Nutritionists have warned that copying the fasted-training routines used by footballers Sergio Ramos and Marcos Llorente without adjusting intensity and diet can trigger blurred vision and a loss of energy, according to studies cited by specialists.
Training before the day's first meal has become a habit among several elite footballers, a practice that has gained visibility thanks to Ramos and Llorente, who have both described how they arrange their meals around physical training. Specialists say their example requires substantial context, since both athletes follow individualized programs and are monitored by professionals who oversee their preparation.
Copying only the fasting hours leaves out variables that completely change the outcome, nutritionists say. The type of training session, rest, hydration, calories consumed during the rest of the day and overall health all determine how the body responds. A regimen that a trained professional can tolerate may not suit someone else.
Intermittent fasting restricts eating to a set window of the day, such as the 16/8 schedule, but does not by itself determine the quality of the diet. It can also reduce daily calorie intake simply by shortening the time available to eat. Weight loss, specialists stress, does not depend on any automatic advantage from the timing of meals.
The weight of the evidence
A Cochrane review published in 2026 pooled 22 clinical trials involving 1,995 overweight or obese adults. Compared with conventional dietary advice, intermittent fasting produced little or no difference in weight loss or quality of life. The finding is useful against the spread of false health experts, since the popularity of a regimen does not prove it works better.
Sergio Ramos has said he practices fasting two or three times a week, training without breakfast and following it with a protein shake. Marcos Llorente concentrates his meals during daylight hours, eats dinner early and avoids ultra-processed foods, according to the magazine Lecturas. Both cases combine timing with planning, a detail that disappears when their routine is reduced simply to skipping breakfast.
Eider Sanchez, a nutritionist at Policlinica Gipuzkoa, said the strategy should be reserved for the right person and ruled it out for anyone with a poor relationship with food, binge eating, anxiety or particular nutritional needs. The assessment, she said, has to be individual. That same caution extends even to services where ChatGPT reads medical data, whose results still require review by a professional.
Training and warning signs
Ana Lucia Silva, a nutritionist who has assessed Llorente's routine, sets the limit at the level of exertion carried out without breakfast. To avoid harm, she recommends low-intensity exercise. The warning matters because a demanding session raises the body's energy needs, even as devices such as running watches help track load, pace and recovery.
Blurred vision and loss of energy are two of the signs Silva links to raising the intensity of exercise during a fast. Quironsalud adds migraines, dehydration, irritability, difficulty concentrating and disrupted sleep to the list of effects that can appear when the approach is poorly planned. Sensors continue to advance, including prototype rings that measure glucose, but their data still cannot replace a clinical evaluation.
During the hours when eating is allowed, the specialist recommends that the menu cover the day's needs with vegetables, fruit, legumes, protein, quality fats and nuts. For athletes, recovery adds a further demand. Fasting can fit into some routines, nutritionists say, but only when the plan is adapted to the person, their training and their health.
