Train Well 1: The Myth of Carb Loading, by Dr. Jeff (Advice from the Medical Tent)

We’ve all heard the advice to carb load before a big sporting activity, such as running a marathon. It’s been said that carb loading, by eating pasta, rice, potatoes, or other high-carb foods before a race, will provide you a good source of energy to help you avoid the dreaded wall. But is that really the case?

Former Medical Director of The Biofreeze San Francisco Marathon, Dr. Jeff Shapiro, sheds some light on the topic:

The Myth of Carb Loading

A large meal before running, or eating while running, frequently causes intestinal upset. This is because, while mechanical (chewing) and chemical (amylase) digestion begins in the mouth within minutes, food remains in the intestines for 1-3 days, depending on the type and size of the meal.

Blood flow at rest     Blood flow during exercise

Since so little digestion occurs during exercise, a large meal the night before a race actually increases the workload of running by adding weight.

As training increases the number of energy producing mitochondria, muscles utilize more fat for fuel during exercise, reducing the need for carbohydrates.

This is why I recommend that runners eat a light lunch and skip dinner on the day before a marathon.

To avoid intestinal upset: Run light. Run empty.

Wishing you healthy organs,

Stay Tuned For: The Benefits of Skipping a Meal Before Running.

Put this advice to work at The 2018 San Francisco Marathon! #ThisIsHappening

“If I can motivate an attendee/reader to change a habit to improve their health, it makes my day job easier.” – Dr. Jeff Shapiro

A graduate of Yale & Stanford, Jeff coaches (since 1993) those seeking peak wellness through science. Jeff appeared on ABC News 20/20 (“Super Humans”), and consulted for CBS News 60 Minutes (“The Toughest Race”) and The Late Show with David Letterman. Jeff has completed 50 marathons, served as medical director for the San Francisco Marathon, and lectured at numerous organizations, including Google, B of A, Merrill Lynch, and SanDisk.

Save the Date!

Join Jeff at the next Golden Gate Relay – California’s Longest Party, held the first weekend in May. In the long run (walk or ride), organ donation saves lives!

Gather 12 friends/2 vans. Dress your best (costumes/decorated vans optional). Walk (125 miles, 6-12 walkers), run (125, 160 or 190 miles, 6-12 runners), or ride (30, 65, 130 or 190 miles, 1-3 riders).  Support 125,000 Americans waiting for organs as a runner, walker, rider, volunteer or organ donor!

4 Replies to "Train Well 1: The Myth of Carb Loading, by Dr. Jeff (Advice from the Medical Tent)"

  • comment-avatar
    June 21, 2018 (3:53 pm)

    Are you saying that carbo loading is bad or is it just bad the night before the race? Very misleading title.

    • comment-avatar
      The SF Marathon
      July 2, 2018 (4:07 am)

      Hi Lanika, Thanks for reading, and for your comment! Dr. Jeff has written a response to your question in his most recent blog post, Train Well 2: Carb Loading Myth Pt. II. Check it out to learn more!

  • comment-avatar
    July 1, 2018 (4:48 pm)

    Thanks for a clear, science-based explanation of why carb loading pre-race doesn’t work. What dietary strategy would you recommend to keep up energy during a race? Are you advocating running empty the whole way?