“Flexible dieting” is a popular weight loss program that’s based on a sensible theory.

Also called If It Fits Your Macros (IIFYM), it promotes the notion that there are no “bad foods” and allows you to choose any food, as long as it fits within your macronutrient needs.

Flexible dieting has risen in popularity due to its adaptable nature, which allows followers to still indulge in their favorite foods as part of their eating plan.

There are many ways to approach this diet, including subscribing to a flexible dieting website for set meal plans, or calculating your needs and planning meals on your own.

This article explains flexible dieting and explores its benefits and possible downfalls.

Friends Eating Out

Flexible dieting is not a diet. It’s more of a lifestyle.

It puts the control in the hands of the dieter, meaning there are no meal plans or food restrictions that need to be followed.

You may be wondering how people lose weight if they can eat whatever they want.

When you’re following a flexible diet, your calorie and macronutrient needs are calculated according to how much weight you want to lose.

Dieters must determine their total daily energy expenditure (TDEE) and macronutrient needs before beginning the diet.

This is most commonly done by using one of the “macro” calculators available on the many websites that promote flexible dieting, but you can do it by hand as well.

Calculating Your Energy Needs

Total daily energy expenditure consists of (1):

  • Resting energy expenditure (REE): The number of calories you burn at rest.
  • Non-resting energy expenditure (NREE): The calories expended during exercise, all daily activities and the energy required to digest food.

Resting energy expenditure accounts for more than 60–70% of an individual's total daily calories burned (2).

Non-resting energy expenditure includes calories burned through exercise, fidgeting, shivering or standing, as well as the energy your body uses to digest food.

Calculating total daily energy expenditure gives a dieter an idea how many calories they burn in a given day.

Most websites that promote flexible dieting recommend calculating your total daily energy expenditure with the Mifflin-St Jeor Equation, as explained below.

Many studies have shown that this equation is more effective than others at accurately predicting calorie needs (3, 4, 5).

Based on the equation, you can calculate your total daily energy expenditure as follows (6):

  • Men: (10 x weight in kg) + (6.25 x height in cm) – (5 x age) + 5
  • Women: (10 x weight in kg) + (6.25 x height in cm) – (5 x age) – 161

This number is then multiplied by an activity factor to estimate your total calorie needs (7):

  • Sedentary (little or no exercise): x 1.2
  • Lightly active (1–3 days per week): x 1.375
  • Moderately active (6–7 days per week): x 1.55
  • Very active (every day): x 1.725
  • Extra active (twice or more per day, elite athletes): x 1.9

To lose weight, the dieter then subtracts a percentage of calories from their total daily energy expenditure to create a calorie deficit.

Most websites that promote flexible dieting recommend subtracting 20% from the total daily energy expenditure.

For example, a dieter who calculates his or her need to be 2,000 calories would subtract 400 calories daily to lose weight.

However, dieters can decide their calorie deficit based on their individual weight loss goals and activity levels.

Calculating Your Macronutrient Needs

After determining a calorie goal, you then calculate your macronutrient or “macro” needs.

Macronutrients are the nutrients your body needs in the largest amounts: carbohydrates, proteins and fats.

These nutrients provide calories and have numerous important functions in the body (8).

  • Carbohydrates: 4 calories per gram, typically 45–65% of total daily calories
  • Proteins: 4 calories per gram, typically 10–35% of total daily calories
  • Fats: 9 calories per gram, typically 20–35% of total daily calories

Many websites that promote flexible dieting or sell custom meal plans provide “macro calculators,” where users can plug in their height, weight, age and activity level to obtain a custom macronutrient distribution.

However, dieters can also calculate macros on their own by breaking down their total calorie needs into percentages of carbohydrates, protein and fat based on their specific goals.

The great thing about flexible dieting is that dieters can tweak their macronutrient ranges depending on their lifestyle and weight loss needs.

A dieter looking to shed significant weight may want to go with a lower carbohydrate range, while an athlete may want to opt for a higher carbohydrate range (9, 10).

Flexible dieting also has users track their fiber intake, even though it’s not a macronutrient. Fiber is a type of carbohydrate the body can’t digest.

It's recommended that men consume 38 grams of fiber per day, while women should aim for 25 grams (11).

How to Track Your Macronutrient Intake

After determining their calorie and macronutrient needs, followers of flexible dieting simply track their calorie and macronutrient intake, being sure to stay within their set goals.

There are many ways to do this, though the most popular way is to use one of the many websites or mobile apps available on the market.

Most food-tracking apps have endless databases that allow users to look up any food and portion size to determine calories within seconds.

Apps are helpful because they allow you to track your meals and snacks on the go without the hassle of writing anything down.

Popular apps for tracking calories and macros include MyFitnessPal and My Macros.

