Intermittent Fasting
Let’s break down a topic that is quite controversial and that we get asked about a LOT….
Intermittent fasting (IF)!
In this blog, we will cover:
– What is intermittent fasting
– Potential benefits of intermittent fasting
– How intermittent fasting may affect hormones
– Who should NOT use intermittent fasting
First things first…
What is intermittent fasting?!
Intermittent fasting is simply the process of delaying eating. It is important to note that there is no single “best method”, it truly depends on what works best for you! Some examples of common fasting approaches are:
12/12 Approach– This is where you fast for 12 hours, then eat for 12 hours. For example, fasting from 8 pm until 8 am. This approach naturally mimics sleep and wake cycles and is a great starting point if you are wanting to try IF.
16/8 Approach – You fast for 16 hours, eat for 8 hours. If you are interested to try the 16/8 fasting window we recommend 10am – 6pm as it can be more beneficial from a metabolic health and circadian rhythm perspective. However, the “best time” is always the one you are able to ADHERE to and enjoy the most in your individual and unique life.
1/6 Approach– You fast for 24 hours and eat normally the other six days. This is common amongst religious practices, for example, fasting from 6pm until 6pm the next day.
Although these are common examples, it truly is not about eating within a “strict fasting window”. Instead, you can simply start by delaying your first meal and eating when you are hungry and stopping eating after dinner.
What are some of the potential benefits from intermittent fasting?
Let’s Dive into these in more depth!
Fasting might improve Cell Function and Cellular Health (4)
There is research that fasting might slow down cellular senescence. When our cells senescence, they stop growing and repairing, they release inflammatory markers, and they do not perform the natural process of apoptosis, which is scheduled cell death. So, basically, as we age our senescent cells accumulate and cause inflammation and wear and tear on our bodies. IF has been shown to increase autophagy, which is the process of removing cells that are no longer serving us (like senescent cells). However, it is important to note that both IF and general energy restriction (like that created from a calorie deficit without IF) increase autophagy. So, while IF is beneficial in helping our cells function, it does appear that many of these benefits are from energy restriction.
2. Fasting might Improve Insulin Sensitivity (1, 2, 6, 7)
There is research supporting that insulin sensitivity may be improved by doing IF, with the improvement to insulin sensitivity being documented to a greater extent when used with individuals who would be classified as overweight or obese. However, there may be a benefit to fasting for insulin sensitivity for non-obese individuals, specifically for men. A study by Heilbronn et. Al (2005) tested eight men and eight women, all non-obese, who were instructed to fast on alternate days for a period of three weeks. After the three weeks, men had improved insulin sensitivity, and their glucose response was unchanged. The women, however, showed no change in insulin response, but their glucose tolerance was slightly worse than it was than before the experiment started. Sex differences between IF will be discussed more later on, but it is important to identify that the benefits of improving insulin sensitivity appear to be more prominent for men who use IF, especially if the individual trying IF is non-obese.
3. Intermittent Fasting Might Reduce the Risk of Cancer (6,9)
Cancer is essentially unregulated, uncontrolled growth, and thus, similar to above with cellular health, fasting might impede the development of cancer by dampening cellular growth, reducing supply of nutrients and energy to cancer cells, and increasing cellular repair and cleanup (by process described in benefit #1). Fasting alone has not been shown to prevent or cure cancer, but it may be a beneficial adjunct to treatment.
4. Intermittent Fasting Might Improve Heart Health (1,2,8)
A test of c-reactive protein (CRP) is commonly used to measure inflammation, which is a risk for heart disease. Research suggests that fasting may decrease blood serum levels of c-reactive protein, thus inflammation, therefore being protective to heart health.
In addition, IF has been shown to increase blood lipid profile by lowering total cholesterol, triglycerides and low-density lipoprotein (LDL) while increasing High-density lipoprotein (the good cholesterol). HOWEVER, this affect mostly appears to be tied to a reduction in bodyweight. In healthy individuals who are a healthy bodyweight, IF has little impact on cholesterol and CRP markers.
5. Intermittent Fasting Might Aid Fat Loss (1,6)
Naturally, if you are eating during a smaller window of time, it is likely that you will consume less calories. Because you are consuming less calories, you are in a negative energy balance, which supports fat loss! If reducing your eating window helps you adhere to a calorie deficit easier, then IF is a great tool to use during a fat loss phase!
Let’s dive into point #5
How can IF help with fat loss?
IF might help with cravings! (6)
If we are no longer having small snacks throughout the day and instead having larger, more satisfying meals, cravings might be more controlled during a fat loss phase.
IF will teach you more about your hunger (6)
When you are doing IF, you become more in-tune with hunger and fullness cues as you begin to sense what it actually feels like to be hungry! This awareness can be very beneficial as it will serve you in the future, for example, if you are questioning “am I hungry or just bored?”.
