Recent years have seen the emergence of “weight-neutral” approaches to health, which have various iterations under the umbrella term of “non-diet nutrition”.
Much of what is argued within this paradigm was a refreshing reality check that nutrition and medicine needed to hear.
For example, it is clear that ubiquitous recommendations for weight loss are not benign, but an intervention carrying risks of unintended consequences.
Little to no nutrition trials ever screen participants for disordered or restrained eating at baseline.
Yet mixed in with some of the positive contributions of non-diet nutrition are some claims that are often divorced from evidence, or at least appear like bad stats.
One of those is the contention that “95% of all diets fail”, a myth that often derails discussions around weight loss maintenance. This assertion is often used to frame an argument that:
a) If all diets fail, then recommending weight loss is unethical or bad practice, and/or;
b) If weight loss cannot be sustained then other ways of improving health are not only needed, but de facto superior.
But is this lofty statistic even true?
Torture Data and It Will Talk
The accepted definition of success in a clinical context is a minimum of 5%, with a range of 5-10% deemed desirable.
These thresholds have been established by reference to clinically significant reductions in risk factors for type-2 diabetes and cardiovascular disease.
However, with weight loss research, it would be possible to come up with any percentage statistic we like to support an argument in favour of, or against, dieting success.
It entirely depends on what parameters are set to define long-term and maintenance.
For example, the average weight loss in interventions over 6 months is 3-5kg, and the average weight loss maintained at 2yrs follow-up is between 3-6kg (Franz et al., J Am Diet Assoc. 2007 Oct;107(10):1755-67).
Based on these averages alone, it would be possible to derive a statistic of anywhere between 66-110% of initial weight loss will be regained.
Most research, however, defines “long-term maintenance” as 1yr.
This skewers the definition more in favour of “all diets fail”, because weight regain over 1yr strongly predicts continuing weight regain beyond that point, particularly when evaluating true weight loss maintenance.
Trajectories of Weight Loss and Regain
Building on this further, the crucial period for long-term maintenance appears to be the period beyond 2 years, up to 5 years.
Thus, definitions of “long-term” within the 1-2 year period are not likely to capture individuals who are truly successful at long-term maintenance of weight loss.
These definitions are thus crucial to the debate surrounding effective weight loss maintenance.
In people who begin to regain weight within a 1-2 year period, the odds of continuing weight regain in a near-linear manner are significant.
Mcguire et al. ( J Consult Clin Psychol.1999;67(2):177–85) demonstrated, conversely, that the odds of long-term weight loss maintenance increased with greater duration spent in maintenance.
The analysis compared people successful at maintaining weight loss after a weight loss intervention against participants who had regained weight.
Compared to individuals who had regained weight, successfully maintaining weight loss beyond 2 years reduced the risk of regaining weight by 50%, and maintenance over 5 years reduced the risk of regain by 71%.
Conversely, a meta-analysis by Anderson et al. (Am J Clin Nutr. 2001;74(5):579–584) of 29 long-term weight loss maintenance studies up to 5 years demonstrated that just over half of all weight lost was regained by 2 years, and 80% by 5 years.
How Do We Make Sense of this Evidence?
Several take-home points arise from this research.
The first is that the period between 2-5 years following weight loss appears to be critical.
Specifically, the duration of ongoing weight loss maintenance is seemingly a key factor that significantly increases the odds of maintaining weight loss beyond 2yrs.
Indeed, the evidence indicates that the maintenance linearly improves up to and beyond 5 years.
However, in individuals who regain weight, the weight regain appears to begin almost immediately following weight loss and continues in an equally linear manner.
In this context, up to 5 years is arguably a more appropriate timeframe to consider weight loss maintenance “successful”.
The second important point is the importance of considering both the absolute level of initial weight loss and weight regain, within the context of these timeframes.
Where the focus is on the 1-2 year period, it is possible to play statistical gymnastics to fit any narrative.
Less Bold Statistical Hocus, More Nuanced Appraisal
The statement “95% of diets fail” is simply incorrect, as is the statement “66% of diets fail” or whatever arbitrary definition is applied.
The problem with such statements lies in the operation definitions applied, and the assumption that all interventions are comparable in scope, intensity, type of intervention, etc.
In fact, there are any number of levels we could stratify interventions based on.
A more refined approach would look to state:
“X% of this specific type of intervention using these particular dietary and behavioural modifications results in outcome Y.”
What we do see from the characteristics of successful long-term weight loss maintenance is that the interventions are labour-intensive.
Successful maintenance involves active follow-up, with more positive outcomes from in-person practitioner contacts, more total contacts and frequency of contacts improving outcomes.
An emphasis on behaviours, as opposed to deliberating attempting to solely focus on and prevent weight regain, also emerges as an important determinant.
However, it is unsurprising given the level of follow-up intensity, and the fact that behaviour change is difficult, that long-term weight loss maintenance is so difficult for so many people in the real world, proving that dedicated weight loss maintenance is possible, albeit demanding.
Yours in Science,
Alan
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