In the next article I cover my own experience.
Interest over time
What is Intermittent fasting / Time restricted eating?
feeding/eating window – time during, which you consume food
postprandial state – time referring to after food has been consumed
post-absorptive state – time after a meal has been eaten and ingested, usually 8-12h after the meal
fasting/ fasted state – a period of time during which you voluntarily or involuntarily abstain from food, mostly used in religious practices like Ramadan.
20:4 also called a warrior diet
OMAD (One Meal A Day)
5:2 consisting of two non-consecutive days of low calories (500-600) and five days of higher calorie days
Extended fasts lasting 24+hours
- Alternate Day fasting – alternating between 24h eating and 24h fast
Benefits of Intermittent Fasting and Time Restricted Feeding
stabilized blood sugar,
improvements in memory and stress resistance,
slowed aging, and longer lifespan,
improved metabolic health,
improved hormonal health,
make better eating choices.
be more productive,
get more time that would otherwise be spent preparing food and eating,
it can help you make better nutritional choices
experience the real hunger,
reveal problems like food addictions.
Potential negatives of Intermittent Time Restricted Eating
Just like any other restrictive dietary approach, there are potential downsides to time restricted eating:
It can lead to chronically low energy intake,
- Exacerberate disordered eating tendencies.
- Lower performance in athletes, once again due to low calorie intake
- Dogmatic adherence to fasting can mask other issues,
- Digestive issues if you cannot handle bigger meals,
- Hormonal disregulation, especially in women,
- Can lead to restriction -> binge eating cycle,
- Over long term can cause blood sugar issues in some people,
- It is not a ‘get out of jail free card’ – you should still eat nutritious foods.
Some of the changes in body induced by fasting
- Physical activity helps with blunting insulin and blood glucose after meal.
- Eating protein, fiber, and fat before carbohydrates helps with blunting insulin and blood glucose after meal.
- An Intermittent Fasting Ddiet may provide a significant metabolic benefit by improving glycemic control and insulin resistance in general population. (source)
In humans, six months of a 25% CER has been shown to improve metabolic flexibility, as evidenced by increased shift in fasting-to-postprandial concentrations of acyl carnitine (important for transfer of fatty acids into the mitochondrion prior to oxidation). There are currently no data of the effects of IER on metabolic flexibility in humans. (source)
I suppose the effects of caloric restriction, whether continuous or intermittent will lead to the same metabolic flexibility.
How does fasting affect sex hormones?
Intermittent fasting is a popular diet but there have been concerns about its effect on hormonal health. A meta-analysis from 2022 looked at how fasting affects sex hormones in men and women.
The studies covered in this meta-analysis were predominantly obese, premenopausal women (18-45 y.o.) and included 5:2 fasting protocol as well as 16:8 fasting protocol. One study examined the distribution of energy intake during the day, where more than 50% of calories were consumed by participants either in the morning or in the afternoon.
Studies in men were on young, healthy men 19-35 y.o., all using 16:8 fasting protocol.
The researchers studied testosterone, DHEA-S, Androstenedione, FAI, estradiol, and Sex hormone-binding globulin (SHBG). Without going into too much details, there made some interesting findings.
Estradiol is the main female reproductive hormone and is involved in the development and maintenance of female reproductive tissues and the regulation of the menstrual cycle. We can observe, that obese and overweight women have higher levels of estrogens.
Androgen levels in women
Sex hormone-binding globulin (SHBG)
Intermittent fasting seems to have benefits for women who are overweight, obese, and those suffering from PCOS independent of weight loss, especially when the foods are consumed in the first part of the day. People who do intermittent fasting typically do the opposite – they skip breakfast and have a large dinner.
Note that these beneficial results were obtained in overweight, obese, premenopausal women and women with PCOS and will likely not be the same for healthy and active women. Active women and athletes often struggle with insufficient energy intake, which poses risk to health, including hormonal health.
The researchers studied testosterone and SHBG.
Sex hormone-binding globulin (SHBG)
Is it fasting / time restricted eating or calorie restriction that drives fat loss?
“Intermittent fasting is an equivalent alternative to continuous energy restriction for weight loss.”
Some studies concluded that continuous energy restriction and intermittent energy restriction give similar results (source, source), but fat loss happens as a result of caloric deficit. (source).
Our results suggest that an intermittent fasting program in which all calories are consumed in an 8-h window each day, in conjunction with resistance training, could improve some health-related biomarkers, decrease fat mass, and maintain muscle mass in resistance-trained males.
Intermittent fasting / time restricted feeding and lifespan
Caloric restriction (CR) extends healthspan and lifespan in multiple organisms (Colman et al., 2009,Mattison et al., 2012).
To conclude, timerestricted eating strategies are viable options for weight loss, improvement of health markers, and prevention of several neurodegenerative illnesses.
More long-term studies on humans need to be made to come to viable conclusions, which could prove some of research to be at least partially wrong.
IF and PF, as well as TRF have emerged as potential strategies for avoiding major dietary changes while achieving strong effects not just for one diseases risk factor but for an array of factors that constitutes the foundation for metabolic syndrome, cardiovascular disease, cancer, and possibly neurodegenerative diseases. (source)
However, if time restricted eating works for your life style, it is a good tool to keep your energy balance in check and possibly reap other benefits as well. As we can see in the studies presented, if you are overweight, practicing IF can improve your metabolic health. If you are lean however, you will benefit from a sustainable eating pattern with more frequent feeding pattern.
There are many fasting protocols to choose from, so it is up to your preference if you choose to change your eating schedule. There might be also differences between genders that need more research. Generally, men seem to be less prone to negative effects of fasting.
There is much more to cover
There is much more to cover like how yo break your fast or if it matters what time of day you fast and for how long or fasted training.
I will cover these topics in future articles as well as provide my experience with fasting.