Last Updated on April 12, 2024 by Fasting Planet
You’re looking to lose some weight, but the diets you’ve tried haven’t worked. Sure, the pounds come off while you limit your eating, but they latch right back on once the diet ends. You’ve heard intermittent fasting could be good for burning fat, but how long does it take for this to happen in the body?
You must be on an intermittent fast for at least 12 hours for the most efficient fat-burning. For some, it’s 14 hours, and for others, it could take even longer. It all depends on how much glycogen is in your body, as you have to burn this first, then your system uses fat.
If this is going to be your first intermittent fast, then we recommend you keep reading. In this article, we’ll discuss everything you need to know to burn fat while fasting. From how the process works, how quickly your body torches fat, and even if you can take supplements for more fat-burning on a fast, you’re not going to want to miss it.
Table of Contents
How Does an Intermittent Fast Burn Fat?
Assuming you’ve never gone on an intermittent fast before, you may be fascinated with how this works. How does the body burn fat while fasting? Is it simply by calorie restriction alone?
Actually, no. To understand how your body torches fat, we first have to talk about the body’s energy source.
From the moment you wake up until when you go to sleep (and even while you’re sleeping), your body needs energy. This is what allows you to get up, go about your daily routine, and enjoy your life rather than feel like you’re dragging through it.
This energy comes from glycogen, a polysaccharide of glucose. Bacteria, fungi, animals, and humans alike all rely on glycogen to fuel our daily activities. When our systems receive glucose, a simple sugar, we can synthesize it to glycogen for energy through glycogenesis.
Where does glucose come from? Mostly in the foods we eat. The foods with the highest quantities of glucose are fats, proteins, and carbohydrates. Thus, if you eat a diet rich with olive oil, avocados, peanut butter, cheese, meat, fish, dairy, fruits and vegetables, pasta, rice, and bread, you get plenty of glucose.
If your body has more glucose than it needs, it holds onto it for later. This can increase your insulin, meaning your body will always burn glucose, even if given the chance to burn fat instead. Should you develop an insulin resistance and this becomes chronic, your body increases insulin production when you’re full.
It’s believed that chronic insulin resistance may lead or contribute to type 2 diabetes, high triglycerides, more fat storage in the abdomen, obesity, and metabolic syndrome.
Through intermittent fasting, you stop consuming food for a period. That means you’re providing your body with no fresh glucose. The longer your fast goes on, the more your body uses its glycogen stores for energy.
It’s only once these stores are entirely depleted that your body can begin burning fat. As we said in the intro, this can take between 12 and 14 hours of consecutive fasting. Depending on how much glycogen your system has backed up, so to speak, for some fasters, it may be even longer.
While it would be great if your body only began burning fat from then on in, that’s not exactly how it works. Besides just torching fat for energy, your body can dip into your muscle mass as well for its protein. Both sources give you energy during an intermittent fast.
Here’s how it happens. When your glycogen stores begin running out, your body goes for the protein first, not the fat. That said, by torching both protein and fat at the same time, the two combine into something that’s like glycogen. It has similar components, at least.
If you’ve worked hard at the gym to build muscle and tone, you don’t have to lose it all during an intermittent fast. According to a 2009 study in Medical Hypotheses, mini fasts are one such way you can maintain your muscle. The data noted that by fasting for 14 hours max and exercising at least three days weekly (and even up to five days), you could lose more fat than muscle.
It’s also important that any foods you consume aren’t too high on the glycemic index, says the study. You want to limit your fats as well. The type of exercise you do also matters, added the researchers, in that high-intensity cardio is recommended above all else.
Further, a 2014 Journal of the International Society of Sports Nutrition report said you could boost your “body composition” by exercising four times a week, eating up to eight hours daily, and fasting for 16 hours. Once again, higher-intensity exercise is recommended, such as resistance training.
That said, the researchers also noted that these measures alone might not be all that helps along body composition.
When you fast, it’s believed that fat can have a “protein-sparing effect” in some instances. This happens because proteins fail to oxidize until fat reserves are consumed.
How to Burn Fat with Intermittent Fasting
Now that you understand more about why an intermittent fast burns fat, you’d like to get started. How would you drop a percentage of your body fat while fasting?
