The post-exercise fueling window, or “window of opportunity,” is known to be a crucial part of nutrient timing. In theory, it refers to the time when the muscles are most receptive to taking in fuel after a workout. But there are questions as to when the window actually closes. How important is it to get food and nutrients in within the long-acclaimed 30-minute timeframe?
According to some, the timing of nutritional intake may be more important than the periodic intake of nutrients throughout the day. There are many purposes to fueling correctly after a workout, such as to replenish glycogen stores and restore energy reserves, maintain blood sugar, rebuild protein stores, and decrease inflammation, among others.
Most experts still recommend initially following the 30- to 60-minute rule, meaning aiming to refuel within 30 to 60 minutes of activity. However, the window does vary according to the type of workout done, how trained the individual is and the weather conditions. There is still some uncertainty about when the recovery window actually closes, yet this window can be ideal for endurance athletes looking to refuel, rebuild and repair the muscles that have been broken down during activity.
“If athletes are not able to repair within 30 minutes of activity, the window does not necessarily close,” says Jaren Soloff, R.D., C.L.E. of Empowered RD. “However, if refueling is consistently delayed it can contribute to fatigue, a higher probability of injury and decreased performance.”
“New science provides a bit more flexibility for benefits of fueling up to two hours after a workout,” adds sports dietitian Kelly Jones. “Still, if you did not consume a full meal or ingest adequate carbohydrates before a long run, it’s a good idea to eat as soon as possible after to prevent blood sugar from dipping and avoiding an overactive appetite.”
Post-Workout Fueling Recommendations
Runners should include both carbohydrates and protein for optimal recovery. Carbohydrates, which are stored as a compound called glycogen, are essential to optimal training and performance. As explained in a Sports Medicine article by Charles P. Lambert and Michael G. Flynn, as much as 80 percent of energy production during training comes from glycolysis, the pathway our muscles use to break down glycogen and create energy. Muscles become depleted of these glycogen stores after 60 to 75 minutes of exercise; therefore, it is critical to replace glycogen for further exercise and beneficial training outcomes.
“Your body is more receptive to nutrition following a workout for a few reasons,” shares sports dietitian Jenna Braddock. “You produce an enzyme that stimulates the production of glycogen more rapidly, which benefits you by having more energy to draw from for future workouts.” Additionally, cells are more sensitive to insulin after a workout, which better facilitates the entry of glucose (carbohydrates) into those cells to be used and stored as glycogen.
As explained in an article by Eva Blomstrand and Bengt Saltin published in The Journal of Physiology, replenishing glycogen in the muscles may also hinder muscle protein breakdown, which prevents protein from being able to be used as an energy source. Muscle protein breakdown is typically higher in those who are glycogen depleted, in comparison with those who are glycogen repleted. Some research, including that explored in a 1998 International Journal of Sports Medicine article, shows that delaying carbohydrate intake by just two hours (versus consuming them immediately after exercise) can reduce the rate of muscle glycogen resynthesis by as much as 50 percent.
In addition to carbohydrates, consuming protein (amino acids) after a workout is known to increase muscle protein synthesis in healthy adults. The combination of protein and carbohydrates can increase the rate of glycogen storage, since both are able to work together on insulin secretion and thus move more glucose into the muscles.
There is recent evidence showing that whey and dairy protein specifically may stimulate the greatest increase in muscle protein synthesis and enhance recovery. “Protein should be high quality with a good amino acid profile, particularly leucine,” says Marisa Michael, a registered dietitian and personal trainer. “Whey or cow’s milk is a good option. Runners should aim for 20 to 30 grams of protein, total. The body continues to recover for up to 24 to 48 hours after a workout, so ideally athletes should continue to eat regularly balanced meals with 20 to 30 grams of protein each.”
What if you’re just going out for a short run or workout? “You won’t need to worry too much about refueling outside of normal meals and snacks after lower-intensity exercises, such as yoga or an easy 3-mile run,” Jones adds. Instead, she advises focusing on good sources of carbohydrates and protein the next time you eat. Try to limit foods with excess fat and fiber, which both slow digestion and nutrient delivery to muscles. Eggs and toast, low-fat chocolate milk, soy milk, seasoned poultry with sweet potatoes, yogurt and fruit are all great fueling options with a good leucine profile.
Along with carbohydrates and protein, athletes should also remember to rehydrate with both water and electrolytes, especially in warmer climates and for more intense workouts.
While the window of (re)fueling may be different for everyone, there’s no question that it can better prepare you for future workouts, or even two-a-day workouts. Runners should integrate refueling into their training plans and play around with what protein and carbohydrate foods make them feel best.
Sarah Schlichter is a registered dietitian and marathon runner based in Charlotte, N.C. She works as a nutrition consultant and in private practice, where she writes the blog, Bucket List Tummy, sharing nutrition posts, healthy recipes, running tips and everything on her bucket list.