The Science of Run­ning

Canadian Running - - CONTENTS - By Alex Hutchin­son

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.

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