Intermittent fasting is nothing new. Humans have been fasting for centuries, whether it be therapeutically, for religious reasons, or during periods of food scarcity.
But recently, it has been gaining more and more popularity, and an increasing number of people rely on intermittent fasting to manage their weight, regulate their blood sugar levels, gain muscle mass, improve their health, etc.
But is intermittent fasting actually good for you? What are its benefits? Does it have any downsides?
What is intermittent fasting?
Intermittent fasting is a practice that involves eating during specific periods of time, thus going for extended periods without eating. In most cases, food options and calories aren’t restricted, but can only be consumed within a defined time-frame.
There are many different ways to practice intermittent fasting. The most common one involves eating for a certain number of hours during the day and fasting during the rest of these hours.
The 16:8 method, meaning eating during an 8-hour window and fasting for the remaining 16 hours is the most popular version. A lot of people practice a less restrictive version of this fast naturally when they have their breakfast around 12 hours after finishing their dinner, fasting in between.
Another common way to fast is the 5:2 method, which involves eating normally 5 days of the week, and restricting your calorie intake to around 500 for 2 of those days.
Finally, some people practice intermittent fasting by eating normally for 6 days of the week, and fasting completely for an entire day. Some may choose to have more or less fasting days.
There are many more ways to practice intermittent fasting, but these are the most popular ones. They can be adapted to fit most people’s needs.
What are the benefits of intermittent fasting?
Scientific data is starting to back certain benefits of intermittent fasting.
Weight loss
Many of those who start intermittent fasting in the first place do so to lose weight. Since intermittent fasting involves eating fewer meals, and if those meals aren’t bigger to compensate, then you will end up taking in fewer calories.
A review of studies [1, 2] on intermittent fasting showed that it did lead to weight loss regardless of changes in overall caloric intake. However, these results are comparable to those achieved on calorie-restricted diets. Participants did regain some weight after they stopped intermittent fasting, but for a lot of people, this method of eating is not something they see themselves doing for a few months and then stopping like they would a diet.
The review also showed that hunger levels remained stable or even decreased during intermittent fasting compared to unrestricted calorie consumption. Both BMI and weight circumference decreased with intermittent fasting, and most of the weight loss was fat loss.
Another study [3] showed that intermittent fasting was more effective for the retention of lean mass than calorie restriction.
Ageing prevention
Studies [4, 5] have shown that rats who were only fed every other day had an increased lifespan, and that intermittent fasting could improve survival rates in mature rats. A similar study on mice [6] found that fasting mice survived longer than full-fed mice.
Cell repair
In our cells, certain waste products can accumulate and lead to neurodegeneration. Food restriction is known to induce this removal, which is referred to as autophagy. Studies [7] show that sporadic fasting might be a safe and simple way to promote the removal and recycle of these waste products. Increased autophagy may also provide protection against Alzheimer’s disease [8].
Fighting against certain diseases
Staying on the topic of Alzheimer’s disease, a study in rats showed that intermittent fasting could improve the decline in cognitive function which characterizes the disease. However, similar results were found with calorie restriction [9].
A review of studies [1] showed that intermittent fasting was a promising way to improve glycemic control. Individuals with type 2 diabetes who practiced intermittent fasting had lower fasting glucose levels and increased insulin sensitivity.
Although these are only animal studies [10, 11, 12], some promising results have been achieved with intermittent fasting as a way to slow tumor growth and reduce the incidence of certain cancers. Further human studies are needed before making any conclusions, but it is still interesting to note.
In short, intermittent fasting may improve health and counteract diseases by activating the cellular pathways that enhance mitochondrial health, DNA repair, and the removal of waste products. It also promotes cell regeneration and has long-lasting beneficial metabolic effects 13.
What are the downsides of intermittent fasting?
Even if we’ve seen that intermittent fasting has certain health benefits, there are some things to be wary of.
First of all, if you’re already struggling to meet all of your nutrient requirements, reducing the opportunity to get them in could be a little problematic. It’s pretty hard to get in your 5 servings of fruit and veggies a day if you’re only eating 2 meals in 8 hours!
Intermittent fasting may also lead to rebound overeating. This means that after depriving yourself of food during a certain time-frame, you may eat much more than originally planned once you’re “allowed” to eat again.
In regards to the impact of intermittent fasting on eating disorders, studies are mixed [14, 15, 16]. Some show that intermittent fasting was identified as a risk factor for the development of pathological eating patterns. Some individuals report negative feelings such as loss of control, a worse mood, or eating-related thoughts while fasting intermittently. Others show that it is not associated with disordered eating, and can even improve eating behaviors and mood amongst overweight and obese subjects.
Personally, the main issue I have with intermittent fasting is its disconnection from intuitive eating.
Intuitive eating and intermittent fasting
Intuitive eating is an evidence-based way of eating that promotes a healthy relationship with food. It focuses on your body’s internal hunger and fullness cues instead of outside rules and restrictions.
It’s pretty difficult to fit in intermittent fasting with intuitive eating, because intuitive eating requires listening to your body’s signals in order to meet your needs.
This is not what you’re doing when you’re fasting and are able to eat only within specific time frames. To my mind, intermittent fasting is just another way to follow food rules and to distance yourself from your body’s natural cues.
I still see it as a diet and a way to restrict your calories. This is fine if that’s what you want to do of course, but I just want people to know that it isn’t a gentle, non-diet approach to eating. This is something to keep in mind if you’re on the path to more mindful and tuned-in eating.
Now I know that some people aren’t hungry in the morning and skip breakfast, which looks a lot like intermittent fasting. However, the intention behind it is totally different. In this case, you are listening to your body’s hunger and fullness signals and honoring them— it differs from allowing yourself to eat only after reaching a certain hour.
Intermittent fasting in conclusion
While intermittent fasting does lead to weight loss, studies [17] show that it is equivalent to the one achieved with calorie restriction. The advantage of intermittent fasting may reside in its sustainability— people are more likely to stick to that rather than calorie-restrictive diets.
Regarding other health benefits, the evidence is there but isn’t strong enough to unanimously recommend intermittent fasting. There are certain downsides to be mindful of, especially its disconnection from intuitive eating.
I personally wouldn’t recommend it to people who don’t have a healthy relationship with food to begin with. As with many other things, it’s ultimately up to you to weigh the pros and cons of intermittent fasting depending on your lifestyle, your food goals, and your relationship with food.
If you’re interested in nutrition, its impact on our health, and the science behind it, you should definitely read How Not to Die. In this book, Doctor Michael Greger, founder of Nutrition Facts, examines the top causes of death in America and explains how your diet can prevent— and in some cases even reverse— them. His advice is all backed by science and he writes in a very clear and entertaining way. This book isn’t a list of what you already know. It will teach you the keys to living a long healthy life, in a simple and practical way, and without spending fortunes on supplements and pills!
PLUS if you want to take it a step further, you can check out the How Not to Die Cookbook to implement the advice easily!
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