IIFYM – And the Major Flaws of Flexible Dieting

IIFYM - And the Major Flaws of Flexible Dieting


Before throwing my frustration out there, I need to mention that this write-up should be taken as my personal opinion only, and not some sort of general recommendation for everyone to become orthorexic – in the real sense…

Let’s start with some basic terminology.

For those who don’t know, IIFYM stands for ‘if it fits into your macros’. This is a type of dietary protocol followed by many youngsters (and not only). It has been widely popularized on Youtube (search for ‘IIFYM full day of eating’).

This approach was built on the premise that it does not matter what you eat, as long as it fits into your daily macros (and calories). Let’s be more specific…

The Trouble with IIFYM

Let’s assume that my diet is:

40% carbs
40% protein and
20% fat

My purpose is to build muscle and I want to consume 2,500 kcals/day. This means that:

40% of 2,500 kcals as carbs = 1,000 kcals
30% of 2,500 as protein = 750 kcals
30% of 2,500 as fat = 750 kcals

A similar IIFYM approach would be used for losing weight. I would basically have to manipulate macros and calories in the direction of my goals. And if I stay within my values, everything should be fine.

I can eat all the foods that I want as long as I hit my macros and my calories…

Now, what is wrong here?

I think that this entire dietary cult is built on a shaky foundation.

First of all, it completely ignores the quality of the foodstuff you put into your mouth.

Second of all, it falsely assumes that food, beside its macronutrient content, has no other value to your health. It only provides energy.

This approach completely ignores how food alters the microbiome and how it affects gene expression. More on that in a bit…

Young people may get away with following IIFYM (and flexible dieting) in their youth years. But even so, it is most likely they are going to pay the price later in life.

While still young, these bodies could fairly tolerate the impact of processed (crappy) foods:

– many packaged products
– most low fat labeled products
– many low carb labeled (Atkins, ketogenic) products
– food containing preservatives, coloring agents, artificial sweeteners, and other artificial ingredients

I want to make a distinction though. There are a few packaged products that may not fall into this categorization.

From a personal example, at one of the supermarkets I do my shopping, there’s this sausage that its label reads:

pork meat (from farm raised pigs)
natural condiments
eatable natural membrane.

This may be a good candidate for a legit packaged and processed product. But still, if you want to stretch it even further, you’d still consider the source of the meat, the conditions in which these animals were raised and so on and so forth…

I’ll personally go with the 80/20 here, though in this case it’s more like a 90/10. Caring about further details would mean caring about the remaining 10% which may not make too much of a big difference in terms of quality but it may take away a lot of time and effort to get it 99% right (100% is not possible).

So, it may be sufficient to just go with this product and not care too much about further details because this product is better than 95% of what’s out there. The trouble is that it’s hard to find.

In my supermarket it’s the only product out of the few dozens of similar products in the meats aisle. And it may take a trained eye and a bit of time to spot it. Most folks won’t do that, sadly.

The idea is that it’s not easy to purchase good food, when there’s so much crap out there.

Another Big Flaw

IIFYM also fails to account the fact that different macronutrient partitioning protocols will elicit/allow for using different metabolic substrates for energy. Case in point:

– consuming a diet moderate-to-high in carbohydrates will promote using glucose for energy. Nothing wrong with that, as long as the diet is well formulated.

– consuming a diet very low in carbohydrates will promote the use of fatty acids and ketones for energy. Again, there’s nothing wrong with that as long as the diet is well formulated and as long as fat intake is not taken into the extremes.

Moving on to the second point…

Epigenetics, Nutrigenetics and Nutrigenomics

There’s this relatively new science branch called Epigenetics which is increasing in popularity and interest – from a research perspective. Epigenetics is the study of how environmental stimuli alter gene expression. Now let’s do a Genetics 101 – short lesson.

You have a genetic code – your genome. It’s inside the nucleus of every cell of your body. It consists of DNA, which is basically the blueprint of creating YOU.

Human DNA consists of roughly 3 billion nucleotide base pairs (A- Adenine, C – Cytosine, G – Guanine, T – Thymine) packed into genes (long stretches of DNA – nucleotide sequences) and chromosomes – very roughly speaking.

This is a satellite view of genomics. Genetic-related terminology is much more complex and I’m trying to keep things fairly simple here.

Based on context, necessity, and different stimuli DNA (and more specifically, genes) is translated into proteins. This is how gene expression occurs.

Consider DNA as a list of ingredients. Translating DNA into proteins would be like preparing a meal with the ingredients you have. You could prepare different meals by leaving out or putting in certain ingredients. Similarly, different genes are expressed and/or remain silent based on a specific context – environmental stimuli.

One good example of epigenetics is how people living in colder climates are more adapted to those environments. They became adapted over time. Similarly, people living in tropical climates have darker skins. We adapt to the environment. Stimuli from the environment (and not only) dictate how our genes are expressed.

Food is also a stimulus for gene expression.

That is, food can alter the way in which your genes are expressed.

Sub-branches of epigenetics and nutritional genomics have been created for this study. They are: nutrigenetics and nutrigenomics and they are still in their infancy.

