【Photos Don’t Tell the Whole Story】Fasting Before and After, How Your Body Changes in 1 Week, 1 Month, and 3 Months, with Research Data and Tips to Keep Going

“Does fasting really work? Can I actually keep it up?”

“How much change can I expect in a week or a month?”

I imagine a lot of you are wondering exactly that.

In this article, I’m opening up the real before-and-after stories of people whose lives changed after actually practicing fasting (intermittent fasting).

From weight and blood sugar to mental state and work performance, I’ll walk you through the changes fasting brought, with stories and data.

I’ll also clearly explain what to roughly expect at one week, one month, and three months, what the research data shows, and why results differ from person to person.

What Changes Tend to Happen in a Fasting Before and After?

When people hear “fasting before and after,” most probably picture changes in weight or around the belly.

Of course, changes in appearance are a big part of it, but they’re not the only things fasting tends to change.

The changes that tend to happen with fasting fall broadly into these three categories.

So why do changes like these happen just from limiting the hours when you eat?

The key is that during the fasting hours, the way your body “uses fuel” switches over.

When you eat, your blood sugar rises, and a hormone called insulin is released to move that sugar into your body.

Insulin is, in a sense, like “the person in charge of putting sugar away in the warehouse.”

But when the fasting period gets longer, insulin secretion is held down, and the body starts taking out the fat it had stored in the warehouse and using it.

The “alternative fuel” the liver makes from the fat being broken down at this point is what we call ketone bodies.

In other words, a fasting before and after comes from two things combined: “switching fuels” and “naturally eating less.”

When your eating time is limited to 8 hours, opportunities for snacking and late-night eating naturally decrease, which also helps drive the change.

Conversely, if you binge during your eating window, changes will be harder to see.

A Word of Caution When Looking at Before-and-After Photos on Social Media

With before-and-after photos on social media, the lighting, posture, and even the time of day a photo is taken can change how someone looks a lot.

Even for the same person, the belly area looks quite different on an empty stomach in the morning versus at night after a big meal.

It’s important not to judge by photos alone, but to also look at weight, waist size, and health checkup numbers.

Changes in which belt hole you use or your clothing size are also signs that are easy to notice in everyday life.

For changes you can’t see from the outside, like blood sugar and blood pressure, compare your health checkup results from before and after to confirm them.

Fasting Before-and-After Stories: Minus 15 kg, with Blood Sugar and Blood Pressure Back to Normal

From here, I’ll share stories of people who actually changed by sticking with fasting.

The Real Experience of the Author, Matsu

I started fasting when I was 38.

At the time, I weighed 83 kg (183 lb), my waist was 95 cm (37 in), and my HbA1c was 6.1 (prediabetes).

I had tried dieting several times before, but I couldn’t keep up calorie restriction, and every exercise plan fizzled out after a few days.

Just when I had half given up, thinking, “I’ll never be able to change,” I came across a method called 16-hour fasting.

For the first week, the hunger in the late afternoon was tough, but from the second week I got used to it, and three months later my weight had dropped to 68 kg (150 lb).

That’s a pace of about 5 kg (11 lb) per month.

I haven’t regained it, and I’m still maintaining that weight today.

How My Diet Changed

During the fast (16 hours), I had only water, tea, and black coffee.

I concentrated my meals in an 8-hour window from 12 p.m. to 8 p.m.

I didn’t drastically change what I ate.

Just the small change of “skipping breakfast” meant that my total daily calorie intake naturally went down, and my body started using fat for energy.

Changes in My Blood Tests (After 3 Months)

The effects of fasting aren’t limited to weight.

Big changes show up in metabolic and blood test numbers, too.

I still remember how surprised my doctor was when he saw these changes, saying, “It’s rare to see this much improvement without dietary restrictions or medication.”

I believe these improvements came about because fasting held down insulin secretion and
my body switched to a state of using ketone bodies for energy instead of relying on carbohydrates (ketosis).

Fasting Stories Making the Rounds on Social Media (Reader Stories Roundup)

From the fasting stories readers have sent to my blog and social media, here are the ones that got the biggest response.

A hallmark of fasting stories is how many people say that not only their weight, but also their blood test numbers and even their work efficiency changed.

Fasting Before and After: Changes in Mental State and Work Performance

A fasting before and after can show up not only in your body but also in the state of your mind and mood.

