Flexible Dieting and IIFYM

There’s a concept out there that is termed Flexible Dieting or IIFYM (If it fits your macros). It promises no limits to the types of food you can eat.

Nuts and Bolts of Flexible Dieting

The system is basically this.

  • Calculate TDEE
  • Determine macro ratios (typically from Zone 30/30/40 ratios)
  • Eat to your macros every day (no more, no less)

“Positives” of IIFYM

IIFYM has some obvious benefits. With it you can  “eat whatever you want”. If you want pizza, as long as it fits your macros you can eat it. Same goes for ice cream, etc. Anything you want just not in quantities which will push you past your macros.

Although there is no calorie counting but you weigh/count the surrogates of protein/fat/carb macros. IIFYM macros are typically higher protein than the Standard American Diet (SAD) so they tend to produce good results.

They also tend to be lower than the SAD in carbohydrates which has a positive benefit. And they limit the carbohydrates in quantity which may be the first time someone who tries the diet has ever limited their carbs. This is a way to learn portion control perhaps without feeling like you are not getting something you really want (like cake, ice cream or pasta).

IIFYM requires measurement and recording of food and tracking macros daily. It emphasizes day-to-day consistency in eating which may (or may not) be beneficial. You can use tools like MyFitnessPal or Cronometer to track your macros.

IIFYM Macro Selections

My primary concern about IIFYM is that while the initial selection of macros is great compared to the Standard American Diet (SAD) it’s only so good for someone with Metabolic Syndrome/Insulin Resistance. Setting the protein macro to 30% of calories is going to be a good thing in nearly every case (except in rare cases like kidney failure).

Dropping carb consumption is going to be good for otherwise healthy people. For the 40% of the population with Metabolic Syndrome, eating 30% of their calories from carbohydrates may lead to worsening blood sugar control and hasten the complications from diabetes.

In my case, before LCHF I was eating 200 grams a day of carbs which is about 800 calories a day. That was around 33% of my approximately 2400 calories I ate a day. Increasing my carbohydrate intake to 40% would have been 140 additional calories from carbohydrates or an addition 40 grams of carbohydrates (from 200 to 240g) that my already overloaded system would have pushed into my bloodstream.  That would have meant I would have had to take an additional 10 units of Insulin (at a minimum) and maybe more to cover the carbohydrates. Not the recipe for reducing Insulin Resistance.

Another concern is the idea that the 30/30/40 ratio is somehow a “balanced” ratio. I haven’t seen any evidence in the literature establishing this ratio as ideal in any sense of the word. In particular, the studies on diabetics I have seen show this balance is a bad balance compared to ketogenic ratios.

Fitness World and IIFYM

This approach seems to have gained traction in the fitness community where glycogen stores are important for high intensity work (CrossFit and Nutrition – Part 3). And someone who works out intensely every day can probably tolerate a higher level of carbohydrates than someone who works out much less frequently.

Micro-nutrients and IIFYM

There seems to be a de-emphasis on micronutrients/vitamins/minerals in IIFYML. For instance this article claims that there’s no such thing as clean eating (What is Flexible Dieting? Here’s How to Get Started). A gram of carbs from a twinkie and a gram of carbs from broccoli work just the same in your body. And that’s just simply false. Some carbs are slowly digested and raise blood sugar by a small amount and others send blood sugar up sky high.

Equally there are some IIFYM/Flexible Dieting sources out there who are concerned about micronutrients and vitamins. For instance, this YouTube guy who expresses the idea that micronutrients matter (Flexible Dieting 101: The Simple Facts).

This may be made more difficult to track with MyFitnessPal (MFP). I don’t use MFP but reading the process to see your micronutrients with MFP seems clumsy (Where can I find my micronutrients?).

With Cronometer I see the micronutrients every single day and know exactly where I am at for each micronutrient/vitamin/mineral.

Here are my micro nutrients (averaged for this past week although it’s the same data day-by-day).

And here are my vitamins and minerals for the week (same for the day).

