I practice endurance sports and I have always been told that I need to consume a lot of carbohydrates and energy gels. Is that really necessary? Can a runner develop prediabetes?

Hello, Javier,

This is a matter I find particularly important, because a very widespread idea still persists in the world of sport: "if I do a lot of endurance training, I can — or should — consume large amounts of carbohydrates".

And that is not entirely accurate.

Carbohydrates are an extraordinarily useful fuel for exercise, especially as intensity increases or when we sustain prolonged effort. Muscle and liver glycogen plays a fundamental role in performance.

I am therefore not against carbohydrates. I am against consuming them without regard for the body's actual needs.

An energy gel is not an everyday food

Sports gels are designed to provide fast-absorbing carbohydrates during prolonged efforts.

In a marathon, a multi-hour cycling event, or certain long-duration training sessions, they can make perfect sense.

But going out for a 40- or 50-minute run and routinely taking gels, sugary drinks and energy bars before, during and after training is probably unnecessary for most people.

There are amateur runners who end up consuming considerable amounts of sugar throughout the entire week simply because they believe they "need it to train".

And this is where we can make a mistake.

Can a marathon runner have prediabetes?

Absolutely.

Being an athlete does not confer metabolic immunity.

Physical activity generally improves insulin sensitivity and is one of our most powerful tools for preventing type 2 diabetes. However, a person can run many kilometres and, at the same time, follow an inadequate diet, carry excess visceral fat, have a genetic predisposition, suffer from poor sleep, stress, alcohol consumption or other metabolic factors.

In my practice I have seen long-distance runners with impaired glucose levels, insulin resistance or prediabetes.

That does not mean that running caused the prediabetes.

It means we cannot use exercise as a licence to eat whatever we like.

The problem is not carbohydrates, but the context

A person who trains intensely for two or three hours has completely different carbohydrate needs from someone who goes for a gentle 45-minute run.

Sports nutrition must be adapted to:

training duration;

intensity;

weekly volume;

body composition;

athletic goals;

digestive tolerance;

metabolic health;

and recovery between sessions.

In other words, we must also periodise nutrition, not just training.

There are days when we need more carbohydrates and others when we need far fewer.

What about gels during a marathon?

Here the situation changes.

During prolonged efforts, carbohydrate intake can improve performance and delay fatigue. In trained athletes completing long events, current nutritional strategies may call for significant amounts of carbohydrates per hour.

But these amounts are used during an extraordinarily high energy demand.

We should not apply competition nutrition to our everyday diet.

Taking 60 or 90 grams of carbohydrates per hour during an endurance event may have a physiological justification.

Taking them sitting at home because you are a runner does not.

Why do some runners carry abdominal fat despite being lean?

We must also debunk another myth.

Sometimes we observe endurance athletes who are very lean in their arms and legs but carry some abdominal adiposity.

We should not automatically diagnose 'hypercortisolaemia' or speak of Cushing's syndrome simply based on physical appearance.

Cushing's syndrome is a specific endocrinological condition and requires a medical and hormonal diagnosis.

Intense exercise transiently raises cortisol, and this is completely physiological. Cortisol helps us mobilise energy during physical effort.

The problem can arise when we combine, over a prolonged period, excessive training, insufficient recovery, psychological stress, lack of sleep and inadequate energy availability.

That environment can impair recovery, disrupt certain hormonal functions and promote loss of muscle mass. However, this is very different from claiming that running causes Cushing's syndrome.

Muscle remains essential

A person may weigh very little and yet have a body composition that is metabolically suboptimal.

That is why I place great emphasis with my athlete patients on not looking solely at the number on the scales.

I want to know:

How much muscle do you have? How much visceral fat? What are your glucose levels? Your glycated haemoglobin? Your triglycerides? How are you sleeping? How are you recovering?

For me, a metabolically healthy runner is not simply someone capable of completing a marathon.

They are someone who also preserves good muscle mass, follows a well-balanced diet, rests properly and maintains healthy metabolic parameters.

So, does carbohydrate intake need to be reduced?

Not necessarily.

They need to be used intelligently.

Carbohydrates should be tailored to your training, rather than becoming a permanent obligation simply because you participate in endurance sport.

For everyday meals, I prefer to prioritise whole, nutritionally complete foods, and to reserve fast-absorbing sports products for those situations where they genuinely offer an advantage.

And if you are a regular runner — particularly from the age of 40–50 onwards — I consider it very reasonable to periodically monitor blood glucose, glycated haemoglobin, lipid profile and other metabolic markers according to your personal history.

Because we can run a marathon and still have an underlying metabolic abnormality.

One thing does not exclude the other.

Exercise is medicine, but so is nutrition. And doing a lot of sport does not indefinitely compensate for a misguided nutritional strategy.

Kind regards,

Doctor Florian A. Vallecillo Cabrera