Intermittent fasting has grown increasingly popular in recent years. I’ve gotten a lot of questions about it: does it work? Is intermittent fasting good for you? How will it benefit me? Etc etc. Today, I thought
If I’m being honest, this is a post I’ve put off writing for a long time. There is still much to be learned about the topic, and I’ve shied away from putting out a post based on emerging evidence. That said, I think it’s a good exercise for me to make sense of existing literature about a topic that’s still learned about.
So, take this post with a grain of salt. This is a hot but still-emerging topic in the scientific community. As we learn more about intermittent fasting (IF)
in the coming years we can paint a more complete picture of how IF impacts human beings and their health.
For now, here’s what the science says about IF!
What is intermittent fasting?
Intermittent fasting (IF) Is a diet pattern that focuses on eating during a specific window of time each day. Some people eat only during a 12 hour window, others eat during 6 hour windows. Some people only eat 1 meal a day. There are many different interpretations of intermittent fasting and many different IF eating schedules out there.
IF focuses more on when you eat rather than what you eat. Some people, including people who don’t care for breakfast, or those who like to eat a lot at once, may enjoy this pattern of eating. Others, like those who like snacks every few hours, may not like this pattern of eating.
Is intermittent fasting for everyone?
IF is not safe for everyone. In fact, it may be dangerous for people with certain health conditions like diabetes and kidney disease. It is also not recommended for growing children and teenagers, pregnant or breastfeeding women.
People on medications that work best when taken with food may also find scheduling their medicine and meals challenging.
Additionally, IF may be triggering or unsafe for those with a present diagnosis or history of eating disorders or disordered eating.
Before you begin IF, I’d strongly advise checking with your physician or dietitian to see if it is safe for you.
What does the science say about Intermittent Fasting?
Before we dive into specifics, I’d like to point out that most of the research I was able to find on IF is animal-based research, and/or human research that takes place over a short window of time. There are few long-term human studies focused on IF, which may limit the generalizability of the studies.
Additionally, a lot of the research is based on certain eating schedules, which may not apply to other interpretations of IF or other eating schedules. Furthermore, a lot of studies I was able to find pair intermittent fasting with calorie-restricted diets, which makes it hard to parse apart whether or not results found are due to IF or the lower calorie diets and generalized weight-loss.
Intermittent fasting and weight loss:
First of all, I want to emphasize that weight loss should not necessarily be a goal for most healthy people. We live in a fat-phobic, diet-obsessed, aesthetically-driven society that normalizes disordered eating and exercise behaviors and praises weight loss as if it’s some sort of moral triumph. It is not. Many people pursue weight loss who need not lose weight, and weight loss can actually be damaging to some.
I wanted to make this point clear and emphasize that this is not a weight-loss promoting blog. This is a health-promoting blog. The two concepts are not the same thing.
But, since most people want to know about IF and weight-loss, I will report to you what I have found.
A 2020 review found that IF was successful in helping obese people lose weight, with weight loss percentages ranging form 0.8-13% of baseline weight without any adverse affects for participants. That said, the authors note that many of the studies were short in duration (2 to 26 weeks) and had low levels of participants (10 to 244). Only 2 studies included in the review were of 1-year duration and protocols varied widely.
So, it appears that yes, we know IF may help people successfully lose significant amounts of weight in the short term. My guess is that it’s less due to eating with in a certain time window, and more because people are consuming fewer calories when they have a restricted time window in which to eat.
Either way, we don’t know if the diet is sustainable or helps with long-term weight loss. Research has shown time and time again that most diets don’t work long-term to maintain weight loss, so further research is needed to know if this can be used as a long-term solution.
Intermittent Fasting and Blood Lipid Profiles:
Blood lipid profiles can tell you a lot about your health status. Things like total cholesterol, HDL and LDL cholesterol, and triglycerides can be markers of risk of heart disease and metabolic diseases. So, I reviewed some of the literature about how IF impacts blood lipid profiles.
A 2020 meta-analysis of studies that explored the effects of IF and energy restricted diet (ie, a decreased-calorie diet) found that these diets successfully lowered total cholesterol, LDL-C (“bad” cholesterol; although there is more nuance than just calling it “bad”), and triglycerides concentrations of participants.
Subgroup analyses of the study found that reductions in total cholesterol was decreased more effectively by energy restricted diets compared to IF, and that LDL-C reductions were similar between the groups.
They also found that triglyceride levels were only significantly decreased by energy-restricted diets, not IF diets, but that magnitudes of reductions were similar for both diet types. Importantly, no diets raised HDL (the “good” cholesterol which you want to be higher, not lower), which is important for overall heart health.
What does this jargon all mean? Well, what I take away from this large review is: 1) any diet that leads to weight loss in overweight individuals will improve these blood markers, and 2) energy-restricted diets may be marginally more beneficial compared to intermittent fasting.
Intermittent Fasting and Type 2 Diabetes:
A recent review of animal and human studies on the effects of intermittent fasting and management of Type 2 Diabetes (T2D) found that IF was helpful in some markers of blood glucose management in animals.
However, the same review pointed out that in human studies, any improvements were more likely a result of weight loss (which can independently help with glycemic control), and not a result of IF.
Again, for diabetes, it’s important to maintain a consistent blood sugar level within an acceptable window. While there is no one best “diabetes diet,” it’s important to manage blood sugar, and its typically recommended to do so by eating healthy and consistent meals and snacks throughout the day, and balancing carb consumption with protein and fat while adding fibrous foods.
In overweight and obese individuals with T2D, weight loss can help glycemic control, and IF could be one way for an individual to purse weight loss. But, it is not the only way to lose weight or manage your diabetes.
