Updated 05/20/24 9:38 PM

Health and Performance:
Does a pre-run bagel improve performance?

2002 Nobel Prize winner Professor Daniel Kahneman describes a fast brain system based on emotion and reflex which accepts and believes suggestions, exaggerations and improbable. The slow brain system he describes facilitates critical thinking doubting and listening enhancing learning and change.

From feedback after my 2023 SFM lecture, I learned (again) how confirmation bias influences marathon training Since this article and those that follow present physiology (how the body works), I suggest you engage your slow brain system to consider and learn.

The carbohydrate loading myth is dispelled by understanding physiology. During digestion of a bagel, glucose from carbohydrate, fatty acids from fat and amino acids from protein raise insulin (the storage hormone) for up to 4 hours. Insulin binds to receptors on cells and acts as a key opening a door for nutrient entry to be stored. Chains of glucose are stored as glycogen in muscle, liver, brain, heart, kidney, adipose and blood cells. Insulin also impairs fat breakdown limiting fatty acids available for muscles.

Why is this important?

1. Although both glucose and fat are used for muscle contraction, fat has more stored energy. Only 2000 calories are stored in glycogen (400 in liver, 1600 in muscle). More than 100,000 calories are stored in fat. While carbohydrate and protein release 4 calories/gm, fat releases 9 calories/gm.

During a run, fat use increases while carbohydrate use declines. Training increases muscle mitochondria size and number enhancing your body’s ability to use fat for fuel. Since eating a bagel raises insulin which impairs fat release from fat tissue, your pre-run snack will limit use of your best muscle fuel for up to 4 hours.

2. Exercise reduces insulin closing the door for glucose entry into cells. Active muscles open the door for glucose entry into muscle. When less glucose is able to enter non-muscle cells, more glucose is available to enter the door on muscle membranes opened by exercise. With insulin elevated after eating, glucose can enter cells not used for running reducing glucose for muscles. In addition to insulin, many other hormones change during exercise which I will discuss during my upcoming lecture at SFM on 7/22/24.

The takeaway: skip pre-run calories for efficient fuel use.

We're excited to re-introduce Dr. Jeff Shapiro to our SFM community. If you're looking to improve your health and performance, you know an overwhelming amount of information and opinion is conflicting, counterproductive or harmful.

We're giving Dr. Jeff a platform to address this.

In his articles, Dr. Jeff will discuss exercise and nutrition physiology (how the body works) allowing you to ignore chatter and reject myths. For example, should you carbohydrate load and/or eat during running? Are pills on SFM weekend harmful? After graduating from Stanford and Yale, Dr. Jeff served as medical director of the San Francisco Marathon for a decade, completed and lectured at 50 marathons and trained athletes to achieve peak organ function for 30 years.

Dr. Jeff appeared on ABC News' 20/20 "Super Humans," consulted for CBS News' 60 Minutes "The Toughest Race" and co-produced “Ultra Running” for The Late Show. At the 2023 San Francisco Marathon, Dr. Jeff received a standing ovation for his presentation on exercise/nutrition physiology and adverse effects of pills.

Since he teaches physiology, Dr Jeff’s presentations will read like science instead of a blog. Train Well with Dr Jeff starting in May 2024.