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The 18/21 Nutrition Strategy: A Simplified Diet Approach

Transform Your Physique Using This Easy To Follow Nutrition Plan

By: Zack Mathews, NASM - CPT, CES, & PES, PN-L1


There’s a growing trend relating to flexible eating.

Too many people are rationalizing their food choices by saying “I’m doing flexible eating”.


  • “I’m flexible eating so I can have this doughnut”


  • “I can have drinks at happy hour on a Tuesday night because I’m a flexible dieter”


  • “This bag of chips fits my flexible diet so I’ll eat them”


When you pair those justifications with the fact that most people drastically underreport how much they are really eating, it makes it harder to get results.

Let me make something very clear.  

There is nothing wrong with any of those foods above. 

You can eat all of them and still lose fat, build muscle, or go after any other aesthetic goal of your choosing as long as you are in either a calorie deficit or a calorie surplus.

But there needs to be a level of discipline to your diet if you really want to get results.  

This doesn’t mean you have to eat chicken and broccoli for the next 12 months.  It does mean you have to clean up your diet and pick your spots where you are going to be flexible.

That’s what the 18/21 rule is all about.

What Is The 18/21 Nutrition Strategy?

The 18/21 simplified diet approach is great for people that are inconsistent with their macro tracking, it causes them stress, or they have become “too flexible” like the examples I gave above.

The 18/21 rule is simple.

Most people eat 3 meals a day, 7 days a week.  That’s 21 total meals.  18/21 of those meals must consist of minimally processed foods that are high in protein and micronutrients.  These meals will have a mix of:

  • Lean proteins
  • Healthy carbs
  • Good fats
  • Vegetables
  • Fruits


These meals are your golden tickets to getting results. 

They are REAL foods that are going to fuel your body to better results and you are going to look and feel better when you consistently (18/21) eat like this.

18/21 Sample Meal Recommendations

Simplicity is key for your 18/21 meals. There isn’t more than 6 ingredients (not including seasoning or sauces you use) in any dish below.  Spending 2 hours a day cooking complicated meals you see on Instagram is going to burn you out quick.

Instead, focus on meals like the examples below.

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Foods To Prioritize For Your Simplified Diet

I’m sure you’ve noticed a theme with the sample meals I provided above.

You want foods that are mainly unprocessed, are nutrient dense, and have lots of volume to keep you full.

You can always substitute out certain items for others that you enjoy.  Prioritize these and you’ll be in a good spot:

  • Protein: Meats, fish, and poultry - lean ground beef, lean steak, beef jerky, ground turkey, turkey breast, chicken breast, pork chop, salmon, white fish, shrimp 
  • Protein: Dairy - milk, cottage cheese, greek yogurt 
  • Protein: Other - tofu, eggs, egg whites, edamame, protein powder, protein bars 


  • Carbohydrates: whole grain wraps, whole grain bread, oatmeal, beans, lentils, whole wheat pasta, sweet potatoes, ret potatoes, russet potatoes, white rice, brown rice, quinoa 


  • Veggies: zucchini, tomatoes, all colored peppers, asparagus, onions, broccoli, lettuce, spinach, kale, celery, carrots, green beens, peas, mushrooms 


  • Fruits: bananas, grapes, apples, blueberries, strawberries, raspberries, oranges, peaches, pears, cantaloupe, watermelon 


  • Fats: extra virgin olive oil, avocado oil, flaxseed oil, coconut oil, peanut butter, almond butter, avocados, almonds, walnuts, peanuts, cashews, sunflower seeds, ghee 
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What Are The Remaining 3/21 Meals?

If you eat 18/21 solid meals each week, that will put you at 85% consistency.  That’s a decent spot to be at.

The remaining 3 meals are your flex meals where you can enjoy your favorite foods guilt free.

Pizza and beer with the boys? Enjoy.

Taking your kids out to their favorite restaurant for their birthday?  Enjoy.

Want to make spaghetti and meatballs? Enjoy….now I’m hungry…

I don’t expect you to be a robot with your diet. There has a to be a level of flexibility in order for you to stay consistent with your 18/21 meals.

