intermittent fasting

A Beginner’s Guide to Intermittent Fasting

Introduction to Intermittent Fasting

Although I have always disliked eating breakfast, I have subscribed to the "breakfast is the most important meal of the day" for years...until recently. Over the last three months, I stopped eating breakfast.

That wasn't a crazy experiment.

There is research backing up my desire to eat one less meal per day. It can be good for you.

Missing breakfast is one form of intermittent fasting, or IF, a weight-loss and health-improving approach that Americans quickly adopt. Even stars like Jimmy Kimmel have used fasting. So perhaps skipping breakfast isn't so crazy after all.

What is Intermittent Fasting (IF)?

Fasting is an ancient ritual in which people don't eat for a certain amount of time. Many religions practice forms of fasting, which can be as severe as not eating for days or only eating fish on Fridays.

Intermittent fasting (IF) is fasting some days (or some hours) and not others. It can take the form of calorie restriction or simply not eating a meal. It's pretty flexible, and you get to eat regularly when you are not fasting.

IF has been touted as an alternative to dieting. Rather than extensively plan "healthy" meals with rapidly changing ingredients (low-carb, low sugar, etc.), IF users eat or don't eat. It's more of a behavioral change than a dietary change.

But it can be effective at helping people lose weight. Also, unlike some diets, it has other benefits, which I will talk about in a later section.

How Does Intermittent Fasting Work?

IF takes advantage of the human body's natural rhythms. We've all heard of circadian rhythms, the pattern of light and dark that correlates with our waking and sleeping times. Perhaps you've heard that keeping lights on at night or staring at a blue computer screen will mess up your circadian rhythm.

The circadian rhythm is usually associated with sleep versus waking, but there is also a correlation between fasting/feasting.

We need sleep to be awake, but do we need fasting to feast? Fasting and feasting are two different sides of a coin. While feasting, our bodies are digesting food, converting it to fat and energy. In contrast, our bodies start to burn that fat and energy we stored earlier during the fasting state.

The cycle is gaining weight when eating and then losing it when fasting. Unfortunately, the problem with this cycle today is that many of us don't enter the fasting state very often.

Digesting takes hours. Most people don't call a break between meals a "fast" until at least 10 hours have elapsed. Many people only fast briefly during the night while sleeping. IF extends the period that people don't eat to enter the fasting stage of the cycle.

Due to these additional hours of not eating, people's bodies switch into the fat-burning mode. That is one reason why fasting can be challenging. Many people say that they become so hungry in the last hours of their fast. Why? They are burning off the energy stored in their bodies.

Benefits of Intermittent Fasting

Burning off fat sounds like a great reason to try IF, but it's just the beginning of the health benefits of fasting. Research into this area has exploded in the last few years, as IF has gotten popular.

While some of these benefits are primarily seen in mice and other research animals, recent studies have shown that the same benefits apply to humans.

Lose Weight with Intermittent Fasting

IF can be a form of calorie restriction (CR), the most commonly prescribed way to lose weight. A 2010 study says that calorie restriction decreases the number of calories consumed by 15-40% of the baseline. If someone is eating three equal meals per day, removing one meal would be a 33% decrease.

This is what I'm doing when I skip breakfast. The reason that practitioners prescribe calorie restriction is that it works if people follow the guidelines.

It's hard to eat less food every day, but it may be easier to eat less food a few days per week. Fasting is an alternative to calorie restriction to increase "compliance" with the limits.

The calorie restriction option is to eat only 600 calories every day. The fasting option is to eat some days normally and not eat on others. One study tested the assumption that fasting is more manageable than dieting and found it not valid within their test subjects. However, individual bodies respond differently. So maybe yours will prefer fasting to dieting.

Have More Energy

Contrary to popular opinion, fasting doesn't necessarily make you that tired. If it does make you tired, it's temporary. Research subjects outfitted with pedometers did not walk any less on fasting days than on feasting days. So how can having less food makes you feel more energetic?

