Using intermittent fasting for weight loss is a proven science-backed method to get results fast.
Intermittent fasting is single handedly the most effective way to boost your weight loss results. That is if you’re willing to go through the fasting periods (the biggest side effect haha).
Growing up I thought it was bad for you to skip breakfast. Turns out as long as you have water you’d be healthier living on a desert island after a long weekend of no food than you would eating regular junky meals.
So why is intermittent fasting so effective for weight loss and lowering your body fat?
It essentially puts your body in a highly efficient fat burning environment. Fasting stimulates the hormones responsible for burning fat while simultaneously inhibiting fat gaining hormones.
As humans evolved over hundreds of thousands of years food wasn’t always so readily available as it is today. They certainly weren’t regularly eating three meals a day with snacks in between. So there were some days when we just didn’t have food to eat. The human body had to survive by evolving to use its fat reserves as fuel until it could find the next meal.
Studies show intermittent fasting to be highly effective for weight loss, lowering body fat, improving body composition, lower blood pressure and reversing aging (1).
In one study, 107 young overweight women were separated into two groups. One group reduced their caloric intake by 25% while the other group used a 5:2 intermittent fasting method of 5 days of regular eating followed by 2 days of eating only 25% of their daily calories (2).
The intermittent fasting group had better improvement to their insulin sensitivity than the calorie restriction group. This is key to weight loss since your hormones like insulin play such a vital role in your fat burning metabolism.
Insulin resistance is a huge factor driving weight gain and obesity. The better insulin sensitivity you have then the better you’ll be at burning off body fat (3).
The secret with intermittent fasting for our purposes is to strategically use it to skyrocket our metabolism. This way you’ll maximize burning fat while keeping your lean muscle. The results of fasting even after a month are rather impressive. So if you’re trying to lose weight then the benefits of intermittent fasting could be just for you.
How Much Weight Can You Lose With Intermittent Fasting
For every week you use intermittent fasting you can expect to lose at least 2-10 pounds their first week. Many women lose 10-15 pounds with their first month of fasting. This is as long as you’re eating clean and healthy the rest of the time.
You could easily expect the weight loss to be as much as 20 pounds a month. The more excess weight you have to lose then the easier it’ll be to drop excess pounds. To lose weight it’ll depend on how well you stick to your diet, your workouts and the fasting protocols.
But intermittent fasting isn’t going to be very effective to lose weight if you’re eating bad the rest of the time.
The same rules apply to your diet…
- eat a lot of protein and some good fats
- stop eating sugars, refined carbs, vegetable oils, junk food & processed foods
- get most of your carbs from green veggies
You’ll also have to keep your caloric intake under control to lose weight (4). You shouldn’t have to go so far as to keep a log for every meal you’re eating to measure your calorie intake. But it’ll help to track and measure the food you eat for at least a few days to get a glimpse of how much you’re really eating. Most people vastly underestimate how much they eat (5).
A trick to eating it to eat until you feel slightly full then stop. The trick is to then wait 10-20 minutes before eating anymore. It takes this long for your brain to register its full from the food you just ate (6).
Muscle isn’t only important for your strength but it will give you the toned and attractive appearance. We’ve all seen people who are “skinny fat” where they appear to be thin but in reality their body is the composition of cottage cheese.
A 2018 study published in Nutrients found mice didn’t gain weight on a high fat and high sugar diet when using intermittent fasting (7). Bad heart health and high blood pressure is a serious problem for millions of Americans. Fasting has been found to help lower blood pressure which will help with your heart health (8). Those suffering from type 2 diabetes should try intermittent fasting. Heart disease and diabetes are two of the biggest killers today and it’s critical to get them under control.
The only problem is some people can’t handle not eating for 16 to 24 hours at a time. I’ve found drinking a lot of water, black coffee, green tea, fat-burning MCTs and BCAAs will help get you through it so you can come out leaner and thinner on the other side.
There are other health benefits that intermittent fasting may help (without any major side effects). There’s numerous science-backed health benefits and medically reviewed health information finding intermittent fasting may:
- improve control of blood sugar levels (9)
- lower risk for heart disease (10)
- better body composition (11)
- lower blood pressure
- reduced risk of Alzheimer’s disease (12)
- reversing type 2 diabetes (13)
- reduction waist circumference (14)
But keep in mind this isn’t medical advice and intermittent fasting may or may not improve the above symptoms. It’s always best to go to a doctor for diagnosis or treatment advice. If you’ve suffered from eating disorders the fasting might not be a great choice for you. A history of eating disorders where you restricted your food could come back with fasting (15). Be sure to talk to your doctor or psychologist for medically reviewed health information if you have suffered from eating disorders in the past.