Though it’s harder to see in numbers than weight, it’s one of the changes that’s easy to feel.

Why Brain Performance Improves

During fasting, blood sugar stabilizes and ketone bodies become the brain’s main energy source.

Ketone bodies are a more efficient energy source for the brain than carbohydrates, and improvements in focus, working memory, and decision-making have been reported.

BDNF is known as a substance that works like “fertilizer” that helps the brain’s nerve cells grow.

Fasting also increases BDNF (brain-derived neurotrophic factor), which leads to improvements in learning and memory as well.

The Effect on Your Mental State

People often ask me, “Doesn’t fasting make you irritable?” but once you’re used to it, it’s actually the opposite.

With the sharp swings in blood sugar gone, your mood stabilizes, and many people say that the chronic “vaguely sluggish” and “can’t find any motivation” feelings improved.

Picture the blood sugar roller coaster turning into a gentle slope.

When a carb-heavy meal makes your blood sugar shoot up, it then drops sharply, which tends to bring on sleepiness, irritability, and intense hunger.

It’s said that eating fewer times and having smaller blood sugar waves also makes ups and downs in mood less likely.

Before fasting, I myself often felt like “my motivation switch just won’t turn on,” but now I can get into focus mode at work from the morning.

Changes in Work Performance

In particular, people who used to feel very sleepy after lunch may find their afternoons change once the amount and content of their meals are in order.

However, there may be days when hunger makes it hard to focus, so before important work, don’t push yourself, and adjust as needed.

Changes in mental state and work are hard to capture in numbers, so jotting down simple notes like “Did I get sleepy in the afternoon?” and “How long was I able to focus?” makes it easier to notice your own changes.

Even during periods when your weight isn’t moving, changes like these can keep your motivation going.

Fasting Before and After: What to Expect at 1 Week, 1 Month, and 3 Months

The changes after you start fasting don’t suddenly appear one day.

Here, let’s lay out the changes that tend to happen when you keep up 16-hour fasting, as a rough guide by time period.

However, the size and speed of changes vary from person to person, so please take this only as a general trend.

1 Week: The Period of Getting Used to Hunger

The first week after starting is a period when your body isn’t yet used to the new rhythm.

During the first one or two weeks, you’re likely to feel hungry, and your stomach may growl in the late afternoon or the morning.

The number on the scale may go down a little, but changes during this period are thought to include sugar and water stored in the body being reduced.

Don’t get too caught up in the numbers; make continuing your priority.

Also, while you’re not used to it yet, some people may feel a mild headache or sluggishness from hunger.

A lack of fluids is often the cause, so during your fasting hours, drink water or tea frequently.

1 Month: The Period When the Habit Settles In

By around the one-month mark, more people will probably be able to take hunger in stride, with a feeling of just “Oh, I’m getting hungry.”

With set eating hours, snacking and late-night eating decrease, and this is a period when your overall eating habits tend to fall into place.

As snacking decreases, the times when you crave something to munch on will also gradually get shorter.

Some people may notice small changes outside of weight, such as a different belt hole or pants feeling looser.

With fewer late-night meals, some people may also feel that their morning heavy stomach has eased or that they wake up more refreshed.

3 Months: The Period When You Can Easily See Changes in Your Numbers

Three months is also the point where a new habit shifts from “something you work hard at” to “something you just do.”

If you get a health checkup or body composition measurement around this time, you can clearly confirm your own before and after.

The important thing is to not look for results in a short time, and to first keep going for about three months.

Fasting Before and After as Seen in Research Data

In addition to personal stories, let’s also look at what kinds of changes have been reported in research.

Weight Changes Reported in Research

In a study reported in 2018, 45 adults with obesity limited their eating time to 8 hours, and after 12 weeks, a weight loss of about 3% was confirmed.

For a person weighing 70 kg (154 lb), that works out to a loss of about 2 kg (4.4 lb).

The size of the change varies from person to person, but losing weight at a pace you can keep up without strain helps build a body that’s less prone to rebound weight gain.

Long-Lasting Changes: A Report of Results Maintained After One Year

A study of 99 adults in Spain reported that
with a method limiting eating time to 8 hours, weight loss was still maintained 12 months after the intervention ended.

In this study, the group that ate earlier in the day was found to have a greater reduction in fat mass.

