Intermittent Fasting 101 & Intermittent Fasting For Weight Loss Explained
Intermittent Fasting 101 & Intermittent Fasting For Weight Loss Explained
If you want to lose fat, improve metabolism, and experience other health benefits without giving up your favorite foods, intermittent fasting (IF) might be for you!
There are always emerging studies on the benefits of fasting, and the results are promising. Like calorie-reduced diets, intermittent fasting has benefits for weight loss and metabolic improvements that might improve brain and mental health.
As you know, I don't believe in a one size fits all diet approach.
However, I have found intermittent fasting to be very beneficial for some of my clients.
One of the main benefits of IF is that it helps regulate insulin. Regulating insulin helps control cravings, which makes sticking to a diet plan much more manageable for some people.
I will get into the science below, but I first want to give you a quick overview of how you can incorporate IF into your diet plan.
As always, it is important to consult a professional before making any big changes to your diet.
If you are new to fasting, I suggest you start with the 12/12 plan.
Eat between 7 am-7 pm and nothing again until 7 am the next day, 12 hours of fasting/12 hours of eating. The exact hours you choose don't matter. Change those times if it doesn't work with your schedule.
Gradually increase your fasting window if you are feeling good on the 12/12 plan. Work up to 14/10, 16/8, or even 20/4.
When I practice, IF I prefer the 16/8 window, I eat from about 11 am-7 pm and then fast for 16 hours (7 pm-11 am).
The research below will tell you that most people naturally reduce the amount of food they eat when they practice IF. This is not always true in my experience working with clients.
Why?
Some of my clients begin fasting, and fear creeps in that they won't be eating enough. Or they start to obsess that they can't have what they want when they want it (restriction), so they overeat or binge during the eating window.
This is why it is very important to have a coach available to help you through your health & weight loss journey.
You HAVE to deal with the emotions around food and your weight, or else it will be so much harder to make changes that will last long term.
Intermittent Fasting 101
Intermittent fasting (IF) has a few advantages over regular calorie-reduced diets. Not only is it easier for many people to stick with, but it also seems to have a metabolic advantage, which is beneficial when it comes to long-term health.
Intermittent fasting is just that - fasting intermittently (periodically). It's an "eating pattern," rather than a "diet."
That means regularly reducing your eating and drinking during pre-set times. It's controlling when you eat and drink, as opposed to what you eat and drink. (Though you can choose to do both.)
There are lots of ways to intermittently fast. It can be done daily, weekly, or monthly. After we go over the health benefits, we'll look at some of the most popular methods and who shouldn't, IF.
Background: History and animal studies
In the 1980s and 1990s, U.S. studies looked at the effects of reducing smoking on heart disease risk. Interestingly, the risks seemed to reduce more in members of the churches of Latter-Day Saints and Mormons than in other people. Researchers wanted to know why, and that's when they found a possible connection with fasting.
Researchers started looking beyond smoking and specifically studied people who fasted. In the early 2000s, they found that people who reported routine fasting (for religious reasons or not) had a lower risk of heart disease.
People who reported fasting had lower blood sugar levels, body-mass indices (BMIs), and diabetes risks.
The research then expanded to the effects of intermittent fasting on animals, since it is easier to restrict when and what an animal eats.
These animal studies showed a lot of health benefits of IF, including:
Longer lives
Reduced risk of atherosclerosis (narrowing of the blood vessels due to buildup of plaque)
Metabolic dysregulation (includes type 2 diabetes)
Cognitive dysfunction (ability to learn, remember, solve problems).
In simpler terms, the animals who “practiced” intermittent fasting had lower levels of inflammation and generally lived longer.
So, looks good, right? Read further to understand the specific health benefits IF can have in your life.
Intermittent Fasting for Weight Loss and Fat Loss
For people who have excess weight, losing weight and fat reduces the risk of diabetes, improves a healthy lifespan, and increases the function of both the body and mind.
Once you lose about 5-6% of your current body weight, you will start to see other areas of health falling right in line:
Lower blood lipids (LDL cholesterol and triglycerides),
Better blood sugar management (lower glucose and insulin),
Lower blood pressure
Lower levels of inflammation (C-reactive protein).
