Unlike diets that involve food restriction, proponents describe IIFYM as a flexible diet that can help people lose weight without drastically changing their eating habits.
Little research has investigated the diet, so its effectiveness has not been scientifically established.
In general, many people can lose weight by eating smaller portions, choosing less energy-dense foods, and increasing their physical activity. This does not have to occur as part of a dietary fad.
In this article, we describe how to follow the IIFYM diet and include potential benefits and risks.
What is the IIFYM diet?
People following the IIFYM diet keep track of proteins, carbohydrates, and fats.
The IIFYM diet hinges on the idea that eating fewer calories than the body requires — while still consuming enough protein, carbs, and fats — results in weight loss at a steady and predictable rate.
People following the IIFYM diet keep track of these three macronutrients:
The diet groups fiber with carbohydrates.
A person can consume these macronutrients in varying combinations, as long as the amounts do not exceed the body's macronutrient needs for the day. This means that, if the calculation balances out, a person can eat any type of food, while still meeting their health or weight loss goals.
How to start with the IIFYM diet
Following the IIFYM diet involves:
- calculating how many calories you need to maintain your current weight
- determining how many calories to cut for the desired weight loss
- grouping these calories by macronutrients: proteins, carbohydrates, and fats
The targets and figures vary, based on factors such as age, sex, weight, height, and activity levels.
Start by using the calculator on the IIFYM website or by following the steps below:
Step 1: Calculate current calorie needs
A person's basal metabolic rate (BMR), or resting metabolic rate, is the amount of energy, in calories, that their body needs at rest for 24 hours. This energy goes toward essential functions, such as breathing, circulation, and body temperature.
A person can determine their BMR with an online calculator that uses the Mifflin-St. Jeor equation.
To manually calculate BMR:
- for men, BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) + 5
- for women, BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) – 161
Step 2: Adjust calorie needs for activity level
The next step involves factoring in the average physical activity level, as this affects the number of calories that the body uses. This measurement is called total daily energy expenditure (TDEE).
Step 3: Adjust calorie needs for desired weight
Subtract 15–20 percent of the TDEE to find out, according to the IIFYM website, how many calories a person should eat per day to achieve their weight loss goals.
Step 4: Determine macro needs per day
The final step is to divide the resulting value into what the website calls "adjusted macros." This will determine how many macros a person needs, based on their current body weight:
- protein: calculate this intake at around 0.7–1.0 grams (g) per pound (lb) of body weight
- fat: calculate at about 0.25–0.4 g per lb of body weight
- carbohydrates: this value comprises the remaining calories from the adjusted macros score
Sticking to IIFYM in the long term
To follow the IIFYM diet, a person must determine how many macros they are consuming at each meal and track their daily intake to ensure that it is close to their adjusted goal.
For more accurate results, a person may consider using a digital scale to weigh food.
Many macro-friendly recipes are available online. The IIFYM website provides a range of meal plans, including breakfasts, lunches, dinners, snacks, and desserts.
Benefits of IIFYM
The possible benefits of the IIFYM diet include:
The IIFYM diet aims to make meals enjoyable and stress-free.
The IIFYM website promises "no more dieting" and "no more restrictions." It is advertised as a more flexible dieting stylebecause it incorporates more foods than many other diets.
It encourages people to eat diverse foods, as long as they do not exceed their macro targets.
The aim of the IIFYM diet is to make meals more enjoyable, and meal planning less stressful, which may increase the likelihood of sticking to the diet.
A person usually loses weight if they burn more calories than they take in. This often involves cutting around 500–750 calories each day. People may achieve this by following the IIFYM diet.
Similarly, increasing calorie consumption leads to weight gain. People looking to gain weight may also be able to meet their goals with IIFYM.
May benefit those unable to exercise
Because IIFYM takes physical activity levels into account when calculating macros, a person who gets limited or no exercise may find the diet useful.
Negatives of IIFYM
The IIFYM diet may have the following drawbacks:
No focus on micronutrients
Micronutrients, such as vitamins and minerals, are as important as macronutrients for health and development, but the IIFYM diet does not account for their intake.
The body does not produce micronutrients, so a person must obtain them from their diet. A person following the IIFYM diet may not be getting enough of these vital nutrients.
According to the Centers for Disease Control and Prevention, more than 2 billion people worldwide have micronutrient deficiencies.
Macro calculations are not flexible
People may have difficulties adjusting their macro requirements to account for changes such as illness, recovering from injury, and breastfeeding.
For instance, research indicates that following an illness, the body needs more calories and protein, namely 1.5–2.0 g of protein per kilogram of body weight per day, to make up for the loss of lean body mass and to promote recovery.
Proponents advertise the IIFYM diet as a flexible method of weight loss. It involves counting macronutrients — proteins, carbohydrates, and fats — instead of calories.
However, little scientific research has looked into its effectiveness.
People following the diet must be sure to consume enough micronutrients, such as vitamins and minerals.
If a person uses more calories than they consume, they are likely to lose weight. An individual can do this by following a healthful diet, reducing portion sizes, and getting more physical activity.
For best results, and to ensure that their dieting plan is healthful, a person may wish to consult a healthcare professional.