What are macronutrients?

Macronutrients are those nutrients that provide calories or energy and are needed for growth, metabolism, and for other body functions. They constitute carbohydrates, proteins and fats. The ratio of these in your diet has a significant inlfluence over your energy, strength, power, stamina and body composition.

Carbohydrates

Carbohydrates provide the largest single source of energy in the diet and are defined as either simple or complex.

Simple carbohydrates consist of monosaccharides and disaccharides.

• Monosaccharides are the most basic unit of carbohydrates and consist of single molecules of sugar in the form of glucose, fructose, galactose, xylose or ribose.
• Disaccharides are two monosaccharide sugar molecules joined together. Lactose for example is made from glucose and galactose, and sucrose - common table sugar - is made from glucose and fructose.

Complex carbohydrates consist of oligosaccharides and polysaccharides.

• Oligosaccharides consist of anywhere between three and ten monosaccharide sugar molecules joined together.
• Polysaccharides are more complex than oligosaccharides being made up of many monosaccharides.

Carbohydrates provide the largest single source of energy in the diet providing 45 - 65% of calories consumed daily. They are mainly found in starchy foods such as grain and potatoes, fruits, vegetables, beans, nuts and seeds. They are easily used by the body for energy and all cells of the body require glucose for energy. However, carbohydrates can also be stored for later use in the muscles and liver as a polysaccharide called glycogen.

Fibre

Fibre is made up of a number of complex carbohydrates that can be divided into soluble and insoluble varieties. Insoluble fibre possesses passive water-attracting properties that help to increase bulk, soften stools and shorten transit time through the intestinal tract. Soluble fibre reaches the colon where it is fermented by the colonic bacteria yielding end-products with broad, significant health effects.

Ideally, adults should aim for an intake of fibre of around 18 grams a day. Diets that are low in fibre have been shown to cause problems such as constipation, haemorrhoids and to increase the risk for certain types of cancers such as colon cancer. Diets high in fibre, however, lower cholesterol and have been shown to decrease the risk of developing heart disease and obesity. Foods high in fibre include fruits, vegetables, and whole grain products.

Protein

Protein is made up of building blocks called amino acids. Amino acids can be divided into essential and nonessential varieties. The body is capable of synthesising 13 nonessential amino acids, but for the body to process protein properly foods eaten must contain the nine essential amino acids that are available only from dietary sources. Approximately 20 - 35% of calories should come from protein. Protein is found primarily in meats, poultry, fish, meat substitutes, cheese, milk, nuts and legumes. Protein from animal sources is considered of high biological value or a “complete” protein because all nine essential amino acids are present in these proteins. Plant sources of protein generally do not contain sufficient amounts of one or more of the essential amino acids.

Protein plays a vital role in growth, whilst maintaining and replacing tissues including muscles, organs, skin, and blood constituents. Protein is found in almost every living cell and fluid and is involved in the synthesis of hormones, enzymes and antibodies.

Fat

Dietary fat is defined as either saturated, monounsaturated or polyunsaturated. What really matters is not so much the amount of fat that you eat - within certain limits - but the type of fatty acid present in the fat in your diet.

Saturated fats are so called because each of the carbon atoms in the fat molecule is fully covered in hydrogen atoms, resulting in a straight fatty acid chain. Saturated fat is known as the ‘bad boy’ of all the fats out of the three types because if consumed in relatively high amounts over a period of time it can increase health risks. These fats tend to be solid at room temperature because the straight design of these fatty acids means that they pack together very efficiently, giving a rigid structure.

Foods that contain a high proportion of saturated fat are dairy products and animal fats. Many processed foods such as cakes, biscuits, pastries and crisps also contain saturated fats.

Monounsaturated fats have a single pair of carbon atoms in the fatty acid chain that is not ’saturated’ with hydrogen atoms and so have a ‘kink’ to their structure. As a result the fat molecules cannot fit together as efficiently as saturated fat and hence tend to be fluid at room temperature. The so-called ‘Mediterranean diet’ is rich in monounsaturated fat and offers many protective health benefits, including lowering the risk of heart disease and fewer inflammatory problems. Monounsaturated fats are found in olives, olive oil, groundnut oil, nuts, and avocados.

Polyunsaturated fats have at least 2 pairs of carbon atoms that are not ’saturated’ with carbon atoms, resulting in highly kinked fatty acid chains giving these molecules exceptional fluidity - a property that contributes to their importance for human health. These fatty acids come in two varieties, the omega-3 and omega-6 families. The parent omega-3 fatty acid, alpha-linolenic acid (ALA) and parent omega-6 fatty acid linoleic acid (LA) are short-chain molecules that cannot be synthesised in the body and are hence otherwise known as Essential Fatty Acids (EFAs). Once ingested these short-chain essential fatty acids are elongated by enzymes to produce the omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) or the omega-6 LC-PUFAs gamma-linolenic acid (GLA), dihomo gamma-linolenic acid (DGLA) and arachidonic acid (AA).

Long-chain fatty acids, particluarly of the omega-3 variety as found in fish oil, are especially beneficial for health, supporting the cardiovascular, reproductive, immune, and nervous systems. The human body needs these fatty acids to manufacture and repair cell membranes, enabling the cells to obtain optimum nutrition and expel harmful waste products. These fatty acids are also needed for normal neural development. A primary function of long-chain fats is the production of prostaglandins, thromboxanes and leukotrienes, which regulate body functions such as heart rate, blood pressure, blood clotting, fertility, conception, and play a role in immune function by regulating inflammation and encouraging the body to fight infection.

Oily fish, such as mackerel, salmon, trout, herring, anchovies and sardines, are good sources of the omega-3 LC-PUFAs EPA and DHA. Cooking oils such as safflower and rapeseed are good sources of the short-chain omega-3 essential fatty acid ALA; and sunflower and corn oils are good sources of the short-chain omega-6 essential fatty acid LA.