These are benefits you will see with both calorie-reduced diets and intermittent fasting, which is just one more reason why weight loss is about more than just how you look!
If you are following a typical calorie-reduced diet, you will probably be reducing your calorie intake by 15-60% for targeted fat and weight loss.
This is called "continuous" calorie reduction because one is continuously reducing what is ingested - at every meal and snack, every day. Calorie reduced diets can include eating smaller servings, low-calorie substitutions, or cutting out some snacks or desserts every day.
Please remember that there is a stopping point here. Do not continually keep lowering your calories once you have reached an appropriate amount for your weight loss goals.
If you keep decreasing your caloric intake, you will wreak havoc on your metabolism and more. Our bodies are complex and don't run like a machine, we still need a certain amount of food and calories to function at our highest level.
Now, if we look at Intermittent fasting, we can see that it is not a continuous reduction, but rather an intermittent one. This is an alternative to calorie-reduced diets. It allows you to eat what you want, but only during certain times. IF is a way to diet without really dieting.
Both continuous calorie reduction and IF can have similar weight loss results, but different methods will work better for different people.
Intermittent fasting has a few key benefits!
Many studies prove what we know already: it’s really difficult to sustain a (continuous) calorie-reduced diet for a long time.
Many studies, and my life, if not yours, too, prove what we know already: it is really difficult to sustain a continuous calorie-reduced diet for a long time.
I talk a lot about how our brains are wired to resist change, which is why a weight loss journey can be so difficult in the first place. It is only logical that trying to constantly limit and cut down our food or calorie intake is a very hard thing to do.
This is the reason why many of my clients prefer intermittent fasting. This strategy gets similar weight and fat loss results, but it can be so much easier to stick to.
This makes IF a great alternative for anyone who wants to lose weight and fat but has difficulty sticking with a reduced-calorie diet.
Other advantages to IF over calorie-reduced diets are that it can help you eat more intentionally, and less mindlessly. When you only have a specific period of time to eat, you will find yourself much more aware of the choices you make.
Also, some studies show that IF makes our metabolism more flexible so it starts to burn fat while preserving the muscles. This is a great benefit that can help improve fat to muscle body composition in people with excess weight.
Intermittent Fasting for Metabolic and Heart health
When we talk about weight loss, we know we’re talking about more than how we look. But it sometimes goes deeper than that.
Beyond seeing the number drop on the scale, IF has metabolic benefits that have been seen to help with metabolic syndrome, type 2 diabetes, and heart disease, to name a few.
Some people who practice intermittent fasting have improved insulin sensitivity and blood sugar levels. They also show improved blood lipids and even reduced inflammatory markers. All of these are related to improved metabolism and reduce the risks for many chronic diseases.
One study found that people who intermittent fasted for 6-24 weeks lost weight and also benefited from reduced blood pressure.
I mentioned above that IF can make the metabolism more flexible, helping with fat to muscle body composition, but there is a little more to that. Metabolism flexibility is very important for blood sugar control and diabetes risk.
According to one researcher, “Metabolic inflexibility is thought to be the root cause of insulin resistance” Harvie (2017).
Another study noted, “When taken together with animal studies, the medical experience with fasting, glucose regulation, and diabetes strongly suggest IF can be effective in preventing type 2 diabetes” Anton (2015).
Most researchers find these results promising and recommend more high-quality longer-term trials.
Intermittent Fasting for Brain and Mental Health
Many animal studies show that intermittent fasting can help improve their cognition (ability to think). When mice fasted on alternate days for 6-8 months, they performed better in several learning and memory tests, compared to mice that were fed daily. This improvement even happened in mice who started IF later in life.
Studies also show that alternate day fasting protects brain neurons in animal models of Alzheimer’s, Parkinson’s, and stroke, and reduces oxidative stress in the brain.
When our lifestyles include little exercise and frequent eating (three meals every day plus snacks), this leads to lowered brain function and increases the risk of major neurodegenerative and psychiatric disorders.
