsible for putting another carboxylic acid on to glutamic acid needs vitamin K as a cofactor in order to do so. You can obtain enough dietary vitamin K by including foods with dark-green leaves and those with photosynthetic tissues such as spinach, broccoli, mint, cabbage and lettuce. Vitamin K’s helping hand in the modification of proteins is necessary to circulation, blood coagulation, bone health and other tissues.
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