There are three macronutrients, carbohydrate, protein and fat. The macronutrients are nutrients that provide energy to the body, energy that can

serve a number of functions including movement, growth and repair, maintaining cellular function, and many more.

PROTEIN

The primary function of protein is to provide structure; proteins are used to create other substances within the body. Most notably, via protein synthesis proteins are used to make skeletal muscle, but cardiac and smooth muscle are also made of protein, as are skin and hair.

Protein is also used to synthesise a number of the hormones within the body, including insulin, glucagon, and growth hormone.

In certain circumstances proteins can be broken down to provide energy. The process of gluconeogenesis allows the body to convert proteins into glucose, which can then be utilised as an energy source. This is only really evident during severe caloric restriction or low-carbohydrate diets, although during prolonged endurance exercise the breakdown (oxidation) of the branched chain amino acids to energy is commonplace.

Dietary proteins and amino acids also play an important role in immune function and general health, with recent research indicating a role for dietary proteins in the modulation of gut function, exerting anti-thrombotic activity, modulating blood pressure by inhibiting angiotensin-converting enzyme (ACE).

Also via protein synthesis protein is also used for the repair and replacement of damaged proteins within muscle, bone tendon, and ligaments, and protein intake and elevations in insulin following a mixed meal reduces rates of protein breakdown. A final function of protein is the maintenance of optimal functioning of all the metabolic pathways that utilise amino acids, and supporting lean body mass.

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FAT

Like protein, fat is also an essential macronutrient, meaning the human body cannot create (synthesise)sufficient fat within the body so consuming it via dietary sources on a daily basis is an absolute necessity.

Dietary fat plays several key roles in human physiology and wellbeing. It provides flavour to food; the ingestion of fat is essential for the intestinal absorption of lipid-soluble vitamins like vitamins A, D, E, and K.

Fat is also a source of metabolic energy, especially for lower intensity activities such as walking and jogging lightly. Components of fat are also important building blocks of all cells within the body. Fat, in the form of glycerolipids and sphingolipids, makes up the bulk of cellular membranes. These complex lipids are composed of fatty acids bound to glycerophosphate or sphingosine. Cellular membranes serve as barriers between compartments, such as the inside and outside of the cells, and are important for the maintenance of cellular structural integrity, being insoluble in water allows this to occur successfully.

Fatty acids also play important roles in metabolism, the regulation of cell function and hormone synthesis. Fatty acids also function as signalling molecules, thereby regulating cell function.

CARBOHYDRATE

The primary function of carbohydrate in the body is as a metabolic fuel; carbohydrates are broken down (oxidised) in cells to provide energy through a variety of pathways.

Carbohydrate is the predominant fuel for high-intensity exercise, athletes and exercising individuals therefore have elevated carbohydrate requirements when compared to their sedentary counterparts.

Fatigue; defined as a decrease in force production, during exercise is predominantly associated with the depletion of carbohydrate (glycogen) stores reduced blood glucose concentrations and hypoglycaemia. Therefore athletes and individuals that exercise regularly in are encouraged to undertake specific nutritional strategies, which promote elevated pre-exercise glycogen stores and maintain blood glucose during exercise. Existing evidence suggests that such strategies are effective in increasing performance during exercise through improved maintenance of blood glucose concentrations.

Consuming a diet that contains a mix of all of the macronutrients is of great importance to health and athletic performance. The quantities of each of the macronutrients within the diet generally depends on the level and type of activity you undertake. A sedentary office worker will require less calories and fewer of protein, fat and carbohydrate than an elite athlete, who would require significantly more calories to maximise performance and recovery, and significantly more carbohydrate. But generally speaking all individuals should consume a mixed diet, with daily sources of protein, carbohydrate and fat.

Article by Matt Jones, MSc Nutrition