Fuel for What You're Doing: Rethinking Fueling and Hydration with Dr. Stacy Sims
Play • 54 min

Stacy Sims - Fuel For What You’re Doing: Rethinking Fueling and Hydration


There are a lot of options for fueling and hydration products on the market. But beyond taste and marketing lies efficacy: is the product doing the job you need it to do when you need it to do it? There are also some misconceptions and myths that, while generally accepted, are not actually based in physiological fact. And muddying the waters further are the inherent physiological differences between men and women. If you’ve ever been confused standing in front of a sports drink display, you’re not alone.


Enter Stacy Sims, an Environmental Exercise Physiologist and Nutrition Scientist specializing in sex differences of heat and/or altitude stress, recovery, genetics, and nutrition  to moderate adaptive responses for performance. Stacy is a Senior Research Fellow at The University Of Waikato and author of ROAR, which helps women understand and work with their physiology for better performance.


That’s not to say that there’s no information in here for men. Stacy passionately explains the why’s and when’s of fueling, hydration and more for both men and women. This episode will help you re-evaluate your fueling and hydration strategy to provide more optimal results.


Here are some of the topics we’ll discuss today:


  • Issues with the product functionality of the modern sports drink industry.
  • How to fuel and hydrate while training vs. while racing; and how needs change based on environmental conditions and gender.
  • What causes most cramping while running (it’s not what you think).
  • Why drinking more water isn’t necessarily helpful.
  • The specific needs of female athletes and how oral contraceptives compromise performance.
  • The best natural sources of sugar.


Questions Stacy is asked:

3:37 What is your background in endurance sports?

4:35 What prompted your interest in Nutrition Science and Environmental Exercise Physiology?

5:25 What was your mission with Osmo, what is your mission now with Nuun and what is the history of the sports drink industry?

6:59 Has the sports drink industry been geared more towards palatability than osmolality?

8:55 Have you discovered that it’s better to separate fueling and hydrating altogether?

10:55 How does this play into recovery & post-workout drinks?

12:45 What would be a good fuel strategy during a marathon or long run?

14:36 How do you feel about all natural gels?

16:01 Why are you not a fan of electrolyte pills or salt tabs?

18:34 Does cramping have anything to do with dehydration or potassium deficiency?

19:43 How should a runner determine how and when to hydrate as well as to take electrolytes?

21:57 How do women’s hydration needs vary throughout the stages of their menstrual cycle?

23:49 How should a woman who is having her period leading into a race alter her hydration strategy?

24:40 What do you mean by “Women are not small men” and how do men’s and women’s protein and carb requirements differ?

27:30 Are you not a proponent of oral contraception for high performance female athletes?

29:04 What would you suggest to female athletes as a safe alternative to the pill?

30:07 What is your take on the popular high fat / low carb diet in general and for men vs. women specifically?

33:01 Do women need carbs as endurance athletes?

33:36 Does sugar actually inhibit one’s ability to use fat as fuel?

35:01 Out of all the different types, which sugars are best?

36:39 What about honey?

37:06 What are the best solid foods to use to fuel for training and competition?

38:28 How does ambient temperature affect how people process different foods?

38:41 What should people consume post-run, especially post-workout or post-long run to facilitate glycogen repletion, fluid balance and overall recovery?

40:16 How has your partnership with Nuun been so far and what’s in the works with them?

43:08 What is the new product Nuun just released?

47:50 The Final Kick Round

Quotes by Stacy:



  • “No one’s really pushing down on ‘we need fluid first’, because you can live 3 or 4 days without hydration and you can live 7-90 days without food; so from a functionality and a physiological point, you really want to look at the hydration and not the carbohydrate intake.”
  • “A sports drink is like a sofa bed; it’s not a good bed, it’s not a good sofa, because you’re trying to merge two things that shouldn’t be merged.”
  • “When we think about all this engineered nutrition, you’re taking concentrated carbohydrate and putting it in this compromised gut.”
  • “It’s not about eating a whole bunch of food at once, it’s a sip, sip, nibble, nibble approach.”
  • “Use water for something up to an hour, but if something’s intense you need more than water, because water doesn’t hydrate.”
  • “After 2 hours… your thirst is not a very good representation of what’s happening.”
  • “Getting people to understand that what you read in a general scope does not necessarily apply to women because the research hasn’t been done on women.”



Take a Listen on Your Next Run


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Mentioned in this podcast:

Dr. Stacy Sims - The University of Waikato profile

Book - ROAR: How to Match Your Food and Fitness to Your Unique Female Physiology for Optimum Performance, Great Health, and a Strong, Lean Body for Life

nuun performance

Urine Test Strips

Metromint Water

Dr. Constance Lebrun

"No Sweat": Nina Stachenfeld OCP research article


Running On Real Food blog

Kara Gaucher’s blog

mobilitywod gear

Book: Becoming a Supple Leopard - Kelly Starrett

Follow Stacy on Twitter

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