Flexible dieting is not a new approach, but it’s still one that receives push-back. Old-school competitors and hardcore meal preppers turn their noses up at flexible dieters because this “if it fits your macros” (IIFYM) approach allows, even encourages, eating unhealthy foods as part of a cutting phase. To detractors, this concept of fitting cheat foods into a meal plan just seems like, well, cheating.
But is this perception backed by science? Bill Campbell, Ph.D., CSCS, an associate professor of exercise science and director of the Performance & Physique Enhancement Laboratory at the University of South Florida, and his research team decided to put flexible dieting to the test.
“To the best of my knowledge, we did the first study in resistance-trained individuals with this flexible dieting paradigm,” explains Campbell.
Here are the five key takeaways from his team’s research to help you take a smarter, no-BS approach to flexible dieting.
1. It’s As Healthy As You Make It
One of the biggest criticisms of flexible dieting is that it’s not as healthy as stricter meal planning. After all, you’re allowed to have cheat foods as long as they fit within your macronutrient ratio for each day—hence the IIFYM acronym. But just because someone eats a Snickers bar one day doesn’t mean their entire diet is unhealthy.
According to Campbell, flexible dieting is a more useful educational tool for making smart food decisions than tracking calories alone, and the experience of flexible dieting may lead to greater long-term success.
“If you look at just calories, a donut might have the same total calories as a chicken sandwich, but the macros are completely different,” explains Campbell. “I think everybody would benefit from tracking macros for a period of their life. You learn so much about making food choices.”
Flexible dieting is as healthy or unhealthy as you want it to be, and if you’re in a strict diet phase, your macros won’t allow you to pig out on too many naughty foods, anyway.
Campbell’s research shows the real value of this approach is how it teaches you to make healthier food choices while still fitting in less-healthy options every now and then. Tracking macros through flexible dieting is a great way to learn healthy habits without feeling deprived.
2. It Works Better When You Lift
The appeal of flexible dieting is obvious. In theory, you can eat whatever you want and still lose weight. Many take this concept one step further and start to believe resistance training is not as important for someone sticking to their macros, because that person is already dieting for better body composition.
Campbell and his team made it their goal to specifically study the effects of flexible dieting on a trained population, and the results were clear.
“If your goal is to lose weight, flexible dieting by itself is going to work great,” says Campbell. “But, you’re not going to change your body shape without resistance training. Without it, you’ll just be a smaller, puffier version of yourself.”
Resistance training makes all the difference when you’re already lean and trying to go from a good physique to a great physique. “Lifting weights changes the contours of your physique,” explains Campbell. “It’s what will maintain your muscle mass during a diet.”
The bottom line is that flexible dieting needs to be paired with resistance training if you truly want to change your physique.