≡ Menu

The 3 Week Diet by Brian Flatt: Our In-Depth Investigation

3 week diet

If you are looking to lose weight fast and have the discipline to stick with a tough diet for 21 days, the 3-Week Diet fills your need. It provides a rigorous workout schedule, exacting meal plan, and tips on how to keep with it.

Brian Flatt created the 3-Week Diet through observation of his clients. His goal was to create a diet plan that worked for everyone. His opinion is that this is the diet to end all diets. It’s an amalgamation of low-fat, low-carb, calorie-counting, fasting, and raw foods diet.

You will lose weight on this diet if you follow it exactly.

The 3-Week Diet In Review

When I read about the diet, I found most of the nutritional information to be outdated, disproven, or just plain wrong. He got a few things right, but not much. There is also very little information on how to transition back to a normal life.

attention sign

Then, I read the diet plan and the workout plan. Despite the imaginary nutritional information he created, he actually got the exercises spot on!


He reviewed “over 500 medical studies, dozens of diet books and reviewing hundreds of diet systems, programs, gadgets, pills and potions” (direct quote from the book).

To put that into perspective, as a nutritionist, I read 500 medical and nutritional studies per month. There are over 20,000,000 (that’s 20 million) diet books on the market, and a total of $10,000,000,000 (that’s billion with a B) supplements, gadgets, and pills on the market per year.

He didn't use much information. There isn't even a reference to medical classes or anatomy. His background is like taking a first aid course and calling yourself a doctor.

Rapid Weight Loss

His plan works for people with no health problems, despite being overweight. This is good for a segment of people who are young enough to endure the rapid weight loss and rigorous schedule.

But I am concerned for the population that has diabetes or heart disease, who suffer injury, or who have been sedentary so long that the sudden shock of the 3-Week Diet will cause more problems than weight loss can cure. It’s equivalent to the weekend warrior heart attack.

heart attack

Diabetics and people with any kind of heart or cardiovascular disease especially need to use caution. This diet system is too much of a shock and too lacking on proper nutrition to keep these people healthy.

How We Get Fat?

Flatt clings to the decades disproven calorie-in/calorie-out theory of weight loss. He even goes so far to say that carbs have no impact on weight gain. He does get it right by saying that we don’t get fat by eating fats. (A calorie is a measure of heat that is produced when a substance is burned by fire.)

In the past decade, it has become standard in the medical and nutritional field to not mention calories, simply because they don’t exist in the body. Carbohydrates and sugars do, and have over 10,000 studies to prove excess sugars, especially from processed foods, directly influence obesity, hormonal disruption, diabetes, ADHD/hyperactivity, and mental function.

calories checking

He then goes on to talk about how we need to burn more calories, but never talks about the process of how that is done, just that we need to follow his system. Again, you can’t talk about how to burn calories because calories don’t exist.

Later in the book, he confuses the matter more by free exchanging calorie for sugar. He also has no understanding of the sugar-insulin cycles and the relationship of hormones for hunger, obesity, or energy.

Nutritionally, he tries to narrow what we need into less than 30 vitamins and minerals. Currently, we stand at over 100,000 nutrients that the body uses for health. In a healthy person, we can produce non-essential fats, protein, and phytonutrients from what we eat. But, if there is disease in a person, this ability is greatly reduced and over 80,000 nutrients are suddenly essential for health.

I also have great concerns over his reliance on whey protein. It’s not used in the medical setting because of a lack of bio-available proteins, contamination by anti-biotic and growth hormone residue, and the industry is riddled with recalls and product cancellations. There is a nice link to purchase his preferred brand of supplement, making me concerned that he uses it for profit, not health reasons.

whey protein

Many other supplements are required. The whey protein, omega-oils, and many other vitamins are required for this diet. In Flatt’s opinion, if you aren't willing to do it all, and use his preferred brands, you will fail.

He actually does get it right when he recommends adding healthy fats to the diet. However, this recommendation conflicts with the restricted calorie diet later on.

The Undisputed Rules

​There are 4 rules to not get fat. As a nutritionist for more than a decade, I can say this is the first time I've ever seen them. They have no basis in medicine or nutrition. They may be his rules, but they are not the rules the body follows.


This is used frequently in the 3-Week Diet System. Fasting is good for the body, but it requires at least 48 hours for the body to switch metabolic pathways. This diet recommends less than 24 hours. This is enough time to make a person really famished and uncaring of the plan, but not enough to trigger healing.