Eating a diet filled with processed and low-quality foods will most likely have a different effect than consuming a diet rich in nutrients, especially in micronutrients and phytochemicals that have been shown to have a positive and adaptive impact on gene expression.

And, more importantly!

IIFYM fails to account for the implication of the gut microbiota (the bacteria inside the human gut) in health and disease.

There are more than 1,000 (according to recent data) bacterial families living in and on our bodies. The bacteria in our guts feed on the foods we eat. Different food categories feed different bacterial families. This is how/why some bacteria families grow more than others.

For reference, there are approximately 10 times more bacterial cells in/on the human body than there are human cells. You have bacteria all over you: in your gut, skin, ears, mouth, nose, vagina, etc.

Similarly, the human genome (the total number of genes in the human genetic code) is about 22,000 genes by recent estimates; the microbiome – the collective genome of your bacterial cells is 100 times as much – at least 2 million genes. Roughly speaking, we are more bacteria than human…

Researchers have identified bacteria families that contribute to human health (commensal bacteria), as well as pathogenic bacteria families – leading to disease. Let me give you a personal example:

I had a sweet tooth. I used to load on sweets and junk food (milk chocolate, candy, biscuits, pretzels, bagels, donuts, pizza, etc) once a week every Sunday. It was like a refeeding day when I used to follow the slow-carb diet of T. Ferriss. I craved for those foods.

Switching to very-low-carb and cleaning my diet and sticking to the protocol (no refeed days) made me lose my sweet tooth in a couple of months. I have no interest in those foods anymore. It’s been 2 years now

Back when I use to eat like crap, there was bacteria in my gut that fed on those foods. Staying away from those foods and switching to nutrient rich foods (loads of vegetables and plant foods) allowed for the proliferation of commensal (friendly, good) bacteria in my gut. Taking care of the good bacteria will most likely provide protection from disease – as some research studies show.

Eating low-quality, packaged and processed foods will most likely promote the proliferation of pathogenic (unfriendly, disease promoting) bacteria in your gut.

Building along those lines, it is known that at least 80% of the immune system is in the gut.

One loose, but good, example is what happens when you take a course of antibiotics that destroys your gut bacteria. Your immunity may be affected over the long term.

I remember that I used to get sick a lot back then; and I also remember that I had a severe flu once and I had taken antibiotics for a couple of weeks. I had recurring colds and poor health long after that…

What I Currently Do?

To maintain a fairly good environment for the proliferation of commensal bacteria in my gut I focus on optimizing my nutrition for micronutrient intake.

I consume significant amounts of vegetables and plants foods that are high in micronutrients, vitamins, minerals, phytochemicals and other trace nutrients.

I also consume pre and pro biotic foods that have been shown to increase the number of good bacterial families. Fermented Greek yoghurt, sauerkraut, raw potato starch, and red dry wine are just to name a few.

I also use a pre/pro biotic supplement which contains 6 billion bacteria (vial cells) – about 9 families of good bacteria. Lactobacillus Acidophilus is the predominant bacteria in my pre/pro biotic.

I try to stay away from packaged and processed foods like the ones from the examples above.


The gut is not only involved in your immunity and in your current state of health. Recent research shows there’s a big connection (communication) between the gut and the brain. Researchers are very interested in studying what’s now called the gut-brain axis. I may be talking more about this in a future write-up.

What was the manifesto of this post? I wanted to give you few of the reasons that what you put into your mouth, heavily affects your immunity, your wellbeing, and most especially, the expression of your genes.

In this case and in conclusion, following a dietary protocol, such as the IIFYM, that only focuses on macros and calories may be myopic and mostly inappropriate if you care to remain healthy as you age.


Karolchik, D., Barber, G. P., Casper, J., Clawson, H., Cline, M. S., Diekhans, M., … & Kent, W. J. (2014). The UCSC genome browser database: 2014 update. Nucleic acids research, 42(D1), D764-D770.

Egger, G., Liang, G., Aparicio, A., & Jones, P. A. (2004). Epigenetics in human disease and prospects for epigenetic therapy. Nature, 429(6990), 457-463.

Kaput, J., & Rodriguez, R. L. (2004). Nutritional genomics: the next frontier in the postgenomic era. Physiological genomics, 16(2), 166-177.

Mutch, D. M., Wahli, W., & Williamson, G. (2005). Nutrigenomics and nutrigenetics: the emerging faces of nutrition. The FASEB Journal, 19(12), 1602-1616.

Human Microbiome Project Consortium. (2012). Structure, function and diversity of the healthy human microbiome. Nature, 486(7402), 207-214.

Turnbaugh, P. J., Hamady, M., Yatsunenko, T., Cantarel, B. L., Duncan, A., Ley, R. E., … & Gordon, J. I. (2009). A core gut microbiome in obese and lean twins. nature, 457(7228), 480-484.

Cryan, J. F., & O’Mahony, S. M. (2011). The microbiome‐gut‐brain axis: from bowel to behavior. Neurogastroenterology & Motility, 23(3), 187-192.

Cox, P. J., & Clarke, K. (2014). Acute nutritional ketosis: implications for exercise performance and metabolism. Extreme physiology & medicine, 3(1), 17.

Image: here.

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