What is Flexible Dieting? It’s About Making Your Macros Fit

Despite the overall trend toward cleaner eating (little to no processed foods, limiting or eliminating “bad” foods like sodium and sugar, etc.), as well as our general desire for quality ingredients (such as organic, humanely-raised, etc.), an increasingly popular diet—called “flexible dieting”—favors focusing on quantity.

The premise of flexible dieting is that you eat the right number of calories for you and in the right proportion of macronutrients. You calculate how much of the macronutrient categories you should be eating and then choose what to eat based on those targets. There are three macronutrients—protein, carbohydrates, and fat. As for the vitamins and minerals also in your food—those are micronutrients, and they aren’t addressed in this diet.

To determine your macros, flexible dieters typically use an online calculator. And the calculators also take into consideration your weight loss or fitness goals. Once you figure out what your macro targets are, you’ll need to start to track them so you can hit your daily goals. For most of us, the easiest way to do that is to via an app that lets you easily log everything you put in your mouth. You could also go old school and write everything down and add it up manually, which is more tedious, yes, but if you’re sticking mostly to whole foods and making recipes that come with nutrition information, it might not be as daunting.

As with any diet, especially one where you want to lose weight, or optimize your body composition, there are pros and cons.

Some tout this diet, also called If It Fits Your Macros, or IIFYM for its flexibility—all foods, from earnest to fun, are allowed as long as they fit into your macros ratio. But the reality is that logic also applies to the OG tried-and-true weight loss method: counting calories. Remember it’s possible (though not advised) for some folks to eat 1,500 calories in Twinkies® every day and still lose weight. Is a Twinkie diet “healthy”? No, yet someone could potentially drop a few pounds (maybe even more); though research suggests it may not be ideal to help you keep that lost weight off.

Perhaps the biggest con or negative is that the core principles behind IIFYM is that it doesn’t automatically lead you to a healthy diet. For example, all carbohydrates are essentially equivalent—you’re counting grams of carbs you eat so what’s it matter if it’s Skittles® and white bread or whole grain brown rice and fiber-rich raspberries? OK, so that’s a rhetorical question, but the point is that you can adhere perfectly to your macros and still eat processed junk. Or, equally as concerning as a nutritionist, you could technically sprinkle a decadent chocolate layer cake with protein powder to tweak your macro ratio accordingly. Slightly gross from a culinary standpoint, but also, adding protein powder doesn’t make that cake any more virtuous, even though it improves its macros ratio.

That said, some IIFYM plans available encourage you to eat more whole, unprocessed foods and that typically means less junk, and fewer of those nutrients like sodium and sugar, which we should be limiting. Follow those and you’ll naturally start to eat healthier.

Because flexible dieting plans typically tend to be higher in protein and, sometimes, fat and those two nutrients give you staying power, you’re less likely to crash and turn hangry or ravenous between meals, even if you’re cutting your calories to trim down. In other words, hunger shouldn’t be too much of an issue on this diet.

Another pro? You’re tracking what you’re eating and research has shown that can making shedding pounds more successful.

For any diet to be successful, you have to stick to it! And the research supports that: most weight loss studies that compare different diets find that there is little to no difference in how much weight was lost in participants across different diet groups. The American Heart Association and American College of Cardiology recommendation to manage overweight and obesity is to cut calories “for weight loss regardless of macronutrient content.” However, they do point out that to keep that weight off, your diet composition (aka macros) may play a role—and certain people may have more success limiting carbs and slightly bumping up the unsaturated fats in their diet, and not just because that’s effective, but it’s easier to adhere to over the long haul.

Let’s circle back to our original question: should you try IIFYM? If it intrigues you, and you want to lose some weight or shave a few body fat percentage points, go for it because you’ll likely find success (for reasons mentioned above). But for the sake of your overall health (your heart, your blood sugar, your disease risk), take quality into consideration, too, and err more towards eating healthy foods to hit your macro targets.



Fleming JA, Kris-Etherton PM. 2016. Macronutrient Content of the Diet: What Do We Know About Energy Balance and Weight Maintenance? Current Obesity Reports. 5(2):208-13. doi: 10.1007/s13679-016-0209-8.

Gardner CD, Trepanowski JF, Del Gobbo LC, Hauser ME, Rigdon J, Ioannidis JPA, Desai M, King AC. 2018. Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion: The DIETFITS Randomized Clinical Trial. JAMA 319(7):667-679. doi: 10.1001/jama.2018.0245.

Mateo F, Granado-Font E, Ferre-Grau C, Montana-Carreras X. 2015. Mobile Phone Apps to Promote Weight Loss and Increase Physical Activity: A Systematic Review and Meta-Analysis. Journal of Medical Internet Research 17(11):e253. doi: 10.2196/jmir.4836.

Stewart TM, Williamson DA, White MA. 2002. Rigid vs. flexible dieting: association with eating disorder symptoms in nonobese women. Appetite 38(1):39-44. doi: 10.1006/appe.2001.0445.


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The Author

Brierley Horton, MS, RD

Brierley Horton, MS, RD

Brierley Horton, MS, RD, is a food-loving registered dietitian and fitness enthusiast. When she's not road-testing new, healthy food products or digging into the science behind trendy diets, you can find her at a barre or yoga studio. Based now in Birmingham, Alabama, she received her master's degree in nutrition communications from the Friedman School of Nutrition Science and Policy at Tufts University in Boston. Follow her on Instagram @brierleyhorton.

Photo credit: Carey Norton

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