First, you have to choose a type of fast that works for you. Here is an overview of intermittent fasting types.
Water Fasting
With a water fast, you consume only water, no food. This fast can go on for extended periods of 24 to 48 hours, sometimes more, or be done in smaller periods over longer increments. Since you’re not supplying much if any glucose to your body while water fasting, you can burn through those reserves faster and get to the fat burning.
The 16:8 Method
In the study we cited above from the Journal of the International Society of Sports Nutrition, the fast the participants were on was a 16:8 fast. The 16 stands for 16 consecutive hours of fasting while the eight is the eight hours you’re allowed to eat.
You must watch what you consume in those allotted periods. Healthy fats may be good for you in most situations, but avocado, olive oil, and other fat sources contain a lot of glucose. This will only add to your glycogen stores and prevent your body from burning fat.
Instead, you want to stick to foods such as nuts, tofu, fish, and meat, as these contain a lot of protein. Fiber-heavy foods such as vegetables, fruits, beans, and nuts may extend that full feeling so your fasting hours are not as uncomfortable.
Try to plan for your eating window to be earlier in the day. After 6 p.m., your body may not process sugar as well, which could lead to even more glycogen stores that prevent you from burning fat. Remember to get exercise too so you can prioritize the upkeep of your muscle mass.
Alternate-Day Fasting
You have a larger eating window with an alternate-day fast, as you fast for one 24-hour period and then eat regularly for another. This doesn’t have to be midnight to midnight, but rather, a timeframe that works best for you. For instance, maybe you fast from 8 a.m. one day to 8 a.m. the next or noon to noon.
When you can eat, choose the foods above and not those that restore your glycogen supply. Otherwise, all the sugar burning you did during your fasting day will have been for nothing.
The 5:2 Diet
You could also go on the 5:2 diet, which is more generous for beginners. Two days every week, you’re on a fast, but you’re not restricting all food. Instead, you want to stick to about 500 to 600 calories a day, which is 25 percent of the recommended consumption. On the remaining five days of the week, there’s no fasting.
Since you get the most food with a 5:2 diet, managing what you eat is especially crucial. Fat-heavy and carb-heavy foods should be eliminated if not seriously restricted.
You’ve chosen an intermittent fast for yourself, perhaps even at the recommendation of your doctor. You still have questions, though. Namely, how much fat does fasting burn? Per a 2014 issue of Translational Research, when fasting for three to 24 weeks, body weight can drop by three to eight percent.
Breaking down that information week by week, that’s 0.55 to 1.65 pounds lost, with alternate-day fasting proven to be quite effective. With less belly fat, the waist circumference of the participants dropped by four to seven percent as well.
Which fat does the body burn during an intermittent fast, visceral or subcutaneous fat? Let’s talk about both fat types first. Visceral fat is that in your abdominal cavity. It’s always considered excessive and could be caused by drinking alcohol, being sedentary, or eating too many carbs, fats, and sugars.
Subcutaneous fat is that which is just under our skin. It’s typically jiggly in texture. The main difference between visceral fat and subcutaneous fat is the latter is healthy for you. Too much visceral fat could increase your risk of disease while subcutaneous fat may ward off diseases.
As for which your body burns first during an intermittent fast, that would be oxidized visceral fat. It’s believed this type of fat provides energy better than subcutaneous fat.
What to Do When Water Fasting to Burn Fat Cells
In the last section, we introduced water fasting, a type of intermittent fast that’s come up frequently on this blog. When you drink water, it travels to your body’s cells to keep them hydrated. To speed up water absorption, sip on an empty stomach, such as being on a water fast.
Besides losing weight through calorie restriction on a water fast, you also rejuvenate and detoxify your system, sort of like hitting a giant reset button. Your liver begins breaking down toxins and your digestive system works better due to the oxygen content in water.
As we said before, water fasts can last 24 to 72 hours for the most disciplined fasters. Others water fast off and on so they can maximize their fasting time. Such was the case of a man who fasted for 382 days straight. We’ve talked about this on the blog, but it’s a fascinating story that deserves another mention.
