Carbohydrates provide energy, but they can also make you fat. That’s why many Germans do without it at the beginning of the year, they go “low carb”. But not all carbohydrates are “bad”, it depends on the right ones.

Foods high in carbohydrates undeniably make up the bulk of most people’s diets: bread, pasta, rice, and potatoes in all forms.

But carbohydrates have a bad reputation. It is best not to eat any more carbohydrates in the evening, because they make you fat overnight. It is said that those who also live according to low-carb during the day will become permanently slim. But that does not correspond to the actual facts. Carbohydrates have very different properties and can be used in a targeted manner, then they are quite healthy.

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In order to recognize these relationships, a bit of basic knowledge is required: together with protein (proteins) and fat, carbohydrates are one of the three main nutrients (macronutrients). “In contrast to fat and protein, carbohydrates are not essential, i.e. not vital, our body can certainly live without carbohydrates,” explains Stefan Kabisch, study doctor at the German Institute for Human Nutrition Potsdam-Rehbrücke (DIfE).

However, if the nutrients are available, the body can quickly convert them into energy. In order for all cells to be able to work with it, however, carbohydrates must first be broken down into glucose, which happens in the liver and intestines. Carbohydrates are made up of individual sugar molecules. According to their number, there are two different carbohydrate groups:

1. Single and double (short-chain) carbohydrates with one sugar molecule (simple sugars, i.e. monosaccharides, including glucose, fructose and galactose) or with two sugar molecules (disaccharides, disaccharides such as lactose, i.e. milk sugar and normal household sugar)

2. Long-chain, complex carbohydrates (oligosaccharides and polysaccharides) with at least three sugar molecules, for example in the cellulose of dietary fiber and starch.

The following foods contain a particularly large amount of mono- and disaccharides:

In contrast, these foods are particularly high in the long-chain carbohydrate variety:

In this context, long-chain carbohydrates are often referred to as “good” and short-chain carbohydrates as “bad”. Why are the short-chain ones rather unfavorable?

1. “They are broken down very quickly, so that their individual components, i.e. fructose or glucose, reach the blood quickly, blood sugar rises quickly and steeply,” explains the scientist. The high increase in sugar in the blood requires a lot of insulin to lower the blood sugar again. “This reduction usually occurs just as quickly and means that we are hungry again an hour after this meal.” Inevitably, this means that more is eaten than the body actually needs.

2. The body cannot store glucose indefinitely, only the liver and muscles can accumulate some glycogen. “From 500 to 600 grams, however, these storage sites are full, so to speak,” explains the researcher. If excess glucose is not immediately burned as energy, the body converts it into triglycerides and stores them in fat cells or even organs.

3. And when carbohydrates are already broken down to glucose when they reach the upper part of the small intestine – as is the case with the short-chain ones – the hormone GIP (glucose-dependent insulinotropic peptide) is released in the pancreas. “It seems to cause nutrients in the body to be distributed rather unfavorably, i.e. end up in the liver as fat,” says the expert, describing the fatal effect.

In summary, short-chain carbohydrates make you hungry, fattening and increase the risk of fatty liver.

With long-chain carbohydrates, the individual links in the chain must first be split off as glucose, so it only gets into the blood and into the cells little by little. The blood sugar rises slowly, the saturation lasts longer. “The longer the carbohydrates are, the longer it takes,” reports Stefan Kabisch. Why this is so has not yet been scientifically clarified.

The long-chain carbohydrates are only broken down into glucose in the lower part of the intestine. In this area, the glucose ensures that the pancreas is again stimulated to produce hormones – this time, however, it is not the unfavorable GIP that is released, but the hormone GLP1 (glucagon-like peptide-1), which ensures satiety.

Put simply, this means that long-chain carbohydrates fill you up twice as much.

Because there is no real need for carbohydrates, there is no general guideline as to what percentage of carbohydrates should be in the daily calorie allowance. “Tolerance to carbohydrates varies greatly, so it’s difficult to give a recommendation,” says the scientist. The German Society for Nutrition and the German Diabetes Society used to advise eating a low-fat diet and covering 50 to 55 percent of our energy needs with carbohydrates.

“But that wasn’t proven by really good studies,” says Stefan Kabisch. There are now a number of studies comparing high-carb and low-carb diets – but both types of diet come to similar results, with low-carb doing slightly better on average in terms of weight, blood pressure and blood sugar – but only in the short to medium term.

“But there are also people who live very healthily with 70 percent carbohydrates,” explains the researcher, referring to the population of Okinawa, for example. Most of the world’s over 100-year-olds live on the small Japanese island. This phenomenon also occurs in some indigenous peoples. However, these are people who move a lot and therefore burn the energy from the glucose quickly.

But the opposite, low-carb diets, can also extend lifespan, as observational studies show. However, low carb is not unreservedly recommended. “Anyone who restricts carbohydrates should pay attention to the quality of the fats and proteins, which you then automatically eat more of,” recommends the expert. If you then eat too much meat, for example, you take in too much iron, saturated fatty acids and inflammatory mediators. An animal-based low-carb diet is therefore somewhat less favorable than one that relies more on plant foods.

But eating plant-based low carb is very difficult. Most vegetables are high in carbohydrates. Few foods remain: nuts, vegetable oils, mushrooms. The beneficial effect of almost vegetarian low carb probably also comes from additional factors that are not related to diet, such as a particularly healthy lifestyle with a lot of exercise, without smoking and drinking alcohol. Overall, there are no meaningful long-term studies, the researcher notes. In terms of weight, however, low-carb seems to have advantages – if you don’t eat a lot of meat and other animal products. But no one can really avoid that when they eat a lot of low carb.

The correct handling of carbohydrates would actually be quite simple. The most important thing: “Eat as few short-chain, simple carbohydrates as possible, i.e. sugar.” This doesn’t just mean table sugar, but also fructose in fruit. Anyone who does without sweets but eats a kilogram of grapes a day ended up eating 150 grams of sugar. Honey and the popular because natural concentrated plant juices are ultimately sugar.

“Complex carbohydrates, bound to roughage, on the other hand, are a wonderful food,” emphasizes Stefan Kabisch. Whole grain products, legumes, vegetables – these are recommended foods in this context. Potatoes, on the other hand, should not be on the table that often. They have little dietary fiber and are usually processed high in fat.

And what about carb avoidance by time of day—like no carbs after 5 p.m.? There are hardly any studies on this, and a basis for the corresponding recommendation is still missing, Stefan Kabisch dismisses.

“What matters overall is which carbohydrates you eat and what you eat when you omit them,” he summarizes and recommends the perfect form of nutrition, the original Mediterranean cuisine, i.e. the one from before 1950. That means: without pasta and pizza. Then it is a moderately low-carbohydrate diet, with an emphasis on fish, vegetables, legumes and vegetable oils. Meat, highly processed foods and products containing sugar are hardly intended.