This article was written by Dr Andrew Hulton, a BASES accredited sports scientist, teaching fellow in sport and exercise science at the University of Surrey.
The role of Nutrition for Exercise
Diet and exercise go hand in hand. Nutrients facilitate the activation of energy metabolism, supporting fuel selection to prolong exercise endeavours, through replenishing our energy stores and supporting muscle growth and repair. All these processes and pathways are supported by key nutrients that should, and can, be provided from a healthy balanced diet, fostering an optimal state of health and well-being, but also supporting our physical capabilities to exercise and perform at our best.
While diet supports our ability to exercise, we must be aware of the vast variety of foods we eat, and how they are digested and absorbed within the body. As this varies dramatically and should inform our choices and timing of consumption.
If we follow the correct advice and choose our dietary intake with our exercise goals in mind correctly, we can manipulate energy substrates (type of fuel we use – fat vs. carbohydrate), increase our exercise capacity by delaying fatigue, and augment greater muscle growth.
Sources of Nutrients
What are Macronutrients?
The term ‘macro’ can be defined as something on a large scale, and therefore macronutrients are consumed in large quantities, often in amounts >100 g/day. This contrasts with vitamins and minerals (micronutrients – discussed later) as these are ingested in much smaller amounts, typically milligrams to micrograms per day.
Macronutrients can be divided into three of our main nutrients,
They provide the energy source needed to fuel the body structures to perform physical activity.
Sugars, starches and fibre are carbohydrates, and love them or loathe them, they are generally the main macronutrient consumed within our diet, typically constituting 50% of our energy intake. There is over 100 years of research supporting the consumption of carbohydrates for performance, hence the link between high intakes and athletes.
These links stem from research illustrating increases in exercise capacity and improvement in time trial performance. With evidence highlighting a greater muscle glycogen content (the storage form of carbohydrate) is key for performance gains.
We also know that the higher the intensity you exercise at, the faster you will utilise your glycogen, and therefore need to fuel correctly for the intensity of exercise. Conversely, there is now recent evidence for training adaptations to be amplified when training with low carbohydrate intake. Therefore, the training goals or phase of training need to be clear to optimise carbohydrate intake.
Sometimes referred to as simple or complex based on the number of sugars that make up the food (its chain length). Simple carbohydrates would have 1 or 2 sugars attached to each other and be easier to break down, whereas complex carbohydrates would have many more, suggesting a delayed breakdown.
However, within sport and exercise nutrition there are different classifications used that are more appropriate. These follow a similar trend to simple and complex, but termed the glycaemic index (GI) and classified based on their speed of breakdown/absorption and ultimately the glucose response. Those carbohydrate foods resulting in a faster blood glucose response termed high GI foods, and those that are slow termed low GI. This classification of carbohydrate foods can help plan intake around exercise and will be discussed later.
Proteins form our muscles but also have additional functions within the body. Whenever the body is growing, repairing, or replacing tissue, proteins are involved. Forming the building blocks of all body cells and tissues including muscles, blood, skin, hair and fingernails. The body is continuously depositing protein into new cells that replace those that have been lost.
Guidelines for sedentary individuals to balance protein breakdown and growth is 0.8 g/kg body weight (a 70 kg person should consume at least 56 g of protein i.e. 0.8 x 70), although more may be needed for an older population, and 1.2 g/kg body weight may be better suited (84 g for a 70 kg individual). Further, for the more active individual this recommendation may need to increase due to greater protein breakdown during physical activity. Typical targets would vary depending on the sport and activity undertaken, but research has shown that up to 2 g/kg body weight may be optimal and elicit greater growth (up to 140g for the 70 kg person).
Regular protein intake of around 20 – 25 g of protein every 3 hours would be ideal, although following whole body exercise an increase to 40 g post exercise may be advantageous.
Dietary fats are necessary for a healthy body and have many functions. Along with protein, fats form a basic part of cell membranes and the components for many body compounds. Body fat cushions internal organs and protects them from being damaged, with the fat layer below the skin insulating the body from heat loss. Fats also are important sources of the fat-soluble vitamins, A, D, E and K, and are a concentrated source of energy.
Fats can be classified based on their degree of saturation, with saturated fat, which is typically solid at room temperature, being more harmful to health. Recommendations for saturated fat intake suggest no more than 20 g or 30 g for females and males respectively.
There are some fats that are needed to be consumed for optimal health. The body cannot make the fatty acids omega-3 and omega-6, and therefore these are essential and must be provided from the diet. Examples of omega-3 fatty acids are Oily fish such as salmon, herring and also Chia seeds, whereas sunflower oil, walnuts and pumpkin seeds are examples of omega-6 fatty acids.