Higher Carb Diets Have Lower Compliance

One thing I have observed is that higher carb level diets don’t produce good compliance beyond a very short term. That is because they really don’t blunt carb cravings like a low carb diet does. This means they still have the potential roller coaster of blood sugar spikes.

Eating Carb Macros

Trying a theoretical case with someone who weighs 200 lbs and wants to maintain their weight. That is:

  • Protein = 2000 * 30% = 600 calories or 150 g
  • Fat = 2000 * 30% = 600 calories or 67g
  • Carbs = 2000 * 40% = 800 calories or 200g

Reduced to familiar food, 150g of protein is 26 ozs of boneless, skinless chicken breast. I picked that because it is low fat and there’s no much fat on IIFYM macros. That very low fat option takes up 16 of the 67 g of fat leaving around 51g of fat for the rest of the day.

So we have 200g of protein and only 51g of fat left. If we pick a “healthy” carbohydrate like a potato.

To get to 200g of “healthy” carb choices we would need to eat almost 8 potatoes. If we put a bit of butter or olive oil on the potatoes:

We only get less than 4 tablespoons worth of olive oil and we are out of fat, carbs and protein. This might be where fruit comes in handy since fruit has a lot of carbs and little fat/protein.

Using Healthier Vegetable Choices

Let’s try replacing the potato with a low carb vegetable like broccoli:

At 6g a cup to get 200g of broccoli we’d need to eat 33 cups of broccoli. This demonstrates the difficulty of getting a lot of carbs and doing it with low carb vegetables.

Unhealthier Choices

But none of this matches the promise of IIFYM which is that you can eat whatever you want as long as it fits your macros. And today let’s say I want to eat ice cream, tacos and pizza.

My pizza Choice will be a moderate 2 slices of Little Caesar’s pizza. MFP has lower macros than Cronometer so let’s go with MFP:

What do I have left?

  • Protein = 150 – 28g = 122g
  • Fat = 67 – 22g = 45g
  • Carbs = 200 – 64g = 136g

Now I get my Ben and Jerry’s:

  • Protein = 122 – 8g = 114g
  • Fat = 45 – 25g = 20g
  • Carbs = 136 – 49g = 87g

Still a fair amount left but I haven’t had my four tacos yet.

This is where MFP numbers don’t match the company website. The Taco Bell site has:

  • Protein = 114 – (8*4) 32g = 82g
  • Fat = 20 – (9*4) 36g = -16g <<< OOPS, I’ve already gone over for fat
  • Carbs = 87 – (13*4) 52 g = 35g

This is where the rubber meets the road. I’ve not gone crazy this day. Nothing that I don’t feel like I deserve to eat. But they don’t fit my macros. So I need to only have 2 tacos. It’s lunch time and I feel pretty deprived.

  • Protein = 114 – (8*2) 16g = 98g
  • Fat = 20 – (9*2) 18g = 2g
  • Carbs = 87 – (13*2) 16 g = 16g

So I can have some carbs but I’ve got not much fat so no chips, etc. And I’ve got a whole lot of protein I still need to get in. Sounds like I will be eating two protein shakes that day. So how did I do?

  • Protein = 2000 * 30% = 600 calories or 150 g (I went over by 3g)
  • Fat = 2000 * 30% = 600 calories or 67g (I went over by 15g)
  • Carbs = 2000 * 40% = 800 calories or 200g (I ended up 75g under)

Time for a handful of jelly beans or gummy bears. Trouble is I only have 80 calories and I need to get in 75*4 = 300 calories to hit my carb number. Still not horrible for my first day.

No, don’t worry. I’m not going to do it. Just wanted to demonstrate what I see with people who eat this way. Perhaps they get better at planning and meal prep. Some of them do. And they probably have better compliance.


Author: Doug

I'm an Engineer who is also a science geek. I was pre-diabetic in 1996 and became a diabetic in 2003. I decided to figure out how to hack my diabetes and in 2016 found the ketogetic diet which reversed my diabetes.

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