A female runner, Makenna, and her husband, Mike, start the same low-carb diet. Mike is training for an Ironman, Makenna for a fast 5k.
Week One: Makenna has a great week, feels highly energized, loses a pound. Mike slips up with carbs a couple times, but still loses 3 pounds.
Okay, he weighed more in the first place so it makes sense he'd lose more… kinda.
Week Two: Makenna loses another pound, but feels quite a bit less energy than last week. Great work! Mike dropped five pounds, and is somehow already over his 'keto flu.' What?!
Weeks 3-10: Makenna comes home from a workout run exhausted and with a foggy head. Her intervals were also much slower than she'd planned for. She's fluctuated back up and down to equal zero pounds lost this week. What is happening?!
Mike has reached race weight, and cranked out 175 race-pace miles over swim, bike and run this week. Come on.
Women: To Low Carb Or Not?
Mike's Ironman would not require him to venture too far above ~75% max heart rate during his training and race, while Makenna's 5k required that almost every other day during her training block.
Fats burn slowly. Makenna needed faster fuel to reach her goals, build muscle and recover quickly.
Despite the differences in intensity and speed, a woman's body is just different than a man's body.
Progesterone is then converted to cortisol. When cortisol is raised for long periods it sends yet another signal to the body to store fat.
That's a lot of votes for keeping fat around.
In short: on a diet where carbohydrates are restricted, Makenna's body goes into a state of mild famine. If you think the idea of 'famine' is a myth, call the above three paragraphs whatever you want. I call it famine.
This hunker-down mechanism is actually brilliant.
If your body receives input that all the wheat or apples in your village have rotted, and the stores of carbohydrates are dried up, it takes what glucose the body already has available, and converts it to fat so you can last until the next harvest.
In her book ROAR, Dr. Stacy Sims points out that a man's body’s response to a low-carb environment is "to become fight ready, lean up, increase anabolic activities, and increase testosterone."
Mike is very grateful for this; Makenna, very jealous.
Evolutionarily, men's bodies prepare to hunt, and women's bodies trust that their men-folk aren't as good with a bow as they say they are. The women stay back, survive on extant fat, and keep their uteruses empty. A baby - after all - is just another mouth to feed.
Meanwhile, Makenna - a modern-day runner training for a 5k on a low-carb diet - is at risk for irregular periods or dropping her menstrual cycle entirely: an effective way to save calorie burn and prevent making babies.
Low-carb/high-fat diets will do this to women, even while men thrive on them. (I'll write something soon about intermittent fasting here, too).
Imagine getting all your info from the mounds of medical research out there done on mostly men, because women's hormones are too variable. Oh wait, we’ve all been doing that for decades 🤪.
Low-Carb & Fertility in Women
You may hear about studies that show low-carb diets actually improve female fertility. These studies are valid, they're just very specific, too.
Most of those studies are looking at women with PCOS (polycystic ovarian syndrome) which is related to Type-2 Diabetes, or the inability to properly utilize insulin.
Put simply, a low-carb diet can help women who are overweight and/or have Type-2 Diabetes/insulin resistance by increasing insulin sensitivity and helping them lose weight. All this can improve their chances of getting pregnant.
If you do have PCOS, Type-2 Diabetes, or are otherwise insulin resistant, a short-term low-carb diet may help you to reverse your insulin resistance, and therefore get you to a point where you can improve athletically and... make babies.
If you don't have PCOS, Type-2 Diabetes, and are not otherwise insulin resistant, you're more likely to be negatively affected by intermittent fasting or Ketosis than you are positively. If you're training for, say, a half marathon, you're probably good on these fronts.
Why Athletes Are Attracted to Low-Carb
There are many scientific reasons to get excited about a low-carb diet. I won't go into all of them here.
For me: I'd drop $250 on carbon-plated shoes if it improved my performance by 2%, and many casual runners do the same. These marginal improvements make up a lot of difference on race day, and over the long-haul.
It's not surprising that a serious runner, hearing all the validated benefits of ketosis, would want to try it out. Those potential benefits could be far greater than 2%.
Imagine being able to access (at minimum) 16,000 calories of fat to burn for energy during a marathon... so many upsides.
In practice though, any woman opting for faster paces at higher intensity will do better reaching for a potato than for a stick of butter (natural, healthy fats are still a big part of my diet, btw).
While you certainly can adapt to ketosis successfully, at higher intensities, you'll get tired quicker, and your Vo2 max, peak power, and ventilatory threshold will likely suffer.
Let's Wrap It Up - In a Flour Tortilla
Treat your body right. When she needs carbs for fuel, give them to her without listening the bro in the first 5 seconds of a Youtube ad.
Consider your goals when deciding whether to try low carb. Are you trying to maximize performance as an already intermediate-to-high-performing athlete? Low carb may not be the way to go.
If your goals instead revolve around getting back to a place where you can perform physically, (i.e. you are medically overweight, or just wanting to get back to homeostasis), you might consider doing some more research on a low-carb approach.
Lastly, DO NOT COMPARE YOURSELF, especially to men who are on the same diet as you are. Or just don't do the low-carb diet at all. Diets suck anyway. Feed yourself properly - I'll try to be more and more specific about the word "properly" in future posts.
Love you all.