The timing is also suspect. He recommends starting in the afternoon and run into the next afternoon. No expert recommends this. It’s much easier on the body to follow natural cycles of fasting from morning until night, or for one total day.


functional training

It’s obvious Flatt is an exercise trainer, and I suspect a very good one too. His information on exercise is spot on and good for most people. He gets a bit weird talking about receptor activity and getting fat, most of which is wrong, but otherwise it’s good information.

​3-Week Diet Meal Plan

This is the low-carb diet meets low-fat diet. In order to follow the low-calorie diet restrictions, fats are reduced. Since you reduce your carbs and your fat, your pickings are slim for food. It’s one of the main reasons why the whey protein makes such a starring role: it’s just about the only thing you can eat in quantity.

If this diet went on any longer, I would be scared for nutritional deficiencies. Out of the over 5,000 types of fruits and vegetables available, the 3-Week Diet, Week 1 limits you to 17.

He limits drinks to water. This is a good thing, since most people don’t drink enough water to meet normal needs.

The recommended first meal is lunch, with the last meal being just before bed. This flies in the face of all the studies on eating habits. We require breakfast to lose weight. Skipping it slows our metabolism.

The rest of the plan is a complex mix of calculating out different calories, supplements, and fasting habits. This isn't for the faint of heart.

At the start of the second week, you fast for 24 hours. Supposedly, this is for a detox purpose, but it’s not long enough to actually start the body into any other metabolic pathway other than carbohydrate metabolism. In the end, you are just going to be hungry.

Then, comes the really hard part. This diet wants you to get 80% of your calories from fat, and still keep under about 1200 calories. This means nearly 900 calories come from a source that does not fill you up. Only about 300 calories will come from any food source.

To put that in perspective, a dinner of 3oz of steak, 1 cup of broccoli, and a medium baked potato is 300 calories. That would be your total daily allotment in 1 small dinner. Additional recommendations call for using nuts (50-70 calories per oz), avocado (50 calories per cup), and cream cheese (100 calories per tbsn) as additions. As you can see, it would difficult to include them in the 300 calorie allotment.

3 week diet plan

The diet wants you to have 3-4 meals. I don’t know how it’s possible, unless you are eating nothing but bitter vegetables smothered in butter.

The final phase of the diet depends on a series of complex calculations to know how many supposed calories you spend at different activities and then totaling them up. It takes nearly 5 pages of the book to just explain the process. Now, I have advanced science degrees (yes, plural), with several years of calculus. I still couldn't follow the process:)

3-Week Diet Workout Plan

Here is where the 3-week diet shines. Despite not getting the nutrition background right, these exercises are top notch. He’s also absolutely right saying consistency is the key. This diet has exercises for every single day. It even highlights a warm-up period, necessary to avoid injury.

The book has diagrams of proper positioning and technique for each of the exercises and written descriptions. They even describe the correct ending positions and what to look for in muscle fatigue. I think this is vital information and he does a good job at describing it.

3 week diet Brian Flatt

The plan is intense. You really need to give it your all, just like the diet calls for. There are many reps and cycles in each of the exercises. When you start to build the muscles up, the exercises become easier.

To start it all off, he talks about the easiest, most effective, and universal exercise (plus it’s free): walking. Walking is essential to the diet and overall health. It’s great to see a diet that uses this as such a integral part of the whole.

walking is good for health

Our big concern is pre-existing injuries. This diet supposes you are healthy and injury free, despite being overweight. If you have an injury that prevents you from doing some of the exercises, it may be difficult for you to get the full experience.

3-Week Diet Motivation Plan

Motivation is key to losing weight and keeping it off. This diet has help for motivation.

Keeping a journal is the #1 way to lose weight and keep it off. It helps greatly to know what you have eaten and when you ate it. There is a section in the system dedicated to keeping a journal. Flatt even relates journaling to the rest of your life. He’s right in saying this is a total life experiencing.

There are also several smaller ideas to use. Some of them, like eating out and using seasonings are universal. They are very helpful suggestions. Others, like sleeping less and zero-calorie mouth entertainment (gum), are not so practical.

The basic message is to just keep pushing through. It is tough to lose weight and keep on a good track. The little blurb about Dr. Roy Baumeister, sums it up nicely: will power fatigues the rest of the body. It takes work to keep it up. But, we shouldn't give up because it’s hard.

Can You Lose 10 Pounds in 3-Weeks on This Diet Plan?

Yes, if you follow the meal plan, the exercise plan, and keep it up for 3 weeks, I firmly believe you can lose 10 pound. I think you could follow the 3 week diet plan to lose 15 pounds.

