While “flexible dieting” might sound like an intriguing answer to all of your dieting woes, this style of eating may do more harm than good.

healthy and unhealthy foods for flexible dieting

What Is Flexible Dieting?

Flexible dieting is a term used for a style of eating that is based on eating a specified amount of each macronutrient per day. Meaning, you’re “allowed” a certain number of carbs, protein and fat per day. Typically, this is also paired with a calorie restricted or calorie controlled diet. The goals of those who practice flexible dieting can be varied from seeking weight loss, gaining muscle/body building, and simply those seeking overall health.

Flexible Dieting VS IIFYM

Let’s also just first clarify that the term “flexible dieting” is typically used synonymously with the term “IIFYM” which stands for “if it fits your macros”. For the purposes of this blog post, they’re one in the same.

diet plan for flexible dieting

How Does Flexible Dieting Work?

Flexible dieting works by first establishing a calorie “goal’ and then breaking up those calories between the 3 different macronutrients: carbs, protein and fat. Here is the rough breakdown that is suggested for flexible dieting:

  • Protein: 0.8g/lb of lean body weight
  • Fat: 0.3-0.4g/lb of lean body weight
  • Fiber: 20-25% of lean body weight in grams of fiber per day
  • Water: 3-4L of water in addition to any other liquids you might drink
  • Carbs: Your remaining calories can be made up of carbs

Within your set ranges of macros you can essentially pick whatever you want to eat. This is where the “flexible” part comes in. That 0.8g/lb protein can be a chicken breast, a processed protein bar, or, heck, ice cream. The carbs can be potato chips, whole grain toast, or a cupcakes. The choice is yours.

Additionally, you see they do provide recommendations for water and fiber as well, which we will discuss.

IIFYM Pros & Cons

Pros For Flexible Dieting With Macros

blue cupcakes

Does Not Demonize “Unhealthy” Foods

One of the “benefits” to the flexible dieting approach is that it does not say you’re bad for eating, say, cake. It says, you want cake? Eat the cake! Studies have shown us that when we restrict a food, like say foods with refined sugar, it’s going to lead to us likely eating those foods in a binge-like style. I talked about this idea in my YouTube video on eating dessert every day and why it’s NOT a bad thing (I do it!). The same idea applies here. What you restrict, you’re going to want more of and likely eat it compulsively.

Places An Emphasis On Fiber

As a registered dietitian I’m well aware of the health promoting benefits of fiber such as helping to keep you feeling full longer, may lower blood pressure, cholesterol, and also reduces risk for things like heart disease and stroke.

fiber foods for flexible dieting

When I did a test calculation based on the IIFYM fiber guidelines it came out to ~25g of fiber per day, which is actually pretty in line with what is recommended. The general recommendation if 25g per day for women, 38 for men, or 14g per 1,000 calories.

Adjusting Macronutrient Intake Can Be Helpful For Certain Disease States

Consuming a certain recommendation of macronutrients has been shown to be beneficial for disease states such as metabolic disease and Parkinson’s disease. If you do fall into either of these categories though, I would recommend working with a dietitian 1:1 specializing in these areas, not using an online calculator!

Cons For IIFYM & Macro Counting

Highly Restrictive

While this diet might seem to be super flexible (I mean, it’s in the freaking name!) it’s really not. I used the calculator on the IIFYM website to give me my calorie and macro goals and.. well… let’s just say it was highly unrealistic. And I asked for it to MAINTAIN my weight, not give me weight loss. I can tell you for a fact right now I’m eating about 500+ calories more than they told me to eat, and I’m maintaining my weight. Do we see a flaw there?!

This is the problem with diets and online calculators, like these ones. We take their word as truth when in reality those calculators are kinda utter bogus. So many things impact our calorie needs that those calculators don’t know such as:

  • natural hormone shifts (hello, periods!)
  • illness/infection (even if you don’t see if your body might be fighting it off!)
  • physical activity (not even just working out, like, walking to the bathroom more, grocery shopping, etc. it all adds up!)
  • emotional state, like experiencing stress or anxiety
  • if you’re breastfeeding
  • any medical conditions, such as endocrine disorders
  • heck, even the climate you live in!

