Our stance:
Flipping 50 believes each woman is unique.
That said, we favor fed exercise over fasted exercise when it is intense. That is, high intensity interval training, or strength training with the intent of preserving lean muscle mass and avoiding frailty or fragility occur within the eating window and ideally bookended by protein consumption if for muscle or bone mass.
We do acknowledge that exercise may “feel hard” when exercise is performed fasted giving the perception of “working hard.”
However, we suggest based on research and 4 decades of primary observation, women actually exercise harder related to their capacity for exercise when fueled. That is, they will go faster if being timed, go further within a timed test, lift more weight or perform more reps to muscular fatigue.
Fasted Exercise Pros and Cons During Perimenopause
A 27% muscle loss has been reported between early and late stage perimenopause. This is most likely due to multifactors: insomnia disrupting anabolic hormones and together with other signs and symptoms of menopause interfering with desire to workout, as well as a drop in estrogen, testosterone and growth hormone levels, and an increase in cortisol levels.
This is an important consideration when looking at fat loss vs lean muscle gain and priorities. Mitigating potential loss of muscle is a critical factor in aging well and overall metabolic health.
What Science Says
Some studies (review of literature) suggest that before prolonged exercise, fueling provides more benefit but before short exercise, results are inconclusive. A 2013 study on sumo wrestlers eating a ultra high calorie, 50% fat diet burned more fat after exercise done fasted. However, we’ve got to consider…. How like you are that? Extremely high calorie and 50% fat? In almost the same time frame, college women were fed vs fasted in exercise and showed no difference. Their diets probably reflected at least a little closer to yours and their hormone profiles also at least slightly more like you.
The problem is, few studies about fasting and exercise exist on midlife or postmenopausal women.
Women who are at risk for accelerated muscle and strength losses.
In studies for the last 10 years, fasted vs fed with the same hypocaloric diet there was no difference in increased fat loss due to fasted vs fed.
I hear comments from women who believe they are burning fat for fuel when they’ve fat-adapted, however, without measuring this, we don’t know it to be true. The crossover is only visible when you’re measuring in a lab. It would mean that at the same speed and intensity previously (watts) you were burning fat vs carbs for fuel. We can see that in clinical lab testing during progressive exercise testing using stages. Your cardiovascular fitness level may also improve meaning for the same speed your heart rate isn’t as elevated. That’s another way to hypothesize you’re burning more fat for fuel at higher levels.
I want to remind you that at a certain point we all cross over. If you’re “working hard” in high intensity interval training you are NOT burning fat during. You’re burning a lower percent of fat for fuel during. Because you’re burning calories - that is your energy expenditure is higher - you are still burning more fat.
Your goal is not to burn a high percent of fat for fuel during.. Or you’re doing that best at rest.
The data is not there to support higher fat burning during HIIT fasted. It’s not there to support higher fat burning after HIIT if fasted.
What seems most important is a hypocaloric diet, performing optimal exercise intensity for energy expenditure. And resistance training improves post workout FFA circulation most compared to HIIT.
To support anabolic response to strength training, especially for women when more prone to anabolic resistance, fed exercise makes the most sense.
Fasted Exercise Pros and Cons with Obese Women
For women who can’t seem to lose fat weight, and are in good adrenal health, after employing a foundation of high protein, 3 meals no snacks, fasting at least 12 hours overnight, extending the fast and testing can help shake a plateau.
The approach needs to be unique to individual needs and goals to lose fat weight and gain lean muscle mass. It may need to be addressed step by step to first improve metabolic health (blood lipids, blood pressure, insulin, glucose), with close observations on skeletal muscle to determine success.
For other women though, recomposition is best addressed by focus on gaining lean muscle mass and not slowing progress. We do know strength can be gained during fasting, at least in the beginning. Muscle mass doesn’t improve during fasted exercise.
Again, important to remember, the research featuring women in menopause and post, with anabolic resistance is minimal. Anabolic resistance is the resistance to gaining lean muscle mass. Basically, the older we get the more you have to work for it.
So, if you focus on losing fat, you may also lose lean muscle if you’re doing it by fasting. Like many things including exercise, the solution may be cycling fasting duration with alternating periods of time (weeks/months) with primary focus on muscle gains vs fat loss.
But the one constant should be monitoring your personal results. Is your lean muscle mass going up or down? Is your body fat going up or down? Is your gut health/digestion/elimination improving?
To Unpack Your Personal Fasted Exercise Pros and Cons, Prioritize
Prioritize goals:
Longevity (autophagy)
Avoidance of frailty, fragility
Improvement of balance and stability
Increase in bone density
Gut health
Emotional eating/relationship with food
Consuming inadequate fuel can make women store more fat. It may depend on whether you are in perimenopause vs postmenopause. According to Stacy Sims, it’s the hypothalamus related to the kisspeptin hormone. Thyroid hormone gets down-regulated within a short period of a few days.
You feel like you’re exercising “hard.” But you’re not necessarily exercising to your capacity. You’re simply struggling. It’s not the same as a quality intensity workout.
If you’re more athletic, you want to do more endurance or more peak performance, the more you have low calories while taxing your system.
Increasing protein without changing anything, even without exercise, body fat loss will be facilitated within 3 months.
For women who struggle with dieting or a history restrictive eating or binge-purging, using a time restricted eating window can be complicated by the desire to also restrict calories. The low fuel intake means low micronutrient intake. Frequent testing would be extremely beneficial for women who also ideally will monitor their skeletal muscle mass, body fat percent and blood glucose levels on a daily/weekly basis.
For extremely active women, fasted exercise reflects poorer performance:
- Slower walking pace
- Lower endurance
- Longer recovery periods
- Less muscle mass gains
- Less fat loss (compared to fed exercise at higher intensity)
Resources:
Smart Scales:
https://www.amazon.com/shop/flipping50/list/GFTU3QXMJ07G?ref_=cm_sw_r_cp_ud_aipsflist_aipsfflipping50_7CD0CBB5VP0Q08ZGZ7JF
Dr. Mindy Pelz:
https://www.youtube.com/@DrMindyPelz
5 Day Flip:
https://www.flippingfifty.com/5-day-challenge-new/
References:
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