Before we get to the best fat burner for intermittent fasting (IF), let’s touch on IF and whether you should be using a fat burner while fasting in the first place.
Contrary to what most people think, intermittent fasting is not exactly a diet; it’s an eating pattern. It cycles between periods of fasting and eating.
Intermittent fasting is based on the theory that our ancestors did not eat as frequently as folks in the 21st century, and we could benefit physically from going back to the old ways. Furthermore, research suggests IF can help reduce oxidative stress, improve memory, increase muscle mass and decrease body fat. 
The 16/8 regime is the most popular intermittent fasting routine, which involves fasting for 16 hours and scheduling your meals during the remaining eight-hour window.
Want to learn more about intermittent fasting? Check out our in-depth beginners IF guide.
Should You Take a Fat Burner During Intermittent Fasting?
This is one of the most common questions people have while on the market for a fat burner (or any other supp, for that matter) while intermittent fasting.
During the fasting phase, you should avoid using macronutrient-containing supplements, like protein powders and carb-containing intra-workouts. Eating calories ends your fast by kicking your metabolism into action.
So, to answer the question — most fat burners on the market do not contain any calories and are safe to be consumed during your IF fasting phase.
Pros and Cons
Below are the advantages and disadvantages of using Roar Ambition’s Instant Knockout Cut —
- Each ingredient is optimally dosed.
- Contains all-natural ingredients.
- Made in FDA and cGMP-approved facilities.
- Comes with a transparent label and contains no opaque proprietary blends.
- The vegan capsule is great for vegetarians and vegans.
- Potent appetite suppressing formula.
- High caffeine content keeps you fueled throughout the day.
- Not the most budget-friendly fat-burning supplement.
As you can see, more than half a dozen qualities make Instant Knockout Cut an effective fat burner. If money is not a problem, there should be no reasons why you shouldn’t be getting this supp.
Best Fat Burner for Intermittent Fasting
Roar Ambition’s Instant Knockout Cut is one of the most effective fat burners. Its scientifically proven formula delivers results in the shortest time and can streamline progress on an intermittent fasting routine.
Instant Knockout Cut is a hit amongst professional combat sports athletes like MMA fighters and boxers. What more? Welterweight MMA fighter Jorge Masvidal is the supplement’s poster boy. The fat burner is also promoted by legendary MMA coach Greg Jackson.
Why is this noteworthy, you ask?
MMA fighters often are on a deadline to make weight for a fight, and they need a proven fat burner that can deliver. Notably, they have to shed weight while retaining their muscle and strength.
Also, if you are a UFC fan, you might have noticed that most athletes (up to the welterweight division) have diced physiques. Fat burners and a strict diet and training routine play a role in their aesthetic bodies.
Instant Knockout Cut consists of nine proven fat-burning ingredients. Each bottle contains 120 capsules, providing you with an entire month of fat-burning, appetite-suppressing, and energy-boosting benefits.
Instant Knockout Cut arguably has the most unique bottle design for a fat-loss supplement. The bottle is shaped like a fist, symbolizing a knockout.
It also shows that the fat loss supplement was designed keeping in mind the needs of combat sports athletes.
Now in its fourth iteration, the Instant Knockout Cut formula is better and more effective than ever. The first versions of the fat burner had racy red capsules but have now transitioned to a more subtle beige.
Evaluation of Ingredients
It is no secret that fat burner supps can speed up your fat loss process. There are a lot of fat-burning supplements present on the market, with the main differentiators being their ingredients list and hence their formula’s potency.
Shopping for a fat burner while intermittent fasting will be different than shopping for a fat-burning supp on a regular diet. Instant Knockout Cut contains the following ingredients —
Glucomannan is the main ingredient distinguishing an intermittent fasting fat burner from the rest. It is a type of fiber found in the roots of the elephant yam, which is also called konjac, that can help you stay fuller for longer between meals and can be a game-changer while you’re fasting.
Glucomannan absorbs water and turns into a gel-like substance that sits in your gut. It might sound gross but is incredibly effective at promoting a feeling of fullness and helping you eat fewer calories. 
Notably, glucomannan is the tenth non-digestible carbohydrate to join the FDA’s list of ingredients to be added to the definition of dietary fiber. Although a type of carb, it does not break your fast.
Glucomannan acts as a food source for your gut bacteria but not as a food source for your body. So you can use glucomannan fiber to help combat hunger during fasting without breaking your fast.
Summary — Fiber takes your body longer to digest, aiding your weight loss journey. 1,800mg of glucomannan will keep you satiated throughout the day.
Green Tea Extract (500mg)
Green tea extract can speed up your metabolism and boost fat oxidation via thermogenesis, helping you tap into stored fat. Besides ramping up fat burning by over 15%, it gives you a much-needed energy kick. 
Many human studies have shown that green tea extract, when paired with exercise, can increase fat burning and cause fat loss, especially in the belly area. Furthermore, green tea is recognized as a superfood as it has many health benefits. 
Summary — Green tea is a popular ingredient in many weight loss supplements. It is packed with antioxidants that can help stave off diseases due to dangerous free radicals that damage body cells.
Caffeine Anhydrous (300mg)
Caffeine anhydrous is made from the seeds and leaves of coffee plants. The word “anhydrous” means “without water.” It is a highly concentrated form of caffeine. 
The most common stimulant in fat burners is caffeine, which increases a hormone called epinephrine. When levels of epinephrine increase, it stimulates the breakdown of fatty acids in your bloodstream to use as fuel for energy.
Summary — 300mg of caffeine anhydrous combined with 500mgs of green tea extract will ensure enough gas in the tank to last you a full day.
L-theanine is an amino acid found primarily in green and black tea and some mushrooms that play a role in reducing mental stress and promoting relaxation.
