Hardly any nutrient has a worse reputation than carbohydrates. They are said to make you fat, to ruin your blood sugar and to be responsible for everything that goes wrong in the modern diet. At the same time, sports nutrition regards them as the fuel without which no intense session works. Both cannot be true — the answer is neither «friend» nor «foe», but a question of quantity, timing and your activity level. Here you will find how much you need depending on how active you are, what the glycaemic index is actually worth and why low-carb works, though not for the reason most people assume.
What carbohydrates do in the body
Carbohydrates are not essential: the body can produce them itself, from amino acids for example. Even so, they are the most readily available source of energy we have. Their energy content is 17 kJ per gram, that is 4 kcal — the same as protein and considerably less than fat.
Whatever the body does not burn immediately, it stores as glycogen — the animal counterpart of plant starch. The two stores have different jobs:
- Liver glycogen (around 150 g) primarily keeps blood sugar levels constant.
- Muscle glycogen (200 to 300 g) is the muscle's own energy reserve for itself.
If you train intensely for up to two hours, full glycogen stores are decisive — and they empty quickly, which is why they have to be topped up daily when you train intensely on a regular basis. How the energy systems take turns is shown in the article on energy supply in the body.
If both carbohydrates and fats are missing as energy suppliers, the body breaks down more protein — over time, that means muscle. Conversely, an adequate intake has a protein-sparing effect. Anything in excess moves into fat tissue as soon as the stores are full.
Simple or complex — and the glycaemic index
According to the number of sugar building blocks, we distinguish between simple sugars (in fruit and honey), double sugars (lactose, maltose and table sugar) and multiple sugars, the storage form: starch in potatoes, rice and grain, glycogen in humans and animals. However, «simple equals bad, complex equals good» falls short. How strongly blood sugar rises also depends on the composition of the meal, the degree of processing, the consistency and the quantity.
To make this comparable, the glycaemic index (GI) was developed. The reference is glucose with a GI of 100. The classification used in the course:
- GI above 70 — high-glycaemic food
- GI 56 to 69 — medium-glycaemic food
- GI below 55 — low-glycaemic food
The catch: the GI does not take the quantity into account and is therefore of little practical use in everyday life. As a supplement there is the glycaemic load, which offsets the GI against the amount of carbohydrate in the food. A diet with a high glycaemic load is associated with obesity, type 2 diabetes mellitus, high blood pressure and cardiovascular disease — the culprit being the high insulin level, which inhibits fat burning. More on this in the article on blood sugar and insulin resistance.
How much you need — depending on your activity level
Officially, 45 to 55 % of daily energy requirements should come from carbohydrates. Better than such a percentage figure, however — as with protein — are absolute values per kilogram of body weight:
- Low physical activity: 3 to 4 g per kg of body weight per day
- With increasing activity: rising to a maximum of 10 g per kg of body weight per day
At 70 kg that is around 210 to 280 g for someone with a desk job and little sport — and up to 700 g with a very high training volume. A factor of three between two people: which is exactly why «good or bad» cannot be answered without context.
Why low-carb works — and why not because of the carbohydrates
On a low-carb diet, around 10 to 30 % of energy still comes from carbohydrates. The extreme form is the ketogenic diet with 5 to 10 %, which corresponds to around 20 to 60 g per day. The LOGI method is a low-carb variant with a particular focus on the glycaemic index.
The course draws, among other things, on the results of six randomised controlled trials that compared low-fat with low-carbohydrate diets. The conclusion: low-carb diets and a healthy calorie-reduced mixed diet — the Mediterranean diet — are superior to low-fat diets, both in the short and the long term.
Except: this is not because carbohydrates in themselves make you fat. It is because restricting them — without limiting the other macronutrients — spontaneously leads to a lower total calorie intake. On top of that, protein and fat are more satiating, and dietary fibre increases volume and satiety. Put differently: the calorie deficit remains the prerequisite, low-carb is one effective route to it. What matters most in any case is whether you can stick with a way of eating. If you eat considerably fewer carbohydrates, keep the protein share high and combine the change with strength training, otherwise you will lose muscle mass along with the fat.
