We live in a fast-paced and stressful world, where we are constantly surrounded by the promise and temptation of food. Is it any wonder that people eat so much and so often, typically without thinking about it?
After all, food is available almost everywhere you go, including fast food, grocery stores and snacks that are readily available. We have become so conditioned to eating frequently that many people don’t know any other eating pattern.
In fact, people often think that being hungry at all is a bad thing and will eat as soon as they feel hungry, regardless of when they last ate or what they have eaten that day.
However, this isn’t always good practice, and one of the ways of improving eating habits is an approach called intermittent fasting.
In this article, I want to address the question of, does intermittent fasting work, and I want to do this by considering facts and research, not just theories. After all, there are literally thousands of different pieces of eating advice available online, in books and in the media, many of these contradict one another.
This makes it very difficult to know what to believe, which is why I personally say, start with the facts and the research, and move on from there.
Modern Eating Patterns
How much attention do you really pay to what, and when, you eat?
Society is fast-paced and many people find that it is a struggle to find the time to do everything they need to do, much less all the things they want to do.
Because of this, people look for easy solutions wherever they can, particularly when it comes to food.
How many times have you had fast food for dinner because it was simply too much work to cook a meal? What about grabbing a quick snack from whatever store is nearby?
These practices tend to be common and people often find that the unhealthy, heavily processed, calorie-rich foods are the easiest to access.
To make matters worse, families and individuals are moving away from eating at traditional meal times, instead choosing to eat when the opportunity presents itself, which often promotes poor food choices. At the same time, people tend to be too busy to engage in physical activity.
All of these factors strongly contribute to the development of obesity (1) and are likely to be a significant reason for why obesity is so prevalent among Western populations.
As a result, we need to develop and fine tune our eating patterns around the amount of energy we use each day, rather than how often we want to eat, or how readily available food is.
One of the approaches people often take is eating small meals frequently, an idea that has been promoted as a way to lose weight for quite some time. The problem is, this approach is nothing but myth and hype.
Realistically, eating many small meals in a day does nothing for weight loss and may even promote weight gain for some people. I’ll discuss why this is later in the article.
The other extreme is intermittent fasting, which is the focus of this article. But, what is intermittent fasting?
Modern society is fast-paced, with people often not making good decisions about what and when they eat.
Intermittent Fasting 101
At the most basic, intermittent fasting (or IF) is what the name suggests – you’re fasting some of the time. This places emphasis on when you eat, rather than the specific foods you choose.
There are multiple variations of the diet and people also make adjustments to their own needs.
You can find more details on these in my Understanding Intermittent Fasting guide. But, the general approaches can be broken down as follows:
- 16/8 Intermittent Fasting. This is also simply called the 16:8 or the Leangains technique and is probably the easiest to achieve. This version involves fasting for 16 hours each day and eating within an 8-hour window. I’ve also seen 18:6 or 22:10, so you can vary based on what works for you.
- Alternative Day Fasting. This version of IF is studied the most often but is probably the hardest to actually do. Basically, you’re doing a full fast on alternate days every week. In many cases, people choose the same days each week, so they may fast Monday, Wednesday and Friday, while they eat normally on other days.
- Weekly or Monthly Fasting. Another option is to simply fast periodically. This could be once a week or a few times per month, depending on what works for you.
- Longer Fasts. Some people also fast for longer periods, such as 48 hours or more. In these cases, you might have some calories to keep your body going. Fasting like this does still have some benefits but you need to be careful that you’re not causing yourself harm.
In most cases, intermittent fasting is a full fast, so you’re not consuming any calories over that period. Doing so seems difficult and counterintuitive but it is surprisingly effective. In fact, there are even biological advantages to fasting, ones that you don’t get by eating regularly.
For the alternative day and the weekly/monthly versions, people are typically fasting for 24 hours at a time. A common way is to start at noon one day and go to noon the next, which means you still get at least one meal each day.
Some people do also choose an extremely low calorie intake on the fasting days (like 500 calories), rather than a complete fast.
Doing so may reduce some of the benefits, especially as you aren’t technically fasting. Still, the idea can make fasting more achievable for some people.
At first glance, the idea of intermittent fasting seems horrible, even in the 16:8 form. Yet, many people find it effective. For example, I have a friend who lost close to 80 lbs on intermittent fasting when other approaches have failed.