I don’t want to get morbid on anyone, but this is important to note because of the seriousness of weight loss in our lives.
It is never too late to change your lifestyle habits, and that is why there are strategies like IF that can significantly turn these negative outlooks around.
Researchers are still learning about the brain and mental health benefits of IF in people. Short-term studies show some people report improvement in tension, anger, and confusion from IF, while others report a bad temper and lack of concentration.
I believe this really depends on how your body responds and how you deal with cravings when you are first starting out. This is why it is so important to have consistency when you are starting out on your weight loss journey, so you can develop data on what works for you, what doesn’t, and why.
How intermittent fasting helps our bodies and brains
Intermittent fasting has a significant impact on our bodies and brains. The easiest way to explain this is the “metabolic switch” that is flipped during fasting.
While continuous calorie reduction and IF have many of the same health benefits, IF might have a different biological mechanism at play. Some research suggests that IF might “flip” a metabolic switch.
Here’s how it works.
After we eat, our bodies use carbohydrates (glucose) from our food for fuel. If there is extra leftover, then it’s stored as fat for future use.
With fasting, just as during extended exercise, our bodies flip from using glucose (and storing fat), to using that stored fat and ketones (made from fats) for fuel. Sometimes called the “G-to-K switch” (glucose-to-ketone), the ability to flip what our bodies use as fuel (between glucose and ketones) is called “metabolic flexibility.” This is similar to people who decide to use a Keto diet, it takes your body from using glucose to using ketones.
It’s thought that we, and many animals, evolved to have this ability to survive short periods of fasting from when we were hunter-gatherers.
There were times when people didn’t have a lot to eat, but they still needed to survive and think clearly enough to hunt and gather food successfully. This can explain why our bodies and brains don’t necessarily become sluggish when we’re fasting.
It makes a lot of sense, although it has yet to be tested in current-day hunter-gatherers.
This metabolic switch can explain some of the health benefits of fasting.
When our bodies prefer using fats for fuel, the body starts burning our stored fat.
This is how IF helps with overweight, obesity, metabolic syndrome, and type 2 diabetes. When the body uses fat for energy, this decreases the amount of fat in the body. Reduced-fat reduces weight, and health benefits from weight loss (like lower blood pressure and insulin resistance) are felt.
This “flipping” of the metabolic “switch” happens after the available glucose, and the stored glucose is depleted.
This can happen anywhere from 12-36 hours from the last meal, depending on the person. At this point, the fats in our cells start getting released into the blood and are metabolized into ketones. These ketones then go to fuel cells with “high metabolic activity,” which are muscle cells and neurons.
Since the body is burning fat and using ketones to fuel the muscles, the practice of IF is basically preserving muscle mass. Some studies of IF show that it preserves more muscle mass than regular calorie-reduced diets do.
The other high metabolic activity cells fueled by ketones are neurons. Neurons are found in the brain and nervous system.
Intermittent fasting helps our brains because when our neurons start using ketones for fuel, it preserves brain function and increases brain-derived neurotrophic factor (BDNF) which is very important for learning, memory, and mood.
BDNF also helps enhance synaptic plasticity (changes in our brain that help with learning and memory) and allows our neurons to resist stress better.
These are all improvements in brain function, and some animal studies also show improvements in the structure of the brain too. For example, new neurons are produced in the hippocampus (the part of the brain important for short- and long-term memory) in animals who practiced intermittent fasting.
According to a study on the metabolic switch, researchers found that “events triggered by the metabolic switch may play major roles in the optimization of the performance of the brain and body by IF” (Anton, 2018).
Who shouldn’t try intermittent fasting?
Before you try any major changes to your diet, check with your healthcare provider.
Intermittent fasting can provide a lot of health benefits, and according to researchers Patterson & Sears, “Overall, evidence suggests that intermittent fasting regimens are not harmful physically or mentally (i.e. in terms of mood) in healthy, normal weight, overweight, or obese adults (2017).”
However, there are a few things to keep in mind before considering intermittent fasting.
