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Why women should avoid fasted cardio

Thinking of going for a run after fasting? It may not be ideal as your hormones can end up wreaking havoc on your body

Women may get hungrier with fasted cardio
Women may get hungrier with fasted cardio (iStockphoto)

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At some point, we all treat our bodies like science experiments. You’ll do something you know may have negative ramifications, yet you somehow throw caution to the wind and hope you remain unscathed. Sometimes the experiment proves that you can be the exception to the rule, while others will reveal in no uncertain terms that there is a reason for that rule.

This became very clear to me when I started doing cardio in a fasted state. My workout plan was ticking along as usual, but I didn’t see a change in my measurements “fast enough.” I was getting stronger, faster, and fitter, but I wanted more once I experienced that delicious taste of success. If a little was working, a lot would be much better. This greedy thinking led me to explore ways to shed a few extra pounds. And that, my friends, is I decided to add fasted cardio to my workout plan.

For those who don’t know what fasted cardio is, it’s self-explanatory: don’t eat before your cardio session. Practically speaking, this often means “fasting” throughout the night, which most of us do anyway, and planning our cardio session first thing in the morning before we take a bite of breakfast.

Also read: How to train through your menstrual cycle

A simple way to shed fat?

Fasted cardio started to become all the rage because, in a fasted state, your body has low levels of insulin and hepatic glycogen. When exercise is performed under these conditions, the body is more likely to use fat as fuel, and you can also train your body through fasted cardio to become better at fat oxidization. There is a lot of nitty-gritty science behind wanting to utilize fat rather than carbohydrates during exercise, one of which is that it has the potential to improve athletic endurance. There are many fans of fasted cardio, and not surprisingly, many are men, for whom much of this athletic-based research is conducted. In short, for most of us, fasted cardio could be a simple way to shed extra weight.

Having said that, nothing is ever as simple as it seems, especially when discussing the intricate complexity of our bodies and hormones. It’s fascinating and frustrating how our bodies operate differently from the next, meaning what works for Paul may not work for Priya. The unfortunate fact is that it’s not for everyone, mainly, as I found out by using myself as an unwilling participant, it is not necessarily the best choice for women.

The reason why there may be better choices than fasted cardio for women is described by Dr Stacy Sims, a leading researcher on female physiology and nutrition science. She tells us that because our morning cortisol levels (a stress hormone) are high, adding a high-intensity exercise (another stressor) increases our cortisol levels. High stress isn’t a gender-specific phenomenon, as most of us wake up steaming with stress from the moment we open our eyes.

However, women’s bodies process chronically high-stress levels through cascading events. Hormones go on high alert and start adjusting their output which can impact our reproductive system, depress thyroid function, increase anxiety and fatigue, increase the chance of bone stress injuries, disturbed sleep, and increase belly fat. If the goal is to lose weight through fasted cardio, battling chronically high cortisol levels can do the opposite.

But if that’s not reason enough to ditch the fasted cardio, there’s more. We get hungrier.

The hunger game

Women’s bodies are highly tuned to changes in our energy balance, so our bodies go on high alert when our fuel stores start going low. This happens much faster for us than it does for men. The evolutionary reason for this is to protect and nurture a potential pregnancy at all costs. This isn’t a decision we get to participate in actively, it’s one made for us by our innate survival mechanisms, so we can’t ask our body to squeeze out one more mile. Perceived energy shortages send us physical warning signals—almost driving us to distraction to go and eat something. The problem is this: your body doesn’t care about your fitness goals; it knows you need food to survive.

In my experience with fasted cardio, my hunger suddenly spiked into bottomless starvation. I always felt hungry, and I never felt full. Typically, I can manage my appetite and mindfully eat adequate food at each meal. With fasted cardio, I lost the ability to gauge how much I needed, and I started overeating my calories. The reality is the more you fight these feelings of intense hunger, the more pervasive they feel, which can be mentally exhausting and draining. If the goal was for me to feel fit and strong, I certainly created the opposite situation. Stressed, tired, anxious, and now unbelievably hungry – I was a delight to be around.

And all this could even be unnecessary.

Also read: Not losing weight? Stop overthinking it

The best way to exercise fasted

It turns out science is now pointing to the fact that “fed” cardio and “fasted” cardio may not offer different long-term results, as shown in a study published in the Journal of the International Society of Sports Nutrition that compared ten women (finally, a study conducted on only women!) who did fasted cardio every day for four weeks to 10 women who had a shake before exercising. The results showed no difference in fat loss between the two groups, not in their measurements, fat mass, lean muscle, or BMI.

If that’s the case, I’ll take the shake.

In the end, I abandoned fasted cardio because of the havoc it wreaked on my body and mind and, instead, altered my cardio intensity throughout the week in a fed state. I remember the first day back on the elliptical after eating a snack 30 minutes before my cardio session, feeling energy ping through my muscles. It was fantastic to enter into exercise feeling strong and energized rather than depleted and depressed.

I understand that I am the rule, and there are some exceptions. Some of you reading this may find fasted cardio preferable to regular cardio, even have seen long-term results from it. I certainly won’t stop you from trying to see what works best for you. Some people find working out on an empty stomach helpful because having your oatmeal slosh around your stomach feels less than enticing. For others, it’s the only available time in their day to exercise, and that’s fine. However, there are some guidelines to consider to see the best results.

The first is to consider the intensity of your fasted cardio. Your body tends to use fat as fuel and carbohydrates at lower intensities at moderate and above intensities. If you’re going to engage in fasted cardio, keep your intensity low. This can be achieved through a walk or a swim.

The second is to think of your duration. Sports Dietician Renee McGregor told Women’s Health Magazine that she recommends 60 minutes in a fasted cardio session and a maximum of two sessions weekly. She also recommends doing them on recovery days with no other gym session planned.

The final thing to consider is how you refuel your body post-fasted cardio. Choose a combination of protein and carbohydrate food sources to replenish your muscle’s glycogen stores and help with muscle repair within thirty minutes of completing your fasted cardio.

Jen Thomas is a Chennai-based weight-loss coach

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