Rigid versus Flexible Dieting

What makes a diet successful?

Is it the specific program/diet plan?

Is it the amount of weight you’re able to lose? Or the amount of time it takes you to lose it?

What is it about some dieters that made them successful in their efforts to lose the weight and keep it off?

Not surprisingly, this question still plagues many. This can be supported by the point that a majority of those looking to diet (or those who’ve dieted on and off before) just can’t seem to keep it off afterwards and sustain it long term.

Without context, it’s pretty easy to think that this alone is evidence that diets in general “DoN’t wOrK” for long term weight maintenance. This isn’t the case, though; we have plenty of evidence suggesting that diets do work. The difference, however, is in the approach.

Cognitive Restraint

In this article (2021) we’ll be diving into two different categories of cognitive restraint and the impacts each can have on both the dieter and the outcomes of the dieting phase itself. I’ve written an article about the three primary eating behaviors here (restraint, disinhibition, and hunger) and how they can be impactful on weight loss/gain, but to give some quick background, restraint can be defined as the intentional or conscious restriction of food intake in order to manipulate weight loss/weight gain.

Now, restraint is absolutely necessary for the dieter to develop and employ if their goal is to lose weight… and do so successfully. Cognitive restraint can be divided into two categories: rigid control and flexible control.

Rigid control will often represent an all-or-nothing approach towards dieting and eating behaviors as a whole. Think dichotomous, on again-off again cycles. “Good” and “bad” food choices with little to no variation or flexibility.

Flexible control, on the other hand, represents a more moderate approach to dieting behaviors. It allows for adjustments and substitutions based on the dieter’s palate and preferences without the fear of negating progress because of it. Moderation is a huge element to this. Because of these characteristics, flexible control has been shown to mitigate cravings and have better long term outcomes and successful weight maintenance post-diet.

Methods

39 healthy, resistance-trained men and women participated in this study (with 23 completing it). The subjects were matched according to fat mass and then randomly assigned to two different dieting protocols that would last over a 10-week period: a flexible (FLEX) or rigid (RIGID) diet plan. Prior to this, the subjects completed a three-factor eating questionnaire (TEQ) in order to assess the 3 primary eating behaviors – hunger, cognitive restraint, and disinhibition.

Diet protocols and physical activity

In order for researchers to determine maintenance calories, the subjects were instructed to track and report their usual intake in a 3-day food log (which included one weekend day). Obtaining maintenance calories allowed the researchers to then assign a 25% caloric reduction to all of the participants of each diet group.

Subjects were instructed to eat at least 2g protein/kg of bodyweight each day. As for daily carbohydrates and fats, those were to be split as evenly as possible based on their remaining calories for the day.The RIGID dieting group was assigned a customized meal plan and told to only consume foods included in their specific plan and to not make substitutions. All of these set meal plans were designed by a registered dietitian. RIGID dieters were also given sample meal plans to choose from.

The FLEX dieting participants were given a detailed ebook on how to count their daily macronutrient intakes alongside their assigned macronutrient goals for each day (tracked as daily carbohydrates, protein, fat grams/day). Food sources were to be chosen at the dieter’s preference and nothing was restricted.

Lastly, all participants were told not to change their current physical activity or exercise programs during the entirety of the study period. They were only asked to record the amount of time spent engaging in either resistance training or aerobic exercise.

A note on Macro-based dieting versus flexible control

I appreciated that the authors of this paper (hi Laurin) also touched on the differences that should be distinguished between macro-based dieting/IIFYM approaches and flexible restraint as an eating behavior. Macro-based dieting is not the exact same as flexible control; in the physique athlete and resistance training space, it isn’t unheard of for macro tracking to be a highly rigid dieting approach if one lets it be.

In certain contexts, such as competition prep, it’s standard for athletes to be very strict with hitting specific macronutrient goals. It’s an extreme sport and it comes with the territory. The problem, however, lies in areas where the standard dieter can allow that behavior and control to lead them into a poorer relationship with food and/or body image.

Findings: Is one approach superior to the other?

In a number of ways, yes. As discussed, adopting a more flexible approach and mindset to dieting and eating behaviors comes with a lot of benefits to the dieter both throughout the dieting phase and after the diet is already completed! More on that later.

Based strictly on this study’s findings, though, both methods actually did the job in producing desirable body composition changes after 10-weeks. Both the RIGID and FLEX dieting groups were successful in producing weight loss/fat loss and retaining fat free mass throughout the dieting period. Additionally, there were no differences seen in the amount of time that the participants spent performing resistance training or cardiovascular exercise.

One last, interesting finding among the dieting groups concerns the post diet ad libitum period; the FLEX group seemed to have more improvements in FFM post-diet that were not seen for the RIGID group. The researchers unfortunately do not have a strong reason why this occurred and have opted not to attribute those results to the dieting protocol.

Strictly regarding long term sustainability results just aren’t enough, though. 

For one, these results show what we already know about calorie balance and the basics of weight management. If we’re working under a caloric deficit (more energy expended than energy consumed), weight loss will happen. We’ve seen this done time and time again with fad diets and “quick” fixes. Slash calories, drop a lot of weight, don’t know how to keep it off, regain said weight (and maybe more), repeat.

We need to remember that it’s not just about obtaining the end results and moving on.

Measurements of cognitive restraint were shown to be high in both dieting groups. This means that subjects in both protocols portrayed conscious efforts to monitor their diets and stay on plan. For the RIGID group, for whom these results may look surprising for, it’s thought that subjects within this group found the meal plan easy to follow due to not needing any planning put into their day to day. Less guesswork for the day/week while meals and food sources are decided for them already – this is really the only positive I can give for meal plans. It provides structure and all you have to do is follow through.

With that said, the ultimate goal for any successful lifestyle and diet change is to not only lose the weight, but to do so in a manner that you can sustain so that you can keep the weight off. The approach to dieting and lifestyle changes as a whole need to be something that the client can realistically maintain after the diet is already over. Habits and mindset towards the diet need to be consistent aspects our lives in order to maintain any of the progress we make in those ‘X’ weeks spent dieting.

If the approach is conducive to the client’s goals and realistic for them to follow/sustain given their starting point, all while being something that is enjoyable, you have a recipe for long term success.

So back to the question: Is one approach superior to the other?

Personal preference, your specific barriers/obstacles, your relationship with food and/or dieting, your lifestyle and much more can play into how you decide to answer that question. There are pros and cons to each approach that are worth considering when determining an approach and setup most suitable for yourself.

It’s no secret that I will never recommend meal plans or food lists, but I have had plenty of clients who enjoy using meal plans and the structure that they can provide given their busy schedules or hectic, unpredictable work weeks. The twist here, though, is that they create those meals plans themselves based on their given macronutrient targets and what they enjoy.

Now they can get the best of both worlds: structure via consistent meals that don’t change and the option to swap foods in/out as they please for more diet variety and flexibility! This difference is incredibly important long term.

There’s no “one size fits all” approach for dieting and lifestyle change. It has to be something that you choose every day – something that you can realistically adhere to and maintain no matter the phase you’re working through. This way you reap the benefits of lifestyle change, build up your consistency over time, and enjoy the process.

References:

Conlin, L.A., Aguilar, D.T., Rogers, G.E., Campbell, B.I. Flexible versus rigid dieting in resistance-trained individuals seeking to optimize their physiques: A randomized control trial. Journal of the International Society of Sports Nutrition. 2021. 18:52.