It depends on the type of energy that you are burning. Remember how I said that fasting shifts the body into the fat-burning phase? Mounting evidence shows that are many benefits to burning fat instead of carbohydrates. An NYT article calls fat, or ketones, a "clean" energy source, like "high-octane fuel.

"While some people do feel less energetic at the outset of fasting, people generally report feeling more active as their body adapts to the fasting cycle.

Live Longer with Intermittent Fasting

"Restricting caloric intake to 60–70% of normal adult weight maintenance requirement prolongs lifespan 30–50% and confers near perfect health across a broad range of species," says a 2006 study.

Can you imagine an increased lifespan of 30-50%? These researchers are probably talking about rodents, but other studies have linked calorie restriction and fasting to longevity and lower risk for some diseases.

One reason that IF can increase longevity is that it heightens insulin sensitivity. The opposite, insulin resistance, is linked to chronic diseases; therefore, IF can decrease insulin resistance by improving insulin sensitivity. Are you still following? Fasting reduces a factor that leads to disease.

Fasting also decreases the number of certain substances in your body linked to disease and aging. For example, one pathway, called mTOR, is related to aging responds to nutrients in the body. Fewer nutrients mean that the path is less active, and parts of your body can cleanse themselves of damaged cells more efficiently.

Fasting and weight loss also reduce the number of inflammatory substances in the body, according to a 2014 study. Chronic inflammation is a risk factor for some diseases, so reducing inflammation reduces the risk.

Also, though fasting benefits normal cells, it does not help tumors. This is because cancerous tumors primarily use sugar as energy. With fasting, many people convert their primary energy source to fat. As a result, there is less sugar energy available in the body for tumors to grow. Thus, fasting can starve tumors too.

There are many complex processes in the body, but fasting seems to inhibit many negative processes and boost positive ones generally. However, some potential side effects of fasting, primarily as a woman, will be discussed later.

Boost your Brain Activity

Another benefit of burning fat instead of sugar is that your brain prefers the fat because the higher energy fat fuel meets your brain's manic hunger for energy better than sugar. IF also increases the production of a protein called BDNF, which tells brain cells to convert brain stem cells into neurons. The increase in output can be from 50 to 400%! BDNF is good for neural health, according to Mercola, and protects against Alzheimer's and Parkinson's.

In this video, Dietician Joe Leech talks about 4 Evidence-Based Benefits of Intermittent Fasting.

Intermittent Fasting Plans

When it comes to the human body, there is no one-size-fits-all. The one consistent piece of advice that I read is that you have to do what works best. I can go without eating breakfast, but I can't imagine spending a Saturday night without eating a huge dinner. But someone else may feel differently. I'll outline four possible IF plans here, and you can adjust them as needed.

intermittent fasting

The 5-2 IF Plan

They were made famous by celebrities like Jimmy Kimmel, the 5-2 IF plan has five days of regular eating and two days of fasting. The key to this plan is to figure out how much to eat on the fasting day. For weight loss, people on the 5-2 IF program should consume 25% of their typical calories on the fasting days. 25% of a regular daily caloric intake is about 500 calories for women and 600 for men. However, individual needs may vary.

2010 study compared the 5-2 plan to a typical 25% calorie restriction (every day!) and found that the results were about the same. In addition, research subjects lost weight and reaped the benefits described in the previous section. However, if you are fasting for uses other than weight loss, you may want to eat more calories on the fasting days.

Daily (or Time-Based) Fasting

When I stopped eating breakfast, this fasting plan was what I was doing. In a time-based schedule, people fast every day but only for specific hours. The idea is that the body has at least 10 hours between meals to reset and shift into fat-burning mode.

For many people, this means that they stop eating at 6 pm and don't eat again until lunch. The fasting period is 18 hours, and many people are asleep for nearly half of it.

Some say this plan can be more challenging because people fast every day instead of a few days per week. However, it depends on the person. I like the habit because it's easy to remember. For example, I skip breakfast instead of checking my calendar, thinking, "is today a fasting day?"

