Let's talk about intermittent fasting. It's probably one of the top 5 questions we get on a regular bases - "What are your thoughts on IF?", or we hear things like "I've been doing IF for months and haven't seen a lot of results from it".
If you've been following us for a while, you know that we like to keep things simple, basic and just give you the information you need to make educated decisions on what path you're going to take down your weight loss journey.
So let's break it down!
Intermittent fasting is a pattern of eating between certain periods if time and focuses mostly on when you eat
Now when it comes to women, it gets a little more complicated.
Women's hormones regulates our reproductive system and cycle - ovulation, metabolism, mood- is all regulated by energy availability.
When we fast, it affects the brain region called hypothalamus and also the connection way to hormone gland - called the hypothalamic-pituitary-gonadal axis (HPG axis). This is the way signals from brain are delivered to other regions of the body, signalling to release hormones like luteinizing hormone-LH and follicular stimulating hormone-FSH, which help control the menstrual cycle.
LH- Triggers the release of an egg from ovary.
FSH- stimulates the growth of ovarian follicles in the ovary before the release of an egg from one follicle during ovulation.
At the end, these 2 hormones stimulate estrogen and progesterone production.
The signals released and delivered through HPG axis are sensitive to environmental factors -stress, energy intake and hunger.
So having a consistent inflow of energy is important in supporting all these processes.
Being on negative energy balance too long is a major stressor and can put the body into chronic negative energy balance. Imagine this combined with too much exercise, stress, illness, little rest, low recovery...Can easily be a recipe for disaster,
When this physiological stress is combined with psychological stress it has a huge negative impact on hormonal health by increasing stress hormone called cortisol and it inhibits GnRH hormone (responsible for the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) ) which is vital for reproduction health.)
Many women who try intermittent fasting do experience negative effects on hormones and reproductive health.
Such as thyroid hormone production, menstrual disturbance, appetite hormone dysregulation - higher ghrelin (hunger hormone) and lower leptin levels.
Here are some ways that women function differently than men:
- Many females tend to feel the negative outcomes of intermittent fasting more than males because female hormones have higher sensitivity levels to internal and external changes - especially energy availability. Few studies linking this sensitivity with a protein like molecule called kisspeptin which stimulates sex hormone production on male and female body and also it's sensitive to hunger and fullness hormones ( ghrelin and leptin). However females do have higher levels of kisspeptin and that could be the reason why females are more sensitive to negative energy balance.
- Women tend to eat less protein compared to men and when it's combined with IF, the chances of eating adequate amount of protein is low. When there's not enough protein aka amino acids available in the body, hormones (estrogen receptors and a hormone called insulin like growth factor IGD-1) which are essential for thicken the lining of the uterus during the menstrual cycle can be negatively effected. We can conclude this as low protein diets has a risk of reduced fertility.
- Estrogen hormone is not just for reproduction for females but also for mood, metabolism, and appetite control. When there's change in estrogen levels, your metabolic functions of digestion, protein turnover, cognition, mood, recovery, bone formation and appetite & energy balance . Estrogen hormone stimulates the brain cells that are responsible for production of appetite regulating hormones. So any diet and exercise program that causes your estrogen levels to drop really fast, will make you feel hungrier due to changed levels of hunger hormone (ghrelin) through reduced estrogen levels.
- Long story short, IF in women body is not straight forward and is more complex due to higher sensitivity levels to energy balance of female body. Significant changes in female body disrupt hypothalamic-pituitary-gonadal axis (HPG axis)-signals from brain are delivered to other regions of the body to release hormones (luteinizing hormone-LH and follicular stimulating hormone-FSH) >negatively impact hormonal cycle. When this physiological change is combined with other stressors the intensity of perceived stress goes up. In addition to that, Decreased estrogen levels may increase fat deposition / storage and appetite.
To break it down even further:
1-Disrupted HPG axis > luteinizing hormone-LH and follicular stimulating hormone-FSH >negatively impact hormonal cycle.
2- Negative energy balance > reduced estrogen> increased hunger hormones > increased appetite.
3- Negative energy balance > reduced estrogen > increased fat storage.
3- Higher sensitivity to negative energy balance
4- IF > Low energy intake > low protein intake > low aminoacid available in the body > thicken the lining of the uterus during the menstrual cycle > no pregnancy.
As a summary, if you're thinking about intermittent fasting or if you've been doing it off and on for a while, it might be time to switch it up.
However, as we know, every body is different. And what works for you might not work for someone else. Although this article outlines some science behind how IF can affect parts of our body, it's always best to try things, test them and see if they work for you.
A great place to start, if you ARE going to do IF, is to give yourself a larger eating window, like 8-10 hours. That way your body isn't going without energy intake for too long.