Today I received an email from a rower who had read my book, Fast After 50. In it I comment on the high-fat diet as one alternative to eating for high performance. I also mentioned it in this week's blog on How to Recover (Follow Up). The reader had a couple of good questions. I've posted the email below along with his questions and my answers. This topic is a hot one right now for endurance athletes. His questions get at two of the key issues to be considered. Here's the email reply I sent to him.
Hi CZ,
Thanks for your note. I coached a rower for a few years back in the ‘90s so have a bit of experience with the sport. I know enough to understand your concerns. My answers follow…
Q: "For a race less than an hour, does burning fat provide the same intensity as burning glucose? One of the most interesting parts of your book is the suggestion that fat may be a more generous source of energy, but it sounds best for really long-duration efforts. Maybe carbs are better for higher intensity and short duration."
A: The research is not very robust on the topic of intensity and performance for high-fat vs high-carb diets. Nearly all of it has been done with the event intensity being quite low – around 65% of VO2max. The general thinking is that high-fat doesn’t work as well for providing energy in events that are either very short and therefore high intensity like your 1k rowing races, or events that are long and quite variably based like bike road racing. But that is yet to be tested thoroughly in the research. My guess is that the general thinking is probably right. There's still a lot to be learned about this, however. (See here, here and here.)
Q: "As a subset of this question, do gel packs help for a body that’s trained to burn fat? (I use “GU”, following instructions on the packet.)"
A: There’s actually been some research that may help to answer that question. There have been a few studies in which the subjects were "adapted" to a high-fat diet, then carb loaded in the last couple of days prior to a test and ingested carbs during the test. Intensity of the test becomes the key question again, however. (See here and here.)
One of the other variables that is pretty much left unanswered in the literature is, what is a high-fat diet? Many of the studies used ~60% of calories from fat or less in the diet and called that high fat. Those who propose a high fat diet for athletes believe it should be more on the order of at least 70% with fewer than 50g (200 calories) of carbs per day. Another research issue has to do with when one is “fat-adapted.” Some assume that happens in a few days. Others say a few weeks. My experience has been the latter. Yet another topic has to do with the subjects in the tests. Perhaps some receive a greater benefit from eating a high-fat diet while others respond better to high-carb. And the list of such research matters goes on and on. There’s a lot to be learned on this topic.
Hope this helps a bit.
Joe Friel
