The IIFYM Diet: If It Fits Your Macros, Eat It?

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An IIFYM dieter holding an apple and a donut.Otherwise known as ‘flexible dieting’, IIFYM has become increasingly popular over the past few years.

IIFYM stands for: ‘If It Fits Your Macros’ and it can either be high in carbohydrate or very low in carbs.

But just what is this diet?

And is it good for us, or bad?

Let’s take a look.

What is the IIFYM Diet?

As previously mentioned, the meaning of IIFYM is ‘IIFits Your Macros’ and it’s a diet that’s particularly popular in bodybuilding and weight loss circles.

It’s a diet plan that allows extreme flexibility with the food you eat, as long as you stick to your daily macronutrient target.

The diet takes the position that calories and grams of macronutrients are more important than food quality.

As a result, there is great emphasis on counting the number of carbs, fat, and protein (as well as total calories).

Also, there are all sorts of online dietary tools for the diet such as IIFYM calculators and meal plan generators.

How Does it Work?

Picture showing the macronutrients controled on the IIFYM diet

After calculating how many daily calories, carbs, fat, and protein someone wants to consume, they can eat anything they want as long as they don’t go over these limits.

For example, let’s imagine someone is aiming for a macronutrient ratio of 50/25/25 CFP (carbohydrate, fat, protein) and a maximum of 1800 calories.

In contrast to most conventional diets, there would be no rules on the type of food these nutrients should come from.

Although the creators of the IIFYM plan do encourage healthier choices, there is no limit on the kind of food you can eat.

So pizzas, cakes, and sugary drinks are okay as long as the dieter doesn’t exceed the desired limit of each macronutrient.

Likewise, for a diet higher in fat — say 10/65/25 CFP — foods such as donuts, and cheeseburgers are perfectly fine, as long as it meets the 10/65/25 ratio.

Food Quality Matters

Diets such as LCHF, paleo, and other real food-based diets emphasize the quality of dietary fats.

However, in the IIFYM diet, the source of fat is less important than whether or not it fits into the desired calorie and macro range.

Many claim that this flexible dieting method allows people to meet their goals in an easy way, without being too restrictive.

For some people, this sounds great. But for me, this is problematic and gives the wrong message to people.

The idea of “eat whatever you want” on an energy-restricted diet might be okay in terms of managing body weight, but it’s far from healthy.

The Problem With Counting Calories and Macronutrients

Calories are just a form of energy, and macronutrients can either be nutrient-dense or completely devoid of nutrients.

In short, it’s the quality of the food that matters most.

That said, an IIFYM diet can be healthy if there is an emphasis on nutrient-dense foods.

Therefore, the next few sections will look at the difference between a bad IIFYM diet and a healthier version.

Key Point: IIFYM is a diet plan that emphasizes flexible dieting. In short, if you stick to your calorie and macronutrient targets, you can eat whatever you want.

Everything That’s Wrong With Flexible Dieting

Picture showing a man disapproving

First of all, the idea that counting calories and macronutrients is the most important dietary consideration is totally wrong.

In fact, this is an entirely outdated view of nutrition that belongs in the dark ages. The number of calories—and carbs/fats—is meaningless compared to their quality.

For a simple example:

Extra-virgin Olive Oil vs. Trans-fat.

These are both types of fat, and both are technically allowed in an IIFYM diet. However, olive oil has a mountain of studies showing that it’s heart-protective (1, 2, 3).

On the other hand, trans-fat is just the opposite, and dozens of studies link it to heart attacks (4, 5, 6).

Another good example would be grass-fed steak vs. a tin of spam.

This difference clearly shows why we should care about the quality of the foods we eat, not just how many grams of fat or calories there are.

Paying no attention to nutrient-density is also potentially dangerous in the long-term.

For instance, if someone sticks to IIFYM for many years with no focus on diet quality, then they are increasing the risk of metabolic syndrome and other chronic diseases.

The Dangers

For some IIFYM dieters, foods like soybean oil, sugar, high-fructose corn syrup, and even trans fat are okay if they fit within the daily macronutrient limits.

However, these are some of the very worst and most damaging ingredients in our food chain.

And all of them have significant links to chronic diseases (7, 8, 9).

The key point is this: An 1800 calorie diet full of junk food might not cause weight gain, but there’s no telling what’s happening inside the body.

Being Slim Does Not Automatically Equal Healthy

Picture of a slim girl eating chocolate.Importantly, maintaining a healthy weight may allow for prolonged, undetected damage, under the illusion that everything is working correctly.

As evidence of this, various studies report a high number of diabetes cases in lean people. The simple truth is that people can be insulin resistant whether they are slim or obese (10, 11, 12).

Despite this, it’s not only diabetes that we need to worry about.

Higher blood sugar and insulin levels are damaging whether diabetic or not, and they vastly increase the risk of cancer, dementia, and heart disease (13, 14, 15).

Eating whatever you want may seem tempting, but the simple truth is that eating too much unhealthy food destroys health. And that’s whether it fits your macronutrient ratios or not.

Key Point: On the negative side of IIFYM, many dieters eat whatever they want, which significantly increases chronic disease risk factors.

IIFYM Meal Planning the Healthy Way

Despite being quite hard on the diet so far, the idea behind it can play a role in good health if dieters pay attention to food quality.

In fact, for someone using the diet and focusing on healthy foods, it should work very well.

Here are a few healthier examples of following IIFYM.

Competitive Bodybuilders

I don’t think counting the amount of macronutrients you consume is important for the average person.

However, for elite athletes and professional bodybuilders who rely on building size and muscular power, making sure they are consuming the right nutrients can be important.

With IIFYM, they know exactly what they need to eat to achieve their goals.

A Low Carb Diet For Weight Loss

Let’s presume you want to eat a low-carb diet to lose some weight, but you don’t want to be ultra-strict.

Perhaps you want to eat around 100g carbs per day and still plan on including a bit of fruit and some sweet potatoes.

By using IIFYM principles, you can calculate the amount of carbs, fat, and protein you require and then monitor adherence. In this situation, IIFYM can make sure you don’t go over your desired carb intake each day.

However, there’s no excuse to justify eating poor quality foods such as soda, cakes, and pastries as part of your daily diet.

Yes, maybe you can eat them every day and lose weight if you keep to a certain macronutrient ratio.

But this ignores the unique metabolic pathway different foods have.

Ultra-processed, sugary foods are not good for you and negatively affect blood sugar regulation, as well as various other health markers (16, 17).

A Strict Low Carb/Ketogenic Diet

Picture of steak and vegetables on a ketogenic diet

Maybe you are interested in a ketogenic diet for medical purposes, so getting the right amount of macronutrients would be critical in this case.

After doing some research, you figure out that you need to keep carbs to less than 25g per day.

Through using IIFYM principles, you can calculate exactly the right amounts of different foods you require.

But…Nutrient Quality Does Matter

While there are some positives to IIFYM, it all depends on how you approach the diet.

If you use it as an excuse to eat whatever you want, then while it may keep your weight in check, you are just damaging your health.

On the other hand, if you use IIFYM principles alongside a diet full of healthy foods, then it could work very well.

Final Thoughts

IIFYM is an idea that tries to take the confusion out of dieting by making no food off-limits.

Overall, the diet probably does what it says on the tin. Strictly controlling macronutrient and calorie intake will result in positive changes to body composition – at least in the short-term.

However, just because a diet makes you lose weight doesn’t mean it’s good for you.

For this reason, those who use the diet as an excuse to “have their cake and eat it” are only harming themselves.

In contrast, using IIFYM principles alongside a diet rich in real food is potentially a helpful tool for monitoring dietary adherence.

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