You may have noticed #FlexibleDieting — also known as “if it fits your macros” or #IIFYM — showing up on Instagram photos of everything from Pop-Tarts and cupcakes to rib-eyes and protein shakes. The flexible dieting approach started among bodybuilders, but has become increasingly popular over the last few years as people use it to achieve their health goals without feeling deprived. Fans of flexible dieting say that as long as you eat the right proportion of carbohydrates, protein and fat, it doesn’t matter what foods those nutrients come from. Eat whatever you want and not gain weight, they say. Is this too good to be true? To find out, let’s explore a few key questions:
1. What is flexible dieting?
To understand IIFYM, you need to know what macros are. The term stands for macronutrients, or the nutrients in food that provide energy in the form of calories. The three macronutrients are carbohydrates, protein and fat. IIFYM involves setting daily macronutrient targets for these three macros along with a daily fiber goal. Once you know how many grams of each you need to eat, you track your food intake to hit those numbers.
Theoretically, as long as you meet your prescribed daily targets of carbohydrate, protein and fat (which means you meet your recommended calories, too), you’ll lose weight and body fat. There is no limitation on what foods you can use to reach those numbers, since advocates believe the foods you eat matter much less than sticking to your macro goals. So, technically, you could eat 40 grams of carbohydrates from either a doughnut or whole-grain toast without “cheating” on the plan.
2. How does IIFYM work?
First, calculate your daily calorie needs by working with a registered dietitian or other professional, or by using an online calculator. This number should take into consideration your gender, age, height, weight, activity level and health goals. Once you know your calorie needs, you figure out what percentage of those calories should come from each macronutrient. Most people need 40 to 60 percent from carbohydrates, 20 to 40 percent from protein and 20 percent from fat, although it varies based on activity level. Endurance exercisers, for example, will need more carbohydrates and slightly less protein, while weight-lifters require more protein and not as many carbs.
To put those percentages into practice, you have do a little math using the knowledge that carbohydrates and proteins contain four calories per gram, while fat contains nine calories per gram. So, if you need 2,200 calories and aim for 50 percent of them to be carbohydrates, 30 percent to be protein and 20 percent to be fat, your macro goal would be to eat 275 grams of carbs, 165 grams of protein and 49 grams of fat each day.
3. What are the pros of flexible dieting?
I’m all about being flexible with your diet. As a dietitian, I see how a lack of flexibility most often leads to failure. How many times have you said, “I can’t eat that, I’m on a diet?” But making a particular food off-limits pretty much ensures that all you’ll think about is eating that food, and you’ll probably eventually give in — and then some. The main benefit to IIFYM is that it lets you to eat your favorite foods while still seeing results. Flexible dieting also scores points in my book for its ability to be so personalized. Done correctly, macro numbers are designed for your specific needs and physical activity level. Many other “diets” don’t do this.
4. What are the downsides of flexible dieting?
My biggest problem with IIFYM is that many people use a numbers-only approach at the expense of nutrition. They eat any foods they want as long as they stick to their allotted amount of protein, fat and carbs. This often means that food quality can fall by the wayside. For example, you can get 40 grams of carbs in the form of a cup of quinoa, or you could get it from 16 sour patch kids. While you’ll “hit your macros” either way, each option will have a very different effect on your insulin response, satiety and energy level.
Eating a whole-food form of carbohydrates like whole grains, fruits or veggies has benefits outside of just its carb content. These foods also contain vitamins, minerals and antioxidants that energize our bodies and promote overall health. Plus, whole foods keep you full much longer than a handful of candy or a highly-processed protein bar would.
Another drawback to flexible dieting? Counting your macros can be a lot of work. Not only do you have to track everything you eat and drink, but you also need to measure and weigh all of your food. This can be involved and time-consuming, especially if you’ve never done it before. For many people, this level of detail and tracking is not sustainable and doesn’t work long term.
5. Is flexible dieting for you?
If you are time-pressed and prefer ease in your eating plan, you’re probably better off simply aiming to eat more vegetables, fruits, lean protein and whole grains, and less processed foods without worrying too much about math. But, if you are someone who enjoys tracking your food and has the time to put toward it, IIFYM might be worth a shot. Just be sure to focus on food quality and emphasize vegetables, fiber and high-quality protein, choosing whole foods over heavily-processed foods when you can. Combine this with mindful eating principles, and you’ll be able to indulge in the foods you like most without overdoing it.
Alissa Rumsey, MS, RD, CDN, CSCS, is a registered dietitian, certified strength and conditioning specialist, and the owner of Alissa Rumsey Nutrition & Wellness. She helps people who are frustrated with dieting rediscover the joy of eating and develop long-term, sustainable lifestyle habits. As a freelance writer, speaker and spokesperson, she consults with a variety of companies and frequently appears in national media including NBC Nightly News, ABC News, Prevention, Health, SELF and Women’s Health. Follow her on Instagram and Twitter, or visit her blog.