Are carbohydrates good or bad?
It depends on who is asking! Here we have 3 different persons and the role carbohydrates play for them:
First we have David, who is 54 years old and can no longer run because he has knee and back problems, but has been advised to start cycling. He now cycles twice a week, for about 1-2 hours each time, and enjoys it. He is overweight and would like to lose about 10 kg.
David doesn't need so many carbohydrates. He doesn't exercise very often and he wants to lose weight. A good rule of thumb for David at lunch and dinner is that half the plate should be vegetables, ¼ protein and ¼ carbohydrates. To lose weight, he also needs to reduce the portion size, for example just take one portion.
For David, there is very little room for fast carbs because he doesn't exercise much and wants to lose weight. So cutting down on the juices he drinks every day and reducing his ice cream consumption makes a big difference.
If he does this, he will lose weight and get enough carbohydrates for the amount he exercises.
Carbohydrates can be both dangerous and healthy.
The next person is Andrea, 41 years old, who has always trained a lot and now cycles about 8-10 hours a week. She participates in a few races and competitions every year and is always striving to improve and is very goal-oriented.
For Andrea, carbohydrates are important to be able to train as much as she does. Firstly, that she consume fast carbs when she is training and that she has a proper source of carbohydrates with every meal. Andrea should aim for a high carbohydrate intake before most training sessions. Occasional low-intensity sessions where she wants to train endurance and fat burning can be done with a lower carbohydrate intake.
We also have Marcus, an elite cyclist who wants to be the best in the world. He spends most of his waking hours training, recovering and focusing on eating properly during and after training sessions.
For Marcus, the intake of carbohydrates is crucial to be able to train hard week after week. To have time to recover between sessions, to build up his glycogen stores, to be able to push hard during training sessions, to reduce the risk of immune system suppression.
Marcus needs to eat plenty of carbohydrates at every meal and be sure to consume enough carbohydrates during training sessions.
As you can see, our needs are different depending on how much we exercise. A person who does not exercise at all does not need so much carbohydrates, then the amount Andrea or Marcus eats would be "dangerous" and lead to both weight gain and the risk of high blood sugar, which in turn can lead to metabolic syndrome (high blood pressure, high cholesterol, obesity, elevated blood sugar).
Carbohydrates are broken down into sugars in the gastrointestinal tract, so how much you should eat depends on how much your body uses up. When we exercise, we empty our glycogen stores and when we eat carbohydrates, these are replenished. If we don't exercise, we don't empty our glycogen stores and if we eat too much carbohydrate compared to our energy needs, it is stored as fat tissue.
You can exercise even if you don't eat carbohydrates. What happens then is that your body uses fat as fuel instead. This may seem good if you want to lose weight, but it's not quite that simple.
Fat loss is not the same as weight loss.
You can have high fat oxidation and gain weight and vice versa. Weight has to do with how high your energy intake is compared to your needs. Fat oxidation is only about what fuel you use when you exercise, adipose tissue versus carbohydrates (glycogen).
If you use the fat tissue as fuel, it will be slower, you won't be able to work as hard. Glycogen, on the other hand, is a fast source of energy that allows you to push hard, directly.
If you only do low-intensity workouts using fat as fuel, not eating carbs can work. But there is a risk that you will feel tired and lack energy if you don't eat carbohydrates.
Feeling alert is very much in the brain, which also wants carbohydrates. It can switch to fat burning too and some find it works well while others feel bad (tired, lacking energy, down).