Several adverse effects have been reported, including bad temper, low mood, lack of concentration, feeling cold, nausea, vomiting, constipation, swelling, hair loss, muscle weakness, uric acid in the blood and reduced kidney function, menstrual irregularities, abnormal liver function tests, headaches, fainting, weakness, dehydration, mild metabolic acidosis, preoccupation with food, erratic eating patterns, binging, and hunger pangs.
If done too often or for too many days, IF can have more serious effects.
Fasting for several weeks (about 5-7 weeks) becomes starvation even in healthy adults. At this point, your body starts consuming muscles and vital organs. This can also lead to excessive weight loss, anemia, chronic diarrhea, delirium, lactic acidosis, small bowel obstruction, kidney failure, heart arrhythmias, and, eventually, death.
Excessive fasting can lead to malnutrition (including vitamin B1 deficiency), decreased bone density, eating disorders, susceptibility to infectious diseases, or moderate damage to organs.
Limit fasting to avoid these effects, and make sure you are working with someone who is able to offer advice and coaching when necessary.
We don’t have to go at this alone, and there are resources out there for anyone looking to start their weight loss journey.
How to Intermittently Fast
There are lots of ways to intermittently fast, and we don’t yet know how these different methods have different health effects for different people with different health goals.
Here are some different ways to use intermittent fasting:
Alternate-day fasting (ADF) - One day of fasting, one day of “feasting.” Continue fasting on alternate days.
Alternate-day modified fasting (ADMF) - Eat 25-40% of your daily needs one day, then eat normally the next. Continue alternating days.
Periodic fasting (PF) or “Two day” fasting - Each week has 1 or 2 days to eat very few calories per day (e.g. 0-880 cal/day). The other 5 days you eat normally. Example: 5:2 diet, where you eat no more than 500 calories/day for two non-consecutive days each week.
Time-restricted fasting (TRF) - Fast for 12-16 hours every day and eat normally during the other 8-12 hours.
One 24-hour period of fasting each month
Several researchers suggest that alternate-day modified fasting is preferable because it is likely the easiest to follow and may cause the least amount of stress on the body and mind.
When it comes to preserving muscle mass, there is no definitive research on intermittent fasting, but it is a good idea to eat enough protein (1.2 g protein/kg weight), and exercise, preferably with resistance training.
You may be wondering if fasting intermittently increases what you eat during those times when you do eat.
The interesting thing is, it usually seems not to. Studies show that alternate-day fasting reduces overall calorie intake. Plus, on the non-restricted days, some people naturally reduce their energy intake by up to 20-30%.
But, if you find you are actually eating more or binging during your eating periods, this would be a good time to keep a journal and track both what you are eating, and your feelings when you decide to eat at an increased level.
I have had some clients experience this, and it turned out there were unprocessed emotions associated with eating that we were able to uncover together.
That is why I work on a holistic level with my clients, where one size does not fit all, even within the same diet plan.
Eventually, you will be able to manage your food decisions, and a bonus benefit of IF is that it can help reduce food costs, too!
Remember during this journey that reducing your food intake also reduces your nutrient intake, so make sure that the food you are eating still gives you enough essential nutrients for long-term health.
Conclusion
Intermittent fasting is a way to get the benefits of a regular calorie-reduced diet without restricting what you eat, only when you eat it. Intermittent fasting reduces both weight and fat and can improve blood sugar and blood lipids levels.
It has been shown to lower blood pressure and some markers of inflammation. Many animal studies show improvements in brain health, too.
While these benefits of IF are similar to those with a calorie-reduced diet, IF has some key advantages.
It can be easier for some people to stick with, and it might help people eat more intentionally.
There is also evidence that IF may help our bodies come more metabolically flexible by preferentially reducing fat while preserving muscle.
More research is needed to fully understand the long-term benefits of IF on the body and brain, as well as which IF approach is optimal for different people and different health goals.
Have you tried intermittent fasting? Does it sound like something you would like to try? I would love to hear other opinions! Leave your thoughts in the comments below.