As stated above, fats are a concentrated energy source and provide an almost unlimited source of energy, even on lean individuals. However, fats only act as the main fuel source for light to moderate exercise, up to approximately 65% of our maximum effect . After this intensity there is a crossover effect whereby carbohydrates become the dominant fuel source.
What are micronutrients?
The term ‘micro’ suggests very small or involving minute quantities or variations. This is correct when we consider micronutrients and their intakes of milligrams to micrograms per day. Micronutrients enable the use of macronutrients for all physiologic processes. They are key regulators of health and function, including work performance.
Micronutrients are the vitamins and minerals within our diet, designated as nutrients because they cannot be synthesised by the body, and required to support health and well-being. They catalyse numerous biochemical reactions. Not a direct source of energy; but facilitates energy metabolism.
Foods Before Sport & Exercise
As suggested previously, the timing and variety of foods play a main role to support exercise. Whether it is to provide additional energy for a workout or replenish energy stores and support muscle growth following a workout, below we highlight some important points to consider and some simple examples.
The Timing of Your Pre-Workout Meal Is Key
Great Pre-Workout Foods
Foods After Sport & Exercise
When we think about consuming food and drink after exercise, we are specifically focused on carbohydrates and protein. With regards to carbohydrates, we need to think about the next exercise session or competition. Do we need to recover quickly due to congested competition periods or training sessions? We may be in no rush to replenish our energy stores and therefore carbohydrate may not be essential.
Protein on the other hand is likely to be always key for recovery, as we want to remain in an anabolic (building) state, rather than a catabolic (breaking down) state, to support muscular repair and growth.
The Timing of Your Post-Workout Meal Is Key
Great Post-Workout Foods
Hydration Is Crucial
Fluid is an important nutrient to consider. Approximately 60% of our body is water and dehydration can reduce brain function and exercise performance significantly. Further, only a 2% loss of body weight is reflective of a decrease in performance.
It’s suggested that we should drink 500 ml with each meal to support the absorption of the food consumed, as well as more fluid intake in between. During exercise it may be worth calculating your sweat rate by measuring your weight loss before and after exercise. This would enable you to consume the correct amount of fluid so that you are not losing or gaining weight throughout the session.
A whole food approach and balanced diet should always be a focus when considering your nutrition. Yet, it is understood that some may struggle to consume all nutrients or quantities from diet alone. Therefore, supplementation may be required.
What are food supplements?
Supplements can be pretty much anything. Reasons for supplementation can be to promote tissue growth, repair, and adaptation to training. Promote fat loss or enhance energy supply. Or to promote immune function and resistance to illness/infection.
Micronutrients are commonly supplemented to provide a boost to the immune system, or to support a poor diet that may lack many vitamins and minerals. But as stated previously, no further supplementation is necessary if a balanced diet is achieved.
What are the most common supplements?
Vitamin D is a micronutrient that is highly supplemented. Not necessarily a true vitamin as it is mainly synthesised from UV exposure, and only present in a few foods. Nonetheless, in the UK due to the geographical location, and limited sunlight in the winter months, deficiencies in vitamin D are common, thus a popular supplement for all.
Antioxidants are another common supplement consumed, which is supported within the research literature. Antioxidants such as vitamin C or E, can remove potentially damaging oxidizing agents in a living organism. Or in other words can reduce the muscle damage following exercise.
Protein is another conventional supplement. Primarily due to the ease of intake following exercise owing to the vast availability of protein powders or bars today. Some protein supplements will aid as a further recovery drink by containing carbohydrate, so the initial phase of recovery following exercise is instigated efficiently.
Creatine is a popular sports supplement with strong evidence for its use. By maintaining a constant concentration of ATP (source of immediate energy that is short lived) in muscle during sudden bursts of exercise that would otherwise deplete, supports high intensity and power based activities.
Caffeine is a socially accepted drug that is also well documented to support performance. Consumed in many formats (drink, gel, powder, gum) it is thought to enhance performance in a variety of ways such as stimulating the central nervous system, improving muscle fibre recruitment, and increasing cognitive function.
An optimal nutritional strategy is essential to support training and exercise. It is important to have clear training goals, to therefore enable the structure and clarity of our nutritional approaches. As the food we consume can have such an effect not only on the actual training, but that actual adaptation to the training, it is essential to get training and diet orchestrated correctly.
Dr Andrew Hulton, Teaching Fellow in Sport and Exercise Science at the University of Surrey.
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