Nutrition periodization influences metabolic adaptations much more than training volume alone. An endurance athlete who applies the same intake year-round misses out on crucial physiological levers, particularly metabolic flexibility and substrate oxidation capacity at high intensity.
Carbohydrate oxidation at 90 g/h: protocol and glucose-fructose ratio
Historical recommendations capped exogenous carbohydrate intake at 60 g per hour during prolonged efforts. This limit corresponded to the intestinal transport capacity of glucose alone via the SGLT1 transporter.
The current standard pushes towards 90 g of carbohydrates per hour thanks to the glucose-fructose ratio. By combining glucose and fructose (typically a 1:0.8 ratio), both the SGLT1 transporter for glucose and the GLUT5 for fructose are engaged simultaneously. The result: significantly higher exogenous oxidation, without a proportional increase in gastrointestinal issues.
We recommend testing this protocol in training at least six to eight weeks before a competition. The intestine gradually adapts to these carbohydrate volumes, a process referred to as gut training. Abruptly increasing intake on race day can lead to bloating, cramps, and sometimes withdrawal. To delve deeper into nutrition on Ultra Sport, the field protocols detail this gradual increase.
The choice of carbohydrate vector also matters. Concentrated gels require concurrent water intake, while isotonic drinks combine hydration and energy supply in the same action. During efforts lasting several hours, alternating solid, semi-liquid, and liquid forms limits digestive fatigue.
Fasted training and fat-max: when restricting carbohydrates makes sense
Targeted carbohydrate restriction (train low) is not a trend. It is based on a documented mechanism: by reducing glycogenic availability during certain sessions, mitochondrial biogenesis and the expression of lipolytic enzymes are stimulated.
The goal is not to eliminate carbohydrates but to remove them at the right time. A fundamental endurance session performed fasted or with partially depleted glycogen reserves forces the body to draw more from fatty acids. In the long term, this metabolic flexibility helps preserve muscle glycogen for high-intensity phases in competition.
Implementation requires discipline:
- Schedule train low sessions only at low intensities (zone 1, zone 2). Any threshold or interval session requires full glycogen reserves to avoid degrading effort quality and risking injury.
- Maintain sufficient protein intake around the fasted session to limit muscle catabolism, with at least a protein snack within an hour afterward.
- Avoid chaining more than two train low sessions per week during the training load phase, to prevent transitioning to relative energy deficiency (RED-S).
Post-effort window and recovery: what timing really changes
The post-effort metabolic window has been debated for years. We observe that its importance varies with training frequency. For an athlete who completes two sessions in the same day or runs six days a week, the carbohydrate-protein intake within 30 to 45 minutes after effort accelerates glycogen resynthesis.
For an athlete who trains once a day with 24 hours between sessions, the caloric balance and distribution throughout the day matter more than the precision of timing. Glycogen resynthesis occurs anyway in the following hours, provided the total intake is covered.
In practice, an effective recovery meal combines carbohydrates with a moderate to high glycemic index and complete proteins. White rice, potatoes, well-cooked pasta paired with chicken, fish, or a dairy product meet the need. Commercial recovery drinks are an acceptable logistical shortcut, not a physiological necessity.
Sodium and hydration in long endurance: beyond plain water
Sodium loss through sweat varies significantly from athlete to athlete. Some lose much more sodium than others at the same intensity and temperature. During events lasting more than three hours, drinking only water without sodium intake exposes one to hyponatremia, a risk that standard hydration plans underestimate.
Adding sodium to the effort drink (in the form of tablets, salt, or via a dosed electrolyte drink) improves intestinal water absorption, maintains plasma volume, and reduces the risk of cramps. We recommend athletes test their sweating rate during long sessions to adjust the electrolyte concentration of their drink.
Potassium and magnesium supplements
Sodium grabs attention, but potassium and magnesium contribute to muscle contraction and nerve transmission. A diet rich in vegetables, fruits, nuts, and legumes generally covers these needs without resorting to supplementation. Magnesium supplementation is only justified upon confirmation of a biological deficiency, not based on isolated cramps.
An endurance nutrition plan is built during training, not the day before the race. Each variable (hourly carbohydrate intake, train low strategy, recovery timing, sodium concentration) must be tested under real conditions. Athletes who perform on race day are those who have repeated their nutritional protocol as much as their interval sessions.