IF may help with calorie control (6)
As previously stated, when eating during a smaller time frame calories may naturally be lowered due to a decrease in meal frequency. Therefore, IF may be a beneficial tool for fat loss if someone does not want to use other methods of creating a calorie deficit, such as macro tracking. It can also be a useful tool in addition to macro or calorie tracking by helping with hunger regulation during a calorie deficit.
With their being so many potential benefits, you might be wondering why we said IF was controversial. So, let’s dive into why this is!
What are the downsides of Intermittent fasting!?
IF may negatively impact your relationship with food (6)
This is a BIG one. With intermittent fasting we are delaying our eating window, which may lead to a “build up” of excitement and anticipation for when it is “time to eat”. Because of this, IF has been associated with increasing over-eating. Moreover, as intermittent fasting does often lead to calorie restriction it may lead to increases of ghrelin (our hunger hormone), and decreases in leptin (our fullness hormone) if used for prolonged periods of time. Because of this, it is possible that due to these hormonal changes and the “build up” of excitement for your eating window, you may be promoting a “binge and restrict cycle”.
IF may not align with intuitive eating
Part of IF is delaying your first meal, or only eating during a specific time window. As previously stated, learning about true hunger is a benefit of IF, however, if we ignore these hunger signals because it is “not time to eat”, we are not following one of the principles of intuitive eating – honoring your hunger.
2. IF may decrease athletic performance (6)
IF has been shown to create a decrease in performance in these specific areas:
– activities that require intense effort (such as 200-400 meter runs)
– speed endurance, such as repeated short, intense runs in soccer
– repeated power-explosive movements like jumping
– some types of strength and work capacity
It is possible that with prolonged use of intermittent fasting your body may adapt to your fasting window and you may not notice a reduction in your performance, however, it is likely that initially you will. We recommend that if you train fasted that you consume a larger meal the night before that is high in carbohydrates, protein, and fat, and that you break your fast following working out by having a meal with moderate protein and carbs with little fat (example 2 rice cakes and a protein shake) to begin the recovery/muscle repair process.
4. IF may impact hormones (6,7,10)
Hormones that regulate key functions like ovulation, metabolism, and mood are sensitive to energy intake and energy timing. Changing how much you eat and when you eat can negatively impact your reproductive hormones for both men and woman, however, it does appear woman are more sensitive to these effects.
Let’s dive deeper into intermittent fasting and hormones!
Under-eating in any form, whether by intermittent fasting or another form of calorie restriction for prolonged periods of time will affect hormones (6,7). If you want to learn more about energy balance, and what we mean by calorie restriction, please read our energy balance blog here:. Link to Energy Balance Blog
However, timing of nutrients does also seem to have an impact on hormones, and that is why IF may have a particular negative effect on hormones for some people (6,7).
Fasting affects hormones in both men and women by influencing our hypothalamic-pituitary-gonadal axis, or in other words, our HPG axis (5,6,7). Our hypothalamus releases gonadotropin releasing hormone (GnRH) in regular pulses, which tells our pituitary gland to release luteinizing hormone (LH) and follicular stimulating hormone (FSH). LH and FSH then act on the gonads (5,6,7).
In women, LH and FSH stimulate estrogen and progesterone, which needs to happen to allow for ovulation and all of the benefits from ovulating, as well as the potential for a pregnancy (5,7). In men, LH and FSH stimulate the production of testosterone and sperm (6). The GnRH pulses that create this cascade of hormone production and release appear to be very sensitive to environmental factors, including nutrient timing (5,6,7). Therefore, in addition to things like stress, fasting can throw off these hormonal pulses and may lead to negative hormonal changes. Long-term stressors and use of IF are more likely to have an impact on hormonal changes, with some research suggesting that even delaying even a single meal can impact the hormonal system (5).
Men Vs. Woman
It does appear women are more sensitive to hormonal changes from environmental factors, including IF, and this is believed to be due to the protein like molecule kisspeptin (6,7). Kisspeptin is a molecule that is needed to stimulate the production of GnRH, and women actually have MORE kisspeptin then men! When we fast, it lowers kisspeptin, which can lead to a decrease of production in GnRH, which in turn lowers production of LH and FSH creating a negative menstrual cycle and over all hormonal health ramifications (6,7).
Important caveat…
Woman with polycystic ovarian syndrome (PCOS) have higher levels of kisspeptin than woman without PCOS (10). Therefore, research supports that when women with PCOS do IF their levels of kisspeptin can lower to normal levels, which may actually improve reproductive function (10).
As you can see, there is no “one size fits all” answer to whether or not IF will work for you. What we recommend is that you assess how IF makes YOU feel. If your goal is fat loss, it does appear IF may be a better protocol for men, as research does suggest that for most women, IF is not the best weight loss protocol (6,7).