Weekly or Monthly Fasting

This IF plan is a 24-hour fast on your schedule. Many people do a 24 hour fast by beginning the fast after lunch and not eating until lunch the following day. This plan can be weekly or monthly, depending on what you want to do.

A benefit of this plan is that it doesn't require much planning, and you can move it around to suit your schedule. This plan is also suitable for people who want the health benefits of fasting but are not interested in losing weight. Missing two meals a week will bump your body into a fat-burning mode, but it's not much of a calorie restriction.

I did try this 24 fast once, and it was a long 24 hours. I helped move some boxes in the afternoon, about halfway into the fast, and it wiped me out. Unfortunately, I was not motivated to try this method again. I didn't get used to the 24 hours fast the first time. Maybe if I tried it for a few weeks in a row, I would have adjusted.

Alternate Day Fasting

This IF plan is a favorite of research studies and is often abbreviated ADF. In this plan, you feast for 24 hours and then fast for 24 hours. It's as simple as "I eat today" and "I don't eat today." However, some people find that hard, so they adjust the 24 hours to eat at least once per day. For example, you could eat dinner on Monday night and then eat dinner on Tuesday night, 24 hours later.

I had a friend who tried alternate-day fasting. He was a big guy, and his doctor prescribed a calorie-restricted diet. My friend traveled a lot and didn't always have much control over the food that he ate. However, he always stayed in one place for the weekdays, so he started fasting on Tuesday and Thursday. He would bring in a tiny salad as his only meal.

The other days, I saw him chowing down on his favorite dishes of fried chicken and biscuits. But he reported that he had more energy and that he was losing weight. So, for those like my friend that may need to lose some weight, alternate day fasting could be an effective way to reach that target weight.

This plan has the most prolonged fasts at a regular interval. So, in theory, the ADF plan should boost a person into fat-burning mode quickly and keep them there longer because it spends more time fasting than any of the other plans.

However, it is the most intensive and most likely to cause weight loss. So maybe it's an ideal option to try for a short time (like until your reach your target weight). Then you can shift into one of the less intensive plans.

In this video, Laura Clendenning discusses the nuts and bolts of alternate day fasting!

What to Eat on Non-Fasting Days

People get excited to eat "whatever they want" on non-fasting days. However, certain types of food can promote better health during fasting cycles. Some of the rules that apply to healthy eating also use here. For example, eating a lot of processed food on non-fasting days still has the health disadvantages of when you are not fasting.

What is the best food to eat on non-fasting days? Fats are an excellent place to start. If you think about it, your body is burning fewer carbohydrates and more fats. Therefore, you are going to need more fats to burn and fewer carbohydrates.

Slowly reducing the amount of sugar you consume and increasing the number of healthy fats, like olives and coconut oil, helps your body adjust to this new cycle. It doesn't sound easy, but

Mercola says that as your body adjusts to fasting, your need for sugars and those other tasty treats will start to disappear. Mercola also recommends moderating protein (meat, dairy, and eggs). Pasture-raised and organic protein sources are a good option.

There is no perfect food to eat on non-fasting days. However, considering the changing chemistry of your body can help you make better choices about what you eat on non-fasting days; it is not a diet. It's a new lifestyle.

How IF Affects Women

Most studies, which tout the health benefits described above, merge men and women into a single category, humans. However, men and women often have different bodily responses.

Merging the two genders can obscure any negative impacts on either gender because, as a whole, there were benefits. Unfortunately, there have not been exhaustive studies comparing the differences between men and women who have been fasting. Some studies on other species, like rats, pose questions about how IF affects women compared to men.

Side Effects

There are some risks when adopting an IF plan. For example, a 2011 study on obese young women noted that 8% of the fasting group complained of headaches, cold, lack of energy, and constipation. While it is a low percentage, it is in a controlled laboratory setting with experts monitoring the situation. In addition, some female bloggers have said that their own experiences caused anxiety and insomnia.

