How The 3 Week Diet Will Make You Lose 23 Pounds of Fat in 21 Days.

By | November 23, 2014

Website URL: 3weekdiet.com3weekdieth
Ease of Use: Very easy-moderate.
Guarantee: 60 days.
Cost: $47.
Average Weight Loss: 23 pounds in 21 days.
Overall Effectiveness: 4.5 out of 5 stars (Excellent).

The 3 Week Diet is by far one of the most interesting weight loss plans I have come across and I think you may find yourself of the same opinion after reading this article.

After reading many diet books (some of which are good such as Whole30, Eat Fat, Get Thin, Doctors Diet, ect…) and seeing different strategies, testing them and expanding my knowledge on all of this, I would say this plan stands out in many ways, positively that is, especially when it comes to results. 

Here’s 5 things you need to know about this plan right away:

1) Depending on how you complete it, it can actually be shorter, anywhere from 12 to 21 days long.

2) It is true you can drop as much weight as it claims (20+ pounds and I’ll explain how).

3) You’re not just dieting one way through this plan, you’ll be going through 4 different and proven weight loss strategies.

4) The part where you “Exit” out of the plan is one of the most flexible and pragmatic solutions I have read about. It is not a diet plan where you must eat a certain way for life. In fact, you can literally eat anything you like after it, but with one rule in mind which I’ll also explain.

5) The purpose of this plan is to help release the fat you have stored in your body and transfer it into energy to build muscle and/or flush it out. Whether it’s 10 pounds, 20 or more, this diet helps get rid of it, but in reality, I’d say it really turns that fat into fuel to feed your body and help it improve.

Alright, let’s get into the plan itself. How does it actually work?

Every weight loss plan I have ever read about has focused on 1 type of dieting approach and most of them really come down to eating healthy and exercising, which to this day is still the most stable way of gradually reducing weight that frankly, I recommend everyone do…

But the 3 week diet is not a “single style plan”. It is actually a combination of 4 different weight loss strategies, proven to work. What are these strategies? 

Here is the summary:

Phase 1: Eat low carb foods for about 7 days.

Phase 2: 1 day fast (intermittent fasting strategy).

Phase 3: High fat diet eating for 4-5 days. Yes. High. Fat. Hold of on the skepticism until you read why this works below.

Phase 4: Eating ANYTHING you want, but making sure it’s under your BMR (a measure of how much you should eat daily).

And that is the summary of the 3 week diet, but as I’ll go into details, there’s lots of foods, choices and rules that go into each part.

Quick note about the author and his strategy:

Brian Flatt is the creator of this plan. He basically is a very knowledgeable fitness expert who created the strategy to basically remove excess fat from the body as quickly as possible because he sees it as a problem to anyone’s health.

Extra fat in the body, in large amounts especially can lead to people developing diseases and various unhealthy conditions.

Shortly put, Brian says 1 pound of fat is equal to 3,500 calories (well this is more of a fact). Burning that much everyday is very difficult under normal conditions, especially if people are already eating wrong to begin with.

The 3 week diet basically attacks this excess body fat through the 4 phases I am about to explain in more detail so what would usually take someone months to do to burn off 10-20 pounds of fat will take MUCH less with the 3 week diet.

The 4 parts of the plan explained (and why they work), with sample food lists:

Phase 1: This is the low carb phase basically. You’ll eat a combination of vegetables and proteins.p1

It will last for 7 days and you can lose up to 10 pounds during it.

Directions for this phase:

Day 1: Eat nothing but vegetables, 3-4 times throughout the day and drink water. You are allowed to eat as many vegetables as you like.

Days 2-4: Starting the next day, you can add up to 2 protein meals to your meals. You still eat 3-4 times a day, but it rotates:

Meal 1: Vegetable only. Meal 2: Protein only. Meal 3: Vegetable only again. Meal 4: Protein only again. 

While vegetables are allowed in limitless amounts, you are allowed up to 25 grams of protein.

Days 5-7: 3-4 meals once again throughout these days, but now every meal can be mixed. In other words, now you mix vegetables and protein into 1 meal. Same rules for protein & vegetable amounts.

For drinks, only water is allowed.

A sample food list:

  • Vegetables: Tomato, carrots, artichoke, spinach, squash, cabbage, broccoli, boy choy, beets.
  • Protein: Eggs, fish, turkey, chicken, beef.

There are more allowed foods within the book itself.

Why this phase works:

As most of us know, low carb diets work because they restrict carb intake and cause the body to burn of fat storage’s in the body.

This is accelerated in the first phase of this plan which is why it’s not uncommon to lose 5-10 pounds on it within the first week.

By also drinking water, Brian says you will cleanse the liver. This plays a role for future weight loss as it helps the body clean itself.