Changes in Health Checkup Numbers

Some studies report improvements not only in weight but also in numbers such as blood sugar, insulin sensitivity, blood pressure, and triglycerides.

It’s thought that letting insulin rest during the fasting hours makes it easier for the body to regain its ability to process sugar.

The improvements in blood test numbers seen in the personal stories are also likely related to changes in the body like these.

A Change to Watch Out For: Muscle Loss

On the other hand, there’s also something to be careful about.

A study (2020, JAMA Internal Medicine) in which participants followed 16-hour fasting, eating from 12 p.m. to 8 p.m., for 12 weeks
found no major difference in weight loss compared with a group eating three meals a day, and reported that the fasting group lost more muscle mass in their arms and legs.

The researchers pointed to the possibility that skipping breakfast reduced protein intake as one of the reasons.

In other words, it’s not just about limiting the hours; what you eat matters too.

Even if your weight goes down, if you lose muscle as well, your metabolism can slow and leave you with a body that gains weight more easily.

Why Fasting Before-and-After Results Differ, and How to Keep Going

Even among people fasting the same way, some change a lot and some don’t change much.

That difference often comes from small differences in how they go about it.

Here, I’ll introduce the failure patterns that tend to create that gap, and how to keep going so you can actually feel the changes.

Mistake 1: Binge-Eating During Your Eating Window

Rewarding yourself for 16 hours of effort by eating heaping bowls of rice and lots of snacks is a common mistake.

After a long fasting period, your body absorbs sugar easily, and your blood sugar is prone to spiking.

As a result, your daily calorie intake doesn’t go down, and your weight is less likely to change.

Mistake 2: Not Getting Enough Protein

When you eat fewer meals, you tend to run short on protein from meat, fish, eggs, soy products, and so on.

As research has also reported muscle loss, a lack of protein affects how toned you look, too.

Make a point of including a protein dish about the size of your palm at every meal.

Mistake 3: Ongoing Lack of Sleep

It’s said that when you don’t get enough sleep, the hormones that increase appetite tend to rise, making it harder to hold out against hunger.

Staying up late also increases the temptation to snack at night, so sleep is an important factor in getting results from fasting.

Mistake 4: Getting Calories from Drinks

If you drink sweetened café lattes, juice, or sports drinks during your fasting hours, that alone weakens the effects of fasting.

Sweet drinks raise blood sugar and insulin, making it harder for your body to switch into fat-burning mode.

During your fasting hours, the basic rule is to choose zero-calorie drinks such as water, tea, and black coffee.

What to Record Before You Start

To really feel your own before and after, it’s important to properly record your condition before you start.

Without records, even if there are changes, you may feel that “nothing has changed” and quit.

Your weight goes up and down a little every day, so I recommend looking at the weekly average rather than the daily numbers.

If you take comparison photos every two weeks to a month, you’ll start to see changes that are hard to notice yourself.

For health checkup numbers, putting the results from before you started fasting side by side with the results from 3 to 6 months later makes the changes easy to see.

During a Plateau, Think “If I Keep Going, It Will Move”

As you keep fasting, you may hit a plateau where your weight doesn’t move for a while.

It’s a period when your body is trying to get used to its new state, so it would be a shame to quit here.

A plateau is exactly when your records come in handy: if you look back at your waist size, photos, and notes on how you’ve felt, you’ll notice that changes other than weight are still happening.

What creates the gap in before-and-after results isn’t some special talent; it’s the difference in what you eat and how long you keep going.

Frequently Asked Questions About Fasting Before and After

Start Today and Experience Your Own Fasting Before and After

Minus 15 kg (33 lb), blood sugar and blood pressure back to normal, better focus, improved work performance: all of these are real changes drawn from actual fasting stories.

You don’t need difficult dietary restrictions or intense exercise.

All you need is one thing: simply stick to the 16-hour rule of “not eating from dinner until lunch the next day.”

Avoid the failure patterns of binge-eating, lack of protein, and lack of sleep, and start by keeping it up for about three months.

Even if you’re thinking, “This might be impossible for me,” try it for just three days first.

You’re sure to feel your body starting to change.

If jumping straight to 16 hours is hard, it’s fine to start at 12 or 14 hours and extend it little by little.

If you record today’s weight and take a photo, a few months from now, you’ll be able to see your very own before and after.

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