Also, when a sample calculation was done with the IIFYM calculator VS the Mifflin-St.Jeor equation (which is what registered dietitians like myself use to estimate calorie needs) the IIFYM “maintenance” calories were about 100 calories/day less than the Mifflin-St.Jeor equation. This might not sound like much but when you take into account the fact that that’s 700 calories a week, AND that they default to a calories intake for weight loss, not maintenance, you can see how that quickly adds up and is far below your true energy needs.

stepping on the scale

But Doesn’t Cutting Calories Mean Weight Loss, Which Means Healthier?

If you follow my blog regularly you know that I don’t believe in intentional weight loss. I believe strongly in the evidence that supports the set point weight theory (I have a whole blog post on what a set point weight is and why it’s backed by science). A quick run down of that is this:

Our bodies are smart. They have essentially an “internal thermostat” that tries to keep our body at a certain weight, the weight where it functions optimally. As we diet and restrict food, our bodies see that as danger- food is restricted- so it in-turn increases that thermostat to pack on a few extra lbs to protect against that danger in the future if it happens again.

This is why most dieters regain the weight they lost in the long run and then some. It’s not your lack of willpower or inability to “stick to it”, it’s biology. And, well, ya just can’t fight that!

This continual loss then re-gain is called weight cycling, which has been shown to have adverse affects on heath (layman terms: it’s not healthy.) What HAS been shown to increase health status is health promoting behaviors- not weight loss. One study proved that healthy behaviors such as consuming fruits & veggies, not smoking, reducing alcohol intake and physical activity all provided a positive health impact regardless of what happened with weight.

You CAN be healthy at any size. Is everyone healthy at every size? No. But can you be healthy at any size? Yes. This is why it is so so important to find your set point weight. Does that make sense? We all have different body types and how we treat our bodies matters, not the number on the scale. If you want to dig into this topic more I highly recommend the book health at every size which you can snag on Amazon for like $8. (affiliate link)

protein for flexible dieting

More Protein Is Not Always Better

When the protein breakdown was calculated it came to 2.15g/kg/day. The recommended dietary allowance (RDA) for protein is 0.8g/kg/day. The RDA is essentially how much your body needs in order for it to do it’s job. You can see that the flexible dieting recommendation is way above this amount.

And if you’re thinking “Well, more protein is better, especially for athletes” one landmark study found that there were no improvements in lean body mass beyond 1.6g/kg/day protein intake.

Consuming too much protein could also negatively impact bone health, renal status (our bodies natural detoxification!) and possible progression of coronary artery disease. This may be due in part to the fact that you’re placing such an emphasis on protein intake that you’re lacking intake of other foods that help prevent these things, like foods containing calcium and vitamin D which are important for bone health, for example.

The Diet Is High In Fat

Again, when I calculated the amount of fat the IIFYM diet was recommending, it came to 28.9% calories from fat. The recommended range is from 20-35% calories from fat. And while this does fall within there, it may not fall within the distribution recommendations of TYPES of fat. Some fats in our diets are health promoting, and some are less so.

For instance, saturated fat is a type of fat that, well, our bodies don’t necessarily love. It’s recommended that this fat be kept to 10% or less. However, with the flexible dieting approach, they don’t really care if your fat intake is 100% saturated fat. Huge problem there.

sliced bread as carbs for flexible dieting

IIFYM Is Too Low Carb

Again, with the sample calculation done the carbs amount that the IIFYM calculator provided was off. The IIFYM calculator recommended 2.6/kg which is below what the Academy Of Nutrition & Dietetics recommends for the activity level.

This to me again goes back to that restriction we talked about and quite possibly leading to overeating carbs when they’re finally consumed, such as, say, on a “cheat day”. Then again, it would likely go back to that weight cycling we talked about, which is no bueno.

