Fuel management and fat burning

Fuel sources & fuel partitioning
The human body is capable of fuel partitioning: Fat is utilized alongside carbohydrate sources in energy metabolism. The contribution of fat use versus carbohydrate use varies depending on the level of physical activity and with fuel availability and food consumption.

Figure: The body’s main fuel tanks.


Carbohydrates supply the body with glucose. As the body’s prime fuel, it represents the faster and more efficient source of energy. For this reason it permanently fuels the energy metabolism to a large extent, and its contribution in fuel partitioning becomes predominant with physical activity, in particular at high intensity levels. However, the body’s own glucose resources in the form of glycogen are limited, and their depletion determines endurance. Using fat fuel alongside and increasing its contribution in energy metabolism is known as a means to spare limited carb sources.

Fat serves the body as an efficient reserve fuel: Its energy supply is slower, whereas energy storage in the form of fat is more efficient (with 9 calories per gram), and energy resources from fat stores are essentially unlimited. This is equally true for highly trained lean athletes, as well as for everyone else. It becomes evident that the relative contribution of fat utilization in energy metabolism is highest at rest, e.g. during sleep or sedentary activities, or that it comes into play after a period of time during longer-lasting physical activities as a means to spare the body’s own carb resources for longer endurance.

Influence of food & drink intake
Fuel management is influenced by food and drink intake. First and foremost, carbohydrate availability in the form of glucose drives the energy metabolism. Their glucose supply directly affects blood sugar levels, triggers insulin release, and promotes carbohydrate oxidation at the expense of fat oxidation in energy metabolism.

The hormone insulin, which is released from pancreatic cells into the blood due to rising nutrient levels after food intake, plays a key role in the postprandial metabolic regulation. Insulin promotes the uptake of glucose and other nutrients from the blood into the body cells, and it promotes the preferential use of carbohydrate sources (glucose) in energy metabolism, while the mobilization and use of fat is suppressed. Excessive energy is stored in form of glycogen (glucose) in the liver and muscles, or as triglycerides (fat) in adipose tissue.

Smart carbohydrate choices can make a difference for insulin release and fuel management. While those with a high impact on blood sugar levels and insulin, like common sugars and maltodextrin, largely suppress the burning of fat in energy metabolism, choosing a slow release carbohydrate like isomaltulose instead can help to steer the metabolism towards fat burning.

Steering the metabolism toward fat burning with isomaltulose
Isomaltulose supplies carbohydrate energy in a more steady and sustained way and, as result of this, allows for a higher fat burning rate in energy metabolism. This is a rather unique property of isomaltulose, since most traditional sugars and carbohydrates are either readily available or cause higher levels of carbohydrate oxidation in energy metabolism for other reasons, as in the case of fructose.

Higher fat burning rates with isomaltulose versus conventional high glycemic carbohydrates, like maltodextrin or sucrose, have been demonstrated in a comprehensive body of research. The relevant 14 human intervention studies cover different situations with reference to physical activity or weight management in mostly sedentary settings.

Relevance to sports and endurance
The benefits of isomaltulose and its more steady and sustained energy supply are most evident  in endurance exercise. Endurance performance is limited by the availability of fuel in the body, specifically carbohydrates. Where short-duration, high intensity exercise relies heavily on the use of carbohydrates as the predominant energy source, endurance exercise requires the utilization of the body’s fat stores along carbohydrate use. Maximizing the use of fat fuel during endurance exercise helps sparing the body’s glycogen (carbohydrate) stores for later on, an effect known as training target for athletes.

When sports drinks are consumed for addition carbohydrate intake, isomaltulose shows clear benefits: It provides carbohydrate energy with less of an impact on fuel partitioning – allowing for the maintenance of higher levels of fat utilization during exercise, with the potential to spare carb resources and enhance endurance. This is true when consumed before and during exercise as well.

Relevance to weight management & body composition
Steering the metabolism towards fat burning can also positively influence energy and fat storage with relevance – over time – for body composition and body weight, and metabolic health. Benefits of isomaltulose for body composition and body weight goals, with less body fat storage have been demonstrated.

Maintaining lower and more balanced blood sugar levels  and  increasing the rate of fat burning during exercise with a carbohydrate choice like isomaltulose can complement a healthy and active lifestyle and support people aiming to stay fit, lean and in shape.