For one thing, the idea helps to break many unhealthy eating patterns and create a better relationship with food. It also decreases how many calories you consume and can make snacking less likely.
Intermittent fasting comes in multiple forms and can seem difficult - but the process is achievable
Intermittent Fasting: Fat Loss or Fat Gain?
Intermittent fasting is a concept that has been under a lot of debate.
Basically, there are two schools of thought.
One group of people believes that you should eat small meals and eat frequently, an approach that is sometimes known as grazing. The idea is that doing this will stop your body from going into starvation mode, will keep your metabolism working effectively and may also help you to keep to your diet.
In theory, this idea sounds wonderful, and it does work for some people. However, for many others, eating frequently is not a good approach for staying healthy or for losing weight.
The thing is, the human body wasn’t built to consume food that regularly. Regardless of whether you believe we were created or we evolved, the human blueprint is still focused on an environment where food was scarce and people would often go long periods of time without food.
The myth of grazing goes back to the 1980s, and many people continue to believe that this is most effective way to lose weight. While grazing might be a fashionable way to eat, the science backing this approach up is simply not there.
Furthermore, people are told that eating regularly is important for keeping energy levels up, but all that happens is that people increase their intake of calorie-laden snacks and unhealthy foods.
This isn’t a good approach for long-term weight loss, and the thing is, your liver is actually able to compensate for much of the energy that comes from eating infrequently.
Some studies suggest that grazing may be a high-risk behavior and may contribute to weight gain (2).
This isn’t really surprising because it is very easy to eat too much when you are consuming many meals within a given day. Grazing can also make it harder to keep track of what you’re eating, which can contribute to a loss of control (3).
Conversely, if you are only eating a few meals a day, it is harder to eat too much – although you do still have to watch how much you consume in a given meal. The same is true for extended fasts.
Indeed, one study found that the only effect that eating many meals a day has is to make people feel hungrier, contributing to an increased desire to eat (4). That outcome is the opposite to what many people assume about grazing. The site The 10 Principles offers more details about how the grazing approach can be counterproductive.
In contrast, decreasing how often you eat in a day often lowers your calorie intake. After all, there are fewer opportunities to eat. Many people also find that they feel full faster when following intermittent fasting, which reduces the risk of overeating.
Now, we have been taught that hunger is a bad thing, but is it really?
From a weight loss perspective, hunger may be an indication that the weight loss is actually being effective. After all, your body is going to think it needs food before it wants to burn fat because burning fat is supposed to be the last option.
Just because you have an increased desire to eat when you first start eating fewer meals a day, doesn’t mean that it will stay this way.
Realistically eating less often is just like any habit – it gets easier over time.
In fact, one study found that participants tended to feel fuller after three meals a day compared to six, when the total amount of calories per day was the same (5).
Studies have consistently shown that eating small meals frequently has no effect on weight loss (6,7). There has even been some research that indicates that eating a higher number of meals in a day can result in an increased risk of colon cancer (8,9).
All of these factors suggest that eating small meals frequently is an ineffective tool for losing weight while intermittent fasting may be a more powerful approach for weight loss and for overall health.
Additionally, if you have trouble sticking to a diet because you always feel hungry, eating frequently may well make that worse rather than better. With intermittent fasting, you can also reduce the hunger issue somewhat by relying on options that help you to feel full, such as high protein foods.
Eating many meals throughout the day is ineffective for weight loss. In contrast, there are key health and weight loss benefits to being hungry some of the time
Metabolism and Eating Frequency
The concept is, eating many small meals boosts your metabolic rate, which results in improved weight loss.
That’s only part of the story. Whenever you eat, your metabolism does increase a little bit. This happens because your body needs to use a certain amount of energy to break down food.
The more calories you are eating, the bigger the spike of metabolism, because bigger meals require more energy. When you eat a few big meals in a day, your metabolism naturally spikes at that time, and gradually declines throughout the day.
Alternatively, if you eat many small meals, your metabolism does not peak as high and decreases faster. This is not a better outcome.
For example, one meta-analysis found that eating a small meal results in a smaller metabolic boost, while a larger meal is associated with a more significant boost. These approaches balanced out in terms of how many calories were burned (10).
Realistically, it is not possible to manipulate the body’s metabolism by meal frequency, as your metabolism is directly tied to what you are eating.