And as always, if you need help reaching your health and weight loss goals, I am here for you!
Let’s dive deep into what’s been holding you back from living your best life, and find the success you are meant to have. Get in touch!
Sarah Failla
References:
Anton, S. D., Moehl, K., Donahoo, W. T., Marosi, K., Lee, S., Mainous, A. G., … Mattson, M. P. (2018). Flipping the Metabolic Switch: Understanding and Applying Health Benefits of Fasting. Obesity (Silver Spring, Md.), 26(2), 254–268. http://doi.org/10.1002/oby.22065
LINK: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5783752/
Antoni, R., Johnston, K.L., Collins, A.L. & Robertson, M.D. (2016). Investigation into the acute effects of total and partial energy restriction on postprandial metabolism among overweight/obese participants. Br J Nutr, 115(6), 951-9. doi: 10.1017/S0007114515005346.
Brandhorst, S., Choi, I. Y., Wei, M., Cheng, C. W., Sedrakyan, S., Navarrete, G., … Longo, V. D. (2015). A periodic diet that mimics fasting promotes multi-system regeneration, enhanced cognitive performance and healthspan. Cell Metabolism, 22(1), 86–99. http://doi.org/10.1016/j.cmet.2015.05.012
LINK: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4509734/
Carter, S., Clifton, P.M. & Keogh, J.B. (2016). The effects of intermittent compared to continuous energy restriction on glycaemic control in type 2 diabetes; a pragmatic pilot trial. Diabetes Res Clin Pract, 122, 106-112. doi: 10.1016/j.diabres.2016.10.010.
LINK: https://www.ncbi.nlm.nih.gov/pubmed/27833048
Clifton, P. (2017). Assessing the evidence for weight loss strategies in people with and without type 2 diabetes. World Journal of Diabetes, 8(10), 440–454. http://doi.org/10.4239/wjd.v8.i10.440
LINK: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5648990/
Fontana, L., & Partridge, L. (2015). Promoting Health and Longevity through Diet: from Model Organisms to Humans. Cell, 161(1), 106–118. http://doi.org/10.1016/j.cell.2015.02.020
LINK: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4547605/
Harvie, M., & Howell, A. (2017). Potential Benefits and Harms of Intermittent Energy Restriction and Intermittent Fasting Amongst Obese, Overweight and Normal Weight Subjects—A Narrative Review of Human and Animal Evidence. Behavioral Sciences, 7(1), 4. http://doi.org/10.3390/bs7010004
LINK: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5371748/
Headland, M., Clifton, P. M., Carter, S., & Keogh, J. B. (2016). Weight-Loss Outcomes: A Systematic Review and Meta-Analysis of Intermittent Energy Restriction Trials Lasting a Minimum of 6 Months. Nutrients, 8(6), 354. http://doi.org/10.3390/nu8060354
LINK: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4924195/
Horne, B.D., Muhlestein, J.B., Lappé, D.L., May, H.T., Carlquist, J.F., Galenko, O., Brunisholz, K.D. & Anderson, J.L. (2013). Randomized cross-over trial of short-term water-only fasting: metabolic and cardiovascular consequences. Nutr Metab Cardiovasc Dis, 23, 1050–7.
LINK: https://www.ncbi.nlm.nih.gov/pubmed/23220077
Horne, B.D., Muhlestein, J.B., & Anderson, J.L. (2015). Health effects of intermittent fasting: hormesis or harm? A systematic review. Am J Clin Nutr, 102(2), 464-70. doi: 10.3945/ajcn.115.109553.
LINK: https://academic.oup.com/ajcn/article/102/2/464/4564588
Hussin, N.M., Shahar, S., Teng, N.I.M.F., Ngah, W.Z.W. & Das, S.K. Efficacy of fasting and calorie restriction (FCR) on mood and depression among ageing men. J Nutr Health Aging, 17, 674–80.