The biggest thing to remember about this diet is that it’s temporary and it doesn't teach you much about living your life day-to-day.

3 week diet plan

If you go back to eating a poor diet filled with junk, you will put the weight back on. Then, you diet again. This yo-yo effect is known to increase your risk of heart disease 200%. And unfortunately, it’s the stance that the 3-week diet takes.

Don’t take the ‘science’ presented in the 3-week diet to heart either. As we showed, it doesn't follow any of the proven facts about nutrition or physiology.

While the 3 week diet system is a good kick start to exercising healthy, it’s not recommended you follow it for the long-term. After getting started, follow a healthy diet and you won’t ever need to lose weight again.​

Click Here to Learn More About 3 Week Diet Program by Brian Flatt *

About the Author: Christina Major is a Holistic Nutritionist, Traditional Naturopath, and Herbalist. She has a Master’s degree in Holistic Nutrition and an advanced degree in Traditional Naturopathy. Further certifications in herbalism and metabolic typing. She owns and operates Crystal Holistic Health Consulting based in PA, the USA since 2010.

You May Also Like These Posts:

Leave a Comment:

  • Phil says:

    Thanks for this real review. It seems the most of the ones that I’ve read are bought in by just the way the information is presented instead of putting real science and medical evaluation against the claims. I watched half the presentation, noticed that I could not see a status bar and began to question the validity. I even tried to close the site and was “offered” a 50% discount ($27 total cost) if I stayed on the page. Again, thanks for the information, it clarified what I was taking away from it myself.

    • Dima says:

      Hi Phil,
      Thank you for the nice comment. I really try being as honest and objective as I possibly can when reviewing programs and products. I am sorry that this diet is not what you were looking for. I have some other weight loss related material on the weight loss category. Perhaps some of it might interest you. Thank you once again for the positive feedback.

  • Gina Caruana says:

    I have written to Mr Flatt for a refund of my money, as the diet wasn’t working for me, numerous times. He promised me that he would, but as yet have not received one cent back. He should treat his customers with more respect.

    • Dima says:

      Hello, Gina!

      I totally agree with you. You see, our review about his diet program is not completely positive. He promises that “I will refund every single penny of your investment into the system — no questions asked”. If you still cannot get your money back from him directly, I advise you to ask at ClickBank.com support, where this program is hosted. Here is the direct link- http://www.clickbank.com/corp/support/. Hope it helps.

      • Jacqui says:

        The first time I did this diet I cheated slightly and to be honest I could not be bothered to do it properly. I contacted Brian and he immediately gave me my money back. Out of desperation to lose weight I bought the diet again. My head is in the right place and I have followed it to a T. So I’m on my fifth day and I have lost 9.2 lbs already with not much trouble. I have even emailed Brian twice to ask him some questions I had and both times he answered me. What diet plan gives you that. 🙂

        Perhaps it is just second time lucky but I am thrilled and have not managed to get under 11 stone on any diet and trust me I have dieted for years. I have not done the exercise bit apart from the daily walk but that is the lazy in me. I plan to in the next day or so.

        I feel like a new woman already. I hope the rest of the diet is as effective.

        • Christina Major says:

          Hey Jacqui!

          Congratulations on your weight loss. We find this diet does work for people when they do it as recommended. And we agree with you; it is a difficult diet to follow. We hope you continue with the exercise and dietary changes, so you keep the weight off. Let us know how you do!

    • chiqui says:

      Hi Gina,

      I really wanna try the program, however, I’ve seen people complaining about the money back guarantee and that makes me skeptical about the program. How was it like for you? And if it’s okay, do you still have the program, and would you be kind enough to let me have a copy? I would really appreciate it. Thanks!

    • Esbee says:

      Hi Dima
      I just wanted to put this out there that I was able to receive a full refund by calling this number (800) 390-6035. 🙂
      Its the clickbank number. Writing to Brian Flatt was absolutely useless.

      • Dima says:

        Hi, Esbee!

        So glad you’ve found the way to get a refund! Yes, this program is hosted and sold by ClickBank company, so you can ask them for a refund for sure. Here at this page, you can ask for the refund and contact ClickBank customer support. Here is their Return and Cancellation Policy.

        Thank you for sharing with us!


        • Monica says:

          Thank you for this! I sent multiple emails about a refund and was met with complete radio silence. It was very easy to receive a refund after calling ClickBank though!

          • Dima says:

            Hi, Monica!

