Working out on an empty stomach
Working out on an empty stomach
Should I work-out fasted?
Hello lovely people,
Thank you to those who always open these emails and read them regularly. You motivate me to keep writing them.
Today, we discuss working out on an empty stomach.
Should women work out on an empty stomach? What about those with PCOS?
I have fallen victim to this for years in my exercise routine: I get up, have a coffee, and hit the gym. The underlying reason for this is that “training fasted burns more fat.” Well, this is not true and it has not worked for me. Fasted exercise increases fat burning during the exercise, but that doesn’t translate into greater fat loss.
A lot of this research has been done primarily in men. We follow a lot of advice about nutrition and sports that is built for different physiologies. As women, we have more fibres in our muscles that prefer using fat storage for energy than men. Overall, we go into “metabolic flexibility” much more readily than men, so we might not need to train fast.
However, the issue with training fasted is a bit more serious than the fat-burning argument. It can greatly impact our hormones.
For women in general:
when we don’t eat, it causes our brain to perceive that there is not enough nutrition coming to support our systems, let alone carry a pregnancy
this puts stress on our body, seen through a rise in cortisol → “There is no food around. Time to panic.”
cortisol interacts with a key hormone in our brain: Kisspeptin
Kisspeptin regulates the release of Gonadotrophin Releasing Hormone (GnRH), which, if you have been reading this newsletter for a while, you know stimulates our lovely LH and FSH, which helps us ovulate
Cortisol, as a stress hormone, seems to suppress the expression of kisspeptin (Kiss1) genes.
This results in a disrupted endocrine system, which can lead to a worsened LH and FSH and, as a result, irregular periods → this is called hypothalamic amenorrhoea (FHA)
This can also affect the thyroid function - with a drop in T3 seen after training fasted.
In addition, if your body is under ‘stress’, it will hold more fat afterwards. There is also the argument that you can’t push as hard without fuel, so your exercise capacity is low.
Now, does this hold truth for PCOS girlies?
This is where it becomes a bit tricky.
We know that PCOS displays metabolic issues. Higher insulin levels and glucose levels influence our hormones and the other way around.
However, chronic stress is known to disrupt our hormones even further, as seen above. It can disturb appetite regulation, leading to overeating and further fat accumulation, which in turn will affect our PCOS.
There is no research looking specifically at exercising on an empty stomach for PCOS. We have some research on intermittent fasting, which has been shown to help with PCOS parameters and BMI but is not as extensive. If you have a difficult relationship with food or a history of eating disorders, this can trigger unhealthy habits and attitudes.
It’s a bit of a chicken-and-egg situation. Whether PCOS causes metabolic issues or metabolic issues cause PCOS is an ongoing debate, and no answers have been found.
From my point of view, I would prioritise taking care of my hormones and working with my genetics for the answers. Certain people have variations in their genetic code that make them much more prone to using fat as fuel, whilst others don’t (me included). Certain people are also much more sensitive to the stress hormone cortisol than others.
While I keep repeating myself, research and science can help you get some clues about what might be right, but only you can find the answer to your own body. Having power over what works for you and developing a relationship with your body is the most important step for our health. Like any other relationship, it requires time, patience, and trust.
If you train NOT FASTED, Dr. Stacy Sims recommends 15g of protein for strength sessions. If you are about to do a cardio session lasting up to an hour, add 30 grams of carbohydrates to your pre-workout intake along with your protein. This combination helps by bringing blood sugar up and signalling to the brain that nutrition is coming, which prepares the body for exercise and recovery.
See you next Sunday,
Francesca
We are doing a genetic-based program starting in September. If you are looking to get a hold of your PCOS once and for all, join the waiting list here.
References
Katulski, K., Podfigurna, A., Czyzyk, A., Meczekalski, B., & Genazzani, A. D. (2018). Kisspeptin and LH pulsatile temporal coupling in PCOS patients. Endocrine, 61(1), 149–157. https://doi.org/10.1007/s12020-018-1609-1
Sims, S. T., & Yeager, S. (2024). ROAR, revised edition: Match your food and fitness to your unique female physiology for optimum performance, great health, and a strong body for life. Rodale Books.
Xiao, Y., Liu, D., Cline, M. A., & Gilbert, E. R. (2020). Chronic stress, epigenetics, and adipose tissue metabolism in the obese state. Nutrition & Metabolism, 17(1). https://doi.org/10.1186/s12986-020-00513-4