Intermittent fasting is a dieting technique that has become more popular than dance reels on TikTok. What is it? Intermittent fasting involves periods of time where you restrict your food intake and follow it up with intermittent periods of eating.
In this intermittent fasting 101 blog post, I’ll cover the many different intermittent fasting methods. The most common one is 16:8 intermittent fasting, which means that you eat for 8 hours then fast for 16 hours.
So does intermittent fasting work? Is it going to help you to lose weight or not?! The scientific literature says…we’ll see!
In this blog post, I’ll walk you through research about intermittent fasting and its effects on weight loss to find out if it can help you too!
What is fasting?
Fun fact: you’re actually fasting without even realizing it. Each night as you sleep, you’re not eating any new foods or drinking anything so you are, in fact, fasting. And that is why our first meal – breakfast – is called that, you’re actually “breaking your fast” from the last time you ate.
Intermittent fasting is a bit more purposeful: choosing when you eat, and when you fast, in the pursuit of specific health benefits.
What is Intermittent fasting?
Intermittent fasting is an eating technique that has become popular in recent years. It involves intermittent periods of time where you restrict your food intake and follow it up with intermittent periods of eating. There are many different intermittent fasting methods, but the most common one is 16:8 intermittent fasting, which means that you eat all of your meals within eight an hour “window” and don’t eat any calories the other sixteen.
There are other fasting techniques, including fasting for religious reasons, including the Islamic holiday of Ramadan where Muslims refrain from eating or drinking from dawn until dusk (1).
Other health-focused fasting strategies include the fasting-mimicking diet or fasting with different windows than the 16:8, including eating a very low-calorie diet for 1-2 days per week or skipping all meals for 24 hours each week.
For this blog post, we’ll be focusing on the most popular intermittent fasting in the 16:8 window.
What can you eat?
Interestingly, with intermittent fasting, there don’t tend to be many rules or guidelines on what to eat. Most of the programs and research focus more on the window and let the person choose what to eat.
During the fasting period, water and other calorie-free drinks are allowed, including black coffee (no pumpkin spice lattes!), tea, and seltzer water. Some people report drinking more coffee than usual while fasting because caffeine can blunt hunger.
Why do people do Intermittent Fasting?
By and large, the most common reason that people try Intermittent Fasting is to lose weight.
But, that is not the only potential benefit of fasting. Other studies have shown intermittent fasting can enhance the body’s ability to burn fat and help regulate insulin levels.
In addition, intermittent fasting has been shown to decrease inflammation markers in the blood as well as improve brain function, which is an especially exciting benefit.
What happens when you fast?
Your body’s job is to help you survive the conditions that you’re in, even if it means that you’re eating less food than usual. Your body, and metabolism, will adjust as you make changes to your eating habits.
The main side effect of IF? Hunger! Some people drop out of studies simply because they’re hungry and don’t feel good. Can you say hangry? In general, the shorter the eating window being studied, the higher the rate of dropout.
There are changes happening at the cellular level when in a period of fasting. Fasting activates cellular stress responses in the brain, preventing neuronal damage. It has been shown that intermittent fasting can increase BDNF (brain-derived neurotrophic factor) (2).
People who do intermittent fasting are typically eating fewer calories on average throughout the week. In general, the shorter the “eating window” is, the fewer total calories the fasters will consume each day because the sense of fullness after their meal or meals increases.
Does Intermittent fasting work for weight loss?
I’ll answer your question with a question: what do you mean by “work?”
Just about any plan that limits calories will encourage weight loss, whether Intermittent Fasting or another program.
As a dietitian though, I want to ensure that the results are not temporary. Whenever I review the research on any dietary intervention, I want to consider a few things:
- How long was the study period? I.e. – were the participants fasting for a week? A month? Six-months?
- How long were the participants followed after the study?
- How long did the results “stick?”
If the study showed promising results at the end of the intervention period that only lasted for a few weeks, that isn’t actually “working.” Those changes are temporary at best.
I also want to know how the intervention impacts the person’s quality of life. If the dietary plan is a huge pain in the butt and interferes with your ability to live your life and hang out with friends and family or travel, it probably is not going to be a good long-term solution. No wine and no queso? That is a definite no-go for Caroline.
Unfortunately, despite the popularity of IF, most studies only follow their participants for a short time. In general, most IF studies follow their participants for a maximum of six months, which isn’t all that long when you think about it (3).