            I’m glad my advice has helped you. It’s always advisable to ask the service provider that hosts eBook in case the vendor doesn’t answer.

  • chiqui says:

    Hi, Dima!

    Your detailed insights for this program is remarkable. I’ve been reading reviews the whole day because I am planning to purchase the program, but it makes me have a second thought. I am not sure if $47 is really worth it. Thanks for your honest review.

    • Dima says:

      Hello, Chiqui!

      Hope our review will help you to decide. As you said, there were a few people who complained about the money back guarantee. It was a problem to get their money back. Please pay attention.

  • Andrew Neil says:

    Wonderful review thanks

  • Elizabeth says:

    Hi Dima! Thanks so much for this awesome and in-depth review! So helpful!

    One thing I was a bit confused on — you mention that the diet is “low fat meets low carb” but then you discussed how the 3rd phase is mostly fat. I’m assuming that the first phase is low-fat then?
    Are you allowed to eat fruits on this, and if not, this seems exactly like the Atkins diet (with a fast in between), no?
    And, one last question, re: the fat phase, you said “This means nearly 900 calories come from a source that does not fill you up.” — I was a bit confused…I was always under the impression that fat digests slowest and therefore fills you up, no?

    Thanks so much again for all the helpful information and taking the time to write this review and answer our questions — I really appreciate you and your website!! 🙂

    • Dima says:

      Hi Elizabeth!

      Thank you for your questions and your kind feedback.

      You have a sharp eye to pick this out.

      Yes, this diet goes through more changes than the weather. Parts of the diet are extremely fat limiting, other parts are fat focused. It’s one of the reasons we don’t like this plan.

      Parts of the diet are similar to Atkins, but it’s not very close. And the science behind Flatt’s diet is mostly invented by him.

      As for the ‘not filling you up’, fat is not extremely nutrient dense. Yes, it is the macronutrient that stimulates our satiety hormones and makes us think we have had enough to eat to satisfy our nutrient needs.
      However, it does not fill the stomach. Once our body realizes that the stomach does not have enough food and there isn’t enough nutrients, we will revert to being hungry again.
      As a frame of reference, 4.5 oz (100g) of butter is 900 calories. This is 1 stick of butter. Can you imagine going several days with eating barely anything more than 1 stick of butter per day? How full do you think you will be?

  • Jon says:

    I agree with the above commenter…….this does sound a lot like Atkins…….besides the 24 hour fast it seems like the exact same thing……..are you not allowed fruits at all throughout the thing? if thats the case, might as well call this atkins……..lol

    • Christina Major says:

      Hi Jon!

      I’m glad you joined the conversation.

      This diet is a little different than Atkins. In Atkins, they focus on the nutrient intake and vegetables. Atkins sides with nutritionists and realizes calories are nothing but a fictional number.

      Atkins also stresses quality over quantity.

      This diet here is focused on cutting a huge amount of food from your diet based on calories. Pushed to the extreme, you could eat ice cream the entire time because the nutritionals are so poor.

      Atkins is also designed for a lifestyle change. While they do have a huge focus on weight loss, the end of the plan is designed for you to be able to continue to eat healthy foods at an acceptable level for the rest of your life. Flatt’s plan has nothing for a lifestyle change or anything after his 3 weeks.

      Atkins is based on real science. Flatt created most of his ideas around disproven theories.

      The one thing that is better about Flatt’s plan is his exercises. Atkins is only diet. We feel exercise is an important part of weight loss and Flatt’s exercises are very good.

  • Rebecca says:

    Hi Dima

    Very interesting review. I’m on day 1 today. I’m going on holiday for 3 weeks and this diet seemed to suit me perfectly as I never eat breakfast anyway so it’s just a matter of changing what I eat for lunch & dinner. However I found that the high fat stage of the diet is confusing. But I figure if I just follow what he suggests in the book I should be good. My question is, I go to crossfit three times a week after work so do you think I could just substitute the exercises he has suggested with my crossfit classes instead?


    • Christina Major says:

      Hey Rebecca!

      We are not a big fan of this diet, as you read. The nutrition lacks greatly, even though the exercises are wonderful. If you are in perfect health you may be able to succeed on this diet. That means no heart problems, no sugar problems, no injury, no adrenal or hormonal problem… nothing.

      We are firm in our belief that you may lose the weight, but you won’t keep it off. That take real changes this diet completely lacks.

      The fat section is very confusing, and even with well over a decade of studying nutrition, I couldn’t follow it. There was incorrect information and things that were confused. The whole basis of low-fat is now shown to be wrong and in conflict with weight loss.