Science Behind Why Intermittent Fasting Works
When you have too much excess body fat it’s essentially your body’s way of storing extra calories for later use. To burn through these fat stores you’re going to have to force your body to burn through these fat stores. Calorie restriction by fasting is a simple way of achieving this since you won’t be feeding your body calories that can it can use for energy. It’ll then have to turn to your fat stores and burn them off for energy instead.
When you’re in a fast your insulin levels will lower dramatically. With these lower levels of insulin your body will effectively go into fat burning mode (16).
The blood sugar spike and subsequent insulin release that comes shortly after eating carbohydrates and sugars is the big problem. This insulin release triggers a “metabolic switch” that tells your body to stop burning fat. That’s because your body prefers to keep your stored up fat for when it really needs it. And your body will give priority to using the readily available quick-burning carbs you just ate for energy instead.
For this very reason many people aren’t able to lose their stubborn weight. Eating a processed diet that’s rich in carbohydrates and sugar keep your body from ever burning the fat you already have on you. Only when your body is in a fasted state can you finally start burning off the stored fat for energy. A meta analysis study found intermittent fasting to be a proven way to improve insulin resistance and blood sugar control (17).
Leptin is known as the “starvation hormone” and it’s another critical hormone for weight loss (18). It essentially tells your brain and body that you can readily burn body fat since you have enough. But as you gain weight and become insulin resistant you can also become leptin resistant. This will make you want to eat more and more.
Fasting has been shown to have long term effects in preventing leptin resistance (19).
Your human growth hormone (HGH) levels also naturally go up while fasting (20). The more human growth hormone you have then you’ll burn more fat and muscle mass gains you’ll get. Hormonal belly fat can be near impossible to get rid of without getting your hormones under control first.
Your nervous system will also send the hormone norepinephrine to your fat cells. This forces them to break down fat to be burned off as energy (21).
Since with fasting you won’t be eating for an extended period of time then you’ll be instantly practicing continuous calorie restriction. This means weight loss will come naturally without having to even focus on calorie restriction.
You can also expect to keep your hard earned muscle. Studies show those who used intermittent fasting may help with weight loss and had significantly less muscle loss than those who used a continuous calorie restriction diet (22).
Fasting is also a proven way to improve your gut health and heal damaged gut lining (23). Your gut health plays a vital role in your overall fat burning metabolism. If your gut health is out-of-whack then it’ll be difficult for weight loss (24). When you fast your gut gets a break and it’ll allow previous time for it to heal itself.
If you’re pregnant, breastfeeding or diabetic then I wouldn’t recommend intermittent fasting without the approval of your doctor (25). You could experience low blood sugar levels or may not get enough required nutrients.
How to Lose Weight With Intermittent Fasting
Ready to know how to fast for weight loss?
Fasting is really as simple as scheduling your eating pattern. You’re not eating during a timed window then eating during another timed window. But just because it sounds simple doesn’t mean it’s easy.
Now most people are used to eating pattern of three meals a day with breakfast, lunch and dinner. If you’re totally new to fasting you can take baby steps and start by cutting out snacking. Grazing and snacking all day not only increases blood sugar spikes but also doesn’t allow any of the benefits of fasting.
I recommend having your last meal at dinner time and then beginning your fast at that time. You’ll spend a big bulk of your fast sleeping. This will make getting through your fast that much easier.
If you’re used to eating breakfast then you can fully expect to feel hungry when you’re well into your fast. Your body releases the “hunger hormone” ghrelin telling your body it’s time to eat.
Instead you’re going to skip breakfast and keep on fasting. If you’re not used to fasting this is when you can start to feel hungry, stomach growling and irritability. You could even feel a little light-headed as your blood sugar lowers. But the good news is fasting can make you feel an increased sense of achievement and pride in yourself (26). And there are some tricks to staying fasted while fighting off the hunger pangs.
My approved fasting drinks include water, black coffee or steeped green tea. It’ll also be way easier to get through the day without eating if you’re allowed to have some coffee and tea. I’ll add in powerful C8-MCTs in my morning coffee that help to lower my appetite and increase fat burning (27). The MCTs will also help to fight sugar and carb cravings in the morning.
