When I first learnt about If It Fits Your Macros (IIFYM) I thought it was a game-changer. Instead of thinking about potential downsides, I only focused on the positive aspects.

I remember thinking that people often don’t fully appreciate details like how minimal the difference in body composition outcomes is between different forms of carbohydrates, for example.

I was also thinking that if people understood calories in versus calories out, it would be much easier to adjust their intake and find a balance between achieving their goals and enjoying life.

Even just the concept and understanding of IIFYM can be useful. Understanding how it works can be beneficial without even physically tracking macros.

But obviously, it is not that simple. If it were, everybody who tries it would be getting great results. In this post, I am going to talk through some reasons why not everybody will thrive on an IIFYM-style diet, as well as some other points to consider.

Tracking Macros Takes Time

An obvious point to get out of the way before taking this much further is that tracking macros takes time and effort.

The more varied your diet is and the more ingredients you use when cooking foods, the more time it takes as well.

This is an additional point too: Tracking macros typically encourages you to use FEWER ingredients and less variety, since it will be easier to track that. This is not ideal considering that from a gut-health perspective, it is probably a good idea to be aiming for >30 different plant-based foods each week.

From my perspective, this is far from the biggest downside. The time commitment isn’t that significant, especially compared to most other dietary approaches, which require even more time. However, it’s still worth mentioning.

You Still Need to Think and Plan Out Your Intake to a Certain Degree

IIFYM is a very flexible approach. It gives you a lot of choice in how you want to eat. But you also still need to structure your day to ensure you end up eating near your targeted calories and macros.

This requires spending a little bit of time planning things out. A lot of people either struggle with that or would just prefer an approach that does not involve that level of thought.

A lot of people genuinely like structure.

In addition, though, something that I have noticed is that a lot of people also do not do well when it comes to utilising the flexibility that IIFYM provides.

What I mean by that is that I love how IIFYM allows you the opportunity to eat anything, so long as you adjust the rest of your intake.

For example, you could go out for dinner, have a high-calorie meal, and just adjust the rest of your day to be lower calorie, most likely coming from a reduction in carbs/fats. You would not be sacrificing anything and you would still reach your goals.

But in practice, I see a lot of people just continue to follow their normal daily structure, then go out for a meal and overshoot their calories. Flexible dieting allows flexibility, but that flexibility only works if you make the adjustments to make it work.

It still requires a certain level of strictness. Sometimes it means you still need to turn down food as well. There is a saying I like that I heard from Martin McDonald that goes “You can eat anything, but you can’t eat everything.”

And I think that in part because the approach is so flexible, it can sometimes make it hard for people to switch gears and be motivated to exhibit that level of restraint.

Eating Disorders Risk

This is a bit of a controversial topic. People at either end of the opinion spectrum might not like what I have to say here.

Basically, my key points are:

1. Some people can track calories and macros and have a great relationship with food.
2. Some people can track calories and macros and have it contribute towards disordered eating.

I do not think the above two points can be argued with, which is why I want to start there.

I found that learning about flexible dieting and IIFYM was the best thing that ever happened to my relationship with food. It allowed me to switch from being a “clean eater” to having a flexible approach to food.

It also meant I could eat “unhealthy” food with no guilt. It meant that I could eat that food with zero downsides in terms of progress.

Obviously, this gave me a bit of bias in the direction of a favourable view on IIFYM.

At the other end of the spectrum, some people have the opposite outcome. IIFYM may have contributed to disordered eating habits in them and now they are concerned that most people will have that experience.

There are extremes at both ends of the spectrum. I have come to the conclusion that my case is more of an outlier situation than the other end of the spectrum. But there is interesting research to back up the two points I made earlier.

My favourite study on the topic is by Jake Linardon. The graphic below sums up the key points.

This was a study on men. I would wager the numbers would be worse for women.

A few key takeaway points here:

1. Some people can track calories and macros with zero downsides. It can be a great approach for them.
2. An alarmingly high percentage of people feel as though it contributes to disordered eating for them.
3. Due to the disordered eating concerns, it would be insane to recommend an IIFYM-based approach to the broad population.
4. Education can mitigate some of this risk. But it is an incredibly complex topic and knowledge alone probably is not the answer for everybody. It probably is also a good idea to be able to identify red flags when it comes to disordered eating risk and when it might not be a good idea to track macros.

There Is Not Necessarily an Emphasis on Nutrient-Rich Foods

Micronutrients and fibre are important for health and feeling good in general.

I think most people would be surprised at how “healthy” a diet needs to be to reach even just the recommended daily intake amounts for each micronutrient.