      As for the exercises, he has some amazing and helpful exercises. They would be a great way to get variety.

      However, we recommend against skipping your gym routine for this 3 week diet plan. You already established the habit of going to the gym and doing those exercises. Cross-fit is an excellent exercise program. If you take a break, your chances of returning to this good program fall to less than 50%.

      So, you need to ask yourself: what is more important? Long term health and fitness or a short diet that’s really hard and complicated?

      If you want long term health and fitness, stick with your gym and an overall healthy eating pattern.

  • Lynne says:

    This plan is the only plan that has worked for me. I lost 45 pounds after 3 rounds. I highly recommend this plan. I made an excel spreadsheet with the phases, nutritional, exercise, and supplement requirements. That really helped me stay on track and get a better understanding of the plan.

    • Christina Major says:

      Hey Lynne!

      Congratulations on losing the weight.

      Keeping track of what you eat, how you exercise, and what supplements you take are huge steps in any weight loss program.

      We are glad this program worked for you.

      Every diet has worked for somebody, and we evaluated this plan based on how it works for most people.

      What we tried to show where the pros and cons of this program so people can make an honest evaluation.

      We’re glad you had the dedication to follow through.

  • Elan says:

    Hey, anyone.
    So I wanted to buy a copy of the two week diet before and was excited to try it out because i’m desperate to lose weight but what if it doesn’t work for me?
    And its kinda hard to get my money back so could any of you share their copy with me, please I’m really desperate to try it out but I’m down on money and can’t afford to spend that much on a plan that won’t work

    • Christina Major says:

      Hey, Elan.

      Because of the copyright, we can’t share our copy of this diet.

      We recommend contacting the company directly to see if they will send out a complimentary set.

      If you are having difficulty financially, we recommend contacting a local YMCA, a local health clinic, or certain churches that have weight loss classes.

      There was also a tremendous amount of information on the internet for free.

  • Amanda says:

    Hi, I’ve been trying to figure out what I’m specifically supposed to eat during each phase. Specifically day 1. Do you have a food journal from this experience?

    • Christina Major says:

      Hey, Amanda!

      I’m very sorry, we haven’t specific diet plan which describes each meal. Brian Flatt gives the diet overview in his book:

      “The 3-Week Diet is similar to a Protein Sparing Modified Fast, in that we will “trick” the body into entering a 24/7 fat-burning “starvation” mode, while we provide it with the appropriate amount of a protein that it needs so that lean body mass is spared…not to mention the added thermic effect of digesting that protein. In addition to carbohydrate restriction and strategic protein consumption, we will add quality, healthy fats to enhance our fat-burning goals. We limit the fat in this diet to EFAs (essential fatty acids) and the trace amounts of fat in the allowed foods.

      We will increase our protein consumption because it helps preserve lean body mass and it keeps our metabolisms cranked up.

      Drinking adequate amounts of every day is absolutely essential for weight loss. My advice is to drink 8-10 glasses of water every single day.

      Meal frequency is a key component to losing weight on the 3 Week Diet. By eating five meals a day as prescribed in the 3 Week Diet, you will significantly increase your metabolism, effectively build lean muscle and increase the amount of fat you burn on a daily basis”.

  • Mia says:

    I’m not sure what the commotion is about?

    The diet is laid out simply in the book. If you read it and follow it you lose weight, easy.
    I’m on my third week and have gone from 80.7 kilos to 74. 1 and that was with me adding apples and coffee with milk.

    If you want to lose weight just follow it. Easy.

    • Christina Major says:

      Hey, Mia!

      We’re glad you were successful in the program. The review we did lay out the objective scientific basis for the diet. There are good points, and there are not so good points. Many people enjoyed had success, like you. And we agree with you that if people can’t lose weight on this diet, they may be didn’t follow the plan as it was laid out.

  • What the * means above

    Please note that the links that have a * next to them are affiliate links and those help finance the iFocusHealth.com website and provide you with more free content. If you end up purchasing through those links we will earn a small commission. There should be no difference for you whether to go through the affiliate links or directly to the same web address. The cost of the products will never negatively affect you. Actually, the opposite is the truth since in some cases we are able to negotiate a better price for those purchasing through our links.

    The content on this website is never impacted by the affiliate links. All the reviews are non-bias reviews and reflect our real opinions. If there is no affiliate option to a product we recommend, it will still be included in our posts just with regular links pointing to it.