Where is energy stored in food

How food becomes energy

What actually happens in our body with what we eat and drink? And what is different in people with diabetes? Dr. Nicolin Datz describes the connections.

Nutrients: a brief overview

The nutrients ingested with food differ greatly in their function and effect as well as in their use for the human body. The nutrients are absorbed in the human gastrointestinal tract and then transported via the blood and lymph systems to the organs, where they develop their effects.

The nutrients filtered from food include the three so-called basic nutrients: carbohydrates, fat and protein. There are also vitamins, minerals, trace elements and water. Here is a brief overview.


In particular, they provide energy and should make up 50 percent of the daily calorie requirement. Carbohydrates are divided into according to the number of sugar molecules Monosaccharides (= Simple sugar: e.g. grape sugar = glucose, fructose = fructose), Disaccharides (= Double sugar: e.g. malt sugar = maltose, milk sugar = lactose, table sugar = sucrose) and Polysaccharides (= Multiple sugars: e.g. starch). Glucose and fructose are digested in the oral mucosa and then absorbed in the small intestine, while lactose, maltose and sucrose
must first be broken down in the villi by enzymes in order to be absorbed. Starch is the most important carbohydrate carrier in food and is broken down in the small intestine.


Fats also serve as energy suppliers. There are vegetable and animal fats.

Saturated fatty acids of animal origin (whole milk, cheese, butter, meat, lard, tallow) as well trans-unsaturated Fatty acids (in confectionery products such as cakes, biscuits, chocolate) should be consumed in the smallest possible amount. Polyunsaturated fatty acids of vegetable origin (cereals, sunflowers, safflowers, soybeans, grains, oils), on the other hand, reduce the risk of vascular and heart diseases and are therefore recommended, especially omega-3 fatty acids. Also with monounsaturated fatty acids Cis configuration (Olives, sesame, rapeseed and nut oil) have a beneficial effect on lipid levels.


Protein (also called protein) provides the body with essential amino acids that are used to build up the body's own structures, e.g. B. muscles and enzymes are necessary.

There are both animal and vegetable proteins. Proteins of animal origin (in meat, fish, milk, dairy products, eggs) have, compared to proteins of vegetable origin, a higher content of so-called essential amino acids. In contrast, vegetable foods with a high protein content (beans, lentils and other legumes) contain less saturated fats, but more carbohydrates and fiber. A mixture of animal and vegetable protein is therefore recommended for optimal care.


Minerals are essential components of food. This group includes: B. sodium, potassium, calcium, phosphate, magnesium, chloride and sulfate. The intake of salt in the form of sodium chloride is often above the recommended amount, as many finished products contain it. A defect potassium can, for. B. lead to cardiac arrhythmias and a lack of calcium to reduced bone density.


Vitamins are essential nutrients to be taken in with food. The body cannot produce them by itself. Vitamins are mainly found in fresh fruit and vegetables, but also in milk and bread. Inadequate vitamin intake can lead to vitamin deficiency diseases such as rickets, night blindness and scurvy.

Trace elements

Trace elements are also vital components of food. They include B. iron, copper, manganese, iodine, cobalt, zinc and selenium. If you eat too one-sidedly, deficiency symptoms can also occur here. A defect to iron leads z. B. to anemia, a lack of iodine to thyroid dysfunction. Other trace elements are important for the functioning of enzymes in the body, which control many body functions.


Dietary fibers are non-digestible food components such as plant fibers (in vegetables, fruits, legumes, cereals, etc.). They delay the passage of the food pulp through the gastrointestinal tract and thereby reduce the absorption of carbohydrates in the small intestine.


Water is important to regulate temperature and is used as a means of transport.

Important: a balanced ratio of all nutrients

A balanced ratio of all nutrients is necessary for normal growth and age-appropriate development of children and adolescents. Both an excess and a deficiency of certain nutrients can have adverse effects on physical development and performance.

The daily requirement of the nutrients mentioned here depends on the age, gender and size of the child or adolescent. The Research Institute for Child Nutrition gives recommendations on food consumption under the term of Optimized mixed diet can be found.