Phase 2: The intermittent “fast”. Only 1 day long.p2

Day 8: While only allowed water, you are supposed to not eat for 24 hours. Brian suggests a smart strategy to get over cravings you may have by targeting the timing of the 1 day cleanse at a particular time so you basically get through most of it sleeping.

Why this phase works:

Intermittent fasting is proven to cause weight loss for obvious reasons (you eat nothing, so body creates energy from fat deposits).

I have personally tried cleansing before, for a few days actually but in this phase, 1 day is really enough to trigger fat burning since the body is going to be in a fasted state for quite awhile. 


How much weight you can lose here varies because it depends on how much you’ve lost during phase 1 already, but a 24 hour none eating period will add to the weight loss for sure and continue the fasted state and burning from the body.

Phase 3: The most controversial one…a high FAT diet. 3 days long.p3

Directions for this phase:

Days 9-12: If you’re a man, eat under 1,500 calories a day and for women, eat under 1,200 calories a day, but 80% of the food intake has to be from fat. 3-4 meals again. You can drink water and coffee here too.

Sample foods:

Avocado, bacon, salmon, nuts, coconut oil, eggs, mayonnaise, steak, butter.

Why this works (evidence of why eating fat works):

The big deal here is that fat itself is actually good for you. The fat we fear is the one which comes from eating too many carbs which turns into fat that stays in the body. Brian also points to good fats we should be eating vs the bad ones.

The good fat we get from food lowers inflammation via omega 3’s and feeds the body as well as helps it metabolize faster. 

For evidence, Brian points to several studies. I will name 2 which I though were amazing:

Evidence 1: Brian points to 4 groups of people who ate a 1,000 calorie diet, but one group ate a majority of high fat foods. All 4 groups ate for the same number of days and the same number of calories and the HIGH FAT group lost the most weight (this is called the Kekwick and Gaston study).

Evidence 2: On page 82 of the 3 week diet book, Brian cites a man who runs a weight loss blog where he ran a high fat eating experiment by eating 5,000 calories DAILY for 21 days. 

5,000 calories is already more than twice the intake most people need. However, the man who ran this experiment only gained 3 pounds after doing this for 21 days. 

Considering he ate more than twice that type of food and more than twice the intake of calories, he should have, by basic weight loss “facts” gained more…but he didn’t which proves that high fat diet (especially in limited caloric intake) make you lose weight, not gain it.

Phase 4: Days 12-21. Technically the end of the plan because you can eatp4 anything you want.

The key to this final phase is determining your BMR, which is the caloric intake your body needs DAILY. Brian provides a formula for this, one for men and one for women.

I am a male, 29 and almost 6 feet fall and my BMR was around 2,200 calories daily. 

When you determine yours based on his formula, you will eat UNDER than amount until day 21. That is the rule to this phase.

You can eat ANYTHING you like. But if you need to lose more weight, Brian recommends a majority of the food you eat to be low carb again. Also there is a 15-30% goal which is the percent of calories you CUT from your BMR based on how much you want to lose.

People who are happy with their results here can just eat a little bit under their BMR level and enjoy life. People who want to lose more weight will choose to eat from 15-30% less calories than their BMR to lose even more weight.

Why this works:

Despite there being constant contradictions in the weight loss community on what’s good and not good, what has always been agreed upon is that eating “less” calories will always lead to weight loss. However, BMR is considered to be a TRUE indication of how many calories your body needs which is why when you determine it and less than the amount said, you’ll continue to lose weight.

Should you still have fat to lose, this will be done when you eat less than the BMR.

Technically, the whole program shortens if you eat anything you want after day 12.

Although the plan is officially 21 days long, if you eat anything you like by phase 4, you’ve basically finished the plan as it is so basically, it can be anywhere from 12-21 days long. 

Long term plan: Day 22 and on.

By this time, the 3 week diet is complete. If you are happy with it, you just have to keep eating at or under your BMR from now on. Any kind of food is allowed, but Brian recommends you eat less carb and basically more healthy to maintain your weight results and health moving forward.

The 3 week workout plan:

Brian inclues an additional 20-30 minute workout plan that you can do up to 4 times a week which isn’t long, but adds to the results you get. It mixes strength, resistance and cardio training (things like walking) but it does work together with the diet’s effect to further it.

3 Week diet final score:

4.5 stars

4.5 stars out of 5. This is a rapid weight loss plan and as evidenced, it uses proven to work weight loss plans in combination with each other. Excellent plan for people who need to drop 20 or more pounds in a short amount of time and great long term strategy as well.



This weight loss plan is most recommended to people who truly need to drop that weight quickly. This is one of the more natural approaches to losing a lot of weight quickly that really does work well.

