Nutrition for Top Performance in Soccer (eBook)

CHAPTER 2

Some Things You Need to Know About Nutrition and Nutrients

What Are Nutrients?

The Need for Energy

The Major Classes of Nutrients

In order to understand how nutrition can influence football performance and recovery, it helps to know something about the different types of nutrients and the roles that they play in various bodily processes, including energy supply for exercise. That is what this chapter is all about and it should be particularly helpful to the reader who is not too familiar with the sources, properties and roles of various nutrients.

WHAT ARE NUTRIENTS?

Let’s begin by learning exactly what nutrients are: a nutrient is a substance found in food that performs one or more specific functions in the body. Nutrients are usually divided into six different categories: carbohydrates, fats, proteins, vitamins, minerals and water. Functions of nutrients include promotion of growth and development, provision of energy and control of metabolism. Nutrition is often defined as the total of the processes of ingestion (eating and drinking), digestion (breaking down), absorption (moving nutrients from the gut into the blood) and metabolism (processing) of food, and the subsequent assimilation of nutrient materials into the tissues and organs. The energy we obtain from food is mainly supplied in the form of carbohydrates and fats. These are two of the macronutrients (nutrients that are ingested in relatively large – more than 10 g/day – quantities) in our diet; the other two macronutrients are protein and water (table 2.1). All other nutrients that are needed in quantities of less than 10 g/day are classed as micronutrients and they include vitamins, phytonutrients and minerals. All vitamins, and many minerals, are essential for health but are only needed in relatively small amounts; in fact, many are needed in only milligram quantities on a daily basis. Phytonutrients are not considered to be essential but they are needed if you want your health to be optimal – in other words as good as it can be.

THE NEED FOR ENERGY

Our bodies need to take in energy in the form of food regularly in order to be able to expend energy to do useful work, which includes muscle contractions to allow us to move, sending messages via nerves to allow us to sense changes, to react and think, or biosynthetic processes to produce new molecules and cells. Without an input of food energy, we would wither away and die. Energy is expressed in calories (the imperial system) or joules (the metric system). One calorie represents the quantity of heat energy needed to raise the temperature of 1 g (1 mL) of water by 1°C (1.8°F). Thus, food containing 1,000 calories (1 kcal) has enough energy potential to raise the temperature of 1 L of water by 1°C (1.8°F). In everyday language, kilocalories are often referred to as Calories (written with a capital C, although on many food items this is not done, and the energy is listed as calories). Because this may be a source of confusion, the term kilocalorie (abbreviated kcal) is used in this book. The SI (International System of Units) unit for energy is the joule (J), named after the British scientist Sir Prescott Joule (1818–1889). One joule of energy moves a mass of 1 g at a velocity of 1 metre per second (m/s). A joule is not a large amount of energy; therefore, kilojoules are more often used; one kilojoule (kJ) equals 1,000 joules. To convert calories to joules or kilocalories to kilojoules, the calorie value must be multiplied by 4.184. Nowadays, food packaging labels indicate the energy content in both kcal and kJ, but most people still talk in terms of calories although it really should be kcal.

THE MAJOR CLASSES OF NUTRIENTS

In the remainder of this chapter, I will briefly describe the characteristics, roles and sources of the major classes of nutrients. These include the macronutrients (carbohydrate, fat, protein and water), the essential micronutrients (vitamins, minerals and trace elements) and some of the nonessential nutrients including phytonutrients, dietary fibre and alcohol.

Table 2.1 The major classes of nutrients

CARBOHYDRATES

Carbohydrates include sugars, starches and fibre, and we get almost all of our dietary carbohydrate from plants (photo 2.1). Carbohydrates provide 4 kcal of energy per gram (kcal/g) and they are the main source of energy for football match play and intense training. Common food sources of carbohydrate in the form of starch (a large molecule composed of many thousands of linked glucose molecules known as a polysaccharide) include cereal products, corn, potatoes, sweet potatoes, pasta, rice and bread. Sugars (also known as saccharides) are found in fruit juices, fruits, sweetened cereals, baked goods, candy, sweets, soft drinks, energy drinks, sports drinks, milk, beet and cane sugar, brown sugar, table sugar, maple syrup, honey and treacle. Also, many processed foods, including ready meals and sauces, tend to have high sugar content. Sugars in our diet include glucose, fructose, galactose, maltose, lactose and sucrose.