The end result is that the metabolic impacts of intermittent fasting and grazing are surprisingly similar. And, despite all the myths out there, intermittent fasting doesn’t slow down your metabolism.
Intermittent fasting doesn't significantly slow the metabolism. Even if it did, the weight loss benefits far outweigh any minor impacts of metabolism change
Late Night Eating, Weight Implications and Intermittent Fasting
One topic that often comes up in weight loss and health discussions is the idea of eating in the evening or late at night.
Technically speaking, it isn’t the time that you eat that is the issue, but when you are eating compared to when you go to bed. People debate about whether you should eat before you go to bed, or whether this is unhealthy.
If you are trying to lose weight, eating too close to when you go to bed is rarely a good idea and if you really feel like you need to eat something, try to make it something light rather than a full meal.
One of the reasons for this is that if you go to bed on a full stomach, then this can significantly impede sleeping. In fact, many people say that they find it harder to sleep when they have eaten not long before they went to bed.
Additionally, if you have any condition that causes heartburn or an upset stomach, eating close to bedtime can make for an uncomfortable experience, particularly as lying down often makes heartburn worse.
But, more than that, there are behavioral implications of eating later at night. For example, if you do need to eat late, it may be an indication that you don’t have good control over your eating patterns.
This may be why some studies have found that eating late in the evening is associated with an increase in weight (11). The practice of eating at night is often clinically referred to as Night Eating Syndrome (NES) and commonly occurs within populations that struggle with obesity (12).
Exactly what impact eating late at night has on weight gain is an area still under considerable debate and research, with some studies finding a significant effect, but others finding no effect whatsoever (13).
Another factor is that people have a tendency to snack before bed, and these snacks are often high in calories. This means that eating at night can interfere with weight control, particularly as it is very easy to overeat snacks.
So, how does this relate to intermittent fasting?
For one thing, intermittent fasting can help break negative patterns. The process helps people to eat when they need to, rather than because they’re simply craving food or are bored.
And realistically, most of the negative impacts of eating before bed are behavioral. The process of eating before bed isn’t actually unhealthy, as long as you are sensible about what you eat and your own biological needs.
Some people on intermittent fasting even intentionally choose to eat before bed.
For example, if you’re doing a 16:8 version, your eating window could be 12pm – 8pm or even 1pm – 9pm. In that period, you might have two large meals and then one smaller meal later in the evening. Or, you might just have two meals.
Taking that approach can make the early morning easier, as you’ll typically feel less hungry.
On its own, eating at night doesn't cause weight gain - and some people on intermittent fasting do so intentionally. You can still eat at night, as long as you are making healthy decisions
Benefits of Intermittent Fasting
Intermittent fasting involves breaking away from the frequent eating model our society is obsessed with. What this looks like depends on the specific approach you follow. But, for the most part, you do end up eating fewer meals and often snack less as well.
For many people, this aspect is powerful, resulting in decreased calorie intake. As a result, intermittent fasting can directly contribute to diet success and can even be a way to break through a weight loss plateau.
Intermittent fasting also causes biological changes that can improve weight loss. This includes increasing human growth hormone (14), lowing insulin levels (15,16,17) and boosting the hormone norepinephrine, which is associated with fat burning (18,19).
Collectively, these effects mean that intermittent fasting promotes weight loss through changes to food consumption, behavior and also through biological impacts.
A similar pattern can be observed during the festival of Ramadan, where people eat a large meal at night and a light meal very early in the morning, fasting for the rest of the time.
Research has shown that this practice results in significant weight loss, even though the amount of calories consumed during Ramadan is no different than any other time (20).
Intermittent fasting is significant for weight loss - affecting both behavior and biology
Other Health Benefits
The benefits of intermittent fasting aren’t just for weight loss either. Instead, the process can help to promote health in other areas.
For example, one study looked at the implications of 16:8 intermittent fasting for athletes. In that case, participants in the intermittent fasting group ate at 1pm, 4pm and 8pm. In contrast, the control group ate at 8am, 1pm and 8pm.
The amount of calories consumed and the nutrient distribution was the same across both groups. As such, the key difference was simply when the food was eaten. Both groups also engaged in resistance exercise.
The authors found that the intermittent fasting group saw improvements in some health biomarkers, maintained muscle mass and lost fat (21). Such an outcome could be particularly significant for athletes and bodybuilders, helping to promote a desirable body composition.