What the 3 week diet can do in 21 days is something that through normal dieting may take people many months to accomplish and while that works too, I would recommend this plan for those seeking a faster alternative.

And one more very important thing again is that the plan is designed to work long term, without any Yo-Yo effects.

If nothing else, the book itself was a joy to read for me personally and this plan has been one of the ones which really changed my “traditional” way of thinking about weight loss for the better.

In short, this is a very good book and a very good weight loss plan.

47 thoughts on “How The 3 Week Diet Will Make You Lose 23 Pounds of Fat in 21 Days.

  1. Erica

    Hello. Thanks for your post. I’m going to try it. During phase 1 am I allowed to put salad dressing on the vegetables?

    1. Vitaliy Post author

      It’s not recommended Erica, you will however be able to use dressings and other types of condiments during phase 3 as long as they are consistent of healthy fats.

  2. Axis Labs

    I am quite doubtful about losing so much weight in such a short period of time. For burning deposited fat, we can give a try to fat burning supplements.

    1. Vitaliy Post author

      Fat burning supplements tend to force the body into performing unnaturally high operations to burn fat which may sound good, but I have personally never heard anything good post taking fat burning supplements from people. Also people tend to use them as an excuse to keep eating badly, but through these supplements to cheat the weight loss by taking those pills. It’s not something that will end well.

  3. Robin

    The first phase is a good one for me as I have used it before to lose weight. I have never lost a lot in 3 weeks, so I am thinking about getting the book. One thing that I am skeptical about is the high fat phase of the diet. Can you really claim mayonaise is a good fat? I do agree with the avocado and coconut oil as being ok fats, but I always thought mayo was bad! All in all, your content is very detailed and I may be getting this book!

    1. Vitaliy Post author

      Yeah mayonnaise is also something I too am skeptical about but if you’re concerned about that 1 food in the entire list, just omit it and do the fat phase of the diet with foods you can eat.

  4. Keith

    While I am not usually a diet fan this diet does seem to have many legitimate positives. Restricting carb intake is vital to loosing weight and it is an area that people fail in when trying to shed the pounds.
    The 1 day fast does sound very challenging, but it isn’t as extreme as many other weight loss that extend that fast period over a few days.

  5. sarahsalina

    I am quite skeptical about losing so much weight in such a short time. Do you think this is not hard on the body? Isn’t it generally healthier to lose weight gradually and then work on keeping it off? My concern with this diet is that after the 3 weeks, you will pile the weight back on and then some.

    1. Vitaliy Post author

      That’s an argument that is addressed by Brian in the book and people have the option to lose weight gradually via BMR reduction, but he says the bigger problem is the excess fat in people’s bodies that increasing their chances of diseases and other bad conditions and getting rid of it as fast as possible is the better option.

      The long term plan AFTER the diet is stable because after 21 days your cravings are said to change so it’s easier to adopt, plus there isn’t any kind of strict food restrictions.

    1. Vitaliy Post author

      When you complete the 3 weeks, see how your results are in the 4th phase and if you continue losing weight. If you do, then there’s no need to repeat it again. If you do want to do it again, wait sometime before you start up again, but ideally after you finish the diet the first time, you should aim to eat well and exercise to get to a more regulated weight.

  6. Kim James

    I just started the 3 week diet today. Now tomorrow how much meat do I eat with my first and third meal? It says 15-20 grams and that converted into ounces is not even an ounce is that right?

    1. Vitaliy Post author

      I don’t remember it saying that much Kim, but it is less than an ounce. Which page in the book was this specified on?

  7. PRIA

    In Phase 2, Fasting, does it mean no water?
    I can stay without food but without water will be difficult.

    1. Vitaliy Post author

      No matter what kind of fast you do, you can always drink water Pria!

    1. Vitaliy Post author

      You should keep taking any medication while on the 3 week diet Joan. But with diabetes, you will need to ask your doctor about this diet first.

  8. Jessica

    Do you know if veggies are still ok during phase three? I am a bit confused by this phase. I know we are supposed to eat mainly fat, but I need fiber! Lol

    1. Vitaliy Post author

      Vegetables are not part of the third phase Jessica, but this period is very short and after this phase, you can go back to eating any vegetable you want.

  9. Katya

    What if a person has already a very low bmr for example 1300 kcals..

    1. Vitaliy Post author

      If it’s that low, you probably don’t even have to diet Katya. You should speak with a doctor to see if this is normal for you or if you need a supplement.

  10. Christine Abresch

    I have to lose 20 pounds and eat a heart healthy diet, I am taking blood thinners and anti clot meds along with statins to reduce blood cholesterol…..can I follow this plan?

