4. Protein

Are protein requirements increased by physical activity? This seemingly simple question has been hotly debated for years and remains one of the most controversial issues in sports nutrition. Unless you are regularly participating in strenuous strength, speed or endurance exercise for more than an hour each day, then your protein needs are no greater than those recommended for a healthy, balanced diet.

4(i). Protein and Amino Acids
Protein is essential for life and is a major part of the body. It is found primarily in muscle. We need protein for the growth and repair of tissues. During digestion, proteins are broken down into smaller units called amino acids. There are 20 different amino acids, which can be combined to make many different proteins. Our bodies can make proteins from amino acids, but we are unable to produce nine of the amino acids - the essential amino acids - so these need to be supplied by the diet. Only some foods - the complete protein foods - contain all the essential amino acids, shown in Table 1.

Table 1. Complete Protein Foods

Milk and dairy products

Eggs

Fish

Meat and poultry

Corn plus peas or beans

Rice plus beans

Lentils plus bread

Only animal sources contain all the essential amino acids, but by combining different plant proteins you can also make complete protein foods. Therefore, strict vegetarians need to plan their diet carefully to ensure that their combination of plant foods provides them with all the essential amino acids. Protein quality is improved when dairy products are added to a plant food and when plant-based foods, such as wheat and beans, are mixed together. Good matches are muesli and milk, rice pudding, sesame seed bread, pitta bread and houmous, baked beans on toast or lentil curry and rice.

4(ii). Protein Needs
The average daily protein requirements - expressed in grams per day for every kilogram you weigh (g/kg/d) - is summarised in Table 2.

For people who are sedentary or have low levels of activity, the daily protein requirement is equivalent to 0.75g per kg of body weight. So a person weighing 60kg would need 45g (60 x 0.75) of protein per day.

If you are exercising more than an hour each day, then your daily requirement is slightly increased to 1.0-1.2g of protein per kg of body weight - that's 60-72g of protein if you weigh 60kg. However, this requirement is still well within the amount that is typically consumed, on average, in the UK and therefore protein supplements are not necessary.

Experts recommend a further increase for athletes in the order of 1.2-1.4g/kg/d for endurance athletes and 1.6-1.7g/kg/d for strength athletes. When protein requirements are increased, for example, during heavy endurance training, the amount can simply be achieved by increasing the overall energy intake of the diet without altering the proportion of protein consumed. Therefore, no adjustment is necessary to the foods or the composition of the normal diet.

Experts also state that there is no advantage - both in terms of performance or muscle size - to taking more than 2g of protein per kg of body weight per day providing carbohydrate needs are met. Commonly, athletes report excess intakes of 100g of protein per day. If this was all used for muscle protein synthesis, muscle mass would increase by about 500g/d. But, in reality, the extra protein is metabolised and excreted, rather than converted into muscle.

Table 2. Daily Protein Requirements

Activity level	Protein g/kg/d
Sedentary to low levels of activity	0.75
Regular activity > 1 hour per day	1.0 - 1.2
Endurance athletes	1.2 - 1.4
Strength athletes	1.6 - 1.7

In practice, providing you are eating enough food to meet your energy and carbohydrate requirements, achieving an adequate amount of protein is fairly easy. Table 3 lists the protein content of some common foods. Animal sources are richer in protein than vegetable sources and, therefore, a larger quantity of non-animal sources need to be consumed to provide the equivalent amounts of protein. This can be particularly problematic for vegetarian strength and endurance athletes due to the bulk of the fibre-rich vegetables that they need to eat to meet daily protein needs. In this situation a protein supplement may be advisable.

Table 3. Protein Content of Everyday Foods

Portion of food	Protein (g)
150g lean meat or poultry	40
150g fish	33
150g soya beans	21
150g tofu, lentils, kidney beans	12
135g baked beans	10
284ml milk	10
30g cheddar cheese	8
30g cheddar cheese	8
1 egg	7
2 slices of bread	6

4(iii). Protein and Amino Acid Supplements
It is easy to meet your protein needs from food. High-protein diets have been falsely associated with exercise training, due to the mistaken belief that this will lead to greater muscle mass and strength, simply because muscle itself is protein. But, despite the influential power of advertising, all a protein supplement will do is burn a large hole in your pocket! Nor is there a benefit in taking expensive amino acid supplements. It doesn't matter if excess protein is obtained from food or a supplement it still won't be turned into muscle!

During exercise, the body relies mainly on muscle glycogen, liver glycogen and fat stores for fuel. Protein is used as muscle fuel if glycogen stores are low. It is important to ensure that glycogen stores are kept well topped up to stop muscle protein being used as fuel. The best way to achieve this is to eat additional carbohydrate before, during and after exercise - see section on carbohydrates.