Summary To follow the diet, start by developing a baseline for your calorie and macronutrient needs. Flexible dieting websites will help you calculate how many calories and macronutrients you need, while websites and mobile apps can help you track them.

Flexible dieting uses a unique approach to weight loss that many people find attractive.

There are a number of potential benefits to this way of eating.

Easy to Follow

The hardest part of flexible dieting is the process of calculating your calorie and macronutrient needs, which some people may find intimidating.

Luckily, the diet itself is easy to follow. There are no complicated recipes, food plans or endless lists of items that are off-limits.

Dieters simply choose the foods they would like to eat, staying within their set macronutrient range and calorie needs.

May Help Keep Weight off Long-Term

Multiple studies have shown that people who follow programs that allow greater flexibility in food choices are more successful at keeping weight off over time, compared to those who follow stricter diets (12).

What’s more, stricter diets tend to negatively impact the psychological well-being of those who follow them (13).

No Foods Are “Off-Limits”

There’s a never-ending stream of diets that restrict multiple foods.

This can make dieters resentful that they can’t indulge once in a while, and feelings of deprivation can lead to frequent cravings or binges (1415).

Flexible dieting sheds the “good food vs bad food” mentality that many meal plans advocate and may help dieters develop a healthy relationship with all foods.

Gives Dieters Freedom

Following a super-restrictive diet or cleanse can be difficult, especially when you are out with friends or on the go.

Flexible dieting allows users to have more freedom with food choices, making it easier for dieters to stay on track, even at parties, restaurants or when limited food options are available.

Though many diets are hard to stick to, the adaptable nature of flexible dieting may make it easier for people to follow for a longer period of time.

Beneficial for Those With Specific Nutrient Needs

Flexible dieting can be a convenient way for people who follow diets with specific macronutrient needs to meet their goals.

For example, those following very low-carb or high-fat diets can track their macronutrient needs using flexible dieting.

Athletes and those with specific fitness goals can also benefit from flexible dieting, calculating their macronutrient goals based on their training schedules.

Summary Flexible dieting has many benefits, including its adaptability and ease of use. It can be particularly beneficial for people like athletes who have specific nutrient needs.

While flexible dieting has some benefits, it also has some potential downsides.

Structure May Be Too Loose for Some

Although the freedom of flexible dieting may work for those with strong self-control, some people may struggle to hold themselves accountable for their own food choices.

As long as dieters are staying within their macronutrient and calorie range, they could theoretically choose as many unhealthy foods as they want on the flexible dieting plan.

While you can lose weight choosing unhealthy, nutrient-poor foods as long as a calorie deficit is achieved, your health and well-being will suffer.

To stay healthy, dieters should keep highly processed treats to a minimum, while focusing on nutrient-dense foods like vegetables, fruits, lean proteins, healthy fats and complex carbohydrates.

No Emphasis on Micronutrients

While the focus of this plan is on macronutrients, micronutrients are just as important for the body to function optimally.

Micronutrients are vitamins and minerals that your body needs in smaller amounts than macronutrients. They’re critical for many processes in the body, including metabolism and disease prevention (16, 17).

Foods rich in micronutrients, as well as beneficial compounds like antioxidants, should be incorporated into any healthy diet plan.

Dieters Need an Understanding of Nutrition and Weight Loss

Flexible dieting leaves the dieter with the responsibility of calculating their calorie needs and macronutrient ranges, as well as weight loss goals and meals.

Although there are books and websites dedicated to educating people about safe weight loss using flexible dieting, the steps involved may be overwhelming for some people.

To choose optimal macronutrient ranges, realistic weight loss goals and nutritious meals, dieters must do thorough research.

You Need to Track Every Meal and Snack

Although every diet takes effort, having to track every morsel of food that passes your lips may be a turnoff.

Additionally, while tracking food creates awareness of exactly what you are eating, it can lead to unhealthy habits in some people.

Using apps to track calories and macros can keep you on track, but it can easily lead to obsessive behaviors and create an unhealthy relationship with food in some people (18).

Summary Flexible dieting has some downfalls, including the need to track calories and macronutrients, as well as the fact that dieters can choose to eat an abundance of unhealthy foods as long as they meet their calorie and macronutrient targets.

Flexible dieting is a popular and simple weight loss plan that allows foods that fit within your specific daily macronutrient targets.

This way of eating provides dieters freedom in their food choices, which may help keep weight off over time and create a positive and healthy relationship with food.

Plus, it’s easy to stick to, no matter if you’re eating at home or on the go.

However, to stay healthy while following the flexible dieting plan, you must have the self-discipline to make healthy choices and keep junk food to a minimum.

If you have a good understanding of your nutritional needs and strong self-control, flexible dieting may be the perfect plan to help you reach your weight loss goals.