    1. Vitaliy Post author

      Hi Christine, your problem appears to be more about health, not weight but there is a diet known as the DASH Diet which is considered heart healthy I think would suite you better, but of course, talk to a doctor!

  11. Linda

    This is a diet that I want to try, but dread the thought of not having any coffee for a week, since that is what kickstarts my day! Three weeks is not a long time to try out a diet, and from the looks of it so far it could be something I could actually live with, I like most of the foods listed, now I’m trying to see if I can get any results, thank you for the very detailed information.

  12. Madz

    Are there any specific foods that needs to be/ cant be eaten in phase 4?

    1. Vitaliy Post author

      There wasn’t a list for Phase 4, only that you eat less than your calculated BMR.

  13. Rebecca

    I’m on day 1 and was wondering whether I could take Hydroxycut Hardcore Elite in Phase #1 (as that contains caffeine and Yohimbe) and should I have the Whey Protein with with my meals when it demands protein? Or should these wait until Phase #3?


    1. Vitaliy Post author

      I would wait until phase 3 Recebba or even 4 when you won’t have to wonder if this or that food is allowed.

  14. TD

    I’m about to begin this diet, but I have a question. For the first week, you can have NO tea or coffee at all?

    1. Vitaliy Post author

      Hi TD, that is correct, no coffee is allowed for the first week.

  15. Holly

    Thank you for this post. Can you use the whey protein in the first phase for an acceptable protein? I’m in my car a lot for work and it would make life so much easier:)

    1. Vitaliy Post author

      Hi Holly, in phase 1, it is better to use proteins at their source (no powder), so I would not recommend any whey. Try to use hard boiled eggs or chopped pieces of chicken as protein substitutes for this part of the plan.

  16. Nina

    Thanks for this post. I have bought the book and I am on my day 5 (already lost 2kg). I am loving it! I love that it explains the science behind it. It is easy if you drink at least 3 liters of water every day. First week without a coffee is hard but still possible. Every time you have cravings, DRINK A LOT OF WATER, it helps a lot! Fasting i find easy if you do 12 am / 8pm 8 hours of window. Will update you on results.

  17. Laura

    The first day, are mushrooms the only vegy a person can have? I cannot stand mushrooms of any kind. Thanks

    1. Vitaliy Post author

      Hi Laura, there are many more choices than just mushrooms. You can eat from a wide variety (most vegetables).

  18. Keran Elizabeth Fynn

    Hi. Thanks for this. Really cleared up the little bits of confusion I had. Starting this in February. I know we have to use Fish Oil supplements but do you know where the Whey Protein comes in?

    I don’t want to have to spend so much money on something and not end up using it. Thank You

    1. Vitaliy Post author

      Hi Keran, there is no fish oil or whey required in this diet. Those are only things you may want to use if you’re either trying to build muscle or have joint problems. You can use them in the 3 week diet however. If you exercise a lot, take them before or after your workout.

      You also asked about phase 4 and eating breaking, yes it’s ok to do it as long as throughout the day, including breakfast as long as you remain under your BMR.

    1. Vitaliy Post author

      Hi Monica, you can use any of the sample foods in the phase 3 menu. For breakfast, maybe a few eggs and avocado, for dinner, you can also eat that and add some bacon. Chicken high in fat can also be used and if you fry something, use coconut oil, it is high in fat too.

      Phase 4 is easy, figure out your BMR, then eat under the recommended percentage. After phase 4 is complete, just continue that way.

  19. Peter

    Hi Vitality,
    I like the idea of a diet that has an after plan to stop you putting back on the weight you have lost. Phase 3 is interesting where you eat 80% of fats, I recently saw something on TV about this subject. Apparently eating lots of calories from fats will send a signal to your liver to burn off some of your body fat or energy reserves.
    Apart from the fasting this doesn’t seem to be too difficult and I am sure many people could be successful with this diet. It’s good to see the workouts are an integral part of the diet and not too demanding but necessary.

    1. Vitaliy Post author

      Thanks Peter, indeed every phase after the first one is easy to ease into.

  20. ike

    Hi Vitaliy. Phase 3 is the one which interested me most. You’re going to be eating a high fat/low calorie/low carb diet and ironically with what Brian explains and the studies he cites, I guess we can lose weight right now since its the only way to live long.This means you can and will lose weight very fast and make sure it stays off. That’s a good diet.

    1. Vitaliy Post author

      Most people become interested in the high fat section of the diet Ike and that’s because it just sounds way different than anything we’re used to hearing about diets, but you can look up the evidence and see that it’s real!

  21. Ben

    I don’t know about eating only vegetables, fasting, LOL! I guess it’s worth it, considering it’s only one day. Pain makes gain, and not weight gain!


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