All these fasting drinks should help to not only fight the hunger pangs but they’ll also give a boost to your metabolism. You can basically drink anything as long as it’s zero calories. But you’re definitely not allowed to have anything with much caloric content.
A handful of hours after your last meal your body will finally finish digesting it. This is when you’ll start to get the benefits of intermittent fasting. Your body flips the “metabolic trigger” signaling for you to start burning your stored energy for fuel.
You’ll first start to burn through your glycogen (stored carbs) that are in your muscle and liver. Once you hit about 12 hours of fasting is when your body will really start to crank up this process.
Then the goal is to keep on going until your fasting periods are complete. If you feel hungry you can just go back to some of the approved fasting drinks to try and curb your hunger until it’s time to break your fast.
There are quite a few ways to do intermittent fasting that you should know about before picking a fasting program. Now let’s see which intermittent fasting plan is right for you…
16/8 Fasting for Weight Loss
I’m also a big of the 16/8 intermittent fasting eating pattern for burning fat. And this can be better for beginner’s who aren’t quite ready for the 4:3 fasting method.
For this method of intermittent fasting you would fast for 16 hours then go through an 8 hour eating window. It was originally made popular by fitness expert Martin Berkhan.
Eat your last meal at 8pm then go directly into the fasting period. Then at noon the next day you’re allowed to eat again.
I’ve also found some people are better off using this method of a fast since it’s more sustainable than 24 hours fasts. Especially if you’re new to fasting. And studies have found it to be impressive for weight loss (28).
I’ll use the 16/8 method most of the time throughout the year for this very reason. Whenever I’m looking to step up my game I’ll start using more of the 24 hour fasts or even a water fast.
With the 16/8 intermittent fasting schedule you’re essentially just skipping breakfast. I like to use this time to really focus on work and get things done. There’s something about being hungry that can really push you to do your best work.
This study found the 16/8 method of intermittent fasting to be effective for burning fat while maintaining muscle (29).
Even though both groups ate similar caloric and macronutrient content the group using the 16/8 intermittent fasting method lost an average of 3.5 pounds compared to the control group that didn’t lose any.
The researchers concluded the reason why the intermittent fasting plan group lost more fat was due to hormonal releases in the body. This resulted with their metabolism burning more calories
You could say on its most basic level intermittent fasting “tricks” your body into thinking it’s dieting which leads to enhanced fat burning.
18/6 fasting – After building up to the 16/8 fasts the next step is 18/6. A typical intermittent fasting schedule for 18/6 would be to have your last meal at 8pm and then fast until 2pm the next day.
20/4 fasting – Eventually you can build up to the 20/4 fasts aka the Warrior Diet. With this Warrior Diet fasting schedule you’ll only have a 4 hour eating window. You only have a short time with the Warrior Diet to eat so you’ll only be able to eat 1-2 meals in this time frame. Typically most doing the Warrior Diet 20/4 fasting schedule have their eating window between 2pm and 6pm.
Alternate Day Fasting – 24 Hour Fasts
Now the next step in the ways to do intermittent fasting is a 24 hour fast. They also call this OMAD fasting which stands for One Meal a Day.
You’ll definitely get better results with a 24 hour fast (Alternate Day Fasting) but I rarely recommend it if you don’t have a lot of fasting experience. It’s best to workout up to 24 hour fasts with a 16/8, 18/6 and then a 20/4 fast first.
24 Hour fasts shouldn’t be done every day. Doing these OMAD style fasts all the time will be hard on your body. This will start to result with diminishing returns. Going too long with 24 hour fasts will lower your sex hormones, lower your sleep quality and even cause thinning of your hair.
Alternate Day Fasting is essentially when you do a 24 hour OMAD fast for one day then the next day you have a more regular eat schedule. Alternate Day fasting can be highly effective for those who are severely overweight to maximize weight loss. I personally don’t like Alternate Day Fasting since it can throw a monkey wrench in your fasting schedule. It’s more difficult to curb your hunger when you’re still used to eating regularly throughout the day.
You can get away without having to have significant calorie reduction when using an fasting every other day diet. Since you’re only eating once per day you have more ‘wiggle room’ with your diet and don’t have to focus so much on calorie reduction.