Of course, if you have diabetes, you should never take health advice from a blog, but rather, work with your physician and/or dietician to establish a healthy blood glucose management diet that works for you.
Intermittent Fasting and Blood Pressure:
There is some evidence to suggest that IF can help improve blood pressure. Other weight loss diets were also effective in reducing blood pressure, though IF dieters showed larger improvements.
There are several ways to go about reducing blood pressure, but in general, it’s recommended that individuals with high blood pressure consume a diet high in plant foods like fruits and vegetables, nuts and seeds, plenty of whole grains, and moderate amounts of calcium-rich foods like dairy or soy milk, and lean proteins like fish, eggs, or tofu/veggie alternatives.
Additionally, there is an emphasis on consuming lots of potassium (found in things like bananas, potatoes, kiwi, etc) and a lower amount of sodium (which may help some high-renin individuals manage blood pressure, which varies from person to person).
So, could it be a tool to help some people manage high blood pressure? Sure. But I think there’s a more substantial body of evidence behind the above mentioned recommendations, which suggest following the DASH diet to manage blood pressure. But again, whatever works best for the patient works for me!
Intermittent Fasting and Inflammation:
It has been reported that caloric restriction or alternate day fasting lead to decreased cellular oxidative damage (a marker of inflammation).
This finding is a result of the body’s switch to conserve energy, which leads to less energy utilization, and subsequent decreased production of free radicals and less cellular oxidative damage. So, it seems like yes, IF may improve some markers of chronic inflammation.
However, I think it’s worth nothing that pushing the body to switch into its energy reservation mode and being in a long-term caloric deficit (from IF or any other diet) is not always favorable. It can have negative implications, including increases in cortisol, a stress hormone, changes in metabolism, among other things.
To read more about starvation and metabolism see this post.
So, while this results may excite some, they may not be best practice for everyone. Yet another example of why diet and healthcare in general are so individualized, and why you should work with a healthcare team to establish best practice for your unique set of health conditions!
Intermittent Fasting and Cognitive Function:
One thing I hear repeatedly is that “Intermittent fasting improves cognition and helps you think clearly!” But does it?
I was able to find some research that suggests mice who are subjected to IF have some improved markers of cognitive function compared to control mice. Additionally, another mice study found that IF may protect against some inflammatory pathways that may negatively impact cognitive function.
Others have suggested that it may improve age-related cognitive decline and that it can slow neurodegeneration.
While the animal research looks promising, research about IF and cognitive function in humans is sparse. Therefore, it’s hard to make conclusions about how IF impacts cognition humans, especially in the long term, without further research. And considering the brain’s preferred source of energy is glucose, I’d wait before making any grandiose claims.
Intermittent Fasting and Reproductive Health:
One review I found suggested that IF might be helpful to women with PCOS, which is an insulin-resistance condition, likely because IF has been shown improve glycemic control in some individuals who lose weight while fasting.
However, I don’t think this is nearly enough evidence to make any sort of recommendation or claim about the topic, and much like diabetes, those with PCOS should work with a healthcare team to establish eating patterns that allow them to best control their own insulin and blood glucose levels.
Furthermore, research has shown that being in a negative energy balance (ie, when your body has run out of glucose to burn and starts relying on your body’s energy stores) is detrimental to female reproductive hormones.
Furthermore, prolonged caloric restriction of any type can cause amenorrhea (meaning loss of periods), which can not only decrease fertility, but also cause poor bone health and other unfavorable long-term health conditions.
Research on fasting for Ramadan showed no effects on sperm count in males, indicating that fasting may be beneficial or have null effect for some, but may be less than helpful to others.
Take home: Is Intermittent Fasting Good for You?
Based on current existing evidence, I wouldn’t generalize to a simple yes or no. Although some of the animal research shows some promising health effects, there is not nearly enough human research that explores long-term effects of IF for weight-loss or any other condition.
Additionally, intermittent fasting may not be sustainable for many individuals. If you have high caloric needs, are active, have diabetes, are pregnant or breastfeeding, or are recovering from an eating disorder, IF may not be the best dietary pattern for you.
Furthermore, (and this is my personal opinion so feel free to ignore it) I am wary of any diet plan or pattern that guides people away from listening to their hunger and fullness cues. Intermittent fasting may also not lend itself well to certain social aspects of life, like dining out (in a pre or post-COVID world, at least) or enjoying meals and snacks with friends and families.
For those who thrive with consistent meals and snacks, suppressing desires to eat can cause individuals to get out of touch with hunger and fullness cues, which may complicate their relationship with food long-term. IF may not be sustainable long term, and for these individuals, I wouldn’t recommend it.
That said, if someone does not feel hungry in the morning and feels best skipping breakfast, intermittent fasting may very well be the most sustainable and intuitive way for that person to eat. If you find IF to feel good for you, and you’re able to maintain healthy labs and menstrual cycles (if applicable), then I say, go for it.
Either way, intermittent fasting or not, it’s important to make sure you work with your health care team to establish sustainable dietary patterns that help you feel and perform your best. Usually, this means plenty of fruits and vegetables, legumes, nuts, seeds, whole grains and other plant foods, and a balance of protein, carbs and fats to help fuel you to live your best life.
As I always say, there are many many ways to build a healthy diet, and you do not have to subscribe to one diet regime to be healthy! Do what works for you and your current stage of life, environment, and financial situation.
If you liked “Is intermittent fasting good for you?” you may also like:
- Metabolism in Fed, Fasting and Starved States
- The Keto Diet: What Does the Science Say?
- Spilling the tea on Celery Juice Science
- What are Macronutrients? And Should I Count Them?