The distribution of the basic nutrients in the total daily energy intake should then look something like this for children and adolescents:
  • Carbohydrates: 50 percent of total energy intake
  • Fat: 30-35 percent of total energy intake
  • Protein: 10-15 percent of the total energy intake

It should be noted that the basic nutrients provide different amounts of energy: one gram of fat corresponds to around 9 kcal, one gram of protein 4 kcal and one gram of carbohydrates also 4 kcal.

Next page: How energy is generated from food, how glucose is processed in the blood and what happens when there is a lack of insulin.

How does energy come from food?

The digestive process will be explained using the example of cheese bread: The bread mainly contains carbohydrates, especially in the form of starch. The cheese consists of fat, protein and water. The starch belongs to the group of polysaccharides (= multiple sugars), so it consists of several related glucose building blocks.

After passing through the esophagus and stomach, the starch in the small intestine is broken down into glucose molecules by enzymes in the digestive juice. It finally gets into the blood through the villi in the intestinal wall: this is how starch turns into blood glucose (or blood sugar), which is then available to the body to generate energy.

Sugars break down in the small intestine

The multiple and double sugars are broken down in the small intestine in such a way that they can be absorbed as single sugars through the intestinal wall. While glucose can work directly in the blood, the simple sugars fructose and galactose first have to be converted to glucose in the liver.

The breakdown of the protein from the cheese into smaller proteins begins in the stomach by the enzymes present there. The final breakdown into amino acids takes place in the small intestine. The fat from the cheese is also digested in the small intestine. With the help of bile acids and enzymes from the pancreas, it is broken down and enters the body through the intestinal wall.

What if the glucose is in the blood?

If the glucose is absorbed into the blood, the blood sugar rises only slightly in people with healthy metabolism, since the adequate amount of insulin is released at the same time. With the help of insulin, glucose gets to where it is needed: the cells of the muscles, adipose tissue and many other organs. Together with oxygen, this is then used to generate energy.

With a few exceptions, cells cannot absorb glucose without insulin. These exceptions are the cells of the brain, nerves and heart, as well as those of the lens of the eye and the red blood cells.

Glycogen as a short-term storage

Excess glucose is stored in the form of glycogen as short-term storage in the liver and muscles or in the form of fat as long-term storage in adipose tissue. Does the body need additional energy, e.g. B. During sport, glycogen can quickly be converted to glucose and released into the blood. When hungry, the body falls back on the fatty tissue, which leads to weight loss.

The liver can not only make glucose from glycogen and release it into the blood, but also from amino acids. This process takes place especially at night. This is how the liver prevents the blood sugar level from falling too low.

The insulin, in turn, controls how much glucose the liver produces and releases into the blood so that there is no excess sugar.

What happens when there is a lack of insulin, i.e. in people with diabetes?

If there is a lack of insulin, not enough glucose can reach the muscle and adipose tissue cells. So the glucose stays in the blood, the blood sugar rises, and the cells lack energy. In addition, the liver continues to produce glucose unchecked, which causes blood sugar to continue to rise. Despite this excess of glucose in the blood, the cells lack energy.

In this situation, the body begins to fall back on the energy stores glycogen and fat. Since the glycogen stores are quickly empty, the fat stores have to be broken down. The resulting Ketone bodies however, they are harmful to the body as they can lead to over-acidification of the organism. There is a risk of a Ketoacidosis arises.

  • A balanced supply of carbohydrates, fats and proteins is necessary to generate energy.
  • Carbohydrates should make up around 50 percent, fats 30-35 percent and proteins 10-15 percent of the total daily amount of energy.
  • The body's main sources of energy are carbohydrates and fats.
  • When carbohydrates are broken down, glucose is produced, which can be used directly for energy production.
  • Excess glucose is stored in the form of glycogen in the liver and muscles and in the form of fat in adipose tissue.
  • Insulin promotes the uptake of glucose into cells.
  • Insulin deficiency prevents glucose from being absorbed into the cells, thus leading to a lack of energy and uninhibited glucose production in the liver.
  • The supply of insulin and carbohydrates in children with diabetes must be well coordinated.

by Dr. med. Nicolin Datz, Hanover
Senior Physician Pediatrics III, Center for Pediatric and Adolescent Medicine, "Auf der Bult" Hospital

Janusz-Korczak-Allee 12, 30173 Hanover, email: [email protected]

Published in: Diabetes-Eltern-Journal, 2014; 7 (2) pages 22-24

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