But to maximize the benefits of intermittent fasting for 24 Hour I recommend following the below 4:3 fasting protocol. It balances out the 24 hour fasts with breaks between the fasts. Cycling your fasts this way will not only give you better results but it’ll also be more sustainable.
The 4:3 Method of Fasting
An easy way to use the 24 hour fasting days protocol is to divide the week up with 4 days of eating with 3 non-consecutive fasting days.
I’ve found this to be the most effective strategy to using the 24 hour fast when I need to take things to another level while keeping consistency.
Here’s a weekly breakdown of the 4:3 fasting week:
- Monday: Fast
- Tuesday: Eat
- Wednesday: Fast
- Thursday: Eat
- Friday: Fast
- Saturday: Eat
- Sunday: Eat (I like to have a Cheat Day on Sundays)
As you can see the non fasting days are spread out throughout the week. Having these non fasting days are critical to long term success. Otherwise you can quickly get burned out. You can of course change this schedule for what works best for you, but I’ve found for myself, friends and clients it’s the best.
Keep in mind when you’re doing this fasting style you still should be eating something each day. But keep your calorie intake under 500 calories. Usually eating something light like soup for lunch does the job.
Fasting for 3 days of the week for a 24 hour fast is going to be more doable for the average person trying to fasting as a weight loss tool. You’ll still have 4 days a week where you can eat on a more normal schedule.
This will allow you to still eat on the weekends with food restrictions. Weekends can be hardest while fasting because we’re usually hanging out with friends and family at social gatherings. Nothing worse than having to turn down somebody’s home cooking because you’re fasting that day.
Saturday’s I don’t go crazy pigging out, but when Sunday comes around I’ll usually end up splurging a little bit on my diet. This not only helps to refuel my body but it’ll also cause my leptin levels to go back up. Leptin signals for your body to burn more fat. Leptin levels can go down from fasting and restricting calories so it’ll be important to strategically raise them back up (29).
Having a small cheat day here and there will also keep you sane while using intermittent fasting. Taking away all “cheat foods” is going to be hard on anybody. Allowing yourself one day to go all-out will allow you to satisfy your cravings while boosting your motivation for the next fast.
The key is finding something that works for you and then to stick with it. I know so many people who have tried a continuous calorie restriction diet and dropped out shortly after because it was too hard for them.
Meanwhile those who have tried various forms of intermittent fasting have found it works very well for them, and therefore they’ve lost significant weight with it.
Fasting days can be tough but the key is to stay busy. Your fasting days will go by much quicker if you’re not sitting around watching cooking shows on YouTube.
If the 4:3 fasting plan is too hard then you can start with the 5:2 fasting plan. This is when you have 5 non fasting days but then have 2 consecutive fasting days.
What can you eat and drink while fasting?
Unfortunately, when most people hear of intermittent fasting (or intermediate fasting) they immediately take a step back. But the reason fasting is so effective is because it’s the most natural method of weight loss.
Most people who try calorie restriction end up binge eating after a short amount of time. This is due to the “hunger pains” are too much for them.
Intermittent fasting solves this dilemma by only cutting out food for a limited amount of time before allowing your body to eat again without the severe restriction.
To curb these hunger pangs drink my approved fasting drinks. Water, coffee, tea and other zero caloric beverages will be fine. Sparkling waters like La Croix are a favorite of mine. As much as I hate to say it zero calorie energy drinks will work too but have to be careful because of the artificial sweeteners. Even zero calorie artificial sweeteners can cause you to gain weight (30). Coffee is great to have during your fast since it’ll boost your metabolism helping you burn more fat (31).
Can you workout while on a intermittent fasting plan?
With the right kind of workouts you can maximize fat burning on your fasting days. Keep in mind any kind of weight loss method can result in muscle loss. This is why you should strength train to improve your body composition.
Because of your massive decrease in calories it’s probably going to leave your body in prime condition to burn off excess weight for energy.
In the morning A.M. I would recommend doing some form of fasted cardio. You’ll burn more fat when you exercise fasted (32). Plus there are other anti-aging health benefits that come with aerobic exercise while fasted. Working out while fasted can boost fat loss since your body is out of glycogen (stored carbs). Your body will then be forced to burn off fat stores for fuel (33).
Then ideally around lunch time you’ll do a strength training type workout. I personally like and recommend Metabolic Resistance Training (MRT) style workouts. You’ll build muscle and burn fat at the same time.