Fibre is another form of carbohydrate and much of it cannot be digested in the human gut so it has a much lower energy value than starches and sugars. Sources of fibre include whole-grain cereals and breads, oats, fruits, beans and peas, and other vegetables such as cabbage, courgette (zucchini), celery, spinach and salad leaves (photo 2.2). Fibre cannot be digested by enzymes in the human stomach and small intestine, and so it passes into the large intestine (colon) largely unchanged. In the large intestine, most soluble fibre (fibre that dissolves in water) can be broken down into sugars by the resident population of bacteria (in total there is about 1 kg of bacteria in our colon) known as the gut microbiota. The bacteria rapidly ferment these sugars to produce short-chain fatty acids such as butyric acid, which can be used as an energy source by both the bacteria themselves and the human cells that line the colon. Soluble fibre makes up about 70% of the fibre in our diet and has an energy value of about 1.5 kcal/g. Most insoluble fibres (e.g. cellulose and lignins that form the structure of plant cell walls) are not digested or fermented at all and are excreted unchanged in the faeces and hence have zero energy value to humans.

Photo 2.1 A variety of high-carbohydrate foods.

Photo 2.2 A variety of high-fibre foods.

FATS

Fats, also known as lipids, are compounds that are soluble in organic liquids such as acetone, ether and chloroform but have very poor solubility in water. The term lipid, derived from the Greek word lipos (meaning fat), is a general name for oils, fats, waxes and related compounds. Oils are liquid at room temperature, whereas fats are solid. For simplicity, and to avoid confusion, the term ‘fat’ is used throughout this book. Fats provide more than twice the amount of energy as carbohydrates at 9 kcal/g and are an important energy source at rest and during light- to moderate-intensity exercise. Fat in the diet also aids the absorption of the four essential fat-soluble vitamins: A, D, E and K. There are several classes of fats, including fatty acids, triglycerides, lipoproteins, cholesterol and phospholipids. The latter are an important constituent of all cell membranes and intracellular organelles including the cell nucleus and mitochondria. Triglyceride (also known as triacylglycerol) is the main storage form of fat in the body and is also the most abundant form of dietary fat. If we consume more carbohydrate and fat than we need to meet our energy requirements, the excess is mostly stored as triglyceride in adipose tissue. Most sportspeople, including footballers, do not want too much of this in their body as it adds weight, which can slow a player down; however, some body fat is essential (about 3–5% of body mass for men and 10–12% for women). Most professional male outfield players have about 7–15% body fat. We’ll look at the issue of body composition in more detail in chapter 8.

Common food sources of fat include fatty cuts of meat (e.g. beef, pork, lamb) and poultry (e.g. chicken, duck, turkey), animal liver, oily fish such as mackerel, salmon and sardines, egg yolk, cream, cheese, butter, margarine, oils, nuts and avocado (photos 2.3 and 2.4). Many processed foods including ready meals and creamy sauces, plus any foods cooked in oil such as French fries and fish in batter tend to be high in fat.

Triglycerides are made up of a glycerol molecule linked to three long-chain fatty acids. The chains are formed from repeating hydrocarbon units. Fatty acids can be either saturated (meaning they contain only single bonds between the carbon atoms in the chain) or unsaturated (meaning they contain at least one double bond between the carbon atoms in the chain). Monounsaturated fatty acids contain just one double bond in their hydrocarbon chain, whereas polyunsaturated fatty acids (PUFA), including omega-3 and omega-6 fatty acids, contain two or more double bonds. Two of the PUFAs, linoleic acid and alpha-linolenic acid, are essential nutrients for humans. The intake of monounsaturated fats and PUFAs should be prioritised as they support cognitive function, heart health and muscle recovery. Good food sources of PUFAs include oily fish like salmon, tuna and mackerel; vegetable oils like sunflower and rapeseed; and walnuts and seeds like flax, sunflower and chia. Soy products...