This idea strongly ties into the Leangains approach to intermittent fasting, which comes from the site of the same name. This concept was developed in 2010 and you can read more about the system at Leangains itself.
The basic idea is just a 16:8 intermittent fast but the timing is designed around weight training.
The previous study also shows that intermittent fasting has effects that go beyond dieting. After all, both sets of participants were eating the same number of calories, yet the intermittent fasting group lost fat and experienced other improvements.
Those benefits were associated with improved health and decreased disease risk (22) which is a powerful outcome. A key argument for these advantages is the idea that our bodies aren’t meant to be in a constantly fed state. Intermittent fasting offers the body a break from spikes of blood sugar and may promote positive health outcomes as a result.
One particularly relevant mechanism is autophagy, which is a cellular process. Autophagy occurs when we go without food for a while, and it acts to clean out waste products from the cells of the body, while also playing a role in cell creation (23).
To some degree, autophagy occurs in the body regardless. But, intermittent fasting is one mechanism that can help promote the process (24). What’s more, research has linked autophagy to a range of health benefits, including protecting the brain (25,26) and fighting both diseases (27,28) and microbes (29,30).
Recent scientific research has linked fasting with a number of different health benefits, some cellular, some related to improved glucose tolerance and some related to other areas.
For example, one animal study found that intermittent fasting prevented the deterioration of glucose tolerance that typically occurs in a high-calorie diet (31).
Another study reinforced these findings and suggested that intermittent fasting might provide a way to improve blood sugar regulation (32). For that matter, this type of diet may help restore insulin production, although more research is still needed (33).
Research has also indicated that intermittent fasting can improve the function of the mitochondria in non-obese study participants (34). This is a particularly important outcome, because the mitochondria play a key role in energy production within the body, suggesting that the lack of energy often associated with diet or lifestyle changes may decrease over time.
Finally, lifestyle changes that involve the reduction in calorie consumption, including intermittent fasting, can act to decrease the negative aspects of aging and increase overall lifespan (44).
Now, as is always the case, research into intermittent fasting is limited. Realistically, nutritional research is very difficult to conduct, as there is no practical way to force people to follow a diet and people often aren’t honest when they fill out surveys.
Furthermore, most researchers don’t have the funding or capability to study a diet in the long-term, especially not using an experimental model. As a result, there will always be limitations in what we can know about safety and effectiveness.
Even with that issue, research does suggest that intermittent fasting is at least as effective as other approaches for weight loss (45). Furthermore, it may promote specific health benefits. If nothing else, it is a good alternative for some people, especially those that struggle with conventional diets.
Intermittent fasting has been linked to a range of other health benefits, many of which are linked to the cellular process autophagy
Intermittent fasting is unusual, as the emphasis is entirely on when you eat – rather than the foods that you choose. And, doing so can be effective for health and weight loss.
The approach itself can be challenging, especially early on, because the sensation of hunger isn’t exactly appealing, and many people find it tempting to eat whenever they are hungry.
But, the process does get easier over time. And, you can also start slowly. For example, you could begin with an 18:6 version of intermittent fasting and work your way up to 16:8 and perhaps even to alternate day fasting. Or, you could just stick with 16:8, which does offer many benefits.
Nevertheless, when you eat is still only part of the story. In particular, you could heavily rely on processed food and sugar as part of intermittent fasting, which wouldn’t offer many health benefits. As a result, you do still have to make good food choices.
In a similar way, it’s important to simply get enough nutrients on intermittent fasting. This is particularly significant for the 24-hour (or longer) fasts. In both cases, achieving the best results involves relying on options such as healthy fats, fruits and vegetables, protein-rich foods and cooking your own meals.
An additional consideration is who you are as a person. Realistically, intermittent fasting can be relatively intense and it doesn’t work well for everyone.
For example, some women struggle with intermittent fasting, and may experience negative hormonal impacts. On the other hand, other women find intermittent fasting to be powerful.
Intermittent fasting may also be a poor choice for anyone who doesn’t function well when they are hungry. This includes people who tend to get ‘hangry’ or have problems concentrating when they haven’t eaten.
In many cases, you may find that these issues decrease over time as you get used to intermittent fasting, so it’s worth trying out the idea. But, if you continue to experience problems, intermittent fasting may not be right for you.
After all, if you want to lose weight and stay healthy, finding something sustainable is absolutely critical.