Be careful if you ever feel lightheaded while working out while fasted. It’ll be best then to back off and slow things down a notch. If you’re working out fasted try taking some electrolytes such as magnesium, potassium, sodium and calcium.
Although I wouldn’t recommend intense exercise during prolonged fasts. While on a longer fast then going on long walks as much as possible is the best.
What should I eat during intermittent fasting to lose weight?
Most people make the big mistake of eating whatever they want the rest of the time they’re not fasting. Overeating will undo all the benefits of your hard earned weight loss from fasting. It’s smart to consume healthy foods in moderate portions instead of binging on processed junk foods that’ll end up making you gain weight.
One of the greatest benefits of intermittent fasting is the instant elimination of snacking and meals. Since your eating window is smaller you’ll have to cut out meals and snacks. This will greatly contribute to your weight loss results.
Ideally if you’re fasting in the morning your lunch time meal will be the greatest in calories. You’ll lose more weight if your lunch is the bigger meal instead of your dinner. But if this doesn’t work for you then going bigger at dinner time can work too.
Try to eliminate most carbs and sugar from your diet. Your carbs should mostly come from vegetables. Refined carbs, sugar and grain-based foods will take away some of the weight loss benefits that your earn with fasting. Keeping your insulin levels low plays a major factor in weight loss. And the best way to keep your insulin levels low is to reduce your carb and sugar intake.
Instead of eating carbs and sugars eat more healthy fats instead. Pastured eggs, avocados, coconut oil, high quality meats, etc. are all great choices to meet your caloric needs while keeping your insulin levels low. Plus they’re rich in omega-3 fatty acids which will help to lower inflammation.
Consuming a high protein diet will contribute to weight loss and the building of lean muscle mass (34). Your body has to work harder to process protein and this results in more calories burned for you. Your muscles need protein to maintain their mass and rebuild. I eat as much as 2 grams per kilogram of my bodyweight in protein per day. Plus protein is highly satiating so you’ll feel fuller for longer (35). This is quite helpful when fasting.
Can I drink coffee while fasting?
Yes but I’m not a fan of Bulletproof Coffee since it contains butter. It’s very dense in fat and calories it’ll probably end up breaking your fast. Don’t get me wrong it’ll be better than eating a donut or a bagel. Instead I drink my coffee with Keto Elevate to get the benefits of Bulletproof Coffee without having to drink the butter.
The Last Word
Fasting taps into your evolutionary and ancestors way to burn fat for how it was intended. They needed these fat reserves to survive since they couldn’t order McDonald’s at anytime of the day on the DoorDash app.
Your body wants to hold onto your fat reserves like a “piggy bank.” Only on a rainy day when food really is scarce will it tap into these fat stores for energy. This is what makes fasting so effective for weight loss and fat loss.
The ketones your body releases while fasting and on a low carb diet signal for your body to burn more fat. But if you’re eating all the time and eating too many carbs then these powerful fat-burning ketones will not be present in your body.
Now I’ve never really seen people make such progress with losing weight in such a short amount of time as they do with intermittent fasting. And you’ll get even better results when you combine it with a low carb diet (36).
Intermittent fasting isn’t just another health trend. It’s the diet your ancestors had to use. Our bodies are still built the same as them. So it makes sense it’ll work for you too.
There are a handful of different intermittent fasting methods you can use that’ll produce different results. Generally the longer the fast the more weight you’re going to lose. But the trick is going to be to find one that works for you amongst the different fasting weight loss methods.
Going on too long of a fast at the beginning can set yourself up for failure. Many people go about intermittent fasting all wrong and end up crashing and burning.
Intermittent fasting can be a game changer for your body and it’s the best of the weight loss methods. You’ll lose weight, drop stubborn fat and improve many markers of health… time to fast!
Josh holds a Bachelor’s degree in Exercise Physiology and Nutrition Science. He’s a Certified Strength and Conditioning Specialist (CSCS) by the National Strength and Conditioning Association and he’s a Certified Personal Trainer (CPT) by American Council on Exercise. He’s worked as a Strength and Conditioning Coach at the high school and college levels. He has over 15 years of experience as a personal trainer and nutrition coach. He is also the author of The Flat Belly Formula. He strives to bring inspiration and results for people to live healthier lives through smart diet and exercise.