Carbohydrates around training
Here the course works with clear reference values:
- Before exercise: 1 to 4 g of carbohydrate per kg of body weight, 1 to 4 hours beforehand. The closer to the start, the smaller the portion.
- During exercise: up to 45 minutes nothing is needed; 45 to 75 minutes a small amount of glucose; 60 to 120 minutes 30 to 60 g per hour; 120 to 180 minutes 60 to 90 g per hour; over 180 minutes up to 90 g per hour. These amounts apply regardless of body weight.
- After exercise: for rapid recovery 1.2 g per kg of body weight per hour, spread over 2 to 4 portions, for 4 hours or until the next larger meal. Alternatively 0.8 g of carbohydrate plus 0.4 g of protein per kg.
From around 60 g per hour, the type matters: the absorption capacity for glucose is then maxed out. More is only possible with additional fructose, because it is absorbed in the gut via a different transport route.
And one persistent rumour needs correcting: carbohydrates in the last hour before exercise are not harmful. Differences in blood sugar disappear after just 10 to 15 minutes of exercise, that is, during the warm-up.
Fasted training and the immune system
Training with low glycogen stores can increase the muscles' capacity for fat oxidation — the article on fasted training puts this in context. The restriction from the course material is important: such sessions should not take place during high-intensity phases. Because an adequate carbohydrate intake during and after exercise is considered the most effective nutritional measure for protecting the immune system: after intense sessions the immune defences are temporarily weakened, the so-called «open window» with an increased susceptibility to upper respiratory tract infections. Easy base endurance sessions are less problematic here than hard intervals.
Who really should cut back
The problem is not the carbohydrates but the mismatch between intake and activity. A reduction makes sense if you move little in everyday life, if you are overweight and aiming to reduce body fat, and if there are signs of insulin resistance or metabolic syndrome. With diabetes mellitus, carbohydrate intake has to be controlled in any case — that belongs in medical care. Anyone who trains intensely five to seven times a week, by contrast, mainly sabotages performance and recovery with a radical cut. And often quality achieves more than quantity: the article 30 days without sugar shows what happens when it is above all the fast sugar sources that disappear.
Course tip from update Akademie: How macronutrients work, how to determine requirements in grams per kilogram of body weight instead of percentages, and how to assess ways of eating such as low-carb, LOGI or Mediterranean food in a serious way — you learn all of this in the Ernährungscoach programme at update Akademie, including counselling methodology and evidence-based practice. Part-time and practice-oriented.
Frequently asked questions about carbohydrates
Do carbohydrates make you fat?
Not as a nutrient. Excessive carbohydrate intake is converted into body fat as soon as the glycogen stores are full — that applies to any energy surplus. What matters is the energy balance and the question of whether a way of eating satiates you and can be sustained.
How many carbohydrates do I need per day?
With low physical activity, 3 to 4 g per kg of body weight is recommended for healthy adults. With increasing activity the amount rises to a maximum of 10 g per kg. In percentage terms that corresponds to roughly 45 to 55 % of daily energy requirements.
Are carbohydrates with a high glycaemic index generally bad?
No. The GI is a comparative measure, not a judgement. For inactive people, a selection with a low GI and a low glycaemic load makes sense. Around intense exercise, on the other hand, rapidly available carbohydrates are exactly the right thing.
Should I avoid carbohydrates before sport?
No. A carbohydrate intake in the last hour before exercise can even improve performance. The worry about a drop in blood sugar is based on an old study that was refuted by follow-up research.
Which is better: low-carb or low-fat?
Low-carb diets and a healthy calorie-reduced mixed diet in the sense of the Mediterranean diet are superior to low-fat diets — both in the short and the long term. The advantage, however, comes above all from the spontaneously lower calorie intake and the better satiety.
Conclusion
Carbohydrates are neither friend nor foe, but a tool whose dosage depends on your activity level: 3 to 4 g per kg with little activity, up to 10 g per kg with a high training volume. Anyone who moves little and wants to lose weight demonstrably does well with a reduction — but not because carbohydrates make you fat, rather because less of them almost automatically means fewer calories and more satiety. Anyone who trains intensely, by contrast, needs them: for performance, for recovery and for an immune system that is already under strain after hard sessions.