Weight loss highlights
Looking at a recent review article, meaning the authors are compiling the results from many different studies, fasting can lead to a weight loss of 4-10% of your body weight over a period of 4-24 weeks (4).
Many of the studies about IF compare it to a more traditional reduced-calorie diet. Oftentimes, the results show equal weight loss benefits, meaning, pick the plan that works best for you (5).
IF may have a leg up on preventing lean muscle mass, as compared to a lower-calorie diet. When studied head to head, fasting tends to have a lowered impact on lean muscle mass, which is preferred (6).
What other benefits are there?
While weight loss is one of the most common reasons people are giving intermittent fasting a try, there are a few other potential benefits of fasting.
While most of this research has been done in rats – not people – there is some evidence that fasting can improve cognition (7, 8).
Auto-what? Autophagy is your body’s natural response to tidy up and clean out old and damaged cells, kind of like inviting the Home Edit over to clean out your pantry. Fasting can turn this process up and stimulate your body to clear out the proverbial junk drawer, lowering the risk of neurological disease, infection, and malignancy (9).
When compared to a traditional lower-calorie diet, fasting may be better for getting your insulin to respond. When comparing the two, fasting has been found to improve insulin resistance (meaning, your body is able to better listen and respond to insulin) as well as lowering your blood sugar (10). This is great news to lower your risk of type 2 diabetes.
Inflammation – your body’s response to stress, injury, or infection – is a normal and natural response. But chronic inflammation – that reaction sticking around for weeks or months – is a risk factor for everything from cancer and diabetes to Alzheimer’s.
You can measure inflammation with a few different blood lab values.
Fasting has been found to reduce several markers of inflammation (11).
Who should avoid intermittent fasting?
While I am all on board for most people experimenting with which eating patterns support feeling their best and achieving their health and weight goals, I would not recommend Intermittent Fasting for everyone.
People who struggle with blood sugar regulation and/or have a history of disordered eating should always work closely with their doctor before changing up their diet. It is also a no-go for pregnant or breastfeeding mamas.
It should be noted that men and women do not always respond the same way to intermittent fasting. One study found that women had worsened blood sugar control as compared to men (12). The effect was small, but it is worth knowing that if you’re a woman, your body might respond differently to fasting than men.
In addition, Intermittent fasting may impact a woman’s normal menstrual cycle (13).
A drawback to intermittent fasting is that it’s not for everyone — some people can’t fast even one day because they get so hangry.
Worth a try?
If you’re not someone mentioned specifically in the previous section – i.e., you’re a healthy adult – you’re welcome to give intermittent fasting a try.
Interestingly, with this tool, you don’t actually have to do it every single day. Many of the research studies use IF as an intervention intermittently. That offers more flexibility for people wanting to follow the regimen and still be able to have adaptability with changes in their schedule, traveling, and so on.
It is also an eating plan with very few things to keep track of. Unlike trying to track points, calories, or servings, you just have to keep an eye on the clock. In a time where we have to make more daily decisions than ever before, we need eating plans that are simple to manage.
As a dietitian, I am always looking for ways that my clients can take that next step forward towards achieving their health goals in a way that feels good and feels sustainable. No plan is worth doing if it ends up feeling like a total drag to follow. Your diet should not take over your life.
If you do wish to try intermittent fasting, feel welcome to ease into it slowly and to give yourself permission to not do it every single day. You can gradually shorten your eating window by 15 minutes a day until you’ve reached your target. This will be a bit more gentle to your metabolism and perhaps prevent some feelings of the hangry monster.
Just keep in mind that healthy eating goals are the same, no matter what time window you’re following. Just because you’re following IF does not give you permission to ignore all fruits and veggies or to only eat junk food; quality still matters.
Key takeaways: Intermittent Fasting 101
Chances are, you’ve done intermittent fasting without even realizing it. But as someone interested in the Intermittent Fasting 101 overview, there are potential benefits of a more purposeful eating and fasting regime. While it isn’t something I’ll recommend for everyone, IF might benefit healthy adults with little risk.
There is no substitute for a generally balanced eating pattern, no matter when you eat it. Sometimes people can misuse tools, especially around food. For example, taking a multivitamin and skipping veggies: sorry charlie, there is no substitute for real and healthy food.
If you’re interested in trying IF – go for it and see how your body feels.
At the end of the day, nutrition is personal. There is no one-size-fits-all plan that works for everyone. If you’re interested in guidance to achieve your weight and health goals in a personal and sustainable way, please give me a call!