The man, who was 27 at the time of his fast, weighed 456 pounds when he started. For over a year, he consumed supplements and water. He weighted 180 pounds by the time he was done.
If you are eating between water fasting periods, you’re probably doing so nutritiously. While you may supply some glucose to your system, the water fasting periods should burn through this.
Those who water fast for longer periods consecutively add no glucose to their reserves, which allows your body to burn sugar for energy right away. Your body is then left with fat to burn. If you’re feeling up to exercising on a water fast, it’s possible to push your body into burning fat instead of protein.
If you remember from the beginning of this article, we talked about how too much sugar in the system builds up insulin resistance. This hormone manages our glucose so our levels don’t get too high, which puts us at risk of diabetes. With insulin resistance, there’s little regulation of glucose.
Water fasting can change that, too. Our insulin sensitivity increases, meaning our body keeps better track of the insulin it produces and does not make more than necessary.
Which Fat-Burning Supplements Can I Take While Fasting?
Fat-burning supplements, also referred to as fat burners, include L-carnitine, CLA, green coffee bean extract, synephrine, and 5-HTP.
L-carnitine is a type of amino acid that can control metabolism while CLA or conjugated linoleic acid is a fatty acid found in many fat burners. Green coffee bean extract, a very beloved fat burner, has chlorogenic acid within the beans. This acid is what promotes weight loss.
Synephrine, which also goes by the name p-synephrine, is a type of alkaloid that’s used as a weight loss drug. Its analog form is neo-synephrine. Finally, 5-hydroxytrytophan or 5-HTP is another amino acid which is involved in neurotransmitter serotonin biosynthesis as a metabolic intermediate.
While any of these fat-burning supplements may help with weight loss in your day-to-day life, you may wonder if it’s still safe to be on them when fasting. You should always see your doctor first for their approval, but yes, it’s generally okay to take a fat burner during an intermittent fast.
Fat-burning supplements that have no stimulants are best, as otherwise you may end up burning more muscle than fat and losing muscle mass. The Performance Lab SPORT Fat Burner is a highly renowned pick among fasters.
This supplement contains B-hydroxy B-methyl butyrate or HMB, an ingredient specifically included to maintain your lean muscle mass and strength. Coleus forskohlii or forslean is another ingredient, and this is your main fat burner. It also keeps your muscles looking full and toned instead of weak.
Cayenne pepper and black pepper extract help you enter thermogenesis, or an increase in body temperature from warmer foods or ingredients. This may enhance burned calories. Scientifically, this concept is known as the thermic effect of food, which we wrote about in another recent blog post.
When Does the Body Oxidize Fat During Fasting?
As your intermittent fast progresses, it’s possible for fat oxidation to occur. This is when your body consumes fuel, especially during athletic pursuits. The fat becomes energy without the need for intermittent fasting. Instead, it’s all about your level of physical activity.
You can trigger fat oxidation during a fast, too, just that it’s not always necessary. According to a 2004 study in the journal Nutrition, “exercise intensity and duration are important determinants of fat oxidation.”
If your intensity of exercise hits an oxygen consumption rate of 59 to 64 percent as an athlete, your fat oxidation is maximized. Even an oxygen consumption rate of 47 to 52 percent should be okay for the general population.
The journal also notes that fat oxidation happens more with certain exercises than others, such as running and endurance training instead of cycling.
What about when you’re fasting? Nutrition says this: “Ingestion of carbohydrate in the hours before or on commencement of exercise reduces the rate of fat oxidation significantly compared with fasted conditions, whereas fasting longer than 6 h optimizes fat oxidation.”
In other words, avoid carbohydrates, since they’re a source of glucose. Also, it takes six hours or more of consistent fasting to maximize the effectiveness of fat oxidation.
The study also states that you can boost your fat oxidation even more by ingesting low-fat food when you can eat between fasting. This is because your muscle levels must adapt and you’re not feeding your body as much glucose.
Conclusion
It takes your body between 12 and 14 hours to burn fat during a fast, but that timeline can vary. If you have a large supply of glycogen or sugar used for energy, then you may have to wait longer. As you fast, keep up with your exercise to prevent your body from burning muscle protein instead of fat after glycogen runs out. Best of luck!