In short, IF puts stress on your body. Like anything else that causes stress, there is such a thing as too much. Restricting your calories is going to stress your body. At a certain level, that is good.

Exercising breaks down muscles and builds them up stronger thanks to the stress of a workout. But just as an exhausting run can make you vomit, stressing out your body with an IF plan can make it sick and anxious.

Disordered Eating

Suppose you're someone that has struggled with anorexia IF is probably not for you. Restricting calories can mimic how anorexia feels. The memory of this feeling could cause a relapse into anorexia, depending on the person. But, again, everyone has to adjust for themselves and consider their own needs.

Reproductive Cycles

As we've seen from reports on fad diets, the calorie restriction can cause menstrual irregularity. Menstruation can even stop while on an IF plan. Under the stress of calorie deprivation, a women's reproductive cycle may start to shut down.

From an evolutionary perspective, a time of calorie deprivation is a terrible time to have a child. Therefore, to maintain your reproductive cycle, make sure that you are eating enough. 

Even men warn about eating enough during IF. James Clear cautions that it's tempting to eat smaller meals on non-fasting days or during non-fasting times. However, your body needs a certain amount of calories to survive. So if your menstrual cycles start to become irregular, you should stop fasting immediately and probably eat more.


Just don't do IF if you are pregnant. The growing baby will not benefit from a calorie restriction. Instead, eat all the pickles and weird food that you want. If you're worried about the potential side effects of IF, start like I did: skip breakfast. A SquishyFit video said, anecdotally, that many of the women happy with IF and its results were skipping breakfast.

In this video Sugar Mamma discusses how she does intermittent fasting for emotional, scientific and energetic reasons!

Other Expert Tips

If you are thinking about trying IF, these tips will make it easier to get started.

Get enough sleep

When you are sleepy, your body starts craving energy. So increased hunger is a common side effect of not getting enough sleep. When I'm exhausted, I've also found that I gravitate toward the worst foods for me to eat.

Sugar is an easy fuel to burn when looking for a way to get some more energy. However, when you start too fast, you will be hungry, so the increased hunger for sleep will get triggered much harder.

Not getting enough sleep can also negate some of the benefits of fasting. For example, a 2011 study showed that people with only 5.5 hours of sleep per night lost 55% less body weight fraction than those who slept for 8.5 hours.

The people that slept less also lost more body mass that wasn't fatty. If one of your goals is to lose fat, start sleeping at least 8 hours per night.

Drink Water

When you start an IF plan, you are bound to feel hungry at some point. Or are you thirsty? Sometimes it's hard to tell. A different 2011 study shows that thirstiness is common and persists throughout the day. If you are mistaking thirst for hunger, you will feel starving all the time as you start an IF plan.

Adjust the IF plan as Needed. I cannot say this enough: adjust your plan if it's not working for you. It takes about one week to adapt to an IF plan. That one week might be miserable. I found myself staring at Cheerios on the floor in the morning and wondering if it counted as breakfast if I ate them.

But, after a week, the hunger pangs should cease, and your body should be accustomed to the adjustment. This was the case for me. So, I can leave the dirty, spit-sodden Cheerios and wait until lunch, thank you very much.

If you still feel miserable after 1-2 weeks, you should consider altering your IF plan.


While there are some fantastic benefits to intermittent fasting, everyone needs to work to develop their plan. If executed improperly, IF can lead to anxiety and trouble sleeping, as well as menstrual problems.

With the right plan, constantly adjusted, people can reap the benefits of increased longevity, better health, and more excellent protection against some chronic diseases. For example, after an initial adjustment, I found that skipping breakfast fit into my life quickly.

I can't feel my insulin sensitivity increasing or my mTOR pathway slowing down. But I feel pretty good. When I get the occasional hunger headaches in the morning, I have a simple solution. I ignore the IF plan and eat! If you still need more guidance, you can read any of the fantastic intermittent fasting books on the market. Good luck.