That’s Just Too Much Water

The IIFYM diet recommends consuming 3-4 liters of water in addition to your normal liquids. So, 3-4 liters on top of things like your morning cups of coffee, afternoon cup of tea, etc.

Water needs vary, but typically it’s 11.5 cups per day for women and 15.5 for men. BUT, you have to take into account that you also get water from foods, which is said to be about 20% of your fluid needs. This brings the recommendations down to 9 cups for women and 12.5 for men.

Let’s do some math: There are ~4.2 cups in a liter, so that’s 12.6-16.8 cups that flexible dieting is recommending. Then, say you have 2, 8oz cups of coffee in the morning and a 12oz tea in the afternoon, that brings you up to 16.1-20.3 cups of water.

I’m not saying you’re going to necessarily drown yourself with this amount, but it’s likely more than you need. My fear with this is that you are essentially tricking your stomach into thinking it’s full, when it isn’t. And there is a difference between having a full stomach and being satisfied. No matter how much water you put in your body, if you’re not providing it with the nutrients it truly needs you’re going to be driven to eat more food as a result. And, well, that just wouldn’t be comfortable.

All Calories Are Not The Same

The old idea of calories in, calories out is bogus. Even within macronutrient categories, 1+1 does not always = 2. For instance, potato chips are not the same as a sweet potato.

holding an apple and donut for flexible dieting

I’m totally not hating on potato chips by any means. But, my guess is that you’ll feel much more full and satisfied for longer after eating a sweet potato. Further, your body is going to get a lot more nutrients from the sweet potato like vitamin A, vitamin C, and fiber.

What I fear happening here is that “entitlement eating” will happen. meaning, “Oh, I can eat potato chips for all of my carbs?! I’m going to do it!” You’re almost acting as a rebel to healthy eating, VS really understanding what makes your body feel good and what doesn’t.

May Lead To Malnutrition & Nutritional Deficiencies

Going along that same line, it may cause you to develop nutritional deficiencies. The IIFYM plan does state to take a multivitamin, but as a registered dietitian I always recommend food first, not supplement. When a diet tells you to lean on a pill for your nutrient needs, that should be a HUGE red flag.

There was a super interesting study done assessing the nutritional status of macro counting body builders and there were multiple nutritional indecencies found such as vitamins A, D, E, potassium, fiber and, in the women, iron. This seemed to be exacerbated in the women, which I also find very interesting and to me makes total sense. Men and women truly are different beasts and I think this also speaks to the pressure that is placed on women to be “perfect” by society.

holding broccoli and holding and apple for flexible dieting

Bottom Line For The Flexible Dieting Approach

As you can see, it’s obvious that the cons outweigh the pros for flexible dieting and IIFYM. Personally, I do not advocate for tracking or counting anything in one’s diet. This has tendencies to lead to disordered eating and eating disorders, no matter how innocently it starts. Additionally, there is the piece that we just can’t fight out biology and our bodies’ set point weight. Yes this can be very tough to hear, that some people will live in larger bodies their entire lives, but that doesn’t mean you can’t live a healthy and happy one. We need a total societal overhaul of the thin ideal, if you ask me.

I DO think it is important to think about macronutrients as you make your food choices, however. I live by a stance of using gentle nutrition (I have an entire blog post explaining this). It’s totally okay to say “Hey, these potato chips aren’t going to keep my satisfied for long, let me pick the sweet potato with some almond butter drizzled on it”. BUT, here is the kicker, you shouldn’t be so wrapped up in nutrition that you’d feel guilty/stressed/anxious if only the potato chips were available. I teach more about this and guide you to this point in The SociEATy.

I hope this blog post was super helpful showing you the pros and cons of flexible dieting and the IIFYM lifestyle and gives you the knowledge to make an educated decision about your eating style!

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This blog post was written by Colleen Christensen, RD and researched with the help of Amy Scharn, MS RDN.

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