You can reach those targets and have food flexibility, but most of your diet likely needs to be made up of micronutrient-rich foods.

Even as an example – only 5% of Australians reach the recommended amount of fruits and vegetables.

It is great that IIFYM encourages food flexibility. But somebody learning that they can achieve their body composition goals regardless of where the macros come from probably does not motivate them to eat more fruits and vegetables.

The original proponents of IIFYM definitely encouraged micronutrient-rich diets and sufficient fibre. But the interpretation of people over time seems to have diminished this aspect of it.

This raises another question – could you just have a multi-vitamin instead?

If you have a nutrient-poor diet, a multivitamin could help. In fact, I would encourage it for somebody who was consistently consuming a nutrient-poor diet.

But I have hesitations still. Getting nutrients through food consistently seems to be better than through supplements in the vast majority of cases.

There are small components of food that are hard to get into multivitamins. There will almost always be gaps. Another aspect to consider is that the food matrix and the way nutrients in food interact with each other can provide additional benefits.

I am not necessarily a “nature knows best” die-hard fan. But I think it is a safe assumption that we should strive to have nutrient-rich diets and then only supplement to fill the gaps.  

Processed Foods vs Unprocessed Foods Can Lead to Different Energy Expenditure and Absorption Amounts

Something that is a bit of an under-discussed topic in the flexible dieting community is that even foods with the same calories can have different impacts on the calories in vs calories out equation.

We might absorb more or fewer calories from certain foods.

Some might require more or less calorie expenditure during digestion.

My favourite example of this is that we absorb somewhere between 5-30% less calories from nuts than you would expect from reading the nutrition label.

Another study comparing processed vs unprocessed versions of the same food showed that the energy expenditure involved in the unprocessed meal was 50% higher than the processed version.

Does this point matter much? Not really. It is not THAT big of a difference in terms of total calories. If you are consistent with your intake, this will not make a difference. But it is a cool fact to be aware of.

Another factor to consider is that the thermic effect of food (calories burned through digestion) changes even based on the macronutrient composition – as shown below. This is not relevant to the IIFYM discussion, since that is based on macros already, but I think it is worth sharing.

Some People Do Better with More Rules/Guidelines

Building on a lot of previous points, some people actually like more structure.

I like to view nutrition as having shades of grey. But a lot of people are black and white thinkers.

For some people, it happens to be easier to try to avoid carbs than it is to try to moderate your intake of them. Others might like time-restricted eating and just eating whatever they want within that window.

Flexibility is awesome. There is technically no reason you couldn’t alternate between intermittent fasting, low-fat, low-carb, plant-based and other approaches based on whatever is happening each day.

But a lot of people would prefer to stick with one approach that works for them. So, this needs to be acknowledged as well.

IIFYM can be too loose of a concept for a lot of people. The flexibility and quantity of decisions that need to be made can make it a challenge in some cases.

Being Too Flexible Can Lead to Over-consuming Low-Satiety Foods

Volume eating is a strategy that can be used to make it easier to enter and stay in a calorie deficit if that is your goal. The basic premise is that you focus on eating larger volumes of lower-calorie foods, which helps you feel more satiated.

A lot of people undertaking IIFYM might not emphasise this aspect.

The first time I really became aware of this issue being prevalent was early on while on a bodybuilding forum.

One of the bodybuilders said that he taught his mum about IIFYM.

She gave it a try, but every day by 1 PM, she had already hit her calorie target—mostly from junk food. This left her with two choices: either stay hungry for the rest of the day or exceed her calorie target.

As most people would, she would choose the latter.

At the other end of the spectrum, a lot of people who follow other approaches including things like low-carb or plant-based style diets, can simply eat based on their appetite and consume an appropriate number of calories for their goals. Not everybody can do that, but a lot of people can.

Another interesting study on this topic is by Kevin Hall. This study compared diets that were matched for macros, sodium and fibre, but eaten ad-libitum. One diet was more ultra-processed, the other was unprocessed.

The group eating the processed foods ate way more calories.

This is fascinating because macros, sodium and fibre were matched. It makes sense but it is still interesting.

And using common sense, usually macros, sodium and fibre are not matched. Somebody following IIFYM typically consumes more sodium and less fibre, which would usually make it even easier to eat more calories.

Focusing on mostly unprocessed, lower-calorie foods can help counter this, but it’s definitely something to keep in mind.

Summary

IIFYM has a lot of great concepts that are useful for a lot of people. If utilised, there should still be an emphasis on mostly whole, minimally processed, nutrient-rich foods. That being said, even with that kind of mindset, a lot of people still might struggle with IIFYM for a variety of reasons. It is a great approach for some, but not everybody.