The Science of Running
The Other Calorie Question: When?;
Low-Carb vs. Low-Fat; Marathon Pacing Patterns; Estimating Your Heart Rate
For runners who are trying to manage their weight, getting enough calories to fuel your training is just as important as avoiding excess calories. But there’s also a more subtle point: When do you eat? A pair of recent studies from Scandinavian researchers explore the concept of “within-day energy deficiency.” Even if you’re getting enough total calories each day, there may be periods within the day when your body is short on fuel – and that can have serious consequences.
The most recent study, published in the International Journal of Sports Nutrition and Exercise Metablism, collected hour-by-hour data on calorie intake and expenditure from 31 endurance athletes for four days. Many of them ate relatively small breakfasts and lunches, which meant they were running a caloric deficit for most of the morning and early afternoon, especially if they trained early in the day. They then ate large dinners that brought them back into caloric balance – but that wasn’t enough to erase the negative consequences of spending the day in caloric deficit. The athletes who spent the most hours each day with a significant caloric deficit (more than 300 calories in women and 400 calories in men) were more likely to have a suppressed metabolic rate. Also, the athletes who had the biggest single-hour caloric deficit were more likely to have hormonal disturbances like higher cortisol, lower testosterone (in men), and lower estradiol (in women), which can hinder recovery from workouts and lead to problems like menstrual dysfunction.
The solution isn’t necessarily to eat more; it’s to shift when you eat. A typical meal pattern observed by the researchers involved 600 calories for breakfast, 800 for lunch and then 1,600 for dinner. Simply shifting 500 or so calories from dinner to breakfast would have mostly eliminated any periods of caloric deficit throughout the day, while still leaving dinner as the biggest meal of the day.