A 2019 study found combining caffeine, tyrosine, and l-theanine provided enhanced benefits, including improved movement accuracy surrounding bouts of exhaustive exercise. Plus, it can also help to reduce or eliminate the common jitters associated with caffeine. 
Summary — L-theanine works synergistically with caffeine to extend cognitive effects.
Cayenne Powder (100mg)
Cayenne pepper helps boost thermogenesis. The nutrient-dense spice contains capsaicin — a bioactive compound known for its fat-burning ability. Research shows that the capsaicin in cayenne pepper seeds can reduce your desire to eat. 
Cayenne pepper boosts your body temperature, increasing the number of calories you burn at rest.
Summary — If you struggle with hunger during a fast, Instant Knockout Cut might be the perfect fat burner for you due to its appetite-suppressing quality.
Black Pepper Extract (10mg)
Black pepper is another thermogenic in the Instant Knockout Cut formula that works similar to cayenne pepper. Additionally, it aids the absorption and bioavailability of other ingredients in the fat-burning supp, making sure you get the most bang for your buck.
Summary — Black pepper extract improves the bioavailability of certain nutrients, which helps with ingredient absorption.
Vitamin D3 (45mcg), Vitamin B6 (5mg), and Vitamin B12 (10mcg)
Vitamins B12 and B6 can help convert food into energy, transport oxygen to cells, create red blood cells, and use folic acid. On the other hand, vitamin D3 can aid in managing your weight.
Summary — Vitamins go a long way in aiding weight loss while maintaining overall health.
Verdict on Claimed Benefits
Here is our verdict on the claimed benefits of the Instant Knockout Cut fat burner —
|Weight Loss||Strong Evidence|
|Appetite Suppression||Strong Evidence|
|Potent Thermogenic Formula||Strong Evidence|
|Fat Loss without Losing Muscle Mass||Moderate Evidence|
|No Caffeine Crashes||Moderate Evidence|
Side Effects, Safety, and Dosage
The serving size suggestion on the label is one capsule four times a day. The brand recommends taking one cap first thing upon waking and before breakfast, the second between breakfast and lunch, the third an hour after lunch, and the last capsule an hour before dinner. They also suggest taking a serving no later than five hours before bedtime.
There are no noted side effects of Instant Knockout Cut.
However, the fat burner contains 300mg of caffeine anhydrous and 500mg of green tea extract, which can be a high dosage for people not used to high-stim supplements.
Possible side effects from caffeine consumption include impairments in cardiovascular function, sleep disturbances, and substance abuse. 
Cost and Where to Buy
Roar Ambition offers three stacks of Instant Knockout Cut, including —
- 1 bottle/1-month supply: $59 (you pay to ship)
- 2 bottles/2-month supply: $118 (free delivery in the UK and US)
- 3 bottles + 1 free/4-month supply: $185 (free worldwide delivery)
The per-serving cost of the supplement varies depending on the stack you order, with the four-month supply being the most cost-efficient variant.
You could buy the fat burner from the official Instant Knock Out website or Amazon. However, the official website offers a lot more benefits, including —
- FREE Premium Supplement (Worth: $80)
- FREE Boss Shred (Worth: $149)
- Easy to follow video program
- Detailed nutrition E-Books
- 4 Month body transformation
- FREE Worldwide Shipping (4-month plan) / FREE shipping in the USA & UK (2-month plan)
Note: These added benefits are for the four-month and two-month supply variants.
How Instant Knockout Cut Compares to Alternatives
There are many fat burner supplements on the market which are great for intermittent fasting.
A similar product that scores high on ingredient list transparency and quality is Transparent Labs Fat Burner. It contains many of the same ingredients like green tea extract, l-theanine, caffeine anhydrous, and cayenne pepper.
Read our full review of Transparent Labs PhysiqueSeries Fat Burner.
Burn Lab Pro by Performance Lab is another fat burner you can take while intermittent fasting. It contains coleus forskohlii root, HMB, cayenne pepper extract, black pepper extract, GTF chromium, and calcium which will quicken your fat loss progress.
However, Instant Knockout Cut beats both these fat-burning supplements if you are on an intermittent fasting routine.
Can I take fat burner supplements while intermittent fasting?
Yes. You can take a fat burner, pre-workout, or intra-workout supplement while intermittent fasting as long as it does not contain any calories.
Are all fat burners hunger suppressants?
No. However, if you are hungry throughout the day on a fat loss program, you should prefer fat burners that contain glucomannan, cayenne pepper powder, or other appetite-suppressing ingredients.
Is it normal for a fat burner to give you jitters?
The jittery sensation is usually caused due to high caffeine content in a supplement’s formula. If you have high caffeine sensitivity, you should prefer a low or stim-free fat burner.
Check out other fat burners:
- Best Fat Burners for Men
- Best Fat Burners for Women
- Transparent Labs Fat Burner
- Transparent Labs Fat Burner Stim-Free
- Leanbean Fat Burner Review
The Bottom Line
As effective as Instant Knockout Cut might be, it doesn’t work in isolation. Roar Ambition hits the nail on its head when they say, “If you take Instant Knockout with a healthy diet and regular exercise, chances are you won’t need anything else.”
Instant Knockout Cut is great during intermittent fasting because it provides you with the necessary micronutrients, appetite suppressants, and thermogenics to help boost your metabolism, which can help you burn more fat without breaking your fast.
Although intermittent fasting can be effective for fat loss, it can lead to loss of muscle mass if your body starts breaking down muscle tissue to use as fuel. Hence, you need a fat burner that preserves muscle while optimizing fat loss, and Instant Knockout Cut does just this, making it one of the most potent and popular fat burners on the market.
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