Welcome to our Sports Science Interview Series on our Press Play Lab blog. We are very excited and honored to kick-off our first interview with Dr. Stacy Sims of Osmo Nutrition. This is a must read for female athletes as this is just the tip of the iceberg in learning the peaks and valleys of hormonal fluctuations and performance. We look forward to more of Dr. Sims’ research and articles.
About Dr. Sims:
From the Osmo Nutrition website: “Dr. Stacy Sims, MSc, PhD, is the chief research officer and a co-founder of Osmo Nutrition. Stacy is an exercise physiologist and nutrition scientist with almost two decades in the field and is also a longtime endurance athlete.”
Food for thought:
Jessica Greaux (JG): You have talked about carbohydrate intake differences between men and women. Can you explain the carbohydrate and protein needs for women in the different stages of the menstrual cycle?
Stacy Sims (SS): There are sex differences from birth, but they aren’t really apparent until the onset of puberty- when there is the rise in testosterone in boys (stimulating muscle mass development), and the onset of the menstrual cycle. Here, it is always thought that it is the upswing in testosterone is what causes the massive difference in the ability to put on muscle mass in boys vs girls, but the upsurge in estrogen (and progesterone) in women affects the genetic expression for muscle cell turnover/protein synthesis. What I mean by this, is that estrogen turns “down” anabolic capacity of the muscle, and progesterone turns “up” the catabolism of muscle tissue. Additionally, elevated circulating levels of estrogen alters metabolism to “spare” carbohydrate/glycogen and increase circulating free fatty acids. When we look at this from the perspective of what happens during the menstrual cycle, the 10-14days preceeding bleeding is when estrogen and progesterone levels increase; and the effects of these two sex hormones directly affect a woman’s ability to recover well and to hit intensities during exercise. I recommend to pay attention to the timing of protein, post exercise, (within 30 min, getting ~25g mixed protein OR ~10g branched-chain amino acids). and to increase their ratio of carb to other macronutrients during exercise to hit intensities.
JG: High Fat Low Carb diets are popular amongst athletes. Could this be a disadvantage for female endurance athletes?
SS: Ah. yes. Here’s the thing- endurance athletes tend to eat too many of their daily calories from carbohydrate due to the idea of carb is needed for endurance. On the flip side of this, you have the other extreme of go high fat and super low carb (getting into ketosis) to improve fatty acid utilization during exercise. One scientific issue I have with the HFLC diet approach is that the studies have all been done on overweight/obese and/or diabetic individuals. Yes, HFLC works in these populations as they are already compromised from a health standpoint with regards to how they metabolize carbohydrates. In an athletic population, the long term studies are far from being done. Will you rely more on fat if you follow a HFLC diet? Yes, because the body needs to fuel itself- but from a performance metric, the research indicates that a moderate carb vs low carb have no performance differences. In women, the elevated cortisol that comes from HFLC dieting increases catabolism and a subsequent reduction of protein synthesis coupled with immunodeficiency. (note, this is in the healthy athletic population where the immune system is regularly taxed through exercise stress).
What I find works best (from a body composition and performance scope) in my female athletes is ~40-45% dietary intake from moderate glycemic, whole food carbohydrates (eg veggies, fruit, ancient grains), with 30% protein and the rest fat. Timing of intake in and around training becomes a deciding factor in recovery and adaptation gains moreseo than overall daily composition.
JG: Since everyone’s sweat rate is different, how would you recommend an athlete developing a hydration/electrolyte strategy?
SS: Sweat rate, gastric empty, sweat compostion- all different! There is no generalization on what and how much to drink- but remember, it is never about “electrolyte replacement” but about supporting physiology- I say this because I feel I am always answering the question “do I need salt tablets”- the resounding answer is NO! your body has plenty of sodium stores, and if, during exercise, you are eating and drinking fluids/foods with sodium, you are providing your body with sodium needed for fluid balance. Drinking plain water is never a good idea (you need some sodium to help pull fluids across the intestines). As for a general guideline for fluid intake- again there isn’t one- but I have athletes start with a body weight measure (8-12ml/kg/hour, more fluid in hotter conditions) and use pee sticks to determine their hydration status before and after training. This helps them understand their body and how much fluid they need to take in. Women often find they need more during the high hormone phase of the menstrual cycle (progesterone increases total body sodium losses, and the combination of estrogen and progesterone cause ~8% loss of plasma volume with a redistribution of fluid across other body compartments).
JG: Would you recommend women testing sweat rate at different stages of their menstrual cycle? Would their sweat rate differ?
SS: It may vary a bit, but nothing overly significant. It has more to do with fluid redistribution and total body sodium losses (see above) that will dictate if they need more fluid.
JG: Is there any data correlating menstrual cycle stages and performance? If so, is there a nutrition and hydration strategy particularly for women on race day depending on where she is in her menstrual cycle? Do you recommend nutritional supplementation for women before a race?
SS: Multifacted question! In the low hormone phase, women are more like men with regards to fluid balance, core temperature, carbohydrate metabolism, oxygen uptake. But in the high hormone phase, there is a resting elevation of ~0.5’C of core temperature with a shift of sweat thresholds – making women approach fatigue at a faster rate. There is also the effect of estrogen+protesterone on the central nervous system – decreasing time to CNS fatigue. As for VO2- there is a reduction in attaining VO2 max -more so from the lack of carbohydrate utilization rather than oxygen delivery. If a woman is going to race in the 5-0 days leading up to her period, using branched chain amino acids before and after training/racing is going to help with CNS fatigue, using a sodium+water hyperhydration strategy is going to help with the plasma volume drop and total body sodium losses; and increasing frequency of carbohydrate feedings (eg glucose tablets with a bar) is going to help her hit intensities.
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