Rigid vs. Flexible Dieting Approach– Which One is Best?

There’s been many debates whether a rigid diet approach is superior to a flexible one, and vice versa. Most people who go for the rigid diet approach want structure to avoid potential temptations and to also not have to “think” through the day of what they’re going to eat; they want the stress of deciding what to eat to be eliminated. However, those who opt for the flexible approach appreciate the freedom and ability to enjoy a variety of meals with family & friends. 

So the question now is, which one is better? And like most answers that have to do with training and nutrition: it depends. We’ll look at a recent study (listed below) to weigh out the good and the bad for each. 

In this study, which lasted 20 total weeks (10-week diet phase and an ad-libitum 10-week post-diet phase) two groups were compared:

  • Group 1: “rigid” (no substitutions allowed, meal plan-based) diet

    • They were given a meal plan where they were not allowed to make any substitutions

  • Group 2: “flexible” (macronutrient target-based) diet 

    • They were given macronutrient targets to hit each day. They were taught how to do this before starting the study. 

Both groups were placed in a caloric deficit in the diet phase, and given no dietary instruction for the post-diet phase. The variables being recorded were:

  • Differences in body composition

  • Eating behavior

  • Metabolic rate

The result of the study was super interesting! We’ll describe the results in both phases:

There’s a few takeaways from this:

  • If given a rigid meal plan, people will *probably* adhere to it more because all they have to do is follow a plan and use little brain power. However, this is just initial adherence. In the long run, there will be periods of high stress, family events, etc. where a rigid meal plan may not be suitable. Further, our bodies are dynamic systems therefore you should not stick with the same meal plan forever; there will need to be variance based on activity level, metabolic adaptation, and other factors. 

  • Flexible dieting approaches can help enhance nutritional knowledge and tracking experience, thus in the long-run it may be the better option. It exposes one to various food options and learning about their nutritional values.  Therefore when it’s time to change your nutritional approach for whatever reason (increased training volume, etc), one is able to manipulate their own nutrition due to the experience. 

Study: Flexible vs. Rigid Dieting in Resistance-Trained Individuals Seeking to Optimize their Physiques: A Randomized Controlled Trial. Conlin et al. (2021)