LINK: https://www.ncbi.nlm.nih.gov/pubmed/24097021
Keogh, J.B., Pedersen, E., Petersen, K.S. & Clifton, P.M. (2014). Effects of intermittent compared to continuous energy restriction on short-term weight loss and long-term weight loss maintenance. Clin Obes, 4(3), 150-6. doi: 10.1111/cob.12052.
LINK: https://www.ncbi.nlm.nih.gov/pubmed/25826770
Li, L., Wang, Z., & Zuo, Z. (2013). Chronic Intermittent Fasting Improves Cognitive Functions and Brain Structures in Mice. PLoS ONE, 8(6), e66069. http://doi.org/10.1371/journal.pone.0066069
LINK: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3670843/
Mattson, M. P., Moehl, K., Ghena, N., Schmaedick, M., & Cheng, A. (2018). Intermittent metabolic switching, neuroplasticity and brain health. Nature Reviews. Neuroscience, 19(2), 63–80. http://doi.org/10.1038/nrn.2017.156
LINK: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5913738/
Michalsen, A. & Li, C. (2013). Fasting therapy for treating and preventing disease - current state of evidence. Forsch Komplementmed, 20(6), 444-53. doi: 10.1159/000357765.
LINK: https://www.ncbi.nlm.nih.gov/pubmed/24434759
Patterson, R.E. & Sears, D.D. (2017). Metabolic Effects of Intermittent Fasting. Annu Rev Nutr, 37, 371-393. doi: 10.1146/annurev-nutr-071816-064634.
LINK: https://www.annualreviews.org/doi/full/10.1146/annurev-nutr-071816-064634
St-Onge, M.P., Ard, J., Baskin, M.L., Chiuve, S.E., Johnson, H.M., Kris-Etherton, P. & Varady, K.; American Heart Association Obesity Committee of the Council on Lifestyle and Cardiometabolic Health; Council on Cardiovascular Disease in the Young; Council on Clinical Cardiology; and Stroke Council. (2017). Meal Timing and Frequency: Implications for Cardiovascular Disease Prevention: A Scientific Statement From the American Heart Association. Circulation,135(9), e96-e121. doi: 10.1161/CIR.0000000000000476.
LINK: http://circ.ahajournals.org/content/135/9/e96.long
Stockman, M.C., Thomas, D., Burke, J. & Apovian CM. (2018). Intermittent Fasting: Is the Wait Worth the Weight? Curr Obes Rep, 7(2), 172-185. doi: 10.1007/s13679-018-0308-9.
LINK: https://link.springer.com/article/10.1007%2Fs13679-018-0308-9
Teng, N.I., Shahar, S., Manaf, Z.A., Das, S.K., Taha, C.S. & Ngah, W.Z. (2011). Efficacy of fasting calorie restriction on quality of life among aging men. Physiol Behav, 104, 1059–64. LINK: https://www.ncbi.nlm.nih.gov/pubmed/21781980
Teng, N.I., Shahar, S., Rajab, N.F., Manaf, Z.A., Johari, M.H. & Ngah, W.Z.W. (2015). Improvement of metabolic parameters in healthy older adult men following a fasting calorie restriction intervention. Aging Male, 16, 177–83.
LINK: https://www.ncbi.nlm.nih.gov/pubmed/24044618
Tinsley, G.M. & La Bounty, P.M. (2015). Effects of intermittent fasting on body composition and clinical health markers in humans. Nutr Rev, 73(10), 661-74. doi: 10.1093/nutrit/nuv041.
LINK: https://www.ncbi.nlm.nih.gov/pubmed/26374764
Varady, K.A., Bhutani, S., Klempel, M.C., Kroeger, C.M., Trepanowski, J.F., Haus, J.M., Hoddy, K.K. & Calvo, Y. (2013). Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial. Nutr J, 12, 146.
LINK: https://www.ncbi.nlm.nih.gov/pubmed/24215592
Witte, A. V., Fobker, M., Gellner, R., Knecht, S., & Flöel, A. (2009). Caloric restriction improves memory in elderly humans. Proceedings of the National Academy of Sciences of the United States of America, 106(4), 1255–1260. http://doi.org/10.1073/pnas.0808587106
LINK: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2633586/