Energy balance equation
The energy balance equation is the relationship between the energy consumed – measured in calories and the energy expended – also measured in calories. Maintaining a healthy weight requires a balance between energy in and energy out. Too much energy in or too little energy out leads to excess energy being stored as fat. Too little energy in or too much energy out leads to weight loss. Typically, men require 2,500 Kcal per day and women 2,000 Kcal but these general values are affected by four main factors:
- age – in general, adults consume more than children but calorie consumption declines in later life
- gender – in general, men consume more than women
- height – the taller the person, the more that person will need to consume
- energy expenditure – the more active a person is, the more calories are required to maintain weight
Energy in and energy out do not have to balance every day. The energy equation needs to balance over time for people to maintain a healthy weight.
Understanding food – knowing what makes a healthy diet – helps people to manage the energy balance, and people’s levels of physical activity are as important to the energy balance as their diet.
Food types
Nutrients
The body needs a balance of nutrients to stay healthy. There are five groups of nutrients.
| Purpose | Examples | |
|---|---|---|
| Proteins (15-20% of intake) | Tissue growth – known as the body’s building blocks. Athletes frequently use protein supplements in their diet and will consume protein immediately after training, sometimes as a ‘shake’. | Animal products – meat, fish, dairy; plants – lentils, nuts, seeds; protein supplements and shakes. |
| Carbohydrates (55-60% of intake) | Source of energy. Divided into: simple carbohydrates – sugars and complex carbohydrates – starches. Athletes need to consume larger quantities of carbohydrates to fuel their training and performance. Prior to an endurance event such as a triathlon, athletes might ‘carbo-load’ to ensure they have enough to finish the race. | Simple – sugar, glucose, fructose; energy gels; complex – bread, pasta, rice, potatoes. |
| Fats (25-30% of intake) | Source of energy. Four types: monounsaturated, polyunsaturated (omega 3 and 6), saturated and trans fats. Fats are stored under the skin and are essential for health. Too much fat can limit an athlete’s performance due to increased weight. | Monounsaturated – olive oil, avocados; polyunsaturated – oily fish, nuts, sunflower oil, soya beans; saturated – full-fat dairy, fatty meats; and trans fats – many snack foods. |
| Minerals | Essential for many processes, eg bone growth/strength, nervous system, red blood cells, immune system. Need small amounts only. | Calcium – milk, canned fish, broccoli; iron – watercress, brown rice, meat; zinc – shellfish, cheese, wheatgerm; potassium – fruit, pulses, white meat. |
| Vitamins | Essential for many processes, eg bone growth, metabolic rate, immune system, vision, nervous system. Need small amounts only. | A – dairy, oily fish, yellow fruit; B – vegetables, wholegrain cereals; C – citrus fruit, broccoli, sprouts; D – oily fish, eggs, fortified cereals. |
Water/fluids
The body needs to be hydrated to stay healthy. Failing to replace lost fluids can result in dehydration. This is a more serious condition than lack of food. Women should drink around 1.6 litres (approximately 8 glasses) of fluid and men should drink around 2 litres (approximately 10 glasses) of fluid per day. This varies according to the temperature and how rigorous the exercise. All drinks count but water is healthiest. Fruit juices are fine in moderation but do contain high levels of sugar.
A lack of hydration can cause a thickening of the blood known as increased viscosity which slows down blood flow. As a result the heart works harder to produce the same output. The body then becomes hotter and might overheat. Furthermore, reaction time slows down and athletes experience fatigue and cramps. It is therefore essential to stay hydrated before, during and after performance.
Fibre/roughage
Fibre is an important part of a healthy diet. It is only found in plant-based foods. There are two types and each one helps the body in different ways:
- soluble fibre – helps to reduce cholesterol, eg oats, barley, fruit, root vegetables
- insoluble fibre – keeps the bowel healthy, eg wholemeal cereals, wholemeal bread, nuts
Diet
Diet is the variety of foods that are eaten over a period of time. As no single food provides all of the body’s required nutrients, an individual’s diet should be balanced across a variety of foods. Individual foods are not necessarily healthy or unhealthy. Healthy eating requires a balanced diet.
Healthy eating plate
The Healthy Eating Plate, created by nutrition experts at Harvard School of Public Health and editors at Harvard Health Publications, was designed to address deficiencies in the U.S. Department of Agriculture (USDA)’s MyPlate. The Healthy Eating Plate provides detailed guidance, in a simple format, to help people make the best eating choices.
As well as being balanced, a healthy diet includes: Even if their diet is balanced, people still need to consider the energy balance equation. A balanced diet is the starting point for most people but sportspeople may have specific dietary needs. This reflects their personal energy balance equation. When people become more active they use up more energy so they need to take in more to restore their energy balance. Athletes adjust their diets differently depending on their sport and training/performance schedule. On average, men need around 2,500 calories (Kcal) a day while women need around 2,000. When athletes are training intensively this may increase to around 5,000 calories a day. To calculate how much energy the body needs, the following equation may be used: BMR or basal metabolic rate is the amount of energy needed just to keep the body systems working normally. PAL or physical activity level is the amount of energy needed for any activity (sporting or everyday such as housework). A big athlete – such as a shot putter or rugby forward – will have a higher BMR. A runner or a cross-country skier will have a higher PAL. Eating patterns may vary according to the day’s training programme or competition schedule. For example, an elite rower may eat two breakfasts – one before and one after the first of the day’s training bouts. Tennis players often eat a banana between games during a long match. Generally, performers do not eat two hours before performing. Anyway, we can use these advices to eat appropriately: Before exercise – eat a meal at least two hours before exercise, to give the food time to digest; include plenty of complex carbohydrates and fluid for hydration. During exercise – small but regular drinks; glucose-based sports drinks and easily digestible carbohydrates may be consumed in small quantities if the exercise lasts more than an hour. After exercise – eat carbohydrates within 15 minutes if possible, to restore glycogen levels and drink to replace fluids; carbohydrates and proteins should be eaten at least within an hour of exercise to repair muscles and replenish energy stores. Carbohydrates provide energy. The complex carbohydrates – starches – are stored in the body as glycogen and converted into glucose when the body needs more energy. Glycogen is a slow-release form of energy. This is particularly useful to endurance athletes in the last stages of a performance. So, for example, in the week leading up to a race, marathon runners may eat lots of starchy foods, such as pasta. This helps them to keep going towards the end of the race. Protein builds tissue, including muscle. Athletes who want to build up their muscle during strength-training sometimes eat high-protein diets. This includes obvious strength-training athletes, such as weightlifters, but also includes endurance athletes who want to repair or prevent torn muscle. The value of high-protein diets is debatable. Athletes do not need much more protein than other people, protein is difficult to digest and it does not automatically turn into muscle – the athlete still needs to do strength-training, which is fuelled by carbohydrates. Mo Farah’s typical diet during training is pasta, steamed vegetables and grilled chicken. He often eats this for lunch and dinner – every day
Additional advice
Diet and physical activity
How much to eat
When to eat
What to eat – special diets
Carbohydrate loading
High-protein diets
Bibliography: BBC – Education
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