Energy Basics
General information
Energy (supply) is a foundation of life. For your body to function properly, you need to get enough energy through your diet. The energy content of food is given in joules (J) or kilojoules (kJ). To avoid overly large figures in joules, these are usually shortened: 1'000'000 J = 1000 kJ = 1 megajoule (MJ). The unit "calorie" or "kilocalorie" is outdated and is no longer permitted anywhere in the world today; in Switzerland, the ban has actually been in place since 1977. Converting from the outdated calorie to joules is very simple: you multiply the calorie figure by roughly four. Conversely, you divide joule figures by four to get calorie figures (the exact factors are: 1kJ = 0.24 kcal, or 1 kcal = 4.18 kJ).
Energy sources
Carbohydrates, fats and proteins are the three nutrients that matter as energy sources for healthy people. Alcohol is an additional energy source, although its quantitative importance for healthy people is not high. The energy content of the various nutrients is listed below.
| Energy source | Energy content per gram | |
| kJ | kcal | |
| Carbohydrates | 17 | 4 |
| Fats | 38 | 9 |
| Proteins | 17 | 4 |
| Alcohol | 29 | 7 |
The literature still contains countless (mostly questionable) ratios for how energy sources should be distributed in the diet. These recommendations are usually aimed at people who are moderately physically active and often follow the guidelines on reducing fat intake (especially saturated fatty acids) that were considered "valid" for a long time. At the same time, these recommendations quite often include relatively low protein amounts, based on the actual needs of inactive people. This overlooks the fact that higher amounts of protein can also be perfectly fine, or even sensible, and can have a biological effect. Recommendations with low fat and protein amounts automatically lead to a high carbohydrate intake. Many nutrition organisations therefore still support carbohydrate-rich, low-fat diets, despite contradictory study data. This is the case even though there is now solid evidence that physically inactive people should reduce their carbohydrate intake and increase their protein and fat intake.
The current recommendation for energy intake for healthy adults with low physical activity according to the DACH reference values (for German-speaking countries), together with an alternative macronutrient distribution based on currently discussed trends in nutritional science, is listed below.
| Energy source | Recommended intake as a percentage of energy | |
| DACH reference values | Alternative | |
| Carbohydrates | > 50 % | approx. 40-50 % |
| Fats | ≤ 30 % | approx. 30-40 % |
| Proteins | 9-11 % | approx. 15-20 % |
Unlike inactive people, athletes need an increased carbohydrate intake depending on the sport they do, although this poses no health risks for physically active people.
Energy figures: relative or absolute?
Most nutrition and health organisations give their recommendations for macronutrient intake as a % of total energy intake. As long as the target group for the recommendation has a homogeneous energy expenditure, such figures are workable. For athletes, however, relative figures in % of total energy intake make little sense. This is because energy needs in sport can vary greatly depending on the sport and the performance level. For this reason, recommendations in sports nutrition work with absolute values, i.e. g of the nutrient per kg of body mass, although practicality is limited here too (working with food pyramids is better). Absolute values are shown below.
| Intake according to the food pyramid in g per kg of body mass | ||
| Low activity | Athletes | |
| Carbohydrates | 3.5 | 5 to 10 |
| Fats | 1.3 | 1 to 3 |
| Proteins | 1.5 | 1.2 to 2.0 |
Energy needs
Put somewhat simply, basal metabolic rate and the energy needs for physical activity together make up your total energy needs. Basal metabolic rate corresponds to the minimum amount of energy needed to maintain all vital metabolic functions (including digestion = the "thermogenic effect of food") in a healthy person who has been in complete rest for at least eight hours, is awake, and has not eaten for 10 to 12 hours. Work-related energy expenditure reflects the energy used through physical work and depends on the type of work, the intensity and the duration of the activity. In addition, total energy expenditure is also linked to various factors such as growth, pregnancy, breastfeeding, behaviour, illness, stress or environment.
Basal metabolic rate
In people who are not very physically active, basal metabolic rate makes up the largest part of total energy expenditure (approx. 60%). It is determined by various factors such as sex, age, body mass and body surface area or genetics; when it comes to body mass, fat-free body mass is particularly decisive (a large part of the energy expenditure in fat-free mass is needed for muscle protein synthesis). Fat-free body mass decreases with age. Since men have more muscle mass than women, women's basal metabolic rate is around 10% lower than men's. Although many formulas exist for calculating basal metabolic rate, they only approximate the actual basal metabolic rate (individual deviations range from -30 to +40%). Only measuring basal metabolic rate using calorimetry gives a reliable result.
Work-related energy expenditure
Energy is needed for every physical activity (every muscle contraction). For a working person who sits for long periods and moves little in their free time, this low activity level makes up around 20 to 30% of basal metabolic rate (additional energy expenditure on top of basal metabolic rate). Since total energy needs can be expressed as a multiple of basal metabolic rate, basal metabolic rate is multiplied by 1.2, or 1.3, for inactive people (100 % basal metabolic rate plus 20-30% for physical activity). This factor is known as the Physical Activity Level (PAL). An overview of PAL values is shown below.
| Behaviour/situation | PAL | Examples |
| Basal metabolic rate | 1.0 | |
| Exclusively sitting or lying lifestyle | 1.2 | Elderly, frail people |
| Sedentary activities with little leisure activity | 1.4-1.5 | Office employees, precision mechanics |
| Sedentary work, with occasional walking or standing | 1.6-1.7 | Laboratory technician, student, assembly line worker |
| Predominantly walking and standing work | 1.8-1.9 | Sales assistant, waiter, mechanic |
| Physically demanding work | 2.0-2.4 | Construction worker, farmer, forestry worker |
Energy balance
Energy balance corresponds to the difference between energy intake and energy expenditure. When energy intake and expenditure are equal, this is known as a zero balance or a balanced energy balance. Over a longer period, a positive balance leads to weight gain, since the surplus energy is inevitably stored in the body. Conversely, a long-term negative energy balance leads to a decrease in body mass. The key factors influencing energy balance are therefore food intake and energy expenditure. However, since the distribution of energy sources also has an effect on energy expenditure, the type of intake also seems to play a (small) role.
Energy needs for sport
Approximate values for different sports and intensities can be found at https://sites.google.com/site/compendiumofphysicalactivities/.
Energy stores
The body can only store energy in the form of fat or carbohydrates. Fat is the ideal storage substance for the body. It can store a lot of energy in a very small space, because fat contains more than twice as much energy per gram as carbohydrates and, moreover, can be stored almost water-free. When carbohydrates are stored, almost double their storage weight in water has to be stored along with them. In addition, carbohydrate stores are very limited.
