Hard training asks a lot of the body--but not eating enough to support that effort can undermine both health and performance. This imbalance, known as Relative Energy Deficiency in Sport (RED-S), can affect athletes across disciplines and active people more broadly.
When energy intake falls short
RED-S occurs when the energy a person gets from food is not enough to support exercise, daily activity and the body's basic functions. It is more than a short-term calorie reduction: ongoing under-fueling alongside demanding training can leave too little energy for recovery and other processes.
Persistent tiredness may be an early warning sign. Other possible effects include feeling cold, slow recovery, recurring overuse injuries, hormonal changes, reduced immunity and stalled fitness progress. These signs can have many causes, so they are not a diagnosis on their own.
Training trends and appetite changes
Experts point to a mix of restrictive diet culture and high-intensity workout routines that encourage people to do more while eating less. GLP-1 medications may also reduce hunger, making it harder for some users to notice that their food intake is not keeping pace with a new or demanding exercise routine.
Individual energy needs vary. Paying attention to ongoing fatigue, prolonged soreness and declining motivation can help prompt a closer look at nutrition and recovery. Adequate overall intake, including carbohydrates to support activity and protein for recovery, can be part of a balanced approach.
Anyone concerned about their fueling needs can seek guidance from a registered dietitian with sports nutrition experience. A fitness culture that values recovery alongside effort may help more people pursue progress in a sustainable way.