If you are curious about doing IF, we recommend you can try IF only if (6,7):
Your stress is low.
You’re getting quality sleep.
You’re not tormented by hot flashes and mood swings (for woman during menopause)
You don’t have any nutrient deficiencies.
We do NOT recommend doing Intermittent fasting if you meet any of the following criteria (6,7):
you’re pregnant
you have a history of disordered eating
you’re chronically stressed
you don’t sleep well
you’re new to diet and exercise
If you do begin trying IF, pay attention to how you feel, and remember, a little fasting goes a long way! Starting with the 12/12 approach outlined at the beginning is a great place to start!
If you are noticing positive improvements from IF and none of the potential negative downsides, feel free to continue. However, we would recommend stopping IF if you experience any of these signs:
Signs to STOP Intermittent fasting (6,7):
your menstrual cycle stops or becomes irregular
you have problems falling asleep or staying asleep
your hair starts falling out more than usual
you start to develop dry skin or acne
you’re noticing you don’t recover from workouts as easily
your injuries are slow to heal, or you get every bug going around
your tolerance to stress decreases
your moods start swinging
your heart starts going pitter-patter in a weird way
your interest in romance fizzles (and your lady parts stop appreciating it when it happens
your digestion slows down noticeably
you always seem to feel cold
In summary…
IF is a tool that can be used to improve blood sugar regulation, improve cellular health, and manage weight and improve cardiac blood markers through weight loss. It is important to remember that a little goes a long way, and how you feel matters most! Intermittent fasting is NOT magical, with many of the benefits from IF being tied to achieving fat loss and being a healthy bodyweight (6,7). IF is simply one tool to help you do this! As previously stated, it does appear that women are more sensitive to the negative downsides of fasting in comparison to men, so for many women this may not be the best protocol, especially if your goal is fat loss (6,7).
If you are unsure if IF is a good tool for you, please assess whether you meet the criteria for trying IF, and if you do, continue to assess regularly how you are feeling, including how your relationship with food is.
If you would like to learn more about nutrition, or nutritional tools to help you hit your goals, please use this link to book a free consultation call so we can talk about your unique needs and goals.
The big takeaway we want you to have from this blog is that YOU are unique, and this needs to be accounted for when using any nutritional tools, with IF simply being one of many techniques you can use to help you hit your goals! We hope you found this information helpful to you in your own journey.
All the love,
Robyn & Megan , YQL Nutrition
References:
Antoni R, Johnston KL, Collins AL, Robertson MD. Intermittent v. continuous energy restriction: differential effects on postprandial glucose and lipid metabolism following matched weight loss in overweight/obese participants. Br J Nutr. 2018;119: 507–516.
Antoni R, Johnston KL, Collins AL, Robertson MD. Effects of intermittent fasting on glucose and lipid metabolism. Proc Nutr Soc. 2017;76: 361–368.
Anton SD, Moehl K, Donahoo WT, Marosi K, Lee SA, Mainous AG 3rd, et al. Flipping the metabolic switch: Understanding and applying the health benefits of fasting. Obesity. Wiley Online Library; 2018;26: 254–268.
Heilbronn LK, Civitarese AE, Bogacka I, Smith SR, Hulver M, Ravussin E. Glucose tolerance and skeletal muscle gene expression in response to alternate day fasting. Obes Res. 2005 Mar;13(3):574–81. Available from: http://dx.doi.org/10.1038/oby.2005.61
Hill JW, Elmquist JK, Elias CF. Hypothalamic pathways linking energy balance and reproduction. Am J Physiol Endocrinol Metab. 2008 May;294(5):E827-32.-single meal study
Precision Nutrition, (2022). Does intermittent fasting work for women? Retrieved from:https://www.precisionnutrition.com/intermittent-fasting-women
Precision Nutrition, (2022). Everything about intermittent fasting. Retrieved from:https://www.precisionnutrition.com/intermittent-fasting
St-Onge M-P, Ard J, Baskin ML, Chiuve SE, Johnson HM, Kris-Etherton P, et al. Meal timing and frequency: Implications for cardiovascular disease prevention: A scientific statement from the American Heart Association. Circulation. 2017;135: e96–e121.
Thompson HJ, McTiernan A. Weight cycling and cancer: weighing the evidence of intermittent caloric restriction and cancer risk. Cancer Prev Res. 2011;4: 1736–1742.
Wahab F, Atika B, Ullah F, Shahab M, Behr R. Metabolic Impact on the Hypothalamic Kisspeptin-Kiss1r Signaling Pathway. Front Endocrinol. 2018 Mar 28;9:123. Available from: http://dx.doi.org/10.3389/fendo.2018.00123