Snacking On The 18/21 Program

When you consistently eat 3 protein rich, nutrient dense real food meals, it’s going to help keep you full between meals.  

1 optional snack will be allowed each day on this program that will stay within our trend of being REAL food.  No cookies, chips, crackers, or granola bars.

Sample snacks options include:

  • Protein shake
  • Protein bar
  • Any fruit
  • Any vegetable
  • Greek yogurt
  • Cottage cheese
  • Edamame
  • Beef jerky

Daily Flex Allowance

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I’ve always said you need to be at least 80% consistency with your nutrition to see results. 

With the 18/21 technique, that puts you at 85% so if needed, you can have a small allowance of calories each day for flex items, which will bring you to 80% consistency.

I do this to help prevent a binge when your flex meals come and/or to take the edge off after a hard day of work, training, dealing with kids, building a business, school, etc etc.

Up to 100 calories each day can be used as flex calories to use at your discretion.  

These do not replace your 18/21 meals or your 1 protein snack each day.  Those are your priorities and need to be hit each day.

Examples of your flex calories can be:

  • Adding creamer to your morning cup of coffee.
  • Having a piece of Ghiradelli chocolate at the end of the day.
  • Having fruit with whip cream as you watch a Netflix show.
  • A piece of bread with a smear of peanut butter.

As you can see, these choices are small portions meant to take the edge off.  You’re not going crazy with a whole pint of ice cream.  Be smart with your flex calories. 

If you are trying to bulk up, your optional flex calories can go up to 300 - 500 calories.

18/21 Variations

Everyone’s eating styles and goals are different so tweaking the program is acceptable if it will help you be more consistent.

Two primary tweaks based on clients goals include:

  • 12/14 approach for people who don’t want to eat 3 meals.  Instead of 3 meals you will have 2 meals and 2 snacks per day.  12/14 meals a week will be required to hit your 85% consistency.  That will allow you 2 flex meals per week.  Your 2 snacks still need to be protein focused.
  • 18/21 + 1up for a more muscle gain / weight gain approach.  For those looking to bulk up, we’ll need to increase your calories.  Everyday you’ll do the 1up technique that will add a 4th meals, a second snack, or an additional add-on to each meal such as a glass of milk, handful of almonds, etc.

Tracking Progress With The 18/21 Simplified Diet

You’ll want to be aware of your progress and make tweaks when needed.

As we discussed earlier, the only way to lose weight is if you are in a calorie deficit. 

If you are following the 18/21 technique and not losing weight, you need to audit your diet and see where you are eating too many calories. This could be from:

  • Not hitting 18/21 meals each week.  More flex meals usually results in more calories.
  • You’re snacking more than the prescribed 1 protein snack.
  • Portions are too big with your 18 meals (usually this is not the case).
  • Being out of control on your flex days.  There is a difference with having a flex meal of 3 pieces of pizza versus a meal of 6 pizza slices, 10 wings, 5 beers, and a Dairy Queen blizzard.

The alternative is true too.  If you are trying to bulk up and not making progress, you aren’t eating enough calories. This could be from:

  • Portions are too small for your 18 meals.
  • You’re 1up choices aren’t adding enough calories.
  • Skipping meals from your 18/21.
  • Being too flexible and eating too many meals that aren't providing enough nutrients to build muscle.

In order to track progress:

  • Weigh yourself everyday and log it so you can track the trend.
  • Take measurements every two weeks of your neck, chest, stomach, waist, thigh, bicep, and calf.
  • Take a progress photo every two weeks from the front, both sides, and back.
  • Track progress in the gym to ensure you are moving the needle with your weights, sets, and/or reps.

18/21 Simplified Diet Approach Recap

There's nothing special about this way of eating.

Just like any diet out there, you need to eat less calories than your body burns (calorie deficit) to lose fat, or eat more calories than your body burns (calorie surplus) to gain size and muscle.

What it will do is help you stay on track and become disciplined with your eating.

If you stay consistent with your meals, eliminate useless snacking, and eat your flex meals with your goals in mind, you will get results.

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