Fat Burning - Fat Loss
When it comes to weight reduction in the sense of reducing body fat percentage, inappropriate recommendations are increasingly being made. What stands out is the confusion between optimal fat burning and optimal fat loss.
Fat burning refers to a form of energy production. In this process, free fatty acids (FFAs), which are released when stored body fat is broken down, are "burned" (oxidized) in the body without flame. Compared to energy production from glucose, this process is relatively complex, but it releases much more energy from the same amount of fuel. Fat burning takes place in the body at all times and everywhere.
Fat loss describes a sustained process of reducing body weight by decreasing body fat percentage. Fat loss and fat burning must first be considered independently of each other. While fat burning occurs constantly, fat loss only happens when the body receives less energy than it consumes over a longer period of time. In this context, this is referred to as a negative energy balance.
Relative and Absolute Energy Production from Fat
In relation to the required energy, the lower the physical intensity, the higher the proportion of fat burned. At rest, almost the entire energy demand of the body is covered by free fatty acids. The relative energy yield from fat, expressed as a percentage, is therefore very high. However, the absolute amount of energy measured in calories is very low at rest.
When the body is exposed to low-intensity endurance exercise (e.g., steady jogging at 60% of maximum heart rate), it requires large amounts of energy within a relatively short time and increases its metabolic rate. Not only does fat metabolism increase, but glucose (blood sugar) metabolism increases disproportionately because the body can obtain energy more quickly from it. During the run, a relatively larger proportion of energy is derived from carbohydrates compared to resting conditions. However, fat metabolism still accounts for about 80 percent of total energy production.
The high relative proportion of energy derived from FFAs is the reason why low-intensity endurance training is often recommended when fat loss is the goal. For beginners, this certainly makes sense, as higher intensities might be overwhelming. Even if energy production from free fatty acids plays only a minor or no role during high-intensity exercise, this does not mean that intense training is ineffective for fat loss. Strength training, high-intensity interval training, or sprint sessions also contribute to overall energy expenditure. Therefore, in personal training, it must always be distinguished whether the goal is to optimize a specific metabolic process (aerobic capacity, lactate tolerance, etc.) or primarily to increase total energy expenditure in order to support a negative energy balance in combination with proper nutrition.
"Fat Burns in the Flame of Carbohydrates"
This relationship can be illustrated with the following example:
Slow running at around 120 bpm burns about 8 kcal per minute. With approximately 80% of energy coming from fat, about 6.4 kcal per minute are burned from fat.
Running at a heart rate of 150-160 bpm burns approximately 15-18 kcal per minute. Even if only 50-60% of the energy comes from FFAs, at least 9 kcal per minute are still derived from fat. Assuming both athletes sustain the activity for the same duration, the faster runner will have burned roughly twice as much total energy as the slower one.
If both aim to lose weight and have identical food intake, it would be incorrect to claim that the person training at 120 bpm would experience greater weight loss than the one training at 150-160 bpm. Yet this is often asserted.
Pure fat metabolism training is therefore not the ultimate solution for fat loss. Whether the body taps into its fat reserves depends solely on the energy balance. If it is negative - meaning more energy is expended than consumed - the body has no choice but to obtain energy from where it stored it for that purpose: fat reserves.
Carbohydrate stores in muscles and the liver are replenished after training. This also factors into the overall energy balance, as the body then draws more heavily from fat stores post-exercise. This phenomenon is known as the afterburn effect.
Likewise, in healthy, non-starving individuals, the body has no interest in metabolizing muscle protein. The assumption that reduced calorie intake combined with endurance training automatically leads to muscle loss is exaggerated. Muscle cells primarily shrink due to inactivity, a process known as atrophy. Insufficient protein intake can also lead to muscle protein breakdown. Anyone who maintains adequate protein intake and incorporates strength training during weight loss does not need to fear losing muscle mass.
In summary: fat metabolism training is not the same as "fat loss training." Certain elite athletes perform hours of fat metabolism training during specific training phases to optimize this energy system for their sport. Long-duration endurance training is particularly important for marathon runners and cyclists. However, if the objective is simply to expend more energy than consumed, it is inappropriate to transfer such training recommendations directly to recreational and health sports.
What Does Energy Balance Mean in Practice?
From the explanations above, it is clear that to lose weight, energy expenditure must be increased and calorie intake reduced.
For example, a man weighing about 75 kg has a basal metabolic rate of approximately 1600 kcal. His total daily energy requirement is calculated as basal metabolism plus activity and would be at most about 2000 kcal if he works an office job and does not engage in sports. Daily energy needs, which depend on age, sex, body weight, and muscle mass, can easily be increased by up to 30% through exercise.
Fat loss is therefore only possible by, first, reducing calorie intake and, second, increasing expenditure through physical activity. There is no magic formula. A diet that overemphasizes certain food groups is just as unreasonable as food combining or slimming drinks. Ultimately, fat loss is a matter of balance.
A balanced sports-oriented diet that is low in fat, rich in carbohydrates, and contains valuable micronutrients should be the foundation when aiming to reduce body fat. In principle, no food should be completely forbidden. Since fat is very energy-dense, it makes sense to reduce fat intake first. However, fat should not be eliminated entirely, as certain fatty acids are essential for the body. These include essential fatty acids found in high-quality oils.
Integrating sport and movement into daily life is not difficult. While cyclical sports such as cycling, running, or swimming are easiest to control and measure, team and racket sports like soccer, squash, or tennis are also effective for reducing body fat.