For some people, intermittent fasting (particularly the 16:8 version) fills that need and it’s certainly less complicated than having to record food and count calories. Nevertheless, that won’t be true for everyone.
One final note is to be careful if you have a history of eating disorders or a tendency to get obsessional about food. This is true for any diet type but particularly for intermittent fasting.
Intermittent fasting is great for resetting your relationship with food and helps reduce emotional eating. But, it can put some people at risk for eating disorders. The site Psychology Today also provides details about some negative aspects of intermittent fasting.
Now, for most, this isn’t the case. Indeed, research shows that intermittent fasting doesn’t promote disordered eating or a negative relationship with food (46).
It may even improve outcomes in some cases, as there is a strong emphasis on enjoying food when you do eat (47). Nevertheless, if you are vulnerable, it’s always important to be careful and pay close attention to thought patterns and how your body responds. You can even choose to follow some concepts of the technique and not others if you are concerned.
Intermittent fasting does present some challenges, especially for women. More than anything, it's simply important to pay attention to your body and make adjustments based on how you respond
Intermittent Fasting and the Modern Diet
I mentioned before that we live in a very fast-paced environment, and it can often be difficult to find the time to eat properly, particularly when eating well generally involves making your own meals.
Personally, I think that intermittent fasting can be very effective in this situation because it emphasizes filling and substantial meals.
The other advantage is that intermittent fasting means that you don’t have to prepare as many meals. For example, if you’re doing alternative day fasting, you’re eating very little every other day.
Likewise, the 16:8 variation can mean that you miss a meal entirely. For example, many people basically skip breakfast with intermittent fasting, which makes their first meal lunch. Doing so can work very well for people who don’t enjoy breakfast anyway.
On the other hand, some people use three meals for intermittent fasting, in which case, they tend to use the traditional meal types (breakfast, lunch and dinner). But, because the eating window is shorter, you would typically have smaller versions of each meal.
Ultimately, the best approach is to take the intermittent fasting model and adapt it to your own life, working out which elements are most relevant and which ones are not.
Intermittent fasting can fit in well with modern eating and lifestyle patterns. Plus, you can adjust the specific approaches you take to best suit your needs
Which Type of Intermittent Fasting?
If you’re looking at intermittent fasting, then you need to figure out which style you want to try. You may want to start on the 16:8 version, or something similar, as this is easier overall. But, what should your long-term goal be?
For many people, the 16:8 approach makes the most sense.
This style is the easiest to fit into modern eating patterns, especially as you’re basically just missing out on one meal. The style is also less stressful on the body, is likely to have fewer hormonal impacts and is the least likely to cause any nutritional or behavioral issues.
16:8 also tends to work best for weight loss because you’re making changes on a daily basis. As a result, it’s much easier to develop routines and many people find that they lose weight without even thinking about it.
Nevertheless, some people feel that other versions are more powerful. In particular, longer fasts mean that you’re promoting autophagy for longer, as well as any other fasting-related chemical changes. For that matter, some people claim that 16:8 doesn’t have you fasting long enough to see significant benefits.
In many ways, the answer comes down to what you’re looking for.
So, if your main goal is weight loss and/or a sustainable healthy lifestyle, then 16:8 or something similar is the best approach. But, if you’re already following a good diet and are at a healthy weight, then the other versions of intermittent fasting may be worth considering.
16:8 is the best version of intermittent fasting for weight loss but longer fasts could offer more biological benefits
Does Intermittent Fasting Work?
Like any diet, intermittent fasting is not the best approach for everyone, but it can help some people to lose weight efficiently.
One of the most important things to remember is that what and how much you eat is still relevant. For example, many people find that they are tempted to eat high-calorie foods or a large amount of food when they are hungry, which undermines the whole point of intermittent fasting.
In fact, if intermittent fasting makes you eat more, rather than less, it may be a poor choice.
However, many people pair intermittent fasting with other effective lifestyle approaches, such as paleo, veganism or keto. Doing so can be a good way to get the benefits of intermittent fasting, while also being sure that you’re eating healthy foods. Others find that keeping a food diary can help with the process.
One good recommendation is to avoid heavily processed foods and fast foods as much as possible and focus on options that are healthy and offer significant nutrients. Ultimately, an effective diet is what works best for you and that